David Hembrow

Fourteen years of rooftop solar power

2026-06-11T11:57:55.211+02:00

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The solar panels on the roof of our home were installed on the 5th of April 2012. For fourteen years they've produced electricity every day, and though they were expensive to install all that time ago they've more than paid for themselves in reducing our energy costs. The total amount of energy generated by that system over fourteen years stood at 47220 kWh on the 5th of April 2026. On top of that we now generate a considerable amount from extra panels installed on our garage.

Solar power production from our rooftop panels (blue) and additional panels (orange) per year. The total output for 2025-2026 is lower than the year before because we sometimes switch them off to avoid exporting at a negative price

We switched to a dynamic tariff last year. Sometimes the prices go negative and it can be better to switch solar panels off than to continue to supply the grid. That's the reason why the graph shows the panels as having produced a little less electricity than in previous years - they were switched off at times when they would have produced a lot of kWh, but we would have had to pay to send that unwanted electricity to the grid (see later in this article as I'm changing how we do this).

Total energy bill and dynamic tariff
Our total energy bill for the year, from April 2025 to March 2026, was €128.47. That's the total that we paid over the entire year, including the fixed fee for a connection, taxes etc.. Everything in our home runs on electricity. We do not have a gas connection or associated bill.

With a dynamic tariff the amount paid each month varies quite a lot. The largest single month payment was €187.41 which covered our usage in January. Most of the electricity was consumed by our heat pump, and our solar panels were covered in snow for a significant part of that month. The largest negative bill (we received money from the energy company) was €88.42 for July when we exported a lot of electricity. There are more positive months than negative months. We received a payment for eight months and had to pay the energy company for four months.

Making negative prices work for us
This year our panels should be switched off less often than they were last year. For most of last year my software was switching off the panels whenever the price went below 0 c / kWh. That's actually too aggressive and this year they will switch off far less often.

For a start we need to ignore negative prices which are not very negative. Just say that the current price is -0.1 c / kWh. If we switched off our solar inverters for an hour at that price we would prevent paying to export 4 kWh, which would save us 0.4 c. But if we switch off the inverters and use electricity during that hour we'll have to pay the retail price for what we consume including taxes which works out as around 13.5 c / kWh. i.e. we'd have to consume less than 0.1 kW in order to not end up paying more for what we import than we'd lose from exporting the balance.

There's also the issue of how slowly inverters restart. It takes more than a minute for them to come back online and rise back to maximum output. So if you try to switch them on whenever the consumption rises, for instance when you put a kettle on, they'll almost certainly miss the peak. You could consume 0.5 kWh before the inverters get going again, and then have to switch them straight off again once the kettle is boiled.

It makes more sense to only switch off the inverters when the supply is very negative.

There are two reasons for this: first, I realised that I was being too aggressive in switching off the panels last year, which led to us sometimes having to import electricity in order to power things that could have been supplied by our panels, and second that I now have more devices which can be switched on as required to absorb extra electricity.

The problem with switching inverters off is that they take minutes to come back to full power output again, which means we can't accurately match usage. But if we can instead "dump" excess electricity elsewhere, e.g. into resistive underfloor heating elements, these can be switched off immediately when we need the electricity elsewhere. So we now have some resistive underfloor heating, which also makes a difference to our comfort in winter, and I've modified the control of the water heater to also switch more responsively.

This year compared with last year
The changes made to the software have already produced a result. Our bills for April and May 2025 when we were aggressively switching off the inverters whenever the price per kWh went negative were -€43.86 and -€46.66. With the new software, which tries to ensure that we still power as much as possible from our own solar panels our bills were €-62.27 and -€71.41. That's an extra €43 for us due to not switching off our solar panels so aggressively, but allowing some production with a slightly negative price.

Thirteen years of rooftop solar power

2025-04-05T13:45:00.004+02:00

We had solar panels installed on the roof of our home 13 years ago today. Those panels, which face South-West have been supplemented by additional solar panels facing South/South-East, installed in 2022/2023.

Solar power total production in kWh by our rooftop and garage roof panels since their installation in 2012 / 2022. There's still no sign of degradation: Production from the rooftop panels last year was 3% higher than an average year.

I think it's worth noting that the output of the 13 year old panels on the roof of our home is still as good as it was when they were new. In fact, last year's output was 3% higher than the average over their 13 year life so far. The highest single year output was two years ago when they were already 11 years old. Solar panels do not degrade quickly and unless they are physically damaged it's very unlikely that they need to be replaced.

I increasingly see people selling older solar power systems in order to replace their existing panels with new ones, and I do not understand why they do this. Newer panels do have a higher output than the old ones (e.g. our garage panels are rated over 400 Wp each while the rooftop panels are 270 Wp each), but this is mostly because they are larger. Even if the horrible effect on the environment of disposing of products early is disregarded, I can't believe that the slightly increased output per square metre with newer panels makes it financially viable to swap panels.

I suspect that the large number of single phase older equipment on the second hand market is being driven by a hard sell when people "upgrade" their electrical connection from single phase to three phase. But as it's possible to buy a string inverter for three phases to replace a single phase inverter if so required, it seems likely to me that people are being sold something they don't always need. In my opinion, installing a few extra panels alongside the older ones makes more sense than replacing everything.

When we installed our extra panels on the garage I considered buying second hand panels from one of the people who was for some mysterious reason replacing their existing set, but I couldn't find panels locally with prices low enough to make them attractive. The problem is that even if the panels are local and they have a very low price there are still two things working against them: 1. because they're smaller in capacity you need more material per kWh to mount them (and that costs almost as much as the panels do). 2. you don't know what someone has done with the old panels. Have they been removed from the old roof carefully ? There are too many unknowns.

Cleaning solar panels
I've never tried to clean the solar panels on the roof of our home. They're a long way off the ground and trying to clean them would be dangerous. Nevertheless, their output remains at the same level. My recommendation is that you never clean solar panels installed on a roof. If you try to clean them then you may damage them or injure yourself, and I think it's completely pointless anyway because they self-clean remarkably well each time it rains.

Dynamic tariff effect
The graph above will be less meaningful next year because we now deliberately turn our solar panels off for a few hours on some days to balance the grid. We've already been doing that for almost a month so the graph above is already affected slightly. Unfortunately this will make it more difficult compare the performance of our solar panels each year.

Inverters
As those who read this blog before will know, the ABB inverter for our rooftop panels had a five year warranty and failed after just over six years. The company who made it were absolutely no help at all, offering to do nothing more than sell us a complete new inverter. I took the inverter apart and fixed the problem. The factory soldering was poor, with dry joints which heated up and failed, so I replaced a damaged relay applied new solder. That inverter has now worked for more years since my repair than it did from new. But it's now been in use for 13 years, so I have some concerns about whether something else will fail.

The solar panels on our garage are connected using Hoymiles microinverters. These are only a couple of years old so I would hope they still have a long future ahead of them. Time will tell.

Optimising energy usage so we can do everything with a 25 A mains connection and minimally upset the grid

2025-03-18T17:48:00.003+01:00

When our home was built in 1972, people had fewer electrical devices. But more importantly, they heated and cooked with gas, which at that time was not only a cheap energy source but also one which few people in the Netherlands seemed to have realized could eventually run out, or cause earthquakes, or cause sea level to rise which could make much of our country uninhabitable, or that it could warm the planet and make many places uninhabitable.

Anyway, when our home was built the need for electricity wasn't so great and a 25 A connection was considered to be enough for average homes. That's what we have. 25 A * 220 V = 5500 VA (which is not exactly the same as 5500 W). We can therefore only draw a maximum of 5500 VA from the mains before we risk blowing the fuse. It also of course means that we can't send more than that much electricity back to the grid from our solar panels without risking blowing the fuse.

These days many people upgrade their fuse boxes, often switching to a three phase connection (often referred to as "krachtstroom") at the same time. Many newer homes are built with 35 A fuses on all three phases, allowing them to consume more than four times as much energy from the grid as we can take. This is the case even when those homes still use gas for heating. If everyone actually started using so much electricity at once, we'd be in trouble: it would require the grid itself to be upgraded and more power stations to be available to supply the demand.

We've not gone down the path of increasing the supply. Instead, we're trying to limit the energy usage of our home and keep our consumption within 25 A, even though we no longer have a gas connection so all our heating and cooking demands are now met with electricity. To do this we need to match our energy production with our solar panels so closely as we can, and to make sure that heavy users of electricity don't all switch on at the same time.

Balancing supply with demand
The wholesale price of electricity varies per hour depending on the consumption vs. production. The shape of the graph varies per month, with solar panels producing electricity in daytime in sunny months greatly reducing the value of electricity generated during those hours compared with the value at the same time in winter.

Graph of average wholesale prices of electricity per hour (source). Just trying to match this is a good start, but I ended up doing more as you can read below.

The price of electricity is directly related to the demand vs. supply. During the night most people are asleep and inactive thus energy demand is lower. During the day the peak demand is at breakfast time and dinner time, while peak solar production is in the middle of the day.

13 years ago when we first installed our solar panels, we would generally try to wait until the sun was shining before switching on large energy users like our washing machine, but nothing in our home automatically responded to the demand curve. At that time not many homes had solar panels so any electricity that we exported was always useful to someone. Our energy company gave us the same credit for every kWh that we produced as each kWh that we consumed, regardless of the time of day or the season. The situation is quite different now because 35% of homes now have solar panels and there are a great many solar farms in the countryside. That is why the price of electricity now drops so obviously during bright days. There are also many wind turbines now and on windy days the price also drops.

Automatically matching demand to supply
When I first installed our electric water heater it ran on a simple and inexpensive mechanical timer which switched it on at about 10:00 and switched off at 18:00 (it would actually stop much earlier when it reached the set temperature, unless we took a shower in the afternoon).

A now retired simple mechanical timer which used to switch our water heater on and off. I still recommend this as a good first step. It's easily affordable and very easy to use.

The timer was my first attempt at matching demand to supply, and if you can do nothing else I recommend it as it works quite well on average. The timer roughly matched the consumption of our water heater to when the electricity was flowing from our solar panels. However it didn't respond to other appliances using electricity at the same time (e.g. dishwasher, electric water heater in the kitchen, cooker, boiling a kettle) so we would quite often see our total consumption rise above what our solar panels were generating even on sunny days, while later on the same day we'd see the sun shining enthusiastically on our solar panels but the water heater would have stopped ages ago on reaching it set temperature, and we'd be exporting instead. A simple timer is much better doing nothing at all, but we can do better than that.

Reading from the meter
Dutch smart meters have a P1 port from which it's possible to obtain real time readings of the amount of electricity flowing in and out of your home. This provides electrically isolated serial data which it's safe and perfectly legal to use with a DIY project.

This is installed in our meterkast. An Arduino receives serial data from the P1 port, lights LEDs depending on energy usage (three green = 1500 VA export, orange = underfloor heating on) and passes the data to an ESP32 (the blue LED is the ESP32 activity light) which controls other devices in our home.

The first device that I attached to the P1 port was an Arduino programmed to display energy consumption on a set of LEDs so that we could see at a glance whether we were sending electricity to the grid (green LEDs) or consuming energy from it (red LEDs). It also included an alarm which would go off if we were approaching the 5.5 kW limit for consuming energy from the grid and automatically switched on underfloor electrical heating at any time that the temperature in the entrance hall was too low, or at any time that we were exporting a lot of electricity if the temperature was lower than we'd like it to be.

My intention at the beginning was to completely avoid wireless connections. The air filtration system uses a serial link between two Arduinos on the ground floor and the top floor (there was an existing conduit which made this easy). But for this project I realised quite quickly that it would require me to run a lot of cables. I was also going to need to know the time of day and the date. For those reasons I switched to using ESP32 controllers.

The ESP32C3
The ESP32C3 embedded boards that I'm using are very inexpensive, they contain a fast and powerful 32 bit processor, plenty of memory and even built in wifi. They're also smaller than my thumb.

An ESP32C3 controller board resting on my thumb.

The first, master, ESP32 is built into the same case as the Arduino, receiving the P1 data over serial from the Arduino. It couldn't replace the Arduino in that location because it doesn't have enough GPIO pins, but the two devices complement each other nicely. This first ESP32 works as a server and the other ESP32 powered device controllers connect to it to find out what they should do. I can see the status of all the devices on a simple web page at a static IP address hosted by the ESP32:

The single webpage hosted by the master ESP32 within the meterkast. It displays how much power we're importing, exporting, the current price, the rank (in the above this is the 4th cheapest daytime hour today), and also data about the hallway temperature and heating as well as data sent to it by various other connected devices. It's still quite cold outside which is why the temperature sensor by the front door went down to 12.7 C, and a few small heating elements were switched on in order to make sure no condensation can form. The "Tibber price" is the retail price including taxes etc.

The connected secondary devices all have a mains lead, two sockets (one switched with a relay) and use old phone chargers for their 5 V supply. Some of them use Dallas DS18B20 compatible temperature sensors. Some also have an override button which can be pressed to switch on the heater for a short period when it would otherwise not switch itself on.

The master ESP32 downloads the day ahead electricity prices at midnight and calculates a ranking of when the cheapest time is for any devices to operate (that's dayrank and nightrank on the status page above). Secondary devices can then decide on which hours they can best consume electricity in order to reduce the price, and because these things are intrinsically related, best balance the demand on the grid.

For instance, we know that our main water heater heats its contents at a rate of about 7 C per hour. As a result, the controller can calculate ahead of switching on time how many hours it will need to raise the temperature from the currently measured temperature to the target temperature and it can optimise by only switching on for the daytime hours which rank below that value. At times of the year when our solar power can't cover all our demand it also automatically uses the cheapest nighttime hours using the same mechanism and the nightrank. This means in practice that in the morning when it has some value we allow our electricity to be exported to the grid, while around lunchtime when the price is at the lowest for the day the heater then uses the electricity rather than adding to the excess on the grid.

Note that these controllers also continuously monitor how much electricity is available either by importing from the grid or our exporting to it. Thus if we are producing just a little more electricity than the water heater needs and we put on the kettle to make a cup of tea, the water heater controller responds by switching off until the kettle is boiled, before switching itself back on. This means we humans get priority. The kettle, or anything else that we humans switch on and off, automatically gets whatever solar energy we are generating and we never have to manually switch off any of the automatically controlled devices so that we don't exceed the maximum available from our supply on a dull day. The water heater also automatically responds to such things as fluctuations due to clouds coming and going over our panels, and tries to optimise so that to the greatest extend possible we only consume electricity from our panels when we are generating it.

One of the heater controllers. A secondary ESP32 connects to the master and makes decisions about whether to switch on the heater plugged into the socket depending on the temperature measured by the probe, the time of day and the amount of electricity being imported or exported.

Whenever the energy price goes negative (which it did for three hours around lunchtime today), all the heaters are told they can go on and consume as much electricity as they want, pursuing a higher than usual target temperature. The extra solar panels on our garage are also switched off by another secondary ESP32 device when there are negative prices.

This is what is installed inside the controller for the solar panels on our garage. The stripboard includes two transistors used to safely switch the 5 V inputs to the double relay board from our 3.3 V microcontroller. There's also an input for power at the top and at the bottom a connection for the pulse output from an SDM120 energy meter in the garage. A 62 mm long piece of wire connected to one end of the antenna (red object marked C3) makes the ESP32C3 wifi more reliable.

Does it work ?
This system really does seem to do what I designed it to do. But as I've only just "finished" it (what hobby project is actually ever really "finished") I don't have any substantial data yet. When I do, it'll be added here as an update.

Screenshot from my energy supplier's app showing yesterday's electricity price and our consumption per hour (including taxes etc.). Nearly all the system worked yesterday. It should be better than this from now onward. The peak at just before 4 am is from the kitchen boiler, which comes on as a convenience for us during whichever is the cheapest hour at night in order to make sure we have some hot water in the kitchen in the morning. The peak at 12:00 is for an hour when we had negative electricity price, and the hours in the evening are still a bit of a problem even though most of our panels face South West, because when the sun goes down we don't have our own electricity.

An example day (update April 2025)
This graphic shows the electricity that we bought and sold to the grid yesterday (March 31st 2025):

Electricity import vs. export on March 31 2025. The high spikes in the blue on the left are on the hours when the price was negative (note that the price shown here includes tax so almost never goes negative). On those same hours our solar panels were switched off so we did not export any electricity. Note the different scales for kWh on the left of both graphs - that's an artifact of the mobile phone app of my supplier.

During the hours of negative pricing, devices automatically switch on while the solar panels are switched off. We avoid using our own solar electricity on the hours when it has a positive price and do as much work as we can with the negative price electricity, resulting in exports having a higher value than imports. In March we consumed a total of 120 kWh from the grid with a cost of €31, while our exported 230 kWh had a value of €51. Our total energy bill for March was therefore negative €20.

Downloading ?
Once I know that this thing really works, and if people turn out to be interested, I'll make the code available to download somewhere. It's probably easier than starting from scratch. There's nothing amazing or patent-able about any of this - I'm not expecting to make money out of it. Mine is just a small contribution built on the shoulders of giants, including those who wrote the library code for TCP/IP, temperature sensors etc. I used to make a living out of writing code like that, but in the Arduino environment all the low level code for pretty much any device you want already exists. The work of others has made everything really easy to do.

Changing energy supplier
We've changed energy supplier from Pure Energy to Tibber. For the last few years Pure Energy have been paying us about €200 per year more for our exported energy than we paid them. I'm expecting a payment of about €280 shortly to cover the last year + one month that we were with them. Unfortunately, this happy situation wasn't going to continue: Pure's renewal agreement stated that they wanted to start to charge a fine ("terugleverbijdrage") of 14 cents per kWh exported to the grid, regardless of our trying to optimise our exports to be of the most use to them. This would total more than €400 per year. I tried to get a quote from them for a dynamic tariff (with prices per hour) and couldn't seem to get any sense at all from their salespeople.

I'm not expecting to be paid for dumping unusable electricity on the grid at midday in summer when it has no value. I've actually put quite a lot of work into trying to make sure that we don't do that, and to ensure that we use as much of our own electricity as we can, but I couldn't get any sense from Pure. Instead I've had to cancel their contract, which resulted in a snotty email in which they said they were sad to hear that we were no longer interested in using green electricity and gas ("We vinden het erg jammer dat je geen gebruik meer zal maken van onze groene stroom en/of gas!"). There's such a thing as "green gas" ? I don't think so.

Tibber, on the other hand seem to offer a straightforward easy to use dynamic tariff. I'm expecting that our total energy bill for the year will still be negative this year, especially given the recent optimisations detailed above. If you switch to Tibber and use the uitnodigingscode "dyd4ick5" then both you and I will receive €50 in credit for use in their online store - not that I've yet seen anything there which I think I would actually want.

Footnote 1: The ludicrous power of cheap embedded computers in 2025
I've often heard people say things like "this mobile phone has more power than the computers that took Apollo to the moon", but many people have no idea just how much more powerful those things are.

The little ESP32C3 microcontroller boards that I've been using have 160 MHz 32 bit RISC-V processors (including hardware floating point) which execute between 40 and 160 million instructions per second. They have 400 kB of RAM, 4 MB of flash, and include WiFi on chip as well as lots of other neat features. They consume less energy than I can reliably measure and they cost me $1.60 each.

The Apollo Guidance Computer was a truly amazing device given it's design in the mid 1960s. But while the performance was amazing then, it's not so amazing now: The AGC processor was clocked at just 1 MHz, used words 15 bits wide, executed "50000 to 100000 instructions per second" there was just 70 kB of (hand woven) ROM and 4 kB of RAM. They consumed 55 W and cost the equivalent of about $2 M each in 2025 dollars.

So the boards that I'm using execute instructions roughly 1000 times as fast as the AGC, they have about 100 times as much RAM and 60 times as much ROM (flash). And as my code doesn't achieve anything remotely as interesting as landing on the moon, these processors spend most of their time twiddling their thumbs in standby mode waiting for something to happen. By 1960s, 70s, 80s or even 90s standards this is a horrible waste of computing power.

Footnote 2: The ludicrous inefficiency of electric cars
I recently cycled past a garage and saw them advertising "175 kW charging". Yes, while we maintain our entire home on 5.5 kW, charging a single car can pull 175 kW from the grid. That's enough to blow the fuse of 30 homes like ours all at the same time !

Building a computer controlled ventilation system with HEPA filter to improve our indoor air quality

2024-09-30T19:20:00.005+02:00

Introduction - why do we need this ?
In general, the Netherlands offers a reasonably good quality of life. Residential areas are well looked after, noise pollution is greatly reduced by quiet asphalt on roads, air pollution is fairly well controlled in most of the country (but not everywhere: certainly not for those living near the steelworks on the west coast). But there are three things which regularly cause ludicrous amounts of air pollution in this country: fireworks on New Year's Eve, Easter fires, and the idea that people have that it's especially "gezellig" to have a fireplace or stove burning wood in their living rooms. Luckily, none of our neighbours are especially keen on barbecues so the summer air quality is usually OK.

The government advises people not to burn wood for heating when we have weather conditions which will cause the pollution to accumulate, but it seems that almost no-one who burns wood for heating ever takes any notice of this advice. At the time of writing, the "stookwijzer" website advises people in our area that burning wood will cause nuisance to your neighbours and air pollution. From six o'clock this evening they advise that people don't use their wood burners at all because the smoke produced will cause health problems, especially for those with lung problems. But I expect that no-one will take any notice of this and our outside air will be thick with smoke this evening.

What I find especially absurd is that it's still September and we've not even had any cold days yet. Outdoor temperatures have not yet gone under 8 C. We've not yet used any form of heating at all and the lowest indoor temperature that we've seen so far was 19.5 C, in the middle of the night. Why buy firewood and spend weeks in the garden chopping it up (as some of our neighbours do), and then set fire to it when you could insulate your home instead and it'll be warm without any effort being required ?

Air filters
Initially we used air filters quite successfully to improve indoor air quality. They're also good to remove viral particles which visitors might bring with them. Though it's popular to pretend that Covid is "over", it's actually still killing about 200 people each week in the Netherlands, and it's similarly deadly elsewhere.

We have two Philips 800 series air filters. These adjust their speed and run quite quietly unless the air is full of particles, so you can sleep in a room with one active. Other companies produce good products as well, of course. The light on the top is purple because I opened our windows to let in fresh air and the neighbours were burning wood again.

A couple of years ago I also made this super inexpensive air filter. It looks like a cardboard box with a vacuum cleaner HEPA filter on one side and an old computer fan on the other because that's exactly what it is. It doesn't have the same throughput as the Philips filter, but it does clear smoke from the air in a small room surprisingly quickly. The 12 V fan is run from a 9 V "wall wart" power supply, so it runs slowly and reasonably quietly.

A house ventilation system
Free-standing air filters are good at removing smoke from the air, but they can't do much if you open a window for ventilation. Without ventilation, the CO2 level in a room rises rapidly due to nothing other than the occupants breathing. So we needed something else.

For the last couple of years I've been working on improving our indoor air quality. As we no no longer use gas the air inlet in the upstairs (2nd floor - two floors above ground) boiler room was not required for the heating system any more so I now use it to bring fresh air into our home. It opens into the boiler room, allowing air to mix and warm up if the sun is shining, but the air needs filtering before it comes into the rest of our home.

A fan which pulls air through a HEPA filter in the boiler room is controlled by a small computer. The fan is switched on if the downstairs controller indicates that the CO2 level is high. The computer also measures the temperature in the boiler room as well as on the upstairs landing so it can cool or heat the house (slightly) by bringing in cooler or warmer air when that's possible. It also monitors the temperature of the solar power inverter and switches on an external cooling fan when it gets warm. I already had to repair that inverter and I hope that this will extend its lifespan. The computer also can switch on a small heater in the boiler room if the temperature in the room is too low. This has not yet happened.

The wall outside the boiler room: An Arduino mounted on the wall next to the inlet for the incoming air. The green LEDs indicate when the fan is active (there are two speeds). The yellow LED indicates that the cooling fan for the inverter is active. The red LED indicates that the heater has been switched on. I'll cover it up so that it's less ugly some time soon...

Inside the boiler room. No-one usually comes in here, but I still need to cover up the circuitry of course. The HEPA filter is the same as the type used in the Philips air filter. The fan is an inline "quietline" fan from Hornbach, which seems to be one of the quietest inline fans available. The three relays are used to switch the two speeds of the fan and the small electric heater. I recovered them from the old gas boiler.

The other half of the system is downstairs. There's a controller on the wall in the living room where our central heating thermostat used to be. This measures the CO2 concentration and switches on the extractor fan in the kitchen as well as the incoming air fan upstairs (to attempt to create a balanced flow of air). Communication between the two devices works via a serial link using the same cable as linked the old thermostat to the gas boiler.

The downstairs controller measures CO2 concentration and will automatically switch on ventilation if the level is too high. Buttons allow selection of continuous low fan mode, 'visitor mode' which attempt sot keep an even lower CO2 concentration, and off mode which turns off the downstairs and upstairs fans. The latter is intended to be used if we find that the system is somehow overloaded and is bringing in smoke. The controller is also linked to the cooker extractor in the kitchen so that it knows to switch off the house ventilator fan when that is operating, and even if it was not otherwise required it will switch on the upstairs fan to attempt to approximately balance with the cooker extractor. The downstairs controller also has a light sensor so that it can automatically switch to nighttime mode when we go to bed.

We exhaust air from the kitchen on the ground floor, using the same duct as the extractor fan over our oven. Only one fan can operate at a time. Having air travel slowly from upstairs down to the kitchen helps keep cooking smells and condensation out of the rest of our home even after we've stopped cooking

Downstairs controller. This is also Arduino based, using a Nano this time to make the whole thing more compact. Sensors measure CO2 concentration, temperature and humidity. They agree quite well with my Aranet 4. The buttons on the front allow selection of constant low fan mode, visitor mode and no fan mode. The green LED indicates low fan setting, yellow indicates high and red indicates that the fan is currently off because we have a low enough CO2 concentration. The Aranet 4 made me realise that the concentration of CO2 in a house rises quite rapidly just through breathing. We saw the reading rise quite quickly to over 2000 ppm on winter evenings with the windows closed, but that no longer happens due to the ventilation system.

In the kitchen I put a a t-junction in the ducting from the cooker hood on the left of this picture so that an inline fan under the wooden cover on the right can also send air into the duct. It feeds from another duct on the right side of the photo which reaches nearly to the floor next to the refrigerator so that we take air out from a relatively low level in the room where it is cooler. Non return valves are used to prevent one fan blowing air back out the other. It's a bit ugly and I still need to cover the silver tube up. In this location I used a 125 mm version of the same inline fan as upstairs.

How well does it work ?
We now have fresh smelling air indoors even when the neighbours are doing their best to pollute. That was the intention and it's worked out well.

Though the design of the system as a whole takes advantage of latent heat in the boiler room, the upstairs landing and even of heat leaked out by our water heater, it makes no attempt at all to recover heat from the air which we extract from downstairs. This probably results in a slightly higher heating bill than we would have in a completely closed house, but the air quality difference is enormous. In any case, our heating bill is absolutely tiny so there isn't much to save. I may end up building a heat exchanger downstairs as that seems like a fun thing to try to do, but I doubt we'll be able to measure much of an effect.

We went through last winter with an incomplete prototype of the system. I initially had an old computer fan for the air inlet upstairs, but it wasn't adequate to keep up with the downstairs fan. It also initially just switched on and off with a timer and there was no attempt to even try to balance flow with the downstairs fan. A roughly balanced flow of air does seem to create a better result overall.

Something that surprised me is how poorly CO2 travels between rooms. With no open windows but the door between our bedroom and the hallway open, the CO2 level can reach over 1300 ppm in our bedroom despite the hallway being around 700 ppm. I was surprised that diffusion didn't do a better job of lowering the CO2 concentration in our bedroom. Running one of the Philips air filters in the room moves air around enough to lower the concentration by about 200 ppm. But to achieve a really low CO2 concentration around our heads I think we would need a fan blowing air through the doorway.

Of course in the past no-one had a CO2 meter so we could never measure these things. When we first had the Aranet 4 but we didn't have any kind of ventilation system we'd see the CO2 ppm race up and beyond 2000 ppm in the evening in our living room just from our breath. It also headed in the same direction in the bedroom overnight. I suspect that we've unknowingly slept with very high levels of CO2 in past years without realising it and I think the same is true for most people. CO2 rises very quickly in any room with closed windows and doors, and using candles also rapidly increases the CO2 concentration.

I think a ventilation system has much to recommend it. It's a step beyond what can be achieved by air filters on their own. This system works. If there's interest I'll put the Arduino code somewhere that it can be downloaded.

Update January 29 2025
I just replaced the air filter:

Old air filter on the left, new air filter on the right. The old one actually looks worse than this in real life. It was actually slightly used in an air filter in our home before I installed it in the ventilation system in September, but it certainly didn't look like this.

The new air filter is completely white in colour and a little translucent, while the old one which has been installed for about four months is very dark and completely opaque. All that black dust would have been floating around in our home for us to breath in had I not installed the air filtering system. The majority of the dust almost certainly comes from wood burners which some of the neighbours use to heat their homes, but fireworks at new year and road traffic will also add to it.

Another notable change is a reduction in condensation, for instance around the inefficient thin double glazing fitted in our back door. This is because we have lower humidity in our home now because the moist air that we breath out is extracted by the ventilation system.

Saving energy with new appliances ?

2024-06-26T16:01:00.004+02:00

I've always been a bit skeptical about the idea of replacing appliances early in order to save energy. The embedded emissions in creating large appliances are not small, so you'd have to make a pretty big saving in ongoing emissions for it to be worth scrapping a device early to install another in its place. Generally speaking, I prefer to repair things and keep everything working for as long as I possibly can. But sometimes it does make sense to buy something new.

Since we moved into our home in the Netherlands 17 years ago we've done a lot to make our home more energy efficient. We've improved the insulation, replaced the windows, built a ventilation system (which I'll write about in due course), removed the gas supply altogether, and installed solar panels to generate more electricity than we consume. But the inside of our home hasn't seen so much work.

The kitchen was a bit tired looking when we moved in, and it's not got any better with almost two decades of use, so this year I've been working on improving things.

The kitchen cabinets were mostly actually still OK but the doors mounted on them, which were made of thin white plastic coated chipboard, were falling apart and they looked super ugly. Rather than throw everything away I've made new doors from scratch to fit onto the old cabinets, and also constructed new cabinets of plywood where they were needed. This is also much cheaper than a complete new kitchen, so it's a better fit with our limited finances. We then had the question of the refrigerator. The old built-in refrigerator was in the house when we moved in and I always had the idea that it consumed at lot of electricity because it hummed almost constantly. Unfortunately, until I started taking the kitchen apart I couldn't reach the socket where it was plugged in and measure it.

Measuring refrigerator/freezer consumption
The old (late 1990s / early 2000s) refrigerator turned out to use a whopping 500 kWh of electricity per year. That's five times as high as some newer models of the same size, small refrigerators without freezer compartments. We also had a freezer which we'd brought with us from the UK. This was a Liebherr unit which was a well rated model when we bought it. I'd looked around and found one of the first devices available which did not use CFC style refrigerants. But I measured the freezer as consuming 250 kWh per year, which is actually not more than some new comparable models. But 750 kWh per year in total for refrigeration is ridiculous.

New A-rated fridge/freezers with a similar capacity to our old fridge and freezer combined are rated as consuming about 110 kWh per year. None of the A rated devices are built in types so we had to choose between free-standing fridge freezers. We chose an Inventum KV2010B as this company gives a standard 5 year guarantee and provides reasonably economically priced parts for repairs.

New and slightly imposing fridge/freezer in our kitchen, next to kitchen units with newly constructed home made doors. For some reason all the A-rated fridge freezers are black. Whatever happened to "white goods" ?

The real world consumption of the KV2010B in our first week works out as equivalent to 190 kWh per year. That's above the rated 113 kWh / year according to the manufacturer. However the standardized tests are carried out, the conditions are clearly not the same as ours over the last week. Of course a week at the end of June is warmer than the annual average and I expect this appliance will use a bit less electricity in colder months (our old devices also consumed less in winter than in summer).

Energy rating certificate for our new fridge/freezer.

The same refrigerant, R600a, or isobutane, is used in the new fridge freezer as in our old freezer. I don't know what was used in the old refrigerator which we didn't choose, but it was probably something horrible. When we bought the freezer this was an unusual refrigerant but it seems to be commonplace now. That's quite an improvement. R600a has a very low GWP (global warming potential) of 4 compared with CFC refrigerants which can be in the thousands. It's not quite so low as the R290 of our heatpump, though.

The value of the electricity saved
We expect to save almost 600 kWh per year with this new appliance in place of the two old devices. That's significant. It's almost as much electricity as we used for all our heating last winter. It's also about the same as the output from two of our solar panels. I think it's worth noting that much of the saving will occur during night-time, on the shorter days of winter, or when there's not much sun. i.e. at times when it's especially valuable for us to save electricity because we don't have so much of it available from our own panels.

In the Netherlands the total retail cost of electricity including all taxes is currently around 25 c / kWh so a saving of 600 kWh of electricity is worth about €150 annually. Having paid €799 for the appliance the appliance should pay for itself in about five years. It will also save 134 kg of CO2 each year (at 223 g / kWh average emissions for NL). The actual cost for us is much more difficult to work out because we generate more solar electricity than we use.

Disposing of the old devices

The people who delivered the new fridge/freezer took the old fridge away for recycling, but they would only take one appliance, so I had to take the freezer on a 7 km trip to the local recycling centre by bike. Both of the old appliances were the same size as this.

At the recycling centre they picked it this way, putting considerable pressure on the radiator at the back and risking causing a leak of the refrigerant. That's why I didn't buy a CFC containing freezer in the first place. I suspect that even when they're supposed to be safely removed, only a small percentage actually are safely removed.

An earlier trip to the recycling centre. Judy and I transporting parts of the kitchen cabinets, mostly rather nasty damaged doors but also the parts which contained the old built-in fridge.

Update: Energy meter problem
It turns out that our plug-in energy meter has a problem. It's reporting 270 V as the voltage of our mains supply instead of the ~225 V which the multimeter reports. 270 V is above the legal maximum supply voltage. I believe the multimeter. Anyway, this 20% high voltage reading probably translates into a 20% over reading when measuring Watts as well, so the first week of the new refrigerator was probably a lot closer to the manufacturer's specification than what I measured.

Further update: Brennenstuhl PM231 review: it completely failed
In January 2025 I noticed that this energy meter had now completely failed. It usually now doesn't boot up at all, just displaying all segments on as shown in the photo below even when the reset button is pressed, but occasionally when it does get as far as booting it now claims that voltage, current, power and power factor are all "zero". I contacted the manufacturer and they're not interested in doing anything about it. Drilling out the weird three sided security screws allowed me to take a look inside, but there's no obvious failed part so I don't think I'll be able to repair it. The case might be usable for a DIY project with a relay inside.

Don't buy a Brennenstuhl PM231 energy meter. They don't work for long before they start to fail in a way in which they give inaccurate results. The company isn't interested in fixing them.

Brennenstuhl PM231 energy meter. Don't buy one of these. They slowly become less accurate over time and then completely fail. Brennenstuhl won't repair them because the fail occurs outside of the short guarantee period, and is probably unnoticed by most people initially. After all, these gadgets spend most of their time in desk drawers, not constantly in use.

Twelve years of rooftop solar power

2024-04-05T18:01:00.004+02:00

Our rooftop solar power system was installed 12 years ago today. In total they've generated 40900 kWh since installation. While last year (2022-2023) was a record year for output from these panels, this year (2023-2024) was not. The end of 2023 and beginning of 2024 were marked by particularly grey and dull weather so this output is not surprising. But the output of 3362 kWh over the whole year is still only slightly below the 12 year average of 3378 kWh per year.

Total output of our solar power installation per year. The blue columns are the contribution of the 12 year old rooftop system. The red shows the additional power generated by the extra panels we've installed on our garage roof.

The garage roof panels added an additional 1416 kWh to the total for the year. These were installed as we wanted to to compensate for the consumption of the heat pump and electric water heater that we installed when we got rid of our gas connection.

This winter was the dullest that we've recorded, resulting in the blue bar for March 2024 being easily the lowest in the graph. Even the substantial contribution of the new panels, shown in red, didn't result in higher total output than we have seen in brighter March months in past years from the rooftop panels alone. But the extra panels still helped us to generate a higher proportion of our consumption this winter than we have done without them.

Our rooftop panels having been operating for 12 years also of course means that the inverter has been operating for 12 years. The inverter actually only lasted for six years and three months before it failed due to poor soldering and the manufacturer refused to fix it. I fixed it myself and the repair that I made has very nearly doubled the life of the inverter thus far. I am still very irritated that ABB, the inverter's manufacturer, preferred to tell us that the whole inverter had reached the end of its life and needed to be thrown away and replaced with a new one when they could have made the same simple repair in order to keep it operating.

Anyway, the system as a whole is still working very well. It's difficult to work out exactly by which date this system paid for itself because the electricity price has changed over time. But the cost of electricity to consumers, including all taxes etc., has always been higher than 19.5 c, so I think we can now reliably state that the original purchase price of €8000 has been repaid by the solar panels and inverter together. Since 2012 the cost of solar panels has dropped precipitously and I expect the extra panels on our garage will cover their cost in under 4 years.

If you've read this far you'll probably also be interested in my blog post from four days ago about how the heat pump, electric water heater and solar panels together have reduced our energy bill to less than zero.

Relative cost of heating with a heat pump vs. gas (How to reduce your heating bill by 100%)

2024-04-02T00:01:00.096+02:00

We've now had our heat pump for one whole winter. For the purposes of this blog post, "winter" refers to each period of November through to and including March, as those are the months when we use heating. Because we've gone through our first winter period with the heat pump we can now make a comparison with other winters when we used gas for heating and work out both the financial cost and (more importantly) the emissions due to both heating options.

This house was cold
We've lived in our home since 2007 and I've recorded our energy consumption consistently each month. Our home was built in 1972, just after the discovery of gas under the Netherlands. At this time it was assumed that gas would always be an inexpensive fuel source and no-one was making much effort to make housing efficient. We had very little insulation and single glazing in most of the windows. Only the living room, dining room and kitchen had old and basic double glazing.

When we worked out how much the first winter's energy bills were going to be this really shocked us and we ended up setting the thermostat as low as 14 C and in order to reduce the gas consumption we even turned the heating completely off on some of the coldest days of winter until our children were about to come home from school. This was quite unpleasant so we started some steps to insulate our home even in the first winter in order to reduce the energy requirement.

Each insulation job contributed to reduced heating requirements and a warmer house. At first there isn't much of a reduction in consumption to see, but that's because we were compensating by living with a bit more warmth each winter. The difference between the blue and red line was the consumption of the pilot light in an old gas water heater that we replaced with an electric water heater last year.

By the winter of 2022/2023, the last in which we still had a gas connection, our heating consumed just 287 m3 of gas rather than the average of just over 1110 m3 of gas per winter that we had burnt over the first four years that we lived here. That's about a 70% reduction in energy input, without changing the heating system.

This winter we used an air-air heat pump in our living room as almost the only heat source between November and March. There's a heated towel rail / IR panel in the bathroom which comes on with a timer every morning but otherwise no permanent heating upstairs to replace the no longer used radiators. We did make very occasional use of portable electric heaters. We've been quite warm. It's certainly far more comfortable upstairs now without any heating than it was in the first years that we lived here when hot radiators struggled to keep uninsulated bedrooms with large single glazed windows up to a comfortable temperature.

Energy consumed
Our heat pump consumed 682 kWh of electricity over the five month winter period. That's roughly equivalent to the energy content of 68 m3 of gas. i.e. this winter we used only about 6% as much energy to heat our home as was the case when we first moved here.

I have to admit that this was not a particularly cold winter, but it was especially grey and wet so the solar panels that were supposed to run the heating didn't do as well as was expected. Despite that, even this winter, they still generated more than 30% of the electricity that we consumed over those five months so we had to buy just 470 kWh of electricity from the grid to run our heating.

CO2 output
We're signed up to a green tariff which promises us 100% green electricity ("100% groene stroom uit Nederland") but I never know if you can really trust such a claim so I will instead take the an average carbon intensity of 223 g per kWh for Dutch electricity in 2023 as a worst case scenario for our CO2 output.

That worst case scenario suggests that our heating may have produced 105 kg of CO2 this winter (470 * 0.223), which is a huge reduction compared with the emissions of our gas boiler when we first moved in. Our gas heating CO2 output averaged around 2000 kg of CO2 per winter over the first four years that we lived here. i.e. the worst case scenario gives us a 95% reduction in CO2 output for heating due to a combination of insulation and electric heat pump replacing the gas boiler. The first 75% or so of that reduction in emissions is due to the insulation and the heat pump is responsible for the rest.

What would it have cost if we were still using gas ? What has it cost this year all-electric ?
We could never afford that level of gas usage so we shivered more than most when we first came to live in the Netherlands. If we'd continued burning gas at the rate that we did in the first four years that we lived here then it would have cost over €1600 for heating this winter. Instead of this, we insulated our home in order to consume far less heat. If we had stayed as we were last winter, with the same insulation but with gas heating instead of the heat pump, then we'd have consumed about €400 worth of gas over the winter period. That's already quite a saving over the average.

According to our energy supplier, the gas consumption of an average home like ours (semi-detached / 2 onder 1 kap) over the winter period is around 1360 m3, which is actually higher than what we found unacceptable when we moved here. At the current price of gas quoted by the energy that gas costs an average family in an average house like ours about €1930 each winter and each of those homes will produce over 2400 kg of CO2 for heating over that period.

But our gas supply was removed last year and we're all electric now, so what did it actually cost us to heat with the heat pump ?

For the last year we've been paying our energy company €5 per month for the electricity connection only (there is no gas connection). We've just come to the end of the yearly billing period and they now owe us more than €200 for the excess electricity that we produced from our solar panels and contributed to the grid. i.e. our energy bill is negative.

End of year summary from our energy company. They owe us €252, and we can continue to pay them €5 per month next year.

Insulate ! It makes a huge difference to your comfort and your bills. Then you can install a small and inexpensive heatpump.
Every step that we've taken in the past to better insulate our home has led to lower bills, lower CO2 output, and more comfort. It took us a while to do everything because our income is small so we couldn't do it all at once. But do everything you can, as soon as you can. It's really worthwhile to do all of this before you even think of replacing the heating system.

If you're in a rented home that makes things more complicated, but encourage your landlord to everything they can. This is a no-brainer for any sensible landlord as any work done adds to the value of their asset. If you're in an apartment and shared ownership of walls and roofs is a problem, then do whatever you can to get the organisation (probably a VVE in the Netherlands) to make changes. That's a difficult situation because you have to get a lot of people to agree. But it's all worthwhile. Every penny spent on heating is wasted, every penny helps to pollute the planet, so let's stop spending so much on it.

Reducing energy input
Something that seems quite crazy to me is that people replace absurdly oversized gas-powered boilers (ours was rated at 28 kW!) with equally absurdly oversized heat pumps. Yes, they'll cost less to run and have lower emissions than gas heaters, but they still consume a lot of electricity. Those high powered heat pumps require a three phase connection (single phase is limited to 16 A / 3.5 kW in the Netherlands) in order to suck in enough current to produce their huge outputs. What we installed has a 3.5 kW maximum output and it consumes a maximum of about 1 kW when it's in use. It it really warms the room up quickly when it starts up, but it soon settles down to a lower power mode to maintain temperature.

I think it's important that we try not only to switch away from fossil fuels but also to reduce our total energy consumption. The energy transition certainly won't be made easier if we try to achieve that transition by installing lots of electrical devices which consume enormous amounts of energy.

Once a house is well insulated it just doesn't need much heat input. At that point, an inexpensive air-air heat-pump like ours can keep your home at a comfortable temperature. Our heat pump and everything I needed to install it myself together cost significantly less than one year's average winter heating bill. The result of installing this device is that we no longer have a heating bill. Why would anyone not try to do this if they can ? We may now install a second one upstairs in the room where I work, but that's really a luxury: I've been fine this winter. If I didn't work from home I'd probably not be considering it at all.

Effect of heat pump and electric water heating on our electricity bill in December 2023

2024-01-11T15:41:00.009+01:00

Since we had our gas supply removed last year we've used electricity for both our water heating and our home heating. Unsurprisingly, this means we're using more electricity, especially in winter months as we no longer burn gas for heating.

We consumed 222 kWh more electricity from the grid in December 2023 than we did in December 2022.

Our heat pump consumed 168 kWh of electricity in December and the water heater used about 70 kWh. It's been a bit chilly upstairs sometimes so we've also used some small electric heaters occasionally, but clearly we also managed to reduce our consumption of electricity elsewhere as otherwise the numbers don't quite add up.

We had hoped to compensate at least some of the increased electrical consumption by expanding our solar power system. Unfortunately, due to the last quarter of 2023 being incredibly grey and rainy (a new record for rainfall was set, largely due to rainfall in the last three months of the year), the expanded system produced just 42 kWh in December, vs 60 kWh from the smaller system a year before.

Part way into January, waiting for ice to melt off the extra panels so that they could have full performance, if only the sun came out properly...

The gas we didn't burn, and the resulting CO2 emissions
In December 2022 we burnt 125 m3 of gas. That's less than an average apartment and well under half the average for a house like ours. This year we of course burnt no gas at all. 125 m3 of gas contains the equivalent of about 1250 kWh of energy, so the 222 kWh extra electrical energy that we drew from the grid was considerably less than that contained in the gas that we used to burn.

The 125 m3 of gas which we burnt in December 2022 produced 223 kg of CO2 (factor of 1.78). The average CO2 intensity of Dutch electricity for 2022 was 321 g / kWh meaning that our extra 222 kWh of electricity consumption in December 2023 will have led to 71 kg of CO2 emissions if our electricity was of average CO2 intensity for the Netherlands. That's a worst case scenario as even in the exceptionally grey month which just passed, 8% of our electricity still came from our solar panels. We are of course also signed up to a tariff which claims to supply us with zero CO2 green electricity (despite this not always being possible to do).

Therefore in the worst case our emissions in December as a result of replacing the gas supply with electricity were less than a third of what they would have been if we'd continued to burn gas. In the best case we did a lot better than that, but we're then in the realm of guesswork based on where our electricity might really have come from. When a large proportion of Dutch electricity still comes from burning fossil fuels it's nonsense to ever claim that electricity has zero emissions.

An average Dutch household in a home like ours will have consumed around 300 m3 of gas in December, resulting in around 530 kg of CO2 being emitted so in the worst case we had around 1/7th of the emissions of an average household.

Update: Dutch emissions per kWh electricity may actually be much lower.
It's possible that emissions in 2023 per kWh were actually much lower than 321 g. A smart guy on Mastodon calculated that the true figure was actually around 223 g / kWh for the Netherlands in 2023. This would have the effect of reducing our worst case emissions for heating in December to just 50 kg, meaning that we emitted about a fifth so much CO2 this year compared to last, or around a tenth of the amount emitted by an average similar size household using gas for heating.

Costs
It's difficult to work out exactly what the cost of gas would have been, but based on pretending to take a new contract out with our electricity supplier it appears that they would have charged us about €200 for the 125 m3 of gas had we used it in December. The cost of the extra electricity that we used is about €100.

But actually we deliver more electricity to the grid each year than we consume, so we only pay €5 a month for energy. At the moment our supplier says they still owe us about €260. This amount becomes due in mid February so we won't get quite that much returned to us because we expect to use more electricity than we produce for heating in January and February as well.

How well did the heat pump work in the cold ?
The lowest temperature in the morning that we've seen so far was about -7 C. There was plenty of heat from the heat pump. It does need to pause and defrost itself occasionally when it's cold outside.

Onward and hopefully downward
December is the worst month of the year due to the short daylight hours. Let's hope we can take proper advantage of the sun in January, February and March as more sun means lower emissions.

This may look like a grey rectangle but it's an actual photo of the sky today. The sun is roughly in the centre (that's a guess as I couldn't see it). Not exactly ideal weather for solar power.

An all-electric home with air conditioner (aka air-air heat pump) as heating

2023-08-23T19:09:00.016+02:00

Regular readers will know that we had the gas supply removed from our home in April this year. This left us with no central heating in our home. We used a portable 400 W electric infra-red heater in he living room on some of the cooler days of March and April, which worked well enough for those months because our home is now very well insulated, but we knew that in the middle of winter we'd need a more effective form of heating. Having the gas supply taken out meant that we were working under a time constraint - we had to find a solution before next winter. We now have that solution.

Electrical heating
Electrical heating is 100% efficient. All the energy which goes into an electric heater will be turned into heat. Actually, the same thing applies to all other electrical appliances - some of the energy may turn into mechanical movement, calculations, light, sound etc. but it all becomes heat in the end. So everything electrical helps to heat your home at almost exactly 100% efficiency (we lose a tiny bit from light shining out of windows and other small effects).

But just because resistive electric heating is 100% efficient that doesn't mean it's actually a particularly good way of heating your home. Electricity costs more per kWh than gas. Also if gas is being burnt to generate electricity then due to inefficiencies of the power station and transmission lines more gas will be burnt in total to heat your home than would be the case if you had an efficient modern gas central heating boiler.

For a while, around 50 years ago when the future looked like it might be nuclear powered, the idea of storage heaters was popular as they would allow excess "too cheap to meter" electricity generated at night by non-throttle-able nuclear power stations to be used as heat during the day. Homes in the UK were built as "all electric" and I lived in some homes with that type of heating. It worked reasonably well. There was a logic to it, but nuclear is not a technology which is going to come along and quickly save us from ourselves right now. Many of those homes were later retrofitted with gas, which now looks rather unfortunate. Our home in the Netherlands has gone in the opposite direction. Built originally against a promise of cheap endless gas, we've transformed our home to be fully electric.

Heat pumps
Heat pumps on the other hand are popular now. They appear to do something magical in that they generate more heat energy in their output than they consume as electrical energy from their supply. There is of course no magic involved at all. In this house we obey the laws of thermodynamics and we're not creating something out of nothing. Heat pumps actually (mostly) just move heat around. When heating a home in the winter they take heat out of the already cold air, water or ground outdoors, making it even colder, so that that heat can be emitted indoors. It's a neat trick.

The problem with heat pumps sold to replace central heating boilers, providing hot water to flow through radiators or under-floor heating, is that they're very expensive and they're over-sized for many well insulated homes. When I calculated how much gas we burnt last year to heat our home it became obvious that the 28kW gas central heating boiler installed in our home had only burnt enough gas to have operated at full power for the equivalent of about three days in the whole year. The lowest output heat pumps are rated at around 7 kW so one of those would have to run for about 10 days in the year. It would still lose a little in efficiency because the boiler would be on the top floor and the hot water would still have to be piped two floors down to reach the living room, losing some of the heat along the way (even with well insulated pipes), but total energy consumption would be 400 kWh over the year. By comparison, direct electrical heating to provide the same amount of heat would consume about 2000 kWh of electricity in total.

Air conditioners
Air conditioners work in exactly the same way as a heat pump. Many models of air-conditioner can also operate as heaters and when so used they have the same high efficiency as heat pumps. i.e. they produce far more heat as output than they consume from the electricity supply. Even though they don't attract a subsidy they have a much lower price than a heat pump, so we decided to install an airconditioner as our source of heating in the winter.

We could have installed two air conditioners, one up and one down, but we're instead going to try to live with just one in our living room together with occasional use of a portable electrical heater upstairs should it prove to be necessary. We have rarely turned on the upstairs radiators in our home in the past so we clearly don't have much need for heating upstairs, but if it turns out to be necessary nothing excludes the installation of a second air conditioner upstairs. Two air conditioners still cost only about half the price of a heat pump.

The nasty environmental problem with air conditioning and heat pumps
One of the things that has put me off both heat pumps and air-conditioners in the past is the high environmental impact of florinated refrigerant gases. These not only have a disastrous effect on the ozone layer but that also can have a greenhouse effect greater than 10000x that of an equivalent amount of carbon dioxide (GWP = global warming potential). Even the R32 refrigerant often touted as environmentally friendly has about 670x the global warming potential of the same amount of CO2.

While it's supposed to be the case these days that refrigerant is recovered when airconditioning systems are taken out of use, does that actually happen in reality ? Photos showing destroyed airconditioning units dangling from buildings in war-zones and after natural disasters indicate that a considerable number of these units don't get decommissioned in a manner which is sympathetic to the environment, and even if they are, what do we do to ensure that those gases never escape once they are extracted from an old airconditioner? I'm not convinced that these gases can be contained for the rest of time and do all the old gases make their way safely to one of the few plants which can destroy them ? I don't think I'd like the answers to these questions. Luckily, there is an alternative:

The solution: R290
R290 is a refrigerant with a GWP of just three. Not three hundred or three thousand, just three. On release it has a greenhouse effect only three times as bad as CO2 and it has no no effect on the ozone layer. There is very little refrigerant in an airconditioner, less than half a kg. As such, the total harm than can be done by releasing this gas is very small. R290 is actually just propane, so not a florinated gas at all. As a result of this it's also legal for people to work on R290 systems themselves. No "f-gas certificate" is required for working with R290 here in the Netherlands because it is not an "f-gas". DIY is good - it should reduce the total cost and I like doing stuff.

Our choice of airconditioner
R290 split airconditioners have been promised for some years but they still seem to be new on the market. I picked the only model that I could find on the Dutch market earlier this year, a Midea 3.5 kW air-conditioner. This was the first model of airconditioner ever to win German Blue Angel environmental certification. It took a while to find a supplier as seemingly not many people sell them, but I did find a supplier in the Netherlands.

As this airconditioner has an SCOP of 5.2 it will in principle consume only about 400 kWh of electricity a year to provide as much heat directly in our living room as our old central heating boiler put into hot water which it then pumped around the house. It should operate efficiently down to -15 C which is almost as cold as it's ever been here. It's never been that cold for the entire day. But anyway, if it gets really cold I guess we'll have to go out cycling for a bit to warm up.

To provide power we already expanded our solar power installation with two extra solar panels which will produce about 700 kWh of electricity a year. In total we should easily generate enough electricity each year to supply the air conditioner as well as the electric water heater (for which we installed another two solar panels) and every other electrical device in our home. While in winter months even our over-sized solar setup won't generate enough to run everything, the overcapacity should mean we are able to operate at least mostly on our own electricity for most months of the year.

Now some DIY
The airconditioner turned up a couple of days after ordering and then I ordered a few extra parts to complete the installation.

The outdoor unit in a box. Clearly labelled R290 / Blue Angel. Quite heavy to move.

I needed refrigerant lines and electrical cable and I chose rubber feet for mounting the outdoor unit on the ground outside our home. We could have mounted it on the wall but I thought that brought a higher possibility of vibrations being carried into our home (the unit doesn't vibrate much and I now doubt this would have been an issue). Also the wall mounting brackets available didn't seem to be large enough to allow enough space. The outer unit is recommended to be installed 30 cm from a back wall for maximum efficiency.

The first thing was to determine the best place for the inner unit. I decided to place it half way along our living room wall and so high as possible. The instructions suggest a minimum of 15 cm between the unit and the ceiling and that's about the height at which it's mounted. I didn't want visible ducting inside our home so I drilled a single large hole through which all the pipes and wires had to run. This had to run downhill to the outside in order to make sure that the condensate would find its way out through the wall, and in my case I had to run it at a more extreme angle than I otherwise would have because the carport outside our home is attached to the outside wall at the same height as the inner unit of the air conditioner is on the inside wall.

Drill with 70 mm attachment for drilling through concrete. This does not go through in one push. You have to work at it a bit, and stop to let it cool down quite often. You also have to pull out chunks of concrete and brick which fill the tool and stop it from working. It took more than an hour to drill the hole. I had to work from both sides as the wall is over 30 cm thick so I first drilled all the way through both layers of the wall with a long 12 mm drill bit.

Hole in the wall, sloped downward to avoid the carport outside. I lined the hole with PVC pipe, cut lengthwise so that it could adjust to the right shape and sealed with PU foam. Note: a lot of concrete and brick turned into dust. I worked with a mask on as well as ear defenders and had a vacuum cleaner running continuously, which helped to avoid too much dust finding its way elsewhere in our home.

The refrigerant tubing comes as a reel of copper pipe with insulation already fitted. I was cautious of bending this copper tubing as I'd expect it to flatten if bent too sharply but it unwound without causing any harm to itself and could be poked through the wall to the other side also without harm. I could then attach the pipes on the outside to the external unit. In my case exactly three metres of pipe was required. This was supplied with the required flare to fit both units, making the job a bit easier.

Black plastic covers on the piping of the indoor unit. The indoor unit has high pressure nitrogen inside so there is a hissing noise when they are loosened. That does not mean that refrigerant is leaking - the refrigerant is in the outdoor unit. However it's important that there should be a hissing noise as that indicates that the indoor unit has held pressure, also that it's not been contaminated with damp air. This didn't seem to be written down anywhere so I thought I'd add it here.

By this stage I'd put everything together so that in theory it was ready to go, I then tried to find a contractor to carry out the final step: Before you can set an airconditioner into operation it's necessary to draw a vacuum in the pipes so that there is no air in the system. Only after that has been done is it possible to release the refrigerant from the outdoor unit into the system. Some people don't bother with this step and I assume that their airconditioners don't operate to their full potential as a result.

I didn't have a vacuum pump and I thought it reasonable to let someone with experience do this part of the job for me. I even thought it might save a bit of time. However that turned out not to be the case at all. This was the most time consuming part of the whole project ! I waited over a month for more than ten different contractors to get back to me. They either said they would only with a certain manufacturer's airconditioner, or they wouldn't check other people's work, or they said they were too busy. Eventually, one guy said he'd come and do it. He made an appointment for two weeks in the future... and then he didn't turn up. So this was also to be a DIY job.

The standard price for setting an airconditioner in action is €200. That's what everyone who said they could do the job said they'd charge me, though none of them seemed to need the money. In the end I bought a vacuum pump for €115 expecting to need adaptors and pump oil in addition, but it turned out that everything I needed was in the box with the vacuum pump. This was a very simple and quick job to do, apart from the waiting around. No more than half an hour of actual work.

Vacuum pump pulling the air out of the tubing. After half an hour I turned off the blue tap and disconnected the yellow hose.

, which was never an option

The next morning we still have "-1 bar" relative to ambient air pressure so it didn't leak (i.e. close to 0 bar in reality negative pressures can't exist)

So the pump was set up and drew a vacuum for half an hour. I then I disconnected the pump, leaving the pressure gauge displaying -1 bar overnight. After that I let some of the gas into the system, the pressure rising to about two bar so that I could check my connections to the pipework with soapy water to see if there were any leaks (which I'd have to tighten up before going further). There were no bubbles forming so I let the rest of the gas into the system, still no bubbles, then I removed the meter from the outdoor unit, fitted all the covers and switched on. The airconditioner works.

Outdoor unit. The white cover over the cables and tubes goes to just slightly underneath the carport. The inner unit is on the other side of the wall a few cm higher. The switch on the wall is a legal necessity. The watering can catches the condensate so that we can use it in the garden. If the air conditioner is set on cool mode for an hour it produces a surprising amount of water.

The inner unit on the wall in operation. No visible wires or tubes. Everything works. We've used it to cool a couple of times and it's very effective. Heating has been tried only momentarily because it's summer and we really do not need heating yet. Hopefully this will work as effectively as we need it to in winter. It's very quiet in operation. Almost nothing to hear at all, certainly much less noisy than a table fan even on a low setting. The displayed temperature is what we were cooling to in the summer, not what we heat to in the winter.

We have a heating solution!
So we now have a heating solution for next winter. It will consume less electricity than a heat pump but hopefully provide us with enough heat. It's a bit of an experiment for us to say that we're only going to heat the ground floor, so wish us luck. The kitchen is a bit of a worry because it's around the corner from the living room and dining room. But the kitchen also has other heaters in it, such as a small water heater under the sink, the refrigerator etc. The extra insulation job that I did on the kitchen door a few days ago was specifically intended to try to keep the kitchen warm when we are heating just the living room. We have other plans and there are more things that can still be done. Watch this space.

Did I forget to mention summer ? We installed this air conditioner primarily to provide heat in the winter, but obviously an air conditioner can also be used as an air conditioner. We have done that for a couple of afternoons when it was very hot and I have to say that it's very pleasant to have a cooler home when it's hot outdoors. Luckily these times also coincide with our having excess solar power and the grid being quite full due to the amount of sun beating down on everyone's homes, so we find ourselves still exporting electricity while the airco runs. I don't see a downside to using the air conditioner in this way sometimes. With weather becoming more extreme we might well use it more often. But we don't intend to live in a permanently air conditioned home. When the weather allows, it's much nicer to open the windows.

Getting rid of the radiators and central heating boiler
A job that I've not yet done is to get rid of the radiators and central heating boiler from our home. There's a lot of metal involved, a lot of heavy work. They take up a surprising amount of space. We didn't get rid of these things when we first had the gas removed because that would mean burning a lot of bridges. We might have decided to install a heat pump instead of air conditioning, and that could have worked with our existing radiators (which are oversized to suit our originally under-insulated home). While I'm quite confident, this also means that if the air conditioner doesn't work out this winter, we could still make use of the radiators next year with a heat pump. There's no need for us to rush this.

Car airconditioners
What's the deal with car air conditioners ? From what I can tell these leak all the time and drivers respond by having them "topped up" with more refrigerant, sometimes annually. If there's a crash (and there are always crashes) then the refrigerant is released and having its awful effects on our climate and the ozone layer. Air conditioning in cars really should not be allowed, certainly not with use of refrigerants which are more destructive to the environment than R290.

Cars make everything worse.

Update: The first cold month - November 2023
November this year was colder than usual. We had snow and persistent freezing temperatures which we've not had in November for many years. There was also very little sun. So how well did the heat pump work ?

Gas usage November 2022. We consumed 52 m3 of gas, compared with 119 m3 for an average apartment and 217 m3 for an average house like ours.

In November 2022, which was warmer than this year, we used 52 m3 of gas for heating. That was less than half the amount used by an average apartment in the Netherlands. This year we substituted 105 kWh of electricity consumed by the heat pump. 105 kWh of electricity is equivalent to the energy released by burning about 10 m3 of gas so we're now heating our four bedroom semi-detached home with about 1/10 of the energy required to heat an apartment.

And the CO2 footprint ? Burning 52 m3 of gas results in the release of 92 kg of CO2. The average gCO2/kWh for the Netherlands in 2022 is 321 g so consuming 105 kWh of electricity results in the release of 33.8 kg of CO2 on average. That's about a third of what we produced last year with gas. But even with the particularly grey weather that we've had for the last month we still generated 1/4 of the electricity that we used from our solar panels (and we used 80% of that directly, not relying on the grid too much as a "battery"), which brings us down to around 25kg, or not far from a quarter of last year. We're signed up to an energy contract which promises "100% green" electricity but while that provides a stimulus for green energy producers it doesn't really change what comes from the grid. I hope of course that we're at least providing a push towards producing greener electricity.

But even in the worst case we're looking at a far lower CO2 output than the 386 kg which an average semi-detached house like ours produced last November.

Two small insulation jobs

2023-08-15T14:53:00.002+02:00

We've make improvements to the efficiency of our home every year that we've lived here. Over time there are of course fewer large jobs left to do, but there's always something that can be improved. While installing solar panels or getting rid of the gas supply are more dramatic, the small jobs also reduce our energy usage and help to make the larger improvements more effective. The same small improvements will reduce energy usage in any home.

Over the last 12 months we've done two small jobs. Both of them were as a result of measuring indoor temperatures on outside walls or doors. The aim of these jobs was to improve the insulation of a small section of our outside wall and the rear door which leads from our kitchen directly into the garden.

Adding cavity wall insulation

We had cavity wall insulation installed in our home in 2008. It was one of the first things that we had done after moving into our new home because we knew from past experience in other homes that it was a very effective type of insulation. Unfortunately, the installers missed a bit: While they were concentrating on the large area of cavity wall at the end of our home, there was a roughly 2 m tall by 0.75 m wide piece of cavity wall on the other side of our living room next to our front door which they didn't treat at all. Measuring the temperature of the inner wall in winter revealed it to be easily the coldest spot in our living room. As a result some condensation occurred there and there was sometimes a little mildew to wipe away. I asked many companies to come and do this small job, but none of them were interested. They'd either just say no, or they would quote the same price as for a whole house, which is not only ridiculous for a half hour job that they could have done at the end of a working day, but also not cost effective. So this had to be a DIY job and I finally got around to doing it in September 2022.

Obviously I don't have access to a professional machine which can inject insulation at high pressure so I would need the holes to be closer together. I decided to use expanding polyurethane insulation. To begin I drilled a couple of holes just a few cm apart to see if the foam was expanding sideways in the cavity and when this was confirmed I started drilling holes about 15 cm apart in a zip-zag pattern. It took about three hole cans of polyurethane foam to do the job. Much cheaper than the quotes I'd received. The holes were filled with mortar and there's now no sign at all that that was done to the wall.

The two holes near the centre were the first test holes. I then drilled holes in a zig-zag pattern up the wall and squirted in insulation until it was visible in the next hole along.

During winter 2022/2023 I could measure an obvious change. The interior wall was no longer cold, but actually slightly warmer than the opposite wall with the professionally applied insulation. We no longer have a condensation problem anywhere in our living room. So this is a definitely improvement. I can't say how much heating energy it saves as that's almost impossible to measure, but it will mean that we require at least a little less heating.

Insulating the back door

The wooden panel under the window in the back door from our kitchen to the garage is the coldest spot in the whole house. As a result it attracts a lot of condensation in the winter and has to be kept clean, and we also lose quite a lot of heat through it even though it's a relatively small area. The door was on the list of things that I intended to replace, but when I came to look for a more efficient replacement I couldn't find one. No-one seems to sell doors like this with insulation inside them. There are plenty of front doors with insulation, but the back door options all have glass right down to floor level, which is not an advantage for us with dogs which will respond to birds or (worse) cats in the back garden. So I decided instead to try to insulate the door that we already have. It's the least expensive and the least disruptive way of insulating our back door.

For this job I made wooden boxes of nearly the width and height of the wooden panel on the door, one to install inside and the other outside. The outer shell of each box is 3 mm thick marine grade plywood while I used 1 cm square wood to make the box form.

Boxes under construction. Marine ply, one cm square section wood and wood glue.

Each box is filled with two layers of aluminized bubble-wrap material. This is not the best insulating material, but I could fit two layers in each box, so there are four layers in total. I also wanted to use a material which would form a moisture barrier and which should reflect some heat.

Two layers of aluminized bubble-wrap type material fit inside each of the boxes. That's four layers in total either side of the existing wooden door. Opinions seem to vary widely about how good an insulating material this is, but four layers of it will of course work better than one. In this case it was selected because it's clean to work with and I'll be able to easily remove these panels from the door if they turn out to be a problem for some reason.

Each panel is nailed in place, with a layer of sealant between the box and the existing door.

Plenty of nails to make sure that the sealant really does seal. I don't want moisture getting inside.

After fitting the inner and outer panels they were both painted to match the door.

Before and after. The existing door was not in perfect shape, but most of the damage is now under the new panel so it should be more resistant to the weather than it was before. We will see.

So now I wait to see how well this works. In the summer when the door is in full sun I've been able to measure a 10 C difference in temperature on the inside of the door between the outer part of the door not covered by the new panels and the inner part of the door which is covered so it must already be helping to reduce the temperature of our home during the summer months. I'll make measurements during winter and add them here.

I wouldn't have done this to a new door, but our door was showing its age already so I'm hoping this will extend its useful life. While there is no rotten wood (there was some on the inside but I fixed that problem several years ago) there were gaps between the panels into which rain could penetrate. I'm hoping that the new outdoor panel will stop this from occurring, but of course if rain gets inside the panel that could create a problem. It's an experiment.

As with the cavity insulation job, I don't think it will ever be possible to measure exactly how much energy is saved by insulating this door, but it should mean that we need a little less heat next winter. As the next job is to change the way we heat our home, this will be important.

A previous blog post covered other small insulation jobs.

More more solar panels. Do we now have enough energy for a gas free home?

2023-04-17T17:05:00.003+02:00

We now have four solar panels on our garage roof. They're at an angle so that they face exactly toward the south.

Today with help from a friend we installed two more solar panels on our garage roof. This means we have four 400 W panels on the garage roof to work alongside the sixteen 235 W panels which are on the roof of our home.

The original two garage mounted panels were in the shade until about 9 am so you can see from this graph that they suddenly "wake up" at that time. The new panels placed today do better a few minutes earlier as they'll be earlier out of the shade.

The roof of our home is oriented south west, while the panels on the garage are oriented directly toward the south so as discussed a few days ago they compliment each other. The garage is shaded by our neighbour's home early in the morning but as the new panels are further to the south and will be shaded less (even though to arrange this we had to push the older pair slightly further north) we're hoping that we see a little bit more electricity early in the morning than was previously the case.

The new set of panels, closer to the camera, are mounted at just 12 degrees, vs. the 24 degrees of the set which we put up last year. This will mean they have slightly lower output overall, but they will shade the older set behind them less often due to being lower at the back and they will catch the morning sun from the east a bit better due to their lower angle creating less of a self-shadow.

The usual "back of an envelope" design process

Last time I couldn't get commercially made hooks as everything seemed to be sold out everywhere. This time I used commercially made hooks to hold the solar panels in place as they were available inexpensively. Otherwise the frame which these panels are mounted on is very similar to that of the last pair of solar panels except that they're at 12 degrees from horizontal this time instead of 24 degrees. This is to decrease the chance of the new set of panels putting the slightly older set behind them in shade and to hopefully increase their output early in the morning when the sun comes from the east. We'll see if that works out.

So far as possible I collected the parts required for this job by bike. Three meter long pieces of wood do make for a slightly unusual sight on the cycle-path.

In total the bill for the two new panels, all the parts required to make the brackets and all the parts required to make a safe connection to our electricity supply added up to about €550.

Helping a friend with his installation a few days ago. He then helped me today. Doing things for each other certainly helps to keep costs down !

We now should have enough energy

Our gas supply was removed last week so we need to have a heating solution for next winter which does not involve gas. As discussed a couple of weeks ago, we actually didn't use much gas at all, so replacing it shouldn't require too much electricity. Added to the overproduction of electricity which we already had before they were installed, the new panels ought to be enough to make our net electricity consumption very close to zero for the year.

As it stands right now, our energy company is asking us to pay €5 a month for energy, with an expectation that we will have overpaid by €290 at the end of the year. That seems to be working out quite well !

Over the summer we installed the heating system which the two extra solar panels will supply, a poor man's heatpump. This was too inexpensive to attract a subsidy but it should be enough for us.

Eleven years of rooftop solar power - and it's a new record year

2023-04-05T16:38:00.014+02:00

Our rooftop solar panels have been in place for eleven years, and the highest output year was the most recent. In total the rooftop panels have delivered 37591 kWh to date.

When we had our rooftop solar panel system installed in April 2012 we were told to expect an output of no more than 3150 kWh per year due to the angle of the panels and the direction they face on our roof. We were also warned that output would drop slowly over time. In practice we actually saw an average of 3357 kWh over the first ten years. Until now the highest output year was the second year after they were installed with 3516 kWh, but that record was broken in this last year, 2022-2023, which is year eleven for our system. No less than 3614 kWh of electricity came from our panels last year, which is nearly 3% more than the previous record.

We actually generated a little more than this because we added a couple of extra panels in September. But because these have only been operating through the darker months until now, they've only added slightly to the total, bringing it to 3780 kWh.

The new peak output wasn't the result of a particularly sunny winter. March, was particularly cold and dark, with snow and hail and produced the third lowest amount of solar power from our roof top panels since they were installed. Luckily, April has brought far more pleasant weather so far.

March 2023 was one of the darkest ever and even the extra panels didn't bring our total for the month to a total which was as high as the average over the ten previous years

The effect of panels facing in different directions

The extra panels on the garage face are installed facing directly south while those on the top of the house face south-west as that's how our house is built. This means that the sun hits the extra panels on the garage earlier than those on top of the house and that we have significantly more solar power earlier in the day now than was the case when we only had the panels on the top of the house.

Proportion of theoretical maximum output achieved by the solar panels on our house roof and those on the garage roof on the day of writing. Having panels facing in different directions flattens out the production curve meaning that we can cover our own usage for a larger proportion of the day.

Early in the morning all our solar panels are in shade, only receiving indirect light. The output of the panels on the garage suddenly come out of the shade of our neighbour's home at about 9:15, giving a rapid rise in output, today seen as a rise from from 5% to 22% of their potential. On the other hand, the panels on the roof of the house don't see a sharp rise due to an obvious shadow, but because of the angle of the roof they don't reach 22% of their potential on the same day until more than an hour later, around 10:30. This difference means that while on a day like this the output of the roof top system alone wouldn't reach 1 kW until nearly 10:45, adding two extra panels on the garage have brought that forward by more than half an hour.

Our garage roof at just after 09:00 this morning. These panels are at a 45 degree angle because that means they face directly toward the south. The sharp shadow line is due to our neighbour's home. The sun has melted the ice off of most of one panel and output is increasing rapidly as the panels receive direct sunlight. When we install two extra panels these two will be pulled back by about half the width of a panel and the two new panels will see the sun slightly earlier each morning than these do.

Doubling the size of the installation on the garage should mean on a day like this we can reach an output level of 1 kW by about 9:45 and 2 kW by just after 10:30. As such, two extra panels will address a source of slight annoyance - ever since the roof top system was installed we've observed that turning on appliances like our washing machine in the morning meant that we drew energy predominantly from the grid instead of from our solar panels, but with four panels facing south on the garage to take up the slack while the larger array on the roof "wakes up" this will no longer be the case - at least in summer.

No more gas so we will probably need more electricity than before

Our gas supply is being removed next week. We've already not used it for some time. In the future we'll probably need a bit more electricity than now so extra capacity is of course helpful.

Effect on a possible future battery installation

If we install a battery in the future, which we are considering in the future, it will have less to do because we will already have improved our autonomy by covering more of our morning electricity usage directly with solar power, thus reducing stress on a battery as it won't have to cover such a large proportion of our energy usage during mornings. I had hoped to have figures for the year so far showing improved autonomy compared with last year, but due to the very dark winter it hasn't been possible to produce those, so that's something for a future blog post.

Having the gas disconnected

2023-03-21T12:12:00.012+01:00

Having the gas connection removed from a home in the Netherlands costs €869, except that it's subsidized at the moment so costs nothing at all. What better time can there be to remove fossil fuels from your home ? Our gas supply will be cut off in a few weeks time.

It's taken us a bit longer than I'd hoped to get to this point but in a few days our gas supply will finally be cut off. We stopped cooking with gas many years ago, but we still had gas central heating and a gas hot water heater for our shower. It was the latter which stood in the way of getting rid of gas altogether as having no hot water in our bathroom at all, especially over winter, was not at all appealing. However we installed an electric water heater last month which then meant we no longer had a good reason to still have a gas supply to our home.

How much gas, how much CO2 ?
For some odd reason our energy company decided that our annual summary of energy usage should be over a period of February 23rd 2022 to March 11th 2023 this year. That's two weeks longer than a year and includes more of the cold days. The summary shows that we consumed 540 m3 of gas. That's considered to be quite low, but it's still a lot. 540 m3 of gas emits almost a whole ton of CO2 when it's burnt (multiply cubic metres of gas by a factor of 1.78 to find how many kg of CO2 are produced), and that's something that we really do not want to do.

An absurdly over-sized boiler

In February we used 48 m3 of gas, about a third of an average
apartment or under a fifth of an average "2 onder 1 kap" (semi-
detached) home similar to ours.

This morning I worked out that the water heater which we removed last month actually accounted for slightly more than half of our total gas consumption for the year. Subtracting the equivalent of 12 summer months (when the central heating is turned completely off) from the entire years gas consumption suggests that only about 245 m3 of gas was used by the central heating boiler last year.

Burning 245 m3 of Dutch gas (at 33.32 MJ/Sm3) releases about 8163 MJ or 2270 kWh of energy. Our gas heating boiler is a Radson EHRE 240 from 1993 with a rated output of 28 kW. It's been obvious for years that it was grossly over-sized - I had to take action a couple of years ago to make it shut down sooner to stop us from getting too hot - but it wasn't until now that I calculated how absurdly powerful it was. A 28 kW output with consumption of 245 m3 of gas suggests that over the whole year this thing only actually operated for the equivalent of about 3 days at full power, spread over the colder five months of the year when we needed heating. i.e. On average it was used for less than half an hour a day.

The beast awaiting removal

Because we put a lot of effort into insulating our home, we can now make our living room and dining room (i.e. most of the ground floor of our home) heat up slowly with nothing more than a 400 W IR electric heater even on very cold days. Clearly we don't need anything like 28 kW !

The boiler dates from before condensing boilers were common-place. Its rated efficiency is 83%. It also doesn't have a balanced flue but instead takes air from the boiler room in which it sits (getting rid of it means we can insulate that room properly and gain a small storage room on the top floor) and as the heated water we receive from it on the ground floor has travelled two floors down to reach our living room and slowly gurgle around the radiators we clearly don't get the benefit of much of the 2270 kWh of energy released by the gas as heat in our living room.

So what now ?
We have decisions to make. Even a few small resistive electric heaters switched on when we're near them would be a more efficient way to hear our home. A friend of ours has reported good results from using an air conditioning unit to heat his living room this winter, and that's definitely more efficient than a resistive heater, but it does make a bit of noise. We will also need some heat upstairs, in the bathroom, bedrooms, work room etc. We've also been working on improving ventilation in our home so fitting a ventilation system with heat exchanger where the old boiler used to sit on the top floor would probably be beneficial. We have decisions to make over the coming months: By December it'll be cold again.

Hoping to reduce our energy bill further
Last year a quarter of the total gas bill of €1051 was the connection charge. This year our gas bill will be much lower but it won't be zero as we'll still have to pay the connection charge for however long it takes to be disconnected. While gas cost us €1051 last year, our total energy bill for the year was only €587 once we took off the amount that the energy company paid us for nearly 900 kWh of excess electricity that we generated with our solar panels, as well as various other compensations and apparently random things that I've never understood which always appear on energy bills.

Anyway, the energy company decided that we had overpaid by €180 so they're sending us money, which is of course welcome. Then they set our monthly payments this year to be a bit higher than they were last year, which doesn't seem very logical under the circumstances, but they did this last year as well so I'll again have to argue it down this year.

We already added two extra solar panels at the end of last year to roughly cover the water heater's consumption and our plan now is to add a couple more panels again which should leave us with about 1600 kWh per year free compared with last year which we can use for heating. Hopefully that will be about enough. If we end up generating about as much extra electricity as the heating consumes, then not only will we no longer have any fossil fuels in our home but our bills should also be well on the way to zero.

Of course it's impossible to work out exactly what anything will cost because energy bills are absurdly complicated. While we work out how to reduce our energy consumption and CO2 output, perhaps the energy company can put some effort into making their bills understandable.

Job completed earlier than expected

Update 11th April: Our gas supply was removed this morning. Two gentlemen turned up with a digger and made a huge hole in the front garden, removed the supply pipe and the meter from indoors, and then they made everything neat again. So that's it - we no longer have any fossil fuel to burn.

In other news, I took delivery of two more solar panels a couple of days ago. So in a little while I'll write something more about our solar power system.

Over the summer we installed our heating system, a poor man's heatpump. This was too inexpensive to attract a subsidy but it should be enough for us.

Update: Someone was wrong on the internet. Me. So I fixed it.
Somehow I initially made a calculation suggesting that the gas boiler ran for only five minutes last year. This should not have got past my own internal 'smell test'. The boiler actually ran for the equivalent for about three continuous days and the blog above has been updated to reflect this. The other calculations were correct.

Electric water heating - finally got rid of the pilot light !

2023-02-08T18:15:00.009+01:00

There's nothing much more boring than a photo of a cylindrical water heater hanging on the wall, but there it is boringly getting on with its job, heating the water for our shower and bathroom using solar power from our roof and our showers definitely don't mean burning gas any more !

Over three years have passed since I calculated how much gas the pilot light in our water heating system was consuming. It was a bit frightening. 134 cubic metres a year, That means the pilot light wasted almost twice as much gas each year as we just used for heating our home for the whole of January. What's more, 134 m3 at the current price of around €1.80 per m3 works out as about €240, which due to everything else we've already done to reduce our energy consumption is about half of our total annual energy bill for electric and gas combined (we've paid €40 a month for the last year, and the energy company currently owes us money). It's been at the back of my mind literally since I first made that calculation that I had to do something about it, but there are always other things to do and it took until this week until it happened.

Of course I went through all options, including such things as heat pump water heaters. These appear to only be available in absurdly huge sizes meaning more waste, with costs that are simply too high, and with unknown reliability compared with a simple resistive heater. I also considered complete heating systems including water, but most of the year we unplug our heating system so this seemed less than optimal. Eventually I decided that a simple hot water tank, was the best option so long as it could be well insulated and with some kind of control to stop it wasting energy when we didn't need the hot water.

I should have been able to write this last year. I ordered a water heater in September which got delayed due to covid and then didn't turn up at all. After sitting on a waiting list for several months I eventually asked the company I'd ordered it from for a refund which they sent promptly, so I can't really complain about that. Anyway, I then ordered another type which arrived less than 48 hours after I'd ordered it. It's supposed to be a "DAT Arca 80 litre anti-kalk" (anti calcium) boiler, but for some reason what turned up has "GOT" written on it instead. Before ordering I tried to work out whether I'd be able to buy spare parts, and it seems I can. Not that there's much in this thing to go wrong.

Between the two orders I did a bit of extra research which led me to prioritize buying a boiler with a dry heating element which should last longer.

Smart vs dumb boilers

Some boilers are "smart". The main reason why smart boilers are claimed to use less electricity every year than the boilers with dumb controllers is simply that the dumb boilers are typically switched on 24 hours a day, consuming electricity to make warm water when no-one will use it. Smart boilers include such features as analysing your use for the first week and then only warming water when it thinks you'll need it. That's not a bad idea, but we don't really have a fixed weekly pattern of use so I'd have had to use it as a time switch instead.

At the moment the controller consists of a simple analogue clock style time switch and I've also got an energy meter connected up to let me measure electrical consumption over time.

I have no interest in any "smart" IoT product as connecting things like this to the internet means yet another thing to worry about with potential spyware and software updates (if they happen at all they'll be phased out before the lifespan of the product) so I never had any intention of connecting the boiler to the internet. However the company who made the first product only sold the model of their boilers which had thick insulation alongside the smart controller so that forced the issue. Luckily I found an alternative product that combined 30 mm of polyurethane insulation with a simple dumb thermostat. Perfect for us. I think I would have ended up using the smart controller as nothing more than a time switch anyway, and a cheap analogue time switch for then €5 does the same job.

Matching consumption to available solar power

I also found that some companies were offering "anti-salderings" boilers at extra cost. These come with lower power elements than usual as a better match to domestic solar power installations.

Underneath the easily removed plastic base of the boiler is this mess of wires. Disconnecting the two white wires from the second element halves the energy consumption, making it more compatible with using excess solar power.

The idea of this is to ensure that to the greatest extent possible you only use your own electricity. This is because Dutch energy companies don't give you very much for any extra kWh that you export to the grid, and no-one is quite sure what will happen in the future to the existing rules around this. So when I found it was possible to buy a 1500 W boiler which actually has two 750 W elements wired in parallel, that's what I chose because this can also be run as a 750 W boiler which happens to come with a free spare element. The company that we bought our boiler from also offers an anti-salderings version of the same boiler for €50 more. Does this differ in any way other than only having one element wired up ? I don't know.

Size

The size of the boiler was a topic of much discussion. I'd have been happy with a 30 l boiler, but my wife insisted on 80 l.

The biggest problem with buying a fairly large boiler was the weight. This thing weighs 32 kg. Holding up there above my head over the stairs while Judy helped push it into place to hook it onto the supports that I'd already fitted in the wall took a lot of effort. The bathroom is just behind the wall on the right. This was the closest place to the bathroom where we could install the water heater. This means less loss due to long pipes than was the case with the gas water heater. As you can see, I'd not yet done the plumbing or electrical work when this photo was taken.

I'm almost totally bald while Judy has long hair so it's no surprise that she thought a larger boiler would be necessary. I've done calculations which I think reliably indicate that 50 litres would be more enough for Judy, but as we're grandparents now we might actually need to run a bath for our favourite visitor at some point and that could mean needing more water. The extra large boiler will cost a bit of extra energy, but we can compensate by running it slightly cooler and letting the shower mix in less cold water. But in any case we should have solar power to spare - I expanded the solar installation in September when I ordered the first water boiler specifically in order to cope with this.

Tidying up

The water pipes to the gas heater have been removed but the heater is still in place in the boiler room alongside the central heating boiler (which doesn't get used much, but . I'll get rid of it when the gas central heating boiler is removed, a job which I will probably have to get someone else to do so they can do both at once. Until that day it's doing us no harm and it's perfectly safe - the gas pipe the gas boiler has a tap on it which which is now switched off.

How much energy does it use ?

After three weeks of operation, with us having showers as frequently as usual, the water heater had consumed 44 kWh of electricity. That works out as an expected consumption of about 770 kWh per year to cover all our hot water usage, which would cost about €300 at today's electricity prices. By comparison, the consumption of our old gas water heater's pilot light was 134 m3 per year. At today's price that amount of gas would cost over €400 per year, and remember that that was just for the pilot light. i.e. it didn't include the gas used for actually making hot water that we washed with. So all else being equal, replacing the gas water heater with electric would save us about €10 a month. i.e. it would take about three years before the new water heater has paid for itself in reduced cost.

We expect these extra solar panels installed in September to
generate about the same amount of electricity as the water heater uses

But all else isn't equal: The extra 800 W of additional solar panels which we added to our rooftop system a few months ago should generate approximately the same amount of energy each year as the water heater consumes. As a result, our annual energy cost should just drop by the price of the gas that the water heater burnt, which worked out as about €40 a month. That's quite a significant number for us because €40 a month just happens to be exactly the same amount as we've paid for our electricity and gas together over the last year.

So as we stand right now our energy bills ought to be very close to zero in future even if we do nothing more to improve efficiency of our home. But that's not the plan. We will of course continue to do more to make our home more efficient, and there will be more blog posts about it.

It's also a battery / storage heater

An instant water heater would consume electricity when it is used. i.e. nighttime showers could not be powered by our solar panels. But with this hot water tank our showers can be powered by our solar panels even if we shower when the sun isn't shining. Another effect of having a tank of hot water heated from solar power during the day to warm our water is that small amount of heat leaking from the water tank is released 24 hours a day. i.e. some of the energy stored by the water heater during the day is released at night, keeping the upstairs of our home slightly warmer in winter.

Why not install solar thermal water heating ?

A perfectly reasonable question, which someone asked on social media. My answer is as follows:

In total the panels, the boiler and all the parts needed to install everything cost less than €1400. It would have cost at least twice as much to install a thermal solar water heater. Also, we'd still have needed to buy the electric boiler (a more expensive version of it with pipes as well as electric heating) because if we'd gone with solar thermal that would almost certainly not heat the water sufficiently in winter. By doing it this way, all the solar panels on our house & garage combined can contribute to water heating, not just a smaller area so it's likely to work better on darker days.

In addition, the extra solar panels are on the garage roof were easily to reach safely at a low work height while thermal solar panels would have had to be installed on the much higher roof of our home. So in addition to this being a cheaper way of heating water than thermal solar, I also did not have to clamber about on the roof of my house (nor pay anyone to do that dangerous job for me), didn't have to make holes in the roof for pipes which could leak, and there's no risk at all of leakage due to pipes being frozen in winter.

And think of future maintenance. The water heater and solar panels function completely separately from each other. i.e. either can be replaced without affecting the other component of the system.

I don't think that thermal solar makes much sense these days. It did in the past when PV panels were far more expensive than they are now. My father-in-law made his own solar water heating panels in the 1980s. This was an interesting project, they were made of copper sheeting with copper pipes soldered on, all painted black, in an insulated wooden box with glass in front. They were very effective and I enjoyed a few nice warm showers from that system in the summer. But it worked out in large part because they built a home around the system so the panels could be larger than commercial systems and ideally located to work with gravity. Around the same time I was experimenting with my first solar electric panels on my roof, but they produced very little electricity for their size and cost and it would have been completely impractical to use them for heating water. For many years I thought we'd end up with solar thermal water heating, but they were always difficult to install on a standard home, and this is now a better way of doing it.

Anyway, that's another DIY job finished, and we've taken another step in the direction of complete independence from fossil fuel.

Let's have more solar power

2022-09-09T19:11:00.006+02:00

On Wednesday we brought home some solar panels and an inverter and we finished installing them on the roof of our garage today.

These panels are aimed to the south to try to pick up the maximum sun that they can over the whole day, but nearby trees will cause some shading.

We bought this set of parts from a local supplier, Cedel, so that we could pick them up. The panels aren't extremely heavy, at about 18 kg each, but they are large at 1.8 m x 1.1 m each and of course they're made of glass so quite delicate. As a result, this turned out to be one of the very rare jobs which couldn't be done by bicycle but luckily our son-in-law volunteered to drive with a trailer to collect the panels. Cedel sells a set of two 400 Wp panels with a Hoymiles HM-800 micro-inverter for €800, including a plug and play cable which can simply be connected to an electrical outlet, but I paid an extra €50 for an HM-1500 which can run four panels so that we can expand this system economically in the future. An expanded system will require wiring directly to the meter cupboard so that's another thing that I'll had to do if we decide to add those extra panels

Due to supply chain issues, standard mounting parts were not available. However, that's not really a difficult job. A quick bit of SohCahToa remembered from school and some literally back of the envelope calculations allowed me to work out dimensions for the substantial impregnated fence posts which I'd decided to use to construct the supports.

It turned out that when I included the 68 mm width of the posts in the calculation I could make the entire support with wooden parts of 1 m in length for all the horizontal parts and 0.4 m in length for all the vertical parts, dimensions which resulted in the minimum of waste from fence posts of a standard 2.4 m length.

Our garden fence consists of 4 m2 panels each of which is held up by two fence posts of the same type shared with the next panel. i.e. there's about one post per 4 m2. This has stayed intact through every kind of storm for at least 20 years, and the only work I've had to do was to re-enforce a few panels which gone rotten at the base where they're buried in soil. So I think the same type of wood is certainly strong and resilient enough in much shorter lengths when holding a 2 m2 panel at a 22 degree angle from horizontal.

It's recommended that 22 kg of ballast be used for each panel in our location and at the height of our garage roof. These supports much heavier than the commercial systems, already weighing nearly 20 kg for each panel, and I've added quite a lot of tiles from the garden, each of which weighs about 8 kg so in total including the supports we have about 70 kg of ballast per panel. This should be adequate. Note that while that sounds like a heavy thing to put on the roof, I weigh nearly as much as the ballast and panel combined and when I walk on the garage roof all the weight is concentrated in the area of one of my feet. The solar panels mounted in this way spread their similar weight over about 4 times the area that I do when I walk.

This took about two days to do, including all the measuring, lifting, cutting etc. We were also delayed by rain. It's a fairly easy DIY job. And if the panels generate around 800 kWh per year, then at next year's 60 cent per kWh price it'll take less than two years for them to earn back what they cost.

The parts were ordered last Friday and ready for collection on Monday. It then took me two days to arrange collection and today I finished installing this setup on the roof of our garage. It's almost impossible to get anything done quickly by someone else at the moment due to covid related staff shortages, but if you're willing to do some DIY most things can still be done quite quickly.

That's not all

These aren't our first solar panels. Actually, we had 16 235 Wp panels installed on our roof ten years ago which still operate perfectly.

Our original 16 panels oriented south-west and still working as well as when they were first installed 10 years ago.

When the 16 panels were originally installed we expected that they'd fall a little short of covering our annual consumption of electricity, but actually they turned out to produce more than had been estimated and almost exactly the same amount as we used. Over time, our consumption has dropped quite a lot while production of the panels has stayed exactly the same for ten years, so for the last few years we've exported more electricity to the grid than we have taken from it. The only problem we've had with that system in the last ten years is that the inverter failed four years ago, but even though the manufacturer wasn't co-operative at all I fixed it at minimal cost and it's operated perfectly since then.

So you might wonder why we are now installing more panels. The answer of course is that we want to get rid of all our gas appliances. It's been known for many years that fossil fuels are endangering all life on the planet. This has to stop. We can't control everything, but we can control our own consumption. By continuing to buy fossil fuel we empower the companies that produce it and we just can't keep doing that. Insulating our home has already reduced our gas consumption for heating to less than an average small apartment, and we now cook entirely with electricity (the cooker only ever used a fraction of the gas that heating uses). We didn't replace our central heating boiler, which is old and inefficient, because buying a new boiler would lock us in to continued gas usage. Our low consumption is entirely the result of it not having much to do any more because the house is so well insulated. That means we could now economically replace our gas central heating with electrical heating, and that's even more true as of today with the extra pair of solar panels.

Heat pumps which could replace the central heating and heat the entire house in winter are still quite expensive and a bit hard to justify on price grounds, but we could install a small air conditioning unit which can produce heat with about the same efficiency as a heat pump in the living room as that's relatively inexpensive so that may be what we choose. We barely use any heating in the upstairs anyway.

A third smaller, experimental system

We've also been experimenting with smaller scale solar power system. One of our daughters lives in a flat in Assen. Unfortunately we can't fit solar panels anywhere on the outside. The balcony might have been an option but it faces north west so only receives sun just before sun-down which means it's quite a pleasant place to sit on a summer evening, but doesn't make any sense at all for solar panels. The rear windows face south east, but there's no place outside on that side of the building. As there are no really good options I decided to experiment with mounting solar panels inside the double glazed windows. After all, if you don't try it you don't know how well it works.

From the outside it's quite difficult to tell which window is full of solar panels.

They're just the right size to fill this window. Luckily there are other windows in this flat so this doesn't block all light.

The panels for the flat are a flexible type ordered from Aliexpress. I couldn't find them anywhere else. Luckily, one supplier has a depot in Poland which because it's inside the EU meant they were delivered to us promptly and without any unpleasant customs related surprises. These panels are a quarter of the size of the new panels that we've installed on the garage, just 1050 mm long by 550 mm wide. They're also really light in weight. As a result they're much easier to transport, I took both of these panels to the flat packed in their cardboard box by riding my bike with the box wedged under one arm. The inverter in this case is a Hoymiles HM-400, which operates quite well with two of these panels connected in series, though as it's rated for 400 W it's working well under maximum capacity.

These panels are nominally rated at 100 W each. Two of them connected in series and propped up in our garden roughly aimed at the sun on the reasonably sunny day when they arrived together produced 140 W, which seems quite reasonable. In the window of the flat we've not yet seen more than 90 W due to losses caused by the glass and the requirement to mount them vertically. Update later in September: we've now seen over 100 W on several occasions from the panels in the flat window. This might make them more worthwhile.

It's still an experiment. We want to help our daughter with the ever rising energy costs, but will this be worth doing given that the output is quite low ? It seems that mounting the panels inside roughly halves their output. This will vary depending on the glass, of course, and also on the panels due to different panels reacting to different frequencies of light. One smaller 12 V / 20 W panel that I have at home loses only about 20% due to being held inside a double glazed window, but unfortunately these panels are affected to a larger degree.

In total this system cost about €360. Half of the price was for the solar panels and the other half for the inverter. In the first week that they were connected, in September, we saw about 0.25 kWh per day from the panels mounted inside the flat. At the end of the year my daughter's electricity will cost over 60 cents per kWh, so that's worth about 15 cents per day. If we estimate that the average over a year is about half that much the electricity generated by these panels will be worth about €27 a year, which means a payback period of over thirteen years which I think is too long by any way of looking at it.

How about if we add two more panels (connected serial/parallel - making the equivalent of one 400 Wp panel which is still within the specs for the HM-400) ? Obviously this would block another window. It would also increase the cost of the system by 50%, but output would increase by 100%, or perhaps even slightly more if the inverter wakes up earlier due to the increased output of four panels. The result is a would be a payback period of almost exactly ten years, if the electricity price stays at 60 cents per kWh, which is still not great, but it's not far off what I originally expected from the roof-top system. Of course if prices continue to rise then the payback period will become shorter, but they may also drop.

For now I don't desperately need these panels for another purpose so they can stay put for a longer experimental period, or until my daughter says she wants rid of them. They'd perhaps be more effectively deployed on the south west facing wall of our home where they'd pick up the early morning light without their output being reduced by being mounted behind glass, and pay for themselves in about 7 years. I think a set of four of these would make a fairly good easily transportable system for someone who lives in a rented apartment and has a south facing balcony as they'd then pay for themselves in about five years.

Another really small system

I've had a small flexible solar panel on my velomobile for over ten years. In summer it's kept the battery charged so everyday use didn't require plugging in a charger. Unfortunately, the circuit got damaged and I had to replace it. I decided that this time I'd use a much simpler circuit - a shunt regulator with a zener and a single transistor to limit the voltage to about 7 V. Current is limited by the panel itself, the internal resistance of the battery and because once the voltage gets close to the maximum the shunt starts to conduct a bit. This circuit does a reasonable job of keeping a NiMH battery pack topped up and it can't damage that kind of battery. Don't even think about trying this with a lithium battery. I built two of these so that Judy no longer has to charge the battery for her velomobile either:

Velomobiles are the most efficient vehicles on the planet, maximising the potential of human muscle power. Judy's now has a small solar panel, just like that on my velomobile, which keeps the battery used for lighting and indicators topped up.

Of course I've not even tried to work out whether this is economical compared with charging from the mains. I had the parts and it's convenient for us.

Repairing and improving a vacuum cleaner. Samsung SC4580/SC4581 motor replacement and leak fix

2022-08-24T17:52:00.009+02:00

A few days ago our vacuum cleaner stopped working. What actually happened is that it made a rather unpleasant burning electronics smell, accompanied by a significant reduction in suction. I took it apart, and the first thing that was required was a good clean. Clearly the dust which went into this vacuum cleaner did not all end up being collected, but was instead swirling around all the internal parts because there were so many leaks. So the first thing I did was take everything into the garden for a wash.

By connecting the mains electricity directly to the motor instead of running it through the electronic speed controller I could confirm that it was indeed the motor itself which was faulty. The motor is combined with an impeller and put together without any easily removable fasteners. They are not separable or easily maintainable. The bearing seemed to be fine, but it was obvious that the coils had become rather hot and that the insulation on them was no working properly

A direct replacement motor is available from Samsung, but this costs about €90. On the other hand a generic replacement motor with the same dimensions (130 mm diameter, 110 mm height), described as suitable for Samsung / Dyson / AEG and other makes, cost only €30. So that's what I ordered as a replacement. Note that this suggests that all these vacuum cleaners have essentially the same parts inside apart from the plastic mouldings around the motor.

Label on the generic replacement motor. Little information other than diameter, height and wattage.

The generic motor was the same size, but not identical in all ways. In particular, the two holes on the top of the motor must line up with two plastic studs inside the plastic housing which hold in place a piece of rubber which absorbs shock and stops the motor from rotating:

This, of course could be fixed. I cut off the plastic studs, drilled holes in the correct place for the replacement motor and glued some wooden dowels into place with epoxy:

Another small issue was the power connectors were a different place on the replacement motor and the housing didn't provide space for them. I found that they could be bent slightly to fit and then I had to solder wire directly to the terminals instead of using push-on connectors. The parts could then be re-assembled.

While looking for information about these vacuum cleaners I came across an interesting blog from someone who had eliminated the leaks. While re-assembling I followed his suggestions in the hope that this would improve performance.

Result: Our vacuum cleaner now works perfectly again

It's as good as new. Actually it's better than new in three ways:

It sucks better than ever
It is much quieter than it used to be
It uses uses less electricity than before

The replacement motor is rated at 1200 W instead of the 2000 W originally fitted so power consumption is lower (this obviously depends on the power setting), but it's sucking better because sealing the leaks means that less of the effort put in by the motor is wasted. Meanwhile, getting rid of the leaks also means that most of the wind noise that the machine made has now gone away.

Ten years of rooftop solar power - no decline in output can be seen

2022-04-05T16:35:00.004+02:00

Today is the tenth anniversary of the installation of our mains connected rooftop solar panels. In total the inverter reports that 33935 kWh of electricity have been generated in ten years, an average of 3394 kWh per year since they were installed.

After ten years we still can't see any decline in output

Output in kWh per year. Note that there's considerable variation depending on the weather. The lowest output was 3126 kWh in 2018-2019 and the highest 3516 kWh in the second year. Last year was also higher than average, within 0.1% of the highest.

A rough calculation before installation suggested that we could expect around 3478 kWh of electricity each year under ideal circumstances, but our supplier suggested that in practice given the angle of our roof we should expect around 3150 kWh per year. The guarantee with the panels said that a decline in performance of 10% over the first 10 years was within normal bounds. This year's 3392 kWh is only slightly under the ten year average, but as it's higher than four of the previous years (including the first year) it's also far from abnormal. I don't see evidence of a decline in output due to aging.

We still produce more electricity than we consume

Blue and red bars show production and consumption per month. The yellow line shows the cumulative difference which we've exported to the grid. We started consuming less electricity five years ago, but over the last year we've consumed slightly more than the previous four years.

I painted our house last year, but I didn't clean
the solar panels. That doesn't seem to matter at all

Over the ten year period we've produced about 10% more electricity than we've consumed, but actually for the first five years our consumption was close to the production (for reasons explained previously) so it's more accurate to say that we've produced about 20% "too much" over the last five years. In other words, our overproduction over five years is roughly the same as the annual consumption of a household like ours.

Cooking with electricity changes the pattern

You'll notice that the graph showing the cumulative difference between our production and consumption has actually leveled off a bit over the last year. The reason for this is that we've switched to cooking with electricity instead of gas, this being one of the ways we've been trying to further reduce the footprint of our already low carbon diet. There's no new kitchen, that'll have to wait for a while. We've been using a small portable electric hob resting on top of the gas appliance as an experiment, which has worked out very well. An induction hob would probably work better. Anyway, it's nice to see that despite this increase in electricity consumption the yellow line is still heading upward at a faster rate than it did on any year before 2016.

Thoughts about home storage

A smart meter was installed four years ago so we now have three full years of smart meter readings. Though we have a single tariff contract so pay the same for electricity any time night or day, the smart meter nevertheless separates out the low and high rates of electricity which roughly correspond to day and night. Overall through the year, 39% of the electricity that we use comes directly from our own panels while 61% comes from the grid and we use 38% of what is generated by our panels while exporting 62%. Obviously a battery comes to mind immediately when looking at these figures, but I'm still not convinced that it's worth the investment. How much could it change these figures ? I think by less than we might hope:

Home storage batteries have capacities of around half of a day to a whole day of typical usage. It's enough to reliably keep your refrigerator going overnight during summer, but not remotely enough to span the seasons.

In the summer months such a battery would fill up in the first couple of days and then it would stay nearly full for weeks. The battery would allow us to consume our own electricity overnight, so that for periods of nice weather all of the electricity we use would be "our" electricity from our panels, which is of course an attractive idea. During that best case scenario we would increase from the average 60% of our electricity that currently comes from our own panels during summer to 100%. For the six best months each year we produce on average between 1.7x and 2.1x as much electricity as we consume so even with a battery working as well as it possibly could we could still only capture some of our own electricity for our usage and doing this would only actually increase the percentage of our own electricity that we consumed from the current still 30-35%% to about 50-60%. Also, this is Northern Europe. There are periods even during the nicest Northern European summers when the solar panels don't produce as much as we'd like, so the battery will run down and we would still have to buy some of our electricity from the grid.

New, huge, windturbine in Drenthe

And then there's winter: In the winter months there's far less sunlight falling on our panels and we possibly produce enough electricity to cover our own usage without annexing our neighbours' roofs. Because there's so little sun in the winter what comes from our panels currently covers only about 10-15% of our consumption and during these dark months that means we are already consuming 70-80% of our own electricity just with normal daytime usage. During the winter a battery would therefore be empty or near empty most of the time. While a battery would mean we would reliably consume all of our "own" electricity during winter it wouldn't win us much because there's not much to store: It would reduce the proportion of our electricity that we buy from the grid from the approximately 90% during winter now to around 85% with a battery.

Financially I don't see the benefit of a battery at all. It's an expensive gadget which will change very little. Let's also remember that the electricity leaving our home is not wasted. It's used elsewhere, reducing demand for other, on average less green, generation. So what exactly is gained by trying to keep our electricity to ourselves ? It seems more likely to benefit the ego than the environment.

So to summarise, I'm still not convinced that there is actually any real point in home storage using batteries. I think we'd possibly get some real benefit from installing a few more panels on the roof as while these could of course not do anything about our nighttime usage they would mean that we'd cover more of our own consumption during the day and if we get around to installing an electrical heat-pump for heating (instead of the old gas boiler) then balancing the resultant greater electricity consumption with more panels would make sense. I also have doubts about how wise it is to encourage people to install large and potentially highly flammable lithium batteries in their homes. They might be fine when new, but what happens in 20 years time when they've not seen maintenance engineers in many years and they're failing in various unexpected ways? I think it is a better idea to install batteries as large scale devices at substations or next to large solar parks or wind turbines.

Our business is also powered by these solar panels. We sell practical bike parts which help people, especially those in other countries where such parts are not so easy to find, to reduce their impact by cycling. Bicycles are the most efficient vehicles on the planet. We don't use motor vehicles so every shipment begins with at least the first few km on my bicycle, using nothing but human power.

Modifying a thermostat to make our heating more efficient

2021-12-02T14:41:00.012+01:00

It's December 2nd and it snowed today. That was the first time that it snowed this winter, and it reminded me to write about a very cheap modification to our thermostat which made our heating system both more efficient (using less gas) as well as giving us better control of the temperature in our home.

Our central heating system is quite old and inefficient, dating from the 1990s. I've been meaning to replace it since we moved in, but first we did quite a bit of insulating, including the walls, roof, floor and triple glazed windows. All of this dramatically reduced the energy input required to stay warm and as a result we've gone from a home which was expensive to run in winter even while we were still cold to one which is very efficient so the heating doesn't come on very often. Much of our gas usage now is actually due to our even more inefficient and old water heater. We now burn far less gas than average because even though our central heating boiler remains old and inefficient it doesn't come on very often and last December we used less than half the amount of gas that average homes of our size required for heating, less even than an average apartment. Insulation works.

This shows gas usage last December. Our bill for electricity and gas together averages around €45 per month over the year. In part this is because the energy company pays us for our excess solar power.

One of the things that put me off buying newer gas appliances was wanting to get rid of them altogether. Unfortunately, when I first looked into doing this I was getting five figure quotes for heat pumps which made it impossible to justify them on economic grounds. Insulating saved us more money more quickly, and the solar panels were also far easier to justify economically. But the price of heat pumps has come down and I do now want to switch. Unfortunately, the absolutely awful government which this country currently has has ensured that the covid pandemic has already gone on for nearly two years and it'll probably go on for a while yet. I'm not keen on having people come into our home while this disease is spreading so the heat pump will have to wait. However I did think of a way of making our existing system more efficient:

Uneven temperature due to too much insulation and an overenthusiastic central heating system

Our boiler and radiators were designed for a leaky house. The radiators are large and the boiler likes to generate lots of really hot water. I turned down the temperature setting on the boiler a very long while ago and there's no problem with the house heating up (this bodes well for replacing it with a heat pump which will produce cooler warm water) but we still had a problem with excessive heat.

What happens is that thermostat switches on, the radiators heat up and because it takes quite a long time for convection to transport heat from radiator to the thermostat the heating would continue to push out heat for far too long resulting in the temperature overshooting sometimes by 3 C over our selected temperature. Setting the thermostat at a lower temperature doesn't fix this problem because that means that the lower temperature has to be reached before we get any heating at all. We were a victim of our good insulation.

My first thought was to replace the thermostat with an Arduino programmed to turn the heating on only for short bursts and I started working on doing this before I realised I was overthinking it: Couldn't I instead do something to convince the existing thermostat to switch for short bursts ? At first I thought perhaps this could be done by adding something like a 555 timer circuit which would change the state of the relay in the thermostat more often, but then I thought of an even simpler solution:

The solution which costs just a few cents

The thermostat operates by closing a relay contact between two contacts attached to wires from the central heating boiler. Those wires have 24 V AC on them when they're open. When they are shorted that powers something within the central heating boiler which turns on the gas and the pump. I found that a dead short wasn't required. Actually, any low value resistor across the two wires worked just as well as a dead short to make the boiler start up. Trying different values allowed me to calculate that the boiler consumes a constant current of about 80 mA for any low value of resistor across the contacts. A 47 ohm resistor drops about 3.7 V and consumes about a third of a watt itself which is enough to make it slowly warm up. I realised that if I installed this small "heater" inside the thermostat next to the temperature sensor it would give just the desired effect of short bursts of heat from the system before the thermostat thought the room had warmed up and would switch off again.

The temperature sensor is easy to spot. It's mounted such that ambient air can easily influence its temperature.

It was easy to find the temperature sensor inside the thermostat and easy to confirm that that is what it was because holding it between your fingers results in the temperature on the front panel of the thermostat rising quickly.

A 47 ohm resistor wrapped in self-amalgamating tape. This is now installed inside the thermostat next to the temperature sensor in the photo above

I attached a couple of wires to a 5 W 47 ohm resistor from my collection of parts, wrapped it in self-amalgamating tape to ensure that it doesn't cause a short and have installed this next to the temperature sensor in the thermostat. As I didn't need to actually buy anything to make this modification it cost more or less nothing to make it. If I'd had to buy the parts the most expensive thing would have been the roll of tape.

It works !

Now the thermostat can turn on the heating only for a couple of minutes before the resistor has warmed up enough that it thinks the target temperature has been reached. It then switches off again and the thermostat slowly returns to room temperature. If this is still below the target temperature then the heating will switch back on again for a few minutes. It takes a little longer than before to warm from a cold room, but we never overshoot by more than a fraction of a degree. Though the radiators never really get hot any more, there is enough energy in them to heat the room without burning more gas. This results in much more consistent and comfortable temperatures in the room and we hope also to see a lower gas bill due to less gas being burnt.

Next year perhaps we'll look again at replacing our central heating boiler with a heat pump. It's important that we all stop using fossil fuels but for now, with covid raging, the step of using a bit less is still worthwhile.

The result

We consumed 148 m3 of gas in December 2021 vs. 147 m3 in both December 2019 and 2020, the two previous winters with full triple glazing downstairs. Clearly there's no dramatic change there. January, February and March looked a lot better: We consumed 183 m3, 144 m3 and 107 m3 in Jan, Feb and March 2021 vs. 130 m3, 107m3 and 50m3 in 2022. There's still little data and this could be because those months in 2022 were milder. As more time passes there will be more data. But even if this makes no difference to gas consumption it does at least make our home more comfortable.

Our gas consumption in March was really low. Our home is a "2 Onder 1 kap" type so we used under a quarter of the average Dutch home, not only because of the other measures we've taken but also because we turned the thermostat to an even lower temperature than usual in order to avoid funding Putin's war in Ukraine. March was also unusually sunny so the energy company owes us €100 for the electricity that we supplied to the grid in March.

Nine years of solar power. 30 MWh generated.

2021-04-05T17:42:00.002+02:00

Today is an anniversary. Our rooftop solar power setup was installed on this day nine years ago. When the system was first installed I had two concerns, about the inverter and about the panels themselves.

Inverter
The biggest concern was about the inverter. I expected that this would have a limited life because an inverter is inevitably a box of power electronics which has to work quite hard. Power supplies, especially in my experience switched mode supplies, can be quite unreliable after a few years. I've fixed quite a few of them in the past, and switched mode supplies can be quite tedious to work on. An inverter is like a large switched mode power supply which works in reverse so I didn't have huge expectations for longevity and sadly the inverter has actually failed twice, first in 2018 and then in 2020. In both cases it was quite simple to fix and because I know which end of a soldering iron to hold onto I did that myself.

Panels
The other concern was the less well known longevity of the solar panels. There are two main ways in which solar panels degrade. The first is due to corrosion should they become damp and the second due to the sun light falling on the panels degrading them. I've had solar panels on homes that I lived in since the mid 1980s, starting with several 30 cm x 30 cm panels which I used to charge batteries. Those panels were not sealed from the weather so they got damp, there was visible corrosion in some places, and their output dropped markedly over time. But around the turn of the century I bought a 12 V sealed panel to replace them. I still have that on my garage roof and it's output is still close to the specification so I hoped that the panels for the roof be similarly long lasting.

The guarantee said that the output of the rooftop panels would still be at 90% of the initial level after 10 years of use. I realised soon after the panels were installed that their peak output was significantly higher than it the specification suggested. The rated peak output for the installation was 3760 W and the installers suggested that we'd probably not see more than about 3600 W because of the angle of our roof. But within a few days I was seeing ~3990 W. I had some concerns at that time that perhaps there had been a little slight of hand on the part of the manufacturer, who perhaps under specified the panels in order to protect themselves from guarantee claims. i.e. Perhaps we'd see the panels degrade by more than 10% over ten years but that they'd still be within 10% of 3760 W or even within 10% of 3600 W in ten years time, meaning that a loss of almost 20% of output would be possible without being able to claim on the guarantee. But this has not turned out to be the case at all. There is no degradation. I can happily report that the observed peaks last summer were still around 3990 W. What's more, we're not quite at ten years yet, but the total output from the system also seems not to have dropped even slightly. After the first three years passed I noted that the system had generated 10200 kWh in total. Six years further on the total is almost exactly three times this, at 30556 kWh. What's more, if not for the inverter glitch in 2018 which costs us about 250 kWh of output, we'd actually be ahead of the first three years by now.

Graph of output over time

The orange line shows our excess production over time. It goes up in summer and down in winter, and by March we just about break even which is why the last part looks flat. When the panels were installed we had teenage children at home and our consumption was similar to our rate of generation. You can tell how long ago our children left home from this graph (some lower power appliances also made a difference). The glitch three summers ago was caused by the inverter failing and my taking a few days to fix it. The second failure was a year ago in February and lost only one day's winter output so that isn't visible on the graph.

Finance
When the panels were installed I estimated that it'd take about ten years for them to pay for themselves. Because electricity prices change, we've changed our electricity meter once and supplier more than once, it's quite difficult to work out exactly where we are now so far as the return on investment is concerned. However it's quite easy to make an approximate calculation so that's what I'll do. I know that we'd generated 30442kWh up to the end of March, and of that we'd consumed 27767 kWh and exported 2589 kWh. Electricity costs us just under 20c per kWh so we've saved about €5300 from our electricity bill. With our current tariff we get pretty much the same for what we export so that's worth about €500. This leaves us with about €5800 of our original €8000 investment returned, and at the same rate the system will have paid for itself in about 13-14 years after installation. This is about the same result as I came to about three years ago. Just four or five more years to wait, then.

Note that in reality over a whole year we use about 40% of our own generation directly from the panels and export the rest of what we produce. The electricity company doesn't bill based on this, though, so for a purely financial calculation we don't need to take that into account.

Conclusion
I'm happy with the system. The inverter fault was disappointing and the manufacturer's response even more so, but I fixed that. The panels are faultless. Solar panels with lower performance were much more expensive when I first started experimenting with them in the 1980s but when we installed this system it was clear that they'd pay back within a reasonable amount of time. They're now not far from half the price that they were then so someone considering installation these days can expect to see their money back very quickly indeed.

Eight years of solar power. How much of our own generation do we consume ?

2020-04-05T17:33:00.000+02:00

As of today our rooftop solar panels are eight years old. Here's the latest graph of electrical generation vs. consumption. You can see the eight years which have passed, the data neatly making sinusoidal shapes due to changing seasons caused by the rotation of our planet around the sun:

The blip in the graph is due to the inverter failing in 2018. It also failed in January but I got my soldering iron out sooner this time and because it was January and not the middle of summer far less was lost. Therefore no visible second blip.

The red bars show our consumption of electricity each month. The blue bars show the generation of electricity from our solar panels each month and the yellow line shows our total generation vs. consumption. Since the beginning we've generated more electricity each year than we used and in the last four years we've reduced our consumption making this difference between generation and use much greater. This led to the yellow line rising steadily higher. If you live in the Netherlands or anywhere in Europe connected to the same grid then it's possible that during the last eight years you've used some of the electricity generated on our roof as what we don't use goes into the grid.

Over the last eight years the system has produced 27039 kWh of electricity. That's 3380 kWh per year, very close to the estimated 3478 kWh per year predicted before they were installed. But this total over eight years was impacted quite severely by the period when the inverter failed two years ago. Over just the last 12 months we generated 3438 kWh, which is remarkably close to the prediction.

But while it's nice to see that we generate much more electricity than we use and the system is working very nicely, the graph also exposes an obvious problem. We never manage to generate even close to enough electricity in the winter, and of course there's never any output from our panels over night, which is exactly when we turn on our light bulbs. The installation of a smart meter a year ago has given me more data to work with and so now I can see how much of the electricity that we use ourselves comes from our panels and how much of our own electricity we use (these are not the same thing...). When we're not using our own electricity we're using what comes from the grid, and the Dutch grid is far from 100% renewable (we have of course signed up to a 100% renewable contract, but the effect of that is mostly only to make the paperwork say its renewable).

Data from the beginning of January 2019 until the end of March 2020.
Blue: our generation vs. consumption. Any month where this is above one we generated more electricity than we consumed.
Red: the proportion of our consumption which was from our panels, varying between 0.12 in winter and 0.6 in summer.
Yellow: proportion of our generation which we consume, varying between 0.25 in summer and 0.75 in the winter.

This new graph which makes use of the smartmeter data shows a more complicated picture. Though each year we generate far more electricity than we consume (blue bars are often well above 1), our pattern of usage doesn't match the generation very well. We over-produce in summer, under-produce in winter and we keep putting our lights on when it's dark outside rather than in the middle of the day. We come closest to being independent of the grid in the summer when our panels generate more than twice what we consume, and though we don't use much of our own electricity (yellow bars) it does make up nearly 2/3rds of our consumption (red bars). On the other hand, while in the winter we consume most of the electricity that we generate, there is very little of it so it accounts for only about an eight of our consumption, the other 7/8th coming from the grid.

As you can see, having solar panels on the roof, even if they generate far more electricity than we use, does not make us even close to being independent from the grid. What's more, there's no way we could make ourselves so.

Batteries
It is of course possible to buy a relatively small domestic battery which has enough capacity to store about one day's supply. If we had one of those it would allow us to consume exclusively our own electricity for March through to September, pushing the red bars for those months up to 1. However in the winter months it would be nearly idle because we then generate on average only about a quarter of our consumption, falling to a sixth in the worst month, and we are already using a high proportion of our generation (the yellow bars reach as high as 0.9), so the battery could do almost nothing to help in winter.

To be independent from the grid through the winter we'd need to store electricity from June, July, August and September to fill the trough in our production between October and February and there is no possible storage system which could do this. At present we could buy a small unit which we could fit into our garage, costing a not inconsiderable sum, to cover ~24 hours usage but to store enough to go through winter we'd need something about 120 times as large and 120 times as expensive. It's just not a sensible idea on any level.

Quite apart from the cost and I have reservations about the reliability of batteries for home storage. We already know that, as I expected in advance, inverters are not entirely reliable. It's a box of power electronics which works hard and so we should expect less than perfect reliability. A domestic back-up battery adds far more complication and is almost certainly less reliable. Why ? Because such a battery installation would require not only its own inverter circuitry similar to what we already have in association with the solar panels, but also a battery charger and the battery itself. More power electronics means more to go wrong.

Doubling the number of panels on our already full south facing
roof isn't an option. North facing panels won't work so well.

Such a battery would more than double the price of the solar panel system, more than double the embedded carbon cost, more than double the chance of it going wrong and requiring costly maintenance or replacement as a result. None of that is good news for us or for the planet. Even given all those constraints, it seems that the manufacturers' somewhat optimistic assumptions still suggest that a battery could only provide us 100% usage of our own solar power if we also at least doubled the number of solar panels that we have. As our roof is already almost full this would require us to annex our neighbour's roof entirely for our own use. That's not going to happen.

Let us remember that the excess that we generate and do not use is not lost. Investing too much in trying to use our own electricity ourselves is almost certainly counterproductive. A good proportion of our excess is consumed by other electricity users, both domestic and industrial. This leads to those consumers having lower emissions from their electricity consumption.

Reduce consumption!

A domestic battery makes no practical sense and doesn't necessarily make sense for our environment either. The best thing for us to do, and I would suggest for everyone else as well, is to reduce energy consumption as much as possible. We're continuing on that path, making our home more efficient every year. The less we consume, the easier it will be for our grid to operate without fossil fuel input. Any additional loads will keep the fossil fuels burning for longer.

Domestic and commercial
Our domestic solar panel setup is not actually 100% domestic. We operate our business, Dutch Bike Bits, out of our home, so the business is also powered from our solar panels. We try to run our business in the most ethical way we can. Therefore there is no extra energy consumption in another building and we don't use any form of motorized transport so our parcels, all of which contain goods to support people who cycle and are therefore assisting other to also use the most efficient vehicles on the planet, begin their journeys by bicycle.

Low carbon footprint hummus (super fast and economical to make)

2020-03-23T15:00:00.003+01:00

Ingredients: Chick peas, garlic, tahini,
lemon juice, salt

Hummus is one of the tastiest things to eat for lunch on bread. It's also super easy to make yourself, even from a store cupboard if you're trying not to go outdoors (the COVID-19 pandemic is a very big problem at the moment in the Netherlands).

So if you're stuck for something tasty to put on bread for lunch, consider making hummus. It takes far less time than going to the shops, it's cheaper than commercial hummus and the result is tastier.

The ingredients required as all easily stored except for the garlic. The only fresh ingredient needed is garlic, though you can use garlic from jars if required.

In this example I used a 400 g tin of chick peas, one table-spoon of olive oil, a couple of tablespoons of tahini and small squirt of lemon juice, four cloves of garlic and a tea-spoon of salt.

Drain the chick peas, but keep the liquid. You'll find you need to add some liquid while liquidizing and this is the best thing to use. Keep any which is left over for use as liquid in other recipes (it'll go off if left too long - I put seal on the tin and use within a day or so).

The exact proportions of ingredients are not important. You can vary them to suit your taste buds and also to suit what you have in stock. Even the main ingredient, chick peas, isn't really necessary. OK, so real hummus may be a chick pea dish, but exactly the same procedure can be followed with any kind of tinned or pre-cooked bean and it you get a similar tasty result. So if you need something to spread on your bread and don't have any chick peas, try some other bean. For instance, black-eyed beans make a great spread as well.

Super simple - just put everything in a liquidizer. No cooking is required. Note that everything is shown "dry" here. It's always necessary to add some of the liquid from the chick pea tin to make it liquidize properly. You can also vary that according to taste - some like their hummus to be more liquid than others. If you don't have a liquidizer you can simply mash all the ingredients together.

After 30 seconds or so it'll look like this. Stop when you like the consistency. It's immediately ready to serve.

One 400 g tin of chickpeas and the other ingredients together make about enough hummus to fill two average commercial retail hummus containers. We buy these only occasionally and when we do that we keep the containers which can be re-used many times. The red specks are due to an optional extra ingredient - I included a red chilli this time around. Other spices or herbs can be added in the liquidizer at the start.

Lunch. This recipe always makes delicious hummus.

Carbon footprint

As before when I made a pizza, I wanted to calculate the carbon footprint of this meal. It won't be very high for the calories because vegan food never is. And in this case it'll last for a few days of lunches so the cost per day will be low anyway. Unfortunately, I couldn't find accurate figures for the chick peas or tahini, so I warn you in advance that the following figures are to a large extent guess work. Perhaps you can help with this.

The first part is easy. The liquidizer consumes 1000 W but it's required for only a very short time. Less than 30 seconds in total. Therefore the total amount of energy consumed is very small. This works out as about about 8.3 Wh, or 0.0083 kWh. Due to the full sun today the only effect that it really had was to make our electricity meter run backward less quickly but I've calculated here as if we were using the average carbon footprint for electricity across Europe. Even so, the liquidizer doesn't do much harm:

Ingredient	Quantity (g)	CO2 equivalent (kg/kg)	Total CO2 (g)	kcal
Electricity	0.0083 kW	500 g/W	4.2
Chick peas	400	0.7	280	468
Tahini	30	2.3	69	170
Olive oil	10	1.5	15	80
Lemon juice	10	0.5	5
Salt	1	0	0
Total carbon footprint / calories			373.2 g	718 kcal

As explained before, I cannot claim this time that the figures above are in any way accurate. The carbon intensity of tinned chickpeas and of tahini are both based on figures that I found (here) for similar ingredients. I picked "ready to eat meals" for the chick peas and "Nuts and almonds" for tahini (which is ground up sesame seed). As those two items dominate the total this makes the entire result questionable. However I have picked replacement values which are on the high side so I would be surprised if the carbon footprint of hummus made this way is greater than what is shown above.

I hope that readers can contribute better sources for those ingredients.

How much did it cost to make ?

These cheap chickpeas cost about 60 cents a tin, the small amount of Tahini is worth about 20 cents. The other ingredients perhaps 10 cents at most between them. That makes for a total cost of probably less than 90 cents for an equivalent amount of hummus as is found in two commercially made pre-prepared packs which cost about €2 each.

What about dried chickpeas ?

Dried chickpeas have a lower carbon footprint when sitting on your shelf than does an equivalent quantity of tinned chickpeas. However a lot of energy is required to boil them at home. I therefore would expect a higher carbon footprint for chickpeas that I boil myself than is the case for those bought in a tin where economies of scale will make the process more efficient, almost certainly more energy than is consumed in making the small amount of steel in a can. This seems to be confirmed by various sources.

The forgotten energy saving potential of the microwave oven (also quick low impact vegan pizza recipe)

2019-10-30T16:22:00.000+01:00

The recipe book which came with my
first microwave over in the 1980s

Click these links for the recipe without the story, to find out how much CO2 was emitted, or for how far you can cycle using only the energy in the pizza.

Back in the early 80s I bought a microwave oven for my mother with some of my earnings from my first job. Microwave ovens were not really a new invention but they were not entirely commonplace yet in the UK. I don't think my Mum really wanted a microwave at the time, but she became quite convinced by it and made quite good use of it because it allowed some recipes to be cooked just as well before, but in less time. A year or so afterwards I packed in the dead end job and became a student but my accommodation consisted of one room in a building with no shared kitchen. For several months I ate nothing but salad for my evening meal, which was healthy enough but ultimately not so varied, so I bought a second microwave oven and began to learn to cook with it.

Microwave ready meals were not really a thing in the early 1980s so people didn't buy microwave ovens merely to warm up frozen pizzas. Because many owners had no previous experience with microwave ovens they were supplied with information about how the oven worked, what it was useful for, and complete recipe books. My first microwave oven was a Samsung and it came with this book.

They were both full of tempting looking meals,
completely cooked by microwave

Inside the Samsung book there were a wide range of recipes some of which became favourites during my student days. However this book was of course aimed at every potential buyer so it included a lot of non-vegetarian recipes which were of no use to me so I bought a second book which while not completely vegetarian did include a lot more recipes for things that I wanted to eat.

I ate fairly healthy food when I was a student, and very nearly every evening for a period of years I prepared my meal in the microwave oven, everything cooked from fresh ingredients. The budget was small but the food was good.

Microwave ovens are not the best way of cooking every type of food. Some of my experiments as a student were not total successes. For example, at that time I didn't understand about how bread was made and I once ended up making my lunch sandwiches out of incredibly dense lumps of dough for half a week because I couldn't afford to throw anything away. But microwaves have advantages for some kinds of cooking.

The forgotten potential
My old microwave cookbooks include short descriptions of why microwave cooking is advantageous. For instance, the microwave oven consumes far less energy than a conventional oven to achieve the same result, it saves time and it's less dangerous to use because it doesn't get hot in itself.

Much of the potential seems to have been forgotten with microwave ovens now being seen by many people as useful only to warm up low quality frozen food.

We've done this with our produce. Quick, easy and effective.

There is more awareness now than there was 35 years ago that we really should be trying to consume less energy, but while we now have an image of ourselves as being "green", we actually consume twice as much electricity now as we did back then. The average person was actually more frugal before anyone had LED lighting in their home or solar panels on their roofs.

These books are full of recipes for proper food.

Now, more than ever, we need to address our excessive energy consumption and enormous CO2 emissions. We can start in the kitchen. Switching to a vegan diet is of course enormously beneficial because a plant-based diet produces far lower emissions than does a meat and dairy based diet. But we can go beyond just the savings due to the ingredients we use by changing how we cook.

An online discussion a few days ago revealed how remarkably energy and carbon intensive a pizza can be if it is a frozen pizza, warmed up and delivered to your home. There's no obvious reason why a pizza should be so damaging. It is, after all, basically just tomatoes on toast. However this prompted me to think about one of my favourite dishes when I was a student: microwave quick pizza. This took no time to make and included no exotic ingredients so surely had a low footprint.

Quick low impact inexpensive vegan pizza

I clearly referred to this page quite often
when I was a student.

When I was a student, one of my favourite recipes was a basic microwave pizza. This took less than 15 minutes to cook from scratch, it was very simple, it was tasty and it was nutritious.

The original quick pizza recipe which I used as a student of course used cheese as a topping, but I've been vegan for decades now and so I always substitute something else. There are many commercial cheese substitutes. I've tried most of them in the past, some are better than others and you may well find one that you really like. However we cook from basic ingredients every day so we don't usually have things like "vegan cheese" in our refrigerator. For the pizza which I've made for my lunch today I've used nuts as a substitute for cheese. That may sound a bit, well, nuts, but it's not actually a bad substitute. Nuts contrast with the tomato, they provide protein and oil as does cheese and in any case many commercial vegan "cheeses" are made at least in part of nuts.
Ingredients for the base (makes one pizza)
120 g self rising flour
20 ml olive oil
35-45 ml water
pinch of salt

Ingredients for the topping
100 g tinned tomatoes, drained.
10 g peanuts, crushed.
1/2 small onion.
2 cloves garlic.
Basil, oregano, salt and pepper, nutritional yeast to taste.

Instructions
Mix all the base ingredients together into a dough. Add the water slowly as you want a nice dough and not something too sticky.

Slightly oil a plate and spread the pizza dough on it. It's not a bad idea to make sure that the sides are slightly high to contain the topping, but the topping shouldn't really be wet so this isn't actually very important.

Microwave on full power for about 3 minutes. The pizza base will become puffy and rise slightly.

While the base is in the microwave you have time to drain the tomatoes (if they're too wet then the entire pizza will be too wet), chop them, crush the peanuts in a mortar and pestle and also finely chop the onion and garlic.

When the pizza base is ready, spread the onion and garlic on top and microwave for two more minutes. This softens the onion a bit, which doesn't happen so readily if you put it in with the tomato already on top.

Now add the tomato, herbs and crushed nuts and microwave for another 3-4 minutes.

Add salt, pepper, nutritional yeast to taste.

Perhaps not the best pizza in the world. Perhaps some people wouldn't even consider it to be a "true" pizza. I don't much care. It's tasty, nutritious, quick to prepare from scratch and it's all I've got for lunch today.

I like cabbage, perhaps more than most people, so I added some of that to the topping as well at the same time as the onions and garlic. I also added capers before the last microwave step and I topped it off at the very end with a few small tomatoes from our garden (it's nearly November but we still have the last of the fresh tomatoes) and a few basil leaves also from the garden. You can add anything you like.

Obviously if you're alergic to peanuts you should substitute something else. Nothing is very critical. It will probably also work with gluten free flour.

Note: This isn't a real bread recipe. It's more like a recipe for a scone (you can make good scones in the microwave). The rising action in this case is the result of a chemical reaction with the sodium bicarbonate in the self rising flour. This chemical is all that distinguishes self rising flour from normal flour and you can just add a tiny quantity yourself (its sold as baking powder) to normal flour if you want. Baking with yeast is different. If I had know about that difference when I was a student I wouldn't have had to eat solid bread for a week (see story above).

0.08 kWh consumed in
the 19 minutes it took to
make the pizza, write
down what I was doing
and take all the photos.

A low carbon meal

Having cooked and eaten the pizza we can now calculate the CO2 emissions which resulted from it. The electricity is easy: There are articles online which show the carbon intensity of electricity for different countries. Exact figures vary but for the Netherlands, and across Europe, around 500 g/kWh seems to about average. My plug-in usage meter measured 0.08 kWh used in total by the microwave. Generating that amount of electricity would normally result in about 40 g of CO2 being released. Because I cooked this pizza at lunch-time the microwave oven was actually entirely powered by our own solar panels. The electricity meter span backwards the whole time. But I will stick with the 40 g for this calculation as it's more representative.

Impacts for the ingredients are taken from this link (it refers to Finland, but I can't see most of them would vary much elsewhere).

Ingredient	Quantity (g)	CO2 equivalent (kg/kg)	Total CO2 (g)	kcal
Electricity	0.08 kWh	500 g/Wh	40
Flour	120	0.8	96	400
Olive oil	20	1.5	30	160
Water	40	0.5 (for mineral water. I used tap water)	20
Salt	0	0	0
Tinned tomatoes	100	0.3 (vegetable juice)	30	19
Peanuts	10	2.3 (nuts and almonds)	23	61
Onion	30	0.2	6	12
Garlic	10	0.2	2	3
Cabbage	30	0.3	9	7
Capers	5	0.1	0.5
Herbs, salt, pepper	5	0	0
Total carbon footprint / calories			256.5 g	662

So I've calculated that my lunch had a total impact calculated of around 260 g CO2. I've been a bit unkind to myself because our electricity has a lower impact, at least in the daytime, and my water definitely has a lower impact as it came from the tap - I never buy mineral water so in this case around 200 g was probably more accurate. Either way, the total is small enough to fit into most carbon budgets.

The total weight of the finished pizza was about 370 g (very little liquid had a chance to evaporate, and the rest of the ingredients stayed in the plate). So the impact of a pizza made in this was is 0.7 kg CO2/kg food. This makes sense because it's somewhere in the middle of the impact of the ingredients themselves. It's a very long way removed from the 19 kg/kg figure given at the link for "pizza", but it's clear that what they're referring to is a ready made or delivered meal of some kind.

Another study suggested that a frozen pizza in Norway could have an impact on the climate equivalent to as much as 290 kg CO2. My recipe has less than 1% of that impact.

Conclusion
Following the recipe above you too can make a pizza which is quick to prepare, tasty, nutritious and has about 1/30th of the environmental impact of a delivered pizza. If it had been cooked in a conventional oven then the energy consumption would have been far higher. The energy saving potential of microwave ovens is largely not appreciated, but it should be. We are killing our planet with over-consumption of many things, including energy.

Addendum: What can we do with 662 calories?
662 calories is more than a quarter of the daily requirement for an average man and very close to a third of the recommended daily for an average woman. We need to eat that amount every day just to be healthy. We also need to exercise for about half an hour every day. So let's work out what can be achieved by using those calories.

We should always bear in mind that we need 30 minutes of exercise every day just to maintain a healthy body. In 30 minute we can cover 15 km on a bicycle, so by cycling we effectively get 15 km of travel for free every day with no impact on the environment over that of the food we have to eat anyway.

Velomobiles are the most efficient vehicles on the planet. But can you get a
subsidy to buy one of these ? Of course not. However the Dutch government
will give you €6000 to buy an electric car which produces far more pollution.

However if we ignore that and simply plug the calories that we have into a calculator and work out the potential then we find that with a standard town bike we can ride an impressive 32 km at just over 20 km/h using nothing more than the energy from the pizza. If we use a more efficient type of bicycle then we can cover 46 kms at 30 km/h using just that pizza as fuel. That works out as about 5.65 grams of CO2 emissions per km for the efficient bicycle and about 8 g CO2 per km for a standard bicycle. By comparison, in the Netherlands, an electric car produces about 60 g CO2 per km and a diesel car anywhere about 120 g per km.

A cyclist can easily travel with a tenth of the emissions of the driver of even one of the most efficient cars, but even that comparison is unfair because actually we get our first 15 km for free.

The surprising cost of a pilot light (waakvlam)

2019-09-28T16:48:00.004+02:00

We have a low energy bill. This is the case because we've done quite a lot of work in our home to improve the insulation so that our central heating rarely comes on, and we've tackled our electricity consumption by installing solar panels. However, we've not yet done anything to the gas equipment in our home which was already here when we moved in 12 years ago, in part because until now it's not been easy to tell which piece of equipment used most gas so should be targeted first.

While we've had a smart electricity meter for almost a year now, and I've used a plug in measuring device for much longer to check which appliances had higher than expected consumption, our energy company didn't install a smart gas meter until a week ago. The old meter was not easy to read for small levels of usage. But the new meter has made it easy to find out something which I had long wondered about: How much of our not very high gas consumption was wasted to no effect.

The new gas meter. Since installation we've burnt 5.725 cubic metres of gas.

The gas water heater

How much gas does a pilot light (waakvlam) use ?
Our house has three devices which run on gas: The gas hob in the kitchen, the central heating boiler and a separate water heater which heats water only for the shower, bath and bathroom sink.

The water heater is really old. Old enough to use a pilot light (waakvlam) instead of starting itself with an electronic igniter whenever hot water is required.

If you're unfamiliar with what that means, there is a very small flame which burns continuously, 24 hours a day, 365 days a year, just waiting for someone to turn on the hot tap so that it can be used to ignite a much larger flame to heat water.

In the past I've asked several people who work for the gas company, or otherwise seem to know about gas appliances how much gas is used by such a flame and I've always been re-assured that it's "next to nothing", "unmeasurable" or "similar to a mobile phone charger", but I was never quite convinced. The new gas meter has allowed me to measure how much gas is being consumed and the result is surprising.

The pilot light. It's small, but any gas burnt here is wasted.

Meten is Weten. It costs how much ?
One day this week we took readings from the gas meter while avoiding using any gas appliance for 18 and a half hours so that period passed with only the pilot light burning gas. Over 18.5 hours, the meter showed that 0.283 cubic metres had been consumed. That equates to 0.366 cubic metres per day or 134 cubic metres per year.

134 cubic metres of gas isn't insignificant at all ! In fact, it turns out that in summer months our gas usage is dominated by the consumption of the pilot light, which consumes more than we use for hot water and cooking combined. Over the whole year it consumes rather more gas than we use in February to heat our home. It's an appalling waste not only of gas but also of money: That pilot light costs us nearly €90 a year to run.

Like a phone charger ?
The comparison made previously with a mobile phone charger is particularly absurd as phone chargers genuinely do consume an unmeasurably small amount of electricity when they're not in use (unplugging them is something that some people do in an obsessional way because it looks like it'll save energy, when actually the effect is almost nothing at all). But this pilot light consumes a very measurable amount of gas. 134 cubic metres of gas is equivalent to about 1340 kWh of electricity. If a phone charger used that much it would certainly be measurable. It would also add somewhat more than €100 a year to the electricity bill and the charger would be rather hot rather than cold to the touch.

The next step
Obviously this old water heater has to go. That has long been the plan because actually we'd like to get rid of gas altogether. It's not happened yet because we prioritized insulation and electricity first. But discovering how much this thing wastes has given new urgency to the plan. At the very least we need to be rid of this water heater. It appears to be possible to buy an instant electric heater for about the annual cost of the gas for this, and an electric heater would effectively cost nothing to use because it would operate on the excess electricity from our solar panels which we currently export to the grid and for which the electricity company pays us very little. So I expect to change this quite soon.

Update: The pilot light no longer burns!

It took us a few years to get around to it, but we did eventually replace this inefficient water heater, saving both gas and money. Read more about what we replaced the gas heater with and how this change will bring our total future energy bills close to zero.

Seven years of solar power: How valuable is our solar energy ?

2019-04-08T13:31:00.004+02:00

I've been interested in solar energy since before I can remember. My first practical experience beyond things like solar powered calculators was in the mid 1980s when I put a square meter of surplus panels on the roof of my parent's home. These provided 12 V DC which I used, amongst other things, to charge the battery in my then quite new laptop computer. It wasn't until seven years ago, though, that we installed a large system on our home and the seventh anniversary of that system passed on April 5th.

Seven year summary
We have 16 panels each rated for 235 W output for a total of a 3760 W peak. In this part of the world it is usual to calculate the expected total output as the equivalent of 925 hours of full sun each year on the panels, giving an predicted output of 3478 kWh per year. In practice, over the last seven years our system produced 23601 kWh in total or an average of 3372 kWh per year.

Output per month over seven years. Red bars show our electricity consumption, blue bars show the production from our panels and the yellow line shows where we are in total now relative to where we began. Our production in is higher than our consumption on average, though obviously that is not the case in the winter. The kink in the yellow line from July 2018 is the period during which our inverter was not working (I repaired it myself)

Several things contribute to the slightly lower output relative to the estimate: Our panels are mounted at the angle of the roof and not at whatever the ideal angle might be, they face South West rather than directly towards the South. But the most damaging thing so far as the average is concerned is that our inverter failed last year and so we had no output at all for a few weeks during the sunnier than average month of July. Calculating out average output for the six years before the inverter problem we come to 3410 kWh per year which is within 2% of the prediction.

Return on investment
The monetary value of the electricity which we've generated is about 20 cents per kWh for that which we use ourselves and about 7 kWh for the excess that we export to the grid. We have exported about 1200 kWh in total for a value of €84 and consumed about 22400 kWh ourselves for which we would otherwise have had to pay about €4500. In total, then, about €4600 has been returned from our original €8000 investment. If the same rate of return continues then the system will have taken 12 years to pay for itself.

Our new smartmeter. When the photo was taken
everything electrical in our home was powered
from the panels and 2 kW was being exported
to the grid.

If the inverter fails again and this time we have to replace it then that will of course increase the repayment time. This might happen. However the panels themselves are expected to last much longer than the repayment period.

A smart meter
Something else which changed last year was that our electricity meter was replaced in December.

The new meter doesn't give us any real advantage over the old mechanical meter which span backwards just as enthusiastically as forwards for nearly seven years. The electricity costs us the same amount either way around.

Of course it does offer an advantage to the electricity company because they no longer have to ask us to read the meter or visit to do so themselves.

What the new meter does give me, though, is that it counts differently and therefore I have a little more information for future calculations. While we pay the same amount of electricity in peak and off peak periods, the meter displays them separately, for both inbound and outbound electricity. So now we can see how much electricity we consume at night time and we can see how much leaves our home rather than being consumed here.

Solar electricity is more valuable than average because it is
generated at peak times of consumption (source)

Perhaps after a year of recording this information I'll have something which which I can create an interesting graph. Thus far I have just three and a half months of this extra data, all of it from winter and spring. There's not much contrast to see.

What has long been obvious of course, and is also visible even in the small amount of data which I have now, is that our electricity is generated only in the daytime and then mostly on sunnier days. As it happens, solar electricity remains quite valuable in the Netherlands because this daytime generation corresponds reasonably well with peak usage. That means that the electricity which we export, most of what we generate, is almost certainly of use to someone else.

The first thing I made the prototype
hardware do was wiggle a GPIO and
then send serial data as shown here.

Software for a smart meter
I'm late to have a smart meter installed but as it happens, I spent a few months two years ago working on software for the prototype smart meter hardware of one of several competing manufacturers. I'm almost certain that the meter that I have now is not related to the manufacturer for whom I did the work, so my code is almost certainly not involved in reporting my own electricity usage, but as I'll never open the box of the meter and look inside, I'll never know for certain.

It was quite an interesting project for a while because it was like a return to the old days for me, when I worked on 8 bit processors and embedded software. This work was with what for me was a new processor, the Renesas RL78. It's a quirky 8/16 bit design. The RL78 assembler is styled so that the source code looks a bit like that for the Z80, but the processor is really completely different. In total I had 32 kB of flash and 4 kB of RAM to work with. These days that doesn't sound like much at all but that means this device has about the same amount of memory as the guidance computers which took Apollo to the moon so it's enough to do great things. In this case it's in a finger nail sized package which consumes micro-watts, and the little RL78 can of course compute many times faster than the AGC.

Power for a home and a business
We generate more than enough electricity to power both our home and our business, though of course I always point out that we're not actually doing so at night, or on darker days in the winter. Anyway, if you want a support a solar powered bicycle business which uses no powered vehicles then you can do so here:

Upgrading Windows to version 3 (Continuing to insulate our home with triple glazing)

2018-12-17T16:30:00.004+01:00

Our windows were fitted by Van Dijk Services
Assen. They did a good job so deserve a link.

We knew we'd have to do something about the insulation of our home in Assen before we even moved in and every year we've made some change to improve the energy efficiency of our home. One of the oddities of 1970s Dutch homes is that while they had double glazing on the main rooms on the ground floor, it was quite common to have single glazing in places like the hall and all of the bedrooms upstairs. We fixed that problem eight years ago by installing HR++ double glazing to replace all the single glass and this was very effective. But we kept the same older windows downstairs.

It took a while for us to get around to considering the downstairs windows because we were busy with insulating the floor, the roof, the walls, installing solar panels on the roof, our bicycle parts business, and generally getting on with life, but we've now begun. In fact, we did one of the smaller panes last year because the old double glazing had developed a leak and we took this as an opportunity to experiment with triple glazing. We made measurements and found that it was effective. When the outside temperature was -2 C and the inside temperature 17.5 C the temperature of the inside of a double glazed pane was measured as 9 C while the inside of the triple glazed window alongside it measured 14 C. Clearly we could stay warmer with less heating if we replaced more of the old double glazing downstairs in our home with triple glazing.

Thus far we've replaced the glass only on the front of our home. We're still not entirely sure what we'll do on the back of house, but there is less than half the area of double glazing in the living room on the back compared with the front.

One of the old panes being removed

The replacement coming into place. It took some lifting because it weighed 127 kg.

Fixing into place

Just fitted, not made neat and tidy yet.

A tidy job completed. We now have to wait a couple of days before we can clean the glass because the sealant has to dry first.

Travel less, nor more, insulate your home
and don't eat meat.

We hope this will reduce our gas consumption and our heating bill. We already have a very low energy bill because we generate more electricity than we use. The gas bill, which covers cooking and water heating as well as heating, is also low and has reduced each year. Dutch bills are increasing quite sharply this year due to increased tax on gas, but our estimate for next year is the same as this year, and the energy company doesn't know that we've taken measures which hopefully will reduce our usage further.

It's becoming more and more obvious to us that we can't continue to increase our energy usage but must decrease it. We must decrease our burning of fossil fuels. There is little time left to do this. The IPCC report from the 8th of October told us that emissions need to be reduced to zero in 12 years time. Who is doing enough to make that happen ?

Because of our concerns we are not only continuing to make our home more efficient but have also got rid of our car and stopped our business of offering holidays and study tours. Encouraging people to make international journeys to cycle is just not of this time. We must all stop behaving as if we can do whatever we like without consequences. Our children and our grandchildren, not to mention millions of people in poorer countries, are being made to pay for our own selfishness.

Yesterday afternoon. Four identical houses, ours is on the left. We're winning the race to keep ice on the roof from melting. Luckily it was somewhat warmer today.

January Update: Is it effective ?

We will really only know how effective the triple glazing is after the bills come in and we see if we've used less heating. However it's -4 C in the garden today, the sun is still on the side of the house and the inside of the double glazing at the back measure 8.7 C while the inside of the triple glazing at the front measure 14.5 C. Obviously we are loosing a lot more heat through the double glazed panel than through the single glazed panel.

Ice crystals visible on the outside of a triple glazed window when the temperature is -9 C outside. Photographed from the warmth inside.

There's also a very visible difference in that ice crystals form on the outside the triple glazed panel, proving the temperature there stays below freezing while we have a more liveable temperature inside the house. This never happens with our double glazed windows. In fact the closest thing that I have seen to this in the past was when we had ice all over the inside of the upstairs windows of our house before we replaced the single glazed panels there with double glazing. That wasn't comfortable at all !

Update February 2019 - it's working !
The front of our home, with the living room, is now fully triple glazed while the rear with the dining area (open to the living room) and kitchen remain double glazed. There's now an obvious difference in temperature between the front and the rear which I can also measure. Seeing this graph in February 2019 led me to make a simple calculation of consumption of gas for heating:

Source: Martien Visser.

I keep a spreadsheet of our monthly gas and electric consumption. We used less gas in January 2019 than any other January on record, even the somewhat colder 2017. Our gas consumption in January 2019 was 15% lower than the same month in 2016 when the temperature was very similar. A drop in gas consumption of 15% represents a greater than 15% drop in use of energy for heating because we also use gas for water heating and for cooking.

I only have one month of data so far so have to be cautious, but it appears that the replacement of the front windows with triple glazed panels has been effective. At this rate the windows will have paid for themselves in terms of nothing but a reduced heating bill within ten years even if there is no increase in the price of gas. That's a good rate of return and if it's possible I will replace the rear downstairs windows with triple glazing later this year.

Update November 2019
We've just had the rear windows upgraded to triple glazing.

This time the work was done by D & S Glasmontage, a different local company from the one who did the front windows, but known to us already because they installed new windows for us upstairs many years ago.

So now we're completely triple glazed downstairs except for the window in the back door of the kitchen.