Reposting without any links since that seems to get caught in the spam bot filter
The recent energy crisis and conflict in Ukraine has a lot of us worried about living costs especially energy consumption at home, which is often one of the highest regular expenses for many. Rates are shooting up and in my opinion will never return to what they previously were unless there are some drastic changes in the UK government's energy policy.
There have been many questions on /r/ukpersonalfinance and other UK subreddits about whether it is worth getting an air source heat pump (ASHP) or solar PV as a means of reducing energy bills. We moved into our new home last summer which has both an ASHP and a solar PV array, so whilst I can't share costs for retrofitting onto an existing property and return-on-investment times, I can hopefully provide data on how these systems perform in a suitably insulated property. It's going to be a long post with lots of numbers, but I'll summarise as best as I can at the end.
Those that aren't familiar with ASHP should check out the Youtube channel Technology Connections. He did a number of detailed videos about ASHP within a US context but it is the same technology and applications in the UK.
Key facts about our home (most taken from the EPC):
I've unfortunately only got data for the last 6 or so months since that's when I got all the monitoring set up for the smart meter and the solar PV, but it covers the coldest months so is indicative of the max usage. This was our first winter in this house and I was still getting familiar with the optimal settings for the ASHP and heating schedules so we probably used more energy early on in the winter than we would do in the future. I have a Google Sheet set up to read from the Octopus API and my solar API which gives me some nice charts and summary metrics which helped me immensely in fine tuning our energy usage patterns to minimise cost. I'm still developing it and aim to publish a template and guide in the future. We do not have an EV so electricity consumption is primarily heating rooms, the water tank and cooking appliances like the induction hob.
Month
average daily temp
kWh consumed
total solar kWh
average daily consumed
average daily solar
Aug 2021
16.1 C
229 kWh
no data
7.2 kWh
no data
Sept 2021
15.9 C
278 kWh
283 kWh (from 5th Sept)
9.2 kWh
10.9 kWh
Oct 2021
12.1 C
386 kWh
203 kWh
12.5 kWh
6.6 kWh
Nov 2021
7.8 C
530 kWh
118 kWh
17.7 kWh
4 kWh
Dec 2021
6.4 C
702 kWh
50 kWh
22.6 kWh
1.6 kWh
Jan 2022
4.6 C
698 kWh
151 kWh
22.9 kWh
4.9 kWh
Feb 2022
5.6 C
472 kWh
169 kWh
16.9 kWh
6.1 kWh
Mar 2022 (to date)
summary not published yet
353 kWh
334 kWh
12.6 kWh
11.7 kWh
Couple of additional notes: we are on Octopus Go smart tariff which charges 5p per kWh between 00:30 and 04:30 and 15.33p per kWh at all other times (25p daily standing charge). It is an electricity only tariff and you need a smart meter set to report readings every 30 minutes. After months of tweaking the heating settings and schedules (to my wife's annoyance), we've settled on a schedule that heats up the downstair areas to 20C during the day and the upstairs areas in the early evening and early morning. The hot water cylinder heats up between 00:30-04:00 to make the most of the cheaper rate and 11:00-14:00 to make use of any output from my solar array. I don't regularly WFH, but the house is pretty much always occupied so we don't really turn off the heating unless we're all on holiday.
Our bills are generated on the 18th of every month. Our highest bill this winter was £100.84 for Dec to Jan, 2nd highest was Nov to Dec at £92.52. Jan to Feb was lower at £79.97 mostly because we were away on holiday for 5 days so everything was set to standby state, otherwise it woud probably have been roughly on par with the previous billing period.
Is ASHP worth it?
I'm going to give the cop-out answer and say it depends. ASHP as a technology is perfectly suited to our climate (not super cold winters) and even mid-range ASHPs can maintain relatviely high efficiencies or coefficient of performance (the ratio between the power kW that is drawn out of the heat pump as cooling or heat, and the power kW that is supplied to the compressor). My particular model has a COP of 2.68 @-7C, 3.76 @2C and 4.65@7C which are temperature ranges well within the winter temps we experience in the UK.
What makes ASHP less viable in the UK is the cost of electricity and the state of insulation in many UK properties. If your home leaks heat like a sieve, then no matter what heating technology you put in, you're going to be consuming more energy to maintain the internal temperature. Invest in your home's insulation first Our energy consumption / bills would not be so low if we didn't have very good insulation throughout the house, that includes doors and windows. If you want the best ROI, it's in improving insulation first.
As for the high cost of electricity, rates in the UK are expensive and one of the highest in Europe so relying on electricity to heat your home will be more expensive per kWh compared to natural gas for the foreseeable future assuming no changes in the UK's energy policy. The great thing about electricity is that it can be generated by multiple energy sources which include renewables and can include your own solar PV array (more on that later). The optimist in me hopes that recent events encourages greater investment in renewable energies so our energy prices are less reliant on global commodity prices and hopefully help reduce domestive supply rates. In 2019, 40.7% of electricity generation in the UK was from gas.
If your goal is to reduce your household energy consumption then, ASHP is worth it IF you also implement the other necessary improvements to make it as cost effective as possible to run i.e. improved insulation, air tightness etc. At our current rate of consumption we would probably use between 8000-9000 kWh a year which is almost half what Ofgen suggests the average UK household uses in gas and electricty per year (12000 kWh gas + 2900 kWh electricity).
Do I need underfloor heating with an ASHP?
ASHP are designed to heat the water in a wet central heating system to lower temps as a means of improving efficiency / COP. Underfloor heating is the ideal solution for delivering this lower heated water around a home BUT that does not mean you can't have the ASHP deliver higher temp water to standard radiators. My particular model of ASHP runs most efficiently delivering 35C but can also be configured to deliver upto 45C to feed radiators with only a small reduction in COP. Gas boilers typically deliver 60-65C water so an ASHP will obviously take longer to achieve desired temperatures which is why it is so important to make sure you have excellent insulation in place first. Less heat loss means less time to reheat. You may benefit from larger radiators to deliver more BTUs so you can minimise conversion costs, but first make sure you have sufficient insulation.
Is Solar PV worth it?
On its own, I don't think so. I'm sure it made a difference in reducing our overall energy consumption, but we all know that sunny days in the UK are few and far between and more importantly much less frequent in the winter months when a household like mine uses significantly more electricity for space heating. My data table shows how much daily solar production can drop in these months and maybe produce just enough to cover 20% of the demand. The other problem with solar PV by itself is that you obviously only get energy production during daylight hours which again in the winter are significantly shorter. Most of my household's usage occurs in the early morning and early evening, so we don't get the benefit of solar power when demand is highest.
Is solar PV worth it with a battery? In my opinion, yes and in this case I can provide some numbers for ROI on a battery installation since we do not currently have a battery, but have one on order (8.2kWh from GivEnergy). The calculations are pretty simple:
I'm also betting on the fact that the electricity rates will continue to rise for some years so the savings will increase year on year
Summary
This took a while to type up and format correctly so I hope it was helpful to some people. Unfortunately there is no "magic-bullet" solution. Our old home was old, had poor insulation and would have cost 10's of thousands to get to a modestly energy efficient state. We sacrificed internal and external space when we sold it in 2019 and bought this new house because we were so worried about our energy bills which were already ridiculous at the time (£200 a month in the winter for gas and electricity). It made more sense to sell the house for a more efficient smaller house than it was to deal with cost and disruption to significantly modernise it. Whether ASHP / solar PV / battery makes sense for you depends on your property, your energy usage and ultimately what you can afford. If I had to give a summary it would be:
The recent energy crisis and conflict in Ukraine has a lot of us worried about living costs especially energy consumption at home, which is often one of the highest regular expenses for many. Rates are shooting up and in my opinion will never return to what they previously were unless there are some drastic changes in the UK government's energy policy.
There have been many questions on /r/ukpersonalfinance and other UK subreddits about whether it is worth getting an air source heat pump (ASHP) or solar PV as a means of reducing energy bills. We moved into our new home last summer which has both an ASHP and a solar PV array, so whilst I can't share costs for retrofitting onto an existing property and return-on-investment times, I can hopefully provide data on how these systems perform in a suitably insulated property. It's going to be a long post with lots of numbers, but I'll summarise as best as I can at the end.
Those that aren't familiar with ASHP should check out the Youtube channel Technology Connections. He did a number of detailed videos about ASHP within a US context but it is the same technology and applications in the UK.
Key facts about our home (most taken from the EPC):
- 4 bedroom detached with a basement - 176 sq metres
- Air source heat pump (ASHP) - NIBE F2040-8
- Underfloor heating (UFH) - Heatmiser central controller, room thermostats and manifold / valves. Rooms are invidually zoned so I can control heating in each room independently.
- Hot taps are fed by a large hot water cylinder heated by the ASHP system
- Solar PV 3.2kWh max - 10 x 320Wh panels on South facing roof in Derbyshire
- Mechanical Heat Recovery ventilation + ducting and vents to all rooms - Franksiche profi-air 250
- EPC A (92 score)
- Wall - Average thermal transmittance 0.17 W/m²K
- Roof - Average thermal transmittance 0.14 W/m²K
- Floor - Average thermal transmittance 0.21 W/m²K
- Air tightness - Air permeability 1.8 m³/h.m² (as tested)
- Triple glazing on all windows
I've unfortunately only got data for the last 6 or so months since that's when I got all the monitoring set up for the smart meter and the solar PV, but it covers the coldest months so is indicative of the max usage. This was our first winter in this house and I was still getting familiar with the optimal settings for the ASHP and heating schedules so we probably used more energy early on in the winter than we would do in the future. I have a Google Sheet set up to read from the Octopus API and my solar API which gives me some nice charts and summary metrics which helped me immensely in fine tuning our energy usage patterns to minimise cost. I'm still developing it and aim to publish a template and guide in the future. We do not have an EV so electricity consumption is primarily heating rooms, the water tank and cooking appliances like the induction hob.
Month
average daily temp
kWh consumed
total solar kWh
average daily consumed
average daily solar
Aug 2021
16.1 C
229 kWh
no data
7.2 kWh
no data
Sept 2021
15.9 C
278 kWh
283 kWh (from 5th Sept)
9.2 kWh
10.9 kWh
Oct 2021
12.1 C
386 kWh
203 kWh
12.5 kWh
6.6 kWh
Nov 2021
7.8 C
530 kWh
118 kWh
17.7 kWh
4 kWh
Dec 2021
6.4 C
702 kWh
50 kWh
22.6 kWh
1.6 kWh
Jan 2022
4.6 C
698 kWh
151 kWh
22.9 kWh
4.9 kWh
Feb 2022
5.6 C
472 kWh
169 kWh
16.9 kWh
6.1 kWh
Mar 2022 (to date)
summary not published yet
353 kWh
334 kWh
12.6 kWh
11.7 kWh
Couple of additional notes: we are on Octopus Go smart tariff which charges 5p per kWh between 00:30 and 04:30 and 15.33p per kWh at all other times (25p daily standing charge). It is an electricity only tariff and you need a smart meter set to report readings every 30 minutes. After months of tweaking the heating settings and schedules (to my wife's annoyance), we've settled on a schedule that heats up the downstair areas to 20C during the day and the upstairs areas in the early evening and early morning. The hot water cylinder heats up between 00:30-04:00 to make the most of the cheaper rate and 11:00-14:00 to make use of any output from my solar array. I don't regularly WFH, but the house is pretty much always occupied so we don't really turn off the heating unless we're all on holiday.
Our bills are generated on the 18th of every month. Our highest bill this winter was £100.84 for Dec to Jan, 2nd highest was Nov to Dec at £92.52. Jan to Feb was lower at £79.97 mostly because we were away on holiday for 5 days so everything was set to standby state, otherwise it woud probably have been roughly on par with the previous billing period.
Is ASHP worth it?
I'm going to give the cop-out answer and say it depends. ASHP as a technology is perfectly suited to our climate (not super cold winters) and even mid-range ASHPs can maintain relatviely high efficiencies or coefficient of performance (the ratio between the power kW that is drawn out of the heat pump as cooling or heat, and the power kW that is supplied to the compressor). My particular model has a COP of 2.68 @-7C, 3.76 @2C and 4.65@7C which are temperature ranges well within the winter temps we experience in the UK.
What makes ASHP less viable in the UK is the cost of electricity and the state of insulation in many UK properties. If your home leaks heat like a sieve, then no matter what heating technology you put in, you're going to be consuming more energy to maintain the internal temperature. Invest in your home's insulation first Our energy consumption / bills would not be so low if we didn't have very good insulation throughout the house, that includes doors and windows. If you want the best ROI, it's in improving insulation first.
As for the high cost of electricity, rates in the UK are expensive and one of the highest in Europe so relying on electricity to heat your home will be more expensive per kWh compared to natural gas for the foreseeable future assuming no changes in the UK's energy policy. The great thing about electricity is that it can be generated by multiple energy sources which include renewables and can include your own solar PV array (more on that later). The optimist in me hopes that recent events encourages greater investment in renewable energies so our energy prices are less reliant on global commodity prices and hopefully help reduce domestive supply rates. In 2019, 40.7% of electricity generation in the UK was from gas.
If your goal is to reduce your household energy consumption then, ASHP is worth it IF you also implement the other necessary improvements to make it as cost effective as possible to run i.e. improved insulation, air tightness etc. At our current rate of consumption we would probably use between 8000-9000 kWh a year which is almost half what Ofgen suggests the average UK household uses in gas and electricty per year (12000 kWh gas + 2900 kWh electricity).
Do I need underfloor heating with an ASHP?
ASHP are designed to heat the water in a wet central heating system to lower temps as a means of improving efficiency / COP. Underfloor heating is the ideal solution for delivering this lower heated water around a home BUT that does not mean you can't have the ASHP deliver higher temp water to standard radiators. My particular model of ASHP runs most efficiently delivering 35C but can also be configured to deliver upto 45C to feed radiators with only a small reduction in COP. Gas boilers typically deliver 60-65C water so an ASHP will obviously take longer to achieve desired temperatures which is why it is so important to make sure you have excellent insulation in place first. Less heat loss means less time to reheat. You may benefit from larger radiators to deliver more BTUs so you can minimise conversion costs, but first make sure you have sufficient insulation.
Is Solar PV worth it?
On its own, I don't think so. I'm sure it made a difference in reducing our overall energy consumption, but we all know that sunny days in the UK are few and far between and more importantly much less frequent in the winter months when a household like mine uses significantly more electricity for space heating. My data table shows how much daily solar production can drop in these months and maybe produce just enough to cover 20% of the demand. The other problem with solar PV by itself is that you obviously only get energy production during daylight hours which again in the winter are significantly shorter. Most of my household's usage occurs in the early morning and early evening, so we don't get the benefit of solar power when demand is highest.
Is solar PV worth it with a battery? In my opinion, yes and in this case I can provide some numbers for ROI on a battery installation since we do not currently have a battery, but have one on order (8.2kWh from GivEnergy). The calculations are pretty simple:
- The battery, inverter and installation cost £5000 and comes with a 10 year warranty.
- I'm going to ignore solar production for the purpose of this calculation to keep it simple.
- My current Octopus Go rate will expire in August 2022, so I've calculated return based on the current Go rate which is 7.5p off and 34.43p on (!!!)
- I would have the battery charge during the off period which would cost £0.61 for 8.2kWh.
- That 8.2kWh is now available to be used during the on-peak hours when the rate is 34.43p per kWh, which equates to 34.34p x 8.2kWh = £2.54
- The difference between the two prices £1.93 is how much I save per day if I use at least 8.2kWh during on-peak time, which we do on average from Sept to Mar (7 months).
- Approximate winter savings per year is 1.93 x 210 = £405 per year
- I do not have any summer data for our consumption so as a rough estimate I've assumed that we would normally use 4kWh per day on-peak = £1.24 which would cost £0.3 to charge off-peak.
- The summer savings are therefore the difference = £0.94 for Apr to Aug (5 months)
- Approximate summer savings per year is 0.94 x 155 = £145 per year
- Total annual savings = £550
- ROI on battery = £5000 / £550 = 9 years
I'm also betting on the fact that the electricity rates will continue to rise for some years so the savings will increase year on year
Summary
This took a while to type up and format correctly so I hope it was helpful to some people. Unfortunately there is no "magic-bullet" solution. Our old home was old, had poor insulation and would have cost 10's of thousands to get to a modestly energy efficient state. We sacrificed internal and external space when we sold it in 2019 and bought this new house because we were so worried about our energy bills which were already ridiculous at the time (£200 a month in the winter for gas and electricity). It made more sense to sell the house for a more efficient smaller house than it was to deal with cost and disruption to significantly modernise it. Whether ASHP / solar PV / battery makes sense for you depends on your property, your energy usage and ultimately what you can afford. If I had to give a summary it would be:
- Get a smart meter (SMET2) - this will give you access to smart tariffs that I predict will be the more cost effective option for many people. It has also been amazing to be able to see our energy usage in 30 minute increments which really helped me understand how and when we use energy. I would not have been able to optimise our usage (and be tweaking it further once we get the battery) if I didn't have that granularity of data.
- Review your energy usage regulary - are you consuming more than you would expect? Are there periods in the day when no-one is home and you're still consuming a significant amount of energy?
- Understand your home's heating systems - learn how to control them, set timers, put them into standby mode etc. Google the controller model and 90% of the time you'll find a digital copy of the manual. Read it. Consider smart heating controls if your current ones are too basic. Simply being able to have setpoint temps and schedules will help you reduce unnecessary space heating.
- Assess how good your insulation is (including doors and windows) and what options you have for improving it - the biggest ROI will be preventing heat from escaping your home.
- ASHP - great technology, perfect for the UK's climate. Should be mandatory for all new-builds (as well as very high spec insulation and MHRV). Can be retrofitted, but deal with the basics first i.e. insulation and ventilation.
- Solar PV - (my opinion) best paired with a battery for high electricity use households i.e. homes with electric heating or EV owners. Get the smart meter and analyse your electricity usages before investing.