Our heat pump, solar production and the weather – a year in review

by Mars
My Home Farm

As part of our ongoing sustainability journey at Home Farm, we annually review our solar production, air source heat pump efficiency and the weather for the past 12 months.

Somewhat frustratingly, Global Energy System’s online portal has been down for a few days as they have been updating their software, so we weren’t able to access our air source heat pump data, which should make for some interesting reading based on our switch to HVO to help the heat pump run more efficiently this winter. We’ll publish a fresh post later in January that’s dedicated exclusively to the air source heat pump’s performance in 2021. We’ll also discuss running costs.

On the solar PV front, it was a very similar year in terms of electricity generation to 2020. In 2021 our 6.16kW array produced 6.03MWh versus 6.18MWh in 2020. You’ll notice a decrease in consumption and that has to do with our switch to HVO in the winter.

The graph below is interesting in illustrating the strongest months for our system’s solar production, and it shows just how poor production is from November to February compared to the rest of the year. We’re also very pleased that we’ve saved releasing nearly 4,500kg of CO2 into the atmosphere in just under three years.

Solar production

The weather has also been an interesting topic. I must caveat this section by saying that we had a glitch with our Netatmo home weather station in January and February (which I didn’t realise at the time) so our data is incomplete, but it still paints a picture.

So let’s talk global warming. Both Kirsten and I both commented that this year generally felt warmer and the average temperatures, from June onwards, definitely highlight this. July was roasting, and September, October, November and December were extremely mild. What’s crazy is that, on average, most months were over 1.5C warmer than last year.

We have yet to experience an extremely cold spell this winter, which is rare for us. December has been ridiculously warm, and it’s been bordering on T-shirt and shorts temperatures.

This next bit is new to me – the grassland temperature sum. This is used in Europe to determine the date for starting field work. This sum is calculated by taking the positive daily average air temperature starting at the beginning of the year and adding them together.

In January they are multiplied by a factor of 0.5, in February by a factor of 0.75 and from March the full daily value (factor of 1) is included in the calculation. When the sum exceeds 200 in spring, the “sustainable beginning of vegetation” has been reached. For us, we hit that mark around 23/24 April. I’m guessing we’ll hit it earlier in 2022.

grassland temperature sum

To view our comparative weather charts for rain, temperature, pressure and humidity for 2020-2021 please go through the graphs in the gallery below.

Our strongest wind gust was 88km/h on November 28, 2021, when storm Arwen hit us. Hottest day of the year was July 18, when the mercury hit 32.8C.

As a point of reference, we’re in the West Midlands (Welsh borders), and we would love to hear how your weather and solar PV production compared with us. Please leave a comment below.

In closing, we’d like to wish all our followers a safe and prosperous 2022.


Malcolm Ratcliffe 3 January 2022 - 10:13

Wow! An amazingly comprehensive set of data. Too much to take in at my first glance. I will have to find time to look at it in more detail. A great shame all the data is not available and I note you will be updating the post when you have it all.

I note in environmental benefits the saving of 4500kg of C02 emissions saved (over 3 years). But the graph is beneath an annual graph, giving 3 years of data. The casual reader might easily assume this to be an annual figure. I hope this was an oversight and not green washing! I suspect it could be due to the software?

Looking at your energy consumption initially astounded me 17.5 Mwh a year. Till I calculated my own consumption at 16,000 KWh a year. Consumer energy is bought per Kw, that’s what we all understand. I understand the software uses MWhr, and it’s comparative. But most people wouldn’t understand.

I was looking for a summary or conclusion, reading this first could help to explain / guide the reader to understand the data.

I hope your experiences will guide others taking a similar journey, and who knows, influence policy makers? Have you any guidance on things you would have done differently?

Mars 7 January 2022 - 21:58

Thanks for the comments Malcolm.

Your last question intrigued me – would we have done anything differently? The quick answer is yes. I will give it some more thought and maybe post a new article on this subject. Thanks for promoting me.

I also like a lot of your other points. Thanks for taking the time to leave a comment.

Mark Brice 4 January 2022 - 12:09

Hi Mars

Interesting data, as I don’t collect weather data I only have the solar and house consumption numbers as below.

For Solar our 6.63kW predominately ground system we generated 5,356Kwh in 2021 against 5,835Kwh in 2020. 2020 was our second best year since our system was fitted in 2013 whereas 2021 was the 6th of 8 complete years.

Our house usage dropped to 15270kWh from 17,261kWh the year before. We are fully electric property using an ASHP for heating and hot water.

We recently moved over to E7 as we had 2 Tesla Powerwalls fitted, our night cheaper rate usage has increased from 45% to 85% of total daily consumption which helps in reducing our winter electric bills.

As we have gone as far as we can with energy production/efficiency at our property we are looking at a cooperative wind turbine investment through Ripple Energy.

Mars 7 January 2022 - 21:55

Very interesting. Thanks for sharing Mark. Would love to hear more about your experience wit Ripple Energy.

Graham Sauer 7 January 2022 - 11:31

We were considering installing an air source heat pump next year and have been following your experience on YouTube. I recall one of your blogs saying the breakeven electricity tariff for the heatpump vs oil boiler was around 15p/kwh, like you we were on a cheap fixed term deal with a company that went bust. The tariff cap is currently 21p/kwh and is forecast to rise to around 32p/kwh in April and then to about 38p/kwh later on on the year, that is almost three times the rate I was paying early last year. So what is happening with your heatpump, have you gone back to using the oil boiler.
Our oil boiler is now 25 years old but it seems inconceivable that we would replace it with a heat pump until electricity prices come down. Will they ever come down below 15p again.

Mars 7 January 2022 - 21:53

Excellent questions Graham. Our tariff is up to 22p/kWh which makes running the heat pump ridiculously expensive. Having said that, all energy has gone up in price, including gas.

We are fortunate this winter in that we are trialling a new biofuel called HVO, so we have switched our system to run bivalently with the oil boiler doing the heavy lifting when temperatures drop below 8C, so our heat pump is running much more efficiently. More on that here: https://myhomefarm.co.uk/ho-ho-ho-for-hvo-will-it-be-a-warm-christmas

You are correct – electricity tariffs are projected to rise sharply next year in April, but other fuels will also go up in price. It’s the price of gas driving up the prices of electricity, so gas and LPG boilers will also be much more expensive to run. Kerosene at the moment is still a reasonable option, but that too is rising week after week. Our oil price was about 63p/litre last week. What is your rate?

I’m actually working on a new post which I hope to publish this weekend where we have to re-evaluate heating prices. I fear everyone in the UK is going to struggle irrespective of their heat source.

Malcolm Ratcliffe 8 January 2022 - 09:49

Current heating costs. Semi detached, 3 floors, floor area approx 120m2. We use gas to heat our relatively well insulated house. It heats the house till 10am and retains sufficient heat so that we have timed the boiler to come on at 5pm. By that time I manually turn down the boiler and light the solid fuel stove (5kw peak) and burn wood. This keeps the whole house warm. We haven’t bought commercially bought wood for years, as I reckon that it’s too expensive, costing, according to my calculations about 3 times as much as gas (that’s based on £60 for a builders bag)

Annual gas consumption approx 8000 kWh
Annual wood consumption estimates 4000 kWhr
Annual electricity consumption about 2300 kWh

We don’t use any electricity for space heating
(Though for various reasons we have had to heat our touring caravan for a few weeks. That’s using about 20kg a day. Frightening)

Coal and smokeless fuels are costing around £300 a ton. That’s (8000 kWh). Now I don’t know of stove efficiencies but this must be one of the cheapest sources for domestic space heating. And the most CO2 polluting.

Graham Sauer 8 January 2022 - 10:24

Hi Mars.
We live on the Welsh side of Llanymynech, a village split by the Welsh English border. Just had look on boilerjuice.com and was quoted 58p for heating oil, our local supplier generally does it a couple of pence cheaper. The floor area of our house is 170m2, we use between 1600 and 2000 litres, depending on the severity of the winter. If my daughters are living at home the hot water consumption rockets, how do they manage to take 15-20 mins in the shower?. Years ago we were using about 5500 kwh of electricity, its now around 3500 kwh. Replacing every bulb with led made a big difference, the item that saves us the most electricity is a halogen oven, 1.2kw as opposed to a 3 or 4 kw oven, it’s surprising how little the big oven gets used.

Malcolm Ratcliffe 8 January 2022 - 20:44

I came across this comparative cost of fuels and other info. Last updated in October 2021

But interesting if you are into geekery, like me!


Mars 8 January 2022 - 21:59

Nice find Malcolm, and thanks for sharing. If you want to share and indulge in more heat pump and tariff geekery, please head over to https://renewableheatinghub.co.uk/forums

Iain 9 January 2022 - 13:43

Afternoon Mars. Interesting reading on your data, especially your electricity consumption. 19.1 mwh 2020 and 17.5 mwh 2021 with the HVO doing some heavy lifting. Even with the solar input what are your bills like? A fag packet calculation of 13mwh @ .22p per kwh,would be around £3,000 including the HVO cost. Does your consumption indicate that your heat load is well in excess of 19mwh given you’ve previously said that your pump has a COP of around 2.6?

We live in a 4 bed house in NE Scotland with a total heating and power load of around 22mwh, but running on gas at a little under 4p kwh and lecky at just under 20p kwh. We are with Shell Energy, who I believe keep there standard tarriffs a little under the cap.

With regard to HVO have you researched it’s green credentials? The vegetable oil is processed with hydrogen extracted from Methane and other chemicals and heated in a reformer. It certainly helps to reuse the oil but is certainly not low carbon. I wonder about future availability of the fuel as the rail industry and road haulage plan to use it the rail industry uses around 90m litres annually. Do you know how much HVO is produced each year?

Your blogs are very informative and I look forward to the next blog on your pump performance.


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