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

by Mars

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.

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.

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.

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Malcolm Ratcliffe
Malcolm Ratcliffe
5 months ago

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?

Mark Brice
Mark Brice
5 months ago

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.

Graham Sauer
Graham Sauer
5 months ago

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.

Malcolm Ratcliffe
Malcolm Ratcliffe
5 months ago

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
Graham Sauer
5 months ago

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
Malcolm Ratcliffe
5 months ago

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!


5 months ago

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.

4 months ago

It’s interesting to read your experience of heat pumps. I think that the main problem is that we’d all like them but we’d also like to avoid paying a huge capital cost. Sadly I don’t think that it’s possible.

I have been looking at heat pumps (I have a semi-detached 5 bed house in London) for many years but I couldn’t make them add up financially. Even solid wall insulation is hideously expensive (the joy of a 1930s house without cavity walls).

At least there is better information now than when I first looked at heat pumps 10 years ago. As a retro-fit I am convinced that it’s possible to have a 16kW air source heat pump (in London where it’s rarely below freezing) but only as long as all of the radiators are massively upsized.

Take, for example, my 4m x 3m living room. I’ll have to upsize from double panel radiators (two Stelrad 50cm by 60cm) to two 180m by 50cm ones – 4 times the size. Just the radiators alone for that room would cost £852. That assumes a flow temperature of around 45C for a pretty good COP.

I have 8 rooms, 2 bathrooms and a kitchen to heat.

Total upgrade costs, assuming that I DIY it, would be in the region of £12k for a system that I’m fairly sure will work fine. It would be more like £25k if I had an external company do the work instead. Even a smaller 3 bed would probably cost £20k to do well. This is a non-starter for those without significant financial resources.

Given that price tag, I can see why installers will recommend a ‘high temperature’ system without any radiator or other system upgrades to reduce the up-front costs. Inevitably, this will lead to poor performance, high running costs and low COP.

Malcolm Ratcliffe
Malcolm Ratcliffe
Reply to  Jack
4 months ago

Now you are up for DIY radiators, plumbing etc.
first consider advantages of DIY installation!
insulation has no running cost, only savings costs.

solid brick wall has U value of 2.2 watts per sq m per degree C

a double glazed window is around 1.7. So be amazed. Solid brick looses More heat than windows, per sq m.

building regs suggest if you insulate solid brick you should get insulation down to 0.3 (see https://great-home.co.uk/building-regulations-current-u-values-for-insulation-in-homes/ )

so your improved insulation cuts heat loss, through that element, from 2.2 to 0.3. Cuttin heat loss to about 1/7. One seventh. No need to increase radiator size! Now for the heat pump they are oversized,

now you need to look at the whole building. But remember insulation is for life, it works forever. Putting in a heat pump allows just as much energy to be lost, you pay for that … forever.

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