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

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.

Modifying a thermostat to make our heating more efficient

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.

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

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.

Solar power in winter - there isn't much of it

Since the 1980s I've been experimenting on and off with small scale solar power. I first bought about 1/2 a square metre of unsealed glass PV panels from an electronics surplus store in the UK. These worked quite well for several years, producing about half of their rated 12 V / 200 mA on a good day. However by the time we emigrated the output from them had dropped quite a lot so I gave them away to another experimenter in Cambridge on freecycle.

The output of the original panels had dropped in part because this is what happens with solar cells, but it was accelerated a lot because they were not sealed and they had got damp, I'd already bought another solar panel, a 12 V 28 W sealed panel from Maplin shown in the picture to the left, to supplement their output. This came with us to the Netherlands, but for three years after we moved here, it was in a box in the garage.

A few days ago I finally got it out and put it on the garage roof - flat as you see it here to try it out initially - and ran a wire into the garage. I then measured the open circuit voltage at the other end of the wire, about 18 V, and then I hooked it up to a 12 V 20 W halogen bulb in the garage. Nothing happened. Measuring, I find that there is about 0.09 V across the bulb, and the bulb itself has a resistance of 1.2 ohms, so I'm getting a mere 75 mA at 0.09 V from the cells. That's 0.007 W. That's almost nothing. Around 0.02% of the rated output.

My initial reaction was to think that the panels have a bad contact somewhere. That the bonding of wires inside is no longer good. Then I thought a bit about where the panel is located right now. As you can see, one of our neighbours has a good sized tree at the south of our garden which casts a shadow. Also, it's quite overcast weather and of course the panel is not oriented well either. While manufacturers often claim their products will work "in any light conditions" and such like, actually they need very strong sunlight to achieve full output, and it's surprising the extent to which the output is reduced by such things as what looks to a human eye as only partial shadow.

On a brighter evening a couple of days ago I held up the panel to the receding sun and measured about half the rated output, which is probably as good as can be expected at this time of year. However, unless the neighbour cuts their tree down, I don't think I'll ever generate much from a solar panel at this position, except in the summer when the sun is higher in the sky.

I also have a small solar panel on my Mango to keep the battery charged. I built a small charge regulator to go with this, as even though its potential maximum output isn't huge, it could still overcharge the battery on a good sunny day (I've also built similar regulators, but capable of dealing with more current, to work with dynamos on Mangos).

In the summer, I rarely had to use my mains electricity battery charger. Even though the orientation of the panel is never perfect due to it being mounted flat on top of the Mango, the solar panel normally provides enough current to keep the battery charged. You perhaps won't be surprised to hear that it is just about completely inoperative in winter...

Sadly, Freecycle had some problems recently so for similar ideals, you're probably better off looking here.

New glass

One of the oddities of our home in the Netherlands is that while the ground floor was almost entirely double-glazed, the first floor was not. This was apparently the building standard of the time it was built - 1972.

The windows are large in our house, so they're more important than they might be in a house with smaller windows. However, the rooms without double glazing are those upstairs which we don't really need to keep particularly warm.

For some time we've been weighing up the pros and cons of spending money on glazing for rooms which don't necessarily need to be kept at a particularly high temperature, and eventually made the decision to go ahead with the work.

We were influenced more than a little by a study about the effectiveness of HR++ glazing which gives some figures suggesting that the HR++ glass is particularly effective. Also, the cost was more reasonable than expected (the second company we asked have a quote which was less than half that of the first), and as it was possible to replace the glass within the same hardwood window frames and not have to replace the frames as well (we're not huge fans of PVC windows), we decided it was a good idea.

We don't expect it to make the same big difference to our heating bill as cavity wall insulation did, as the thermostat in the house is downstairs and relatively unaffected by the temperature upstairs. However, it will presumably mean the entire house is better insulated so have some effect on the ground floor as well, and of course it also means the end of condensation on the bedroom windows, which froze on the insides in the winter and made it difficult to open the windows.

Yesterday it happened. New glass in the first floor windows.

We're hoping this makes conditions a little more pleasant for our teenage daughter in the front bedroom, which due to receiving least sunlight was the coldest room in the house in the winter.

So far, our heating bills have been lower each successive winter since we've lived here, as each time the house is a little better insulated than the previous winter. It's a pattern I'd like to continue.

Read more about the many things we've done to improve the energy efficiency of our home.
 

Cavity wall insulation effectiveness

Last year we had cavity wall insulation installed. This is the third house we have done this with, and for the third time it has been extremely effective at reducing the heating bill.

January 2008 had an average morning temperature (my measurement taken at whatever time in the early morning that I happen to have looked) of around 5 C. This winter has been the coldest for over a decade and the average temperature taken in the same way in January this year was -0.5 C. Despite this, the gas used was 281 cubic metres this January vs. 274 last January.

I didn't write down the temperatures for December 2007, but remember that the lowest temperature I cycled in was -6 C vs. -11 C this winter. However, our gas consumption was 396 m^2 in December 2007 vs. 298 m^2 in December 2008.

Overall this seems to have been a very effective measure once again. It looks like even though it cost us around 700 Euros to have the insulation installed, it will pay us back in about three years. It's much cheaper to have cavity insulation installed in the UK, so the payback period is even shorter there.

We still have more to do here to get the heating bill as low as we'd like, though.

On the right, another photo of the frozen canal taken yesterday. It snowed a little. The snow was quickly cleared from the cycle path, but rested on top of the frozen canal. I wonder how much insulation the house boats have.

Further updates
Since this blog post we've installed far more insulation and our use of energy for heating is much reduced as a result, along with the cost of energy.

Read more about the many things we've done to improve the energy efficiency of our home.

Photos of the cold weather

Yesterday it was -6 C ( 21 F) and the canal was just about completely solid.
This morning it was -10 C ( 14 F ) and completely solid. So much so that people have been able to skate on it.

It's much the same for all the lakes around this area. No snow as yet, but a very heavy frost.

All the bike paths are kept clear of ice, though.
Icicles on our windows have grown to about 40 cm long.

This hasn't stopped people going out, of course. In fact, it's given them new things to go out for:

Frozen canal

These two photos were taken on this morning's dog walk along the canal which on the western edge of Assen.

The sun is out today which makes it feel a lot warmer than yesterday. However it's actually only 1 degree above freezing, so there is still ice for the birds to stand on next to the house boats.