Hi all,
About 18 months ago I posted a thread detailing my experience with Air Source Heat Pumps and Solar PV. It generated a lot of interest and good discussion and hopefully helped a few people with their considerations of either system.
At the end of that post I mentioned I had ordered a battery for my home with some simplistic ROI calculations to explain how I justified the investment. In summary:
INSTALLATION
In August 2022 we added a 8.2kWh battery to our system (GivEnergy) which is directly inline with the solar PV and the grid. It's all managed by the included inverter which controls where power is diverted based on demand. Both pieces of hardware are BIG. We fortunately have a plant room dedicated to housing the heating and solar power systems for the house, but even that wasn't big enough to squeeze the inverter and battery into the same room. The inverter is wall mounted and we managed to find a spot near the plant room door which leads into the front porch. The battery is a massive 103kg heavy (669H X 223D x 480W) so it had to sit on the floor in the porch and secured to the wall.
Both battery and inverter are IP65 rated so could be installed externally (I think a rain shield / roof would be recommended as an additional thing), but you'd need to consider location for security and routing the cables + possible additional installation costs.
As a side note, our electrician (chap called Ivan - https://www.idelectricalsolutions.co.uk/) did an excellent tidy job of it including trimming the skirting board to allow the battery to sit flush on the wall. If anyone needs an electrician in the Derby / Nottingham area, I would highly recommend him.
OPERATION
The inverter takes care of managing the power flow between the grid, solar PV, battery and house. The house demand is always met first. If there is solar energy available, it is used to meet the house demand. If that isn't enough, then if there is charge in the battery, it will fill the gap. If there's no charge in the battery or the demand is too high, then the grid fills that gap. If there is excess solar energy being produced, then the excess is first used to charge the battery and if fully charged, exported to the grid.
The inverter must be connected to the internet to be commissioned and my electrician probably thought it was a bit of a faff. It was a pain that we had to wait for over a month for the WiFi dongle, but fortunately the latest versions of the inverter do include built in WiFi now. GivEnergy has an online portal and mobile app to access the inverter and view data (sooooo much lovely data). The mobile app is quite handy and during the first few months, I couldn't help myself checking every hour or so how the energy is flowing between my house, the battery, the solar PV and the grid. There are a few good visualisations in the app and online portal, my favourite being the consumption bar charts which help visualise how much energy was consumed by your home every 30 minutes and what supplied the energy (grid, battery or solar). On a good day, very little if any is supplied by the grid and I get a warm fuzzy feeling inside.
There's been a few little blips with the firmware (nothing that stopped my battery from operating) over the last year but always resolved remotely within 24 hours. The online portal has a page showing known and reported issues as well as an Issues and Feedback submission form that seems to be picked up very quickly. My only real complaint so far is that they haven't released additional functionality to integrate solar forecasting to control and manage battery charging. Basically on days with lots of sun forecast, I want my battery to charge as little as possible or not at all at night and just use solar to charge during the day. At the moment if I remember, I manually change the charge settings the night before. Sometimes I forget to change it before a sunny day so I end up exporting a lot to grid (of which I don't get any pay back due to my tariff) and in some rare occassions I forget to change the charge settings back when the next day isn't so sunny, which is worse because the battery runs out during my expensive period. I know there are ways to do this through Home Assistant but it doesn't feel like an extremely difficult thing for GivEnergy to build into their firmware. All the necessary data is there and they even have a solar forecasting widget in the online portal.
Return on Investment
This is the bit I'm sure a lot of you are interested in. Just a reminder that my house came with solar PV already (3.2kWh peak) so my ROI is based on just my battery costs, separated out the calculations for solar to home savings and battery to home savings. Solar savings are calculated as the total kWh provided to home x 37.47p (my on peak rate). Battery savings are calculated as the total kWh to home x (37.47p - 7.14p) which is my on peak minus my off peak rate since that is when I charge the battery. I've included Solar To Battery as well and assumed a 7.14p saving per kWh. I was also part of the Octopus Saving Sessions in the winter which netted me about £35 in "points" and I haven't included that. Table below covers Aug 2022 to July 2023. kWh are rounded to 0dp
Month
Home Consumption
Solar to Home
Savings
Solar to Batt
Savings
Batt to Home
Savings
If I look at just the battery ROI, my initial £5000 investment will take little less than 7 years to break even if I continue to save about £750 a year thanks to the battery.
As a point of interest,the next table shows the % for each energy source to my home for each month (rounded to 0dp so it might not equal to 100 when summed)
Month
Solar%
Battery%
Grid%
It shows how the battery storage makes up close to half my home's consumption on average with the rest seesawing between solar and grid depending on the time of year.
I have given some serious thought to getting another battery. In the winter months, we average about 25kWh per day. Another 8.2kWh battery would definitely mean I'm running off battery during peak time for at least 9 months of the year and cover most of the day and evening during the coldest months. However, the difference between the off and on peak prices for my just renewed Octopus Go rates are less than previously, so the offset savings are less. Plus I was quite lucky with battery prices as they seem to have gone up by at least 50% since last year. My ideal solution would be to have an EV capable of supplying my home.
Hope that's been interesting and useful to a few of you.
Edit: to answer a couple questions popping up
About 18 months ago I posted a thread detailing my experience with Air Source Heat Pumps and Solar PV. It generated a lot of interest and good discussion and hopefully helped a few people with their considerations of either system.
At the end of that post I mentioned I had ordered a battery for my home with some simplistic ROI calculations to explain how I justified the investment. In summary:
- Cost = £5000 (incl installation)
- Estimated annual savings = £550 (ignored solar PV for simplicity)
- ROI = 9 years
INSTALLATION
In August 2022 we added a 8.2kWh battery to our system (GivEnergy) which is directly inline with the solar PV and the grid. It's all managed by the included inverter which controls where power is diverted based on demand. Both pieces of hardware are BIG. We fortunately have a plant room dedicated to housing the heating and solar power systems for the house, but even that wasn't big enough to squeeze the inverter and battery into the same room. The inverter is wall mounted and we managed to find a spot near the plant room door which leads into the front porch. The battery is a massive 103kg heavy (669H X 223D x 480W) so it had to sit on the floor in the porch and secured to the wall.
Both battery and inverter are IP65 rated so could be installed externally (I think a rain shield / roof would be recommended as an additional thing), but you'd need to consider location for security and routing the cables + possible additional installation costs.
As a side note, our electrician (chap called Ivan - https://www.idelectricalsolutions.co.uk/) did an excellent tidy job of it including trimming the skirting board to allow the battery to sit flush on the wall. If anyone needs an electrician in the Derby / Nottingham area, I would highly recommend him.
OPERATION
The inverter takes care of managing the power flow between the grid, solar PV, battery and house. The house demand is always met first. If there is solar energy available, it is used to meet the house demand. If that isn't enough, then if there is charge in the battery, it will fill the gap. If there's no charge in the battery or the demand is too high, then the grid fills that gap. If there is excess solar energy being produced, then the excess is first used to charge the battery and if fully charged, exported to the grid.
The inverter must be connected to the internet to be commissioned and my electrician probably thought it was a bit of a faff. It was a pain that we had to wait for over a month for the WiFi dongle, but fortunately the latest versions of the inverter do include built in WiFi now. GivEnergy has an online portal and mobile app to access the inverter and view data (sooooo much lovely data). The mobile app is quite handy and during the first few months, I couldn't help myself checking every hour or so how the energy is flowing between my house, the battery, the solar PV and the grid. There are a few good visualisations in the app and online portal, my favourite being the consumption bar charts which help visualise how much energy was consumed by your home every 30 minutes and what supplied the energy (grid, battery or solar). On a good day, very little if any is supplied by the grid and I get a warm fuzzy feeling inside.
There's been a few little blips with the firmware (nothing that stopped my battery from operating) over the last year but always resolved remotely within 24 hours. The online portal has a page showing known and reported issues as well as an Issues and Feedback submission form that seems to be picked up very quickly. My only real complaint so far is that they haven't released additional functionality to integrate solar forecasting to control and manage battery charging. Basically on days with lots of sun forecast, I want my battery to charge as little as possible or not at all at night and just use solar to charge during the day. At the moment if I remember, I manually change the charge settings the night before. Sometimes I forget to change it before a sunny day so I end up exporting a lot to grid (of which I don't get any pay back due to my tariff) and in some rare occassions I forget to change the charge settings back when the next day isn't so sunny, which is worse because the battery runs out during my expensive period. I know there are ways to do this through Home Assistant but it doesn't feel like an extremely difficult thing for GivEnergy to build into their firmware. All the necessary data is there and they even have a solar forecasting widget in the online portal.
Return on Investment
This is the bit I'm sure a lot of you are interested in. Just a reminder that my house came with solar PV already (3.2kWh peak) so my ROI is based on just my battery costs, separated out the calculations for solar to home savings and battery to home savings. Solar savings are calculated as the total kWh provided to home x 37.47p (my on peak rate). Battery savings are calculated as the total kWh to home x (37.47p - 7.14p) which is my on peak minus my off peak rate since that is when I charge the battery. I've included Solar To Battery as well and assumed a 7.14p saving per kWh. I was also part of the Octopus Saving Sessions in the winter which netted me about £35 in "points" and I haven't included that. Table below covers Aug 2022 to July 2023. kWh are rounded to 0dp
| Aug 2022 | 239 kWh | 107 kWh | £40.22 | 110kWh | £7.90 | 115 kWh | £35.04 |
| Sep 2022 | 279 kWh | 107 kWh | £40.20 | 107kWh | £7.63 | 154 kWh | £46.66 |
| Oct 2022 | 347 kWh | 99 kWh | £36.92 | 79kWh | £5.64 | 194 kWh | £58.75 |
| Nov 2022 | 468 kWh | 56 kWh | £20.86 | 27kWh | £1.92 | 251 kWh | £76.00 |
| Dec 2022 | 766 kWh | 62 kWh | £23.09 | 35kWh | £2.48 | 286 kWh | £86.89 |
| Jan 2023 | 676 kWh | 74 kWh | £27.86 | 43kWh | £3.09 | 289 kWh | £87.68 |
| Feb 2023 | 537 kWh | 95 kWh | £35.60 | 71kWh | £5.06 | 280 kWh | £84.94 |
| Mar 2023 | 587 kWh | 115 kWh | £43.17 | 67kWh | £4.81 | 270 kWh | £81.74 |
| Apr 2023 | 414 kWh | 145 kWh | £54.33 | 83kWh | £5.89 | 192 kWh | £58.36 |
| May 2023 | 334 kWh | 152 kWh | £57.13 | 138kWh | £9.88 | 144 kWh | £43.79 |
| Jun 2023 | 311 kWh | 155 kWh | £58.42 | 142kWh | £10.15 | 135 kWh | £41.04 |
| Jul 2023 | 366 kWh | 172 kWh | £64.39 | 50kWh | £3.59 | 155 kWh | £46.93 |
Month
Home Consumption
Solar to Home
Savings
Solar to Batt
Savings
Batt to Home
Savings
- Solar to Home = £502.18
- Solar to Batt = £68.06
- Batt to Home = £747.82
If I look at just the battery ROI, my initial £5000 investment will take little less than 7 years to break even if I continue to save about £750 a year thanks to the battery.
As a point of interest,the next table shows the % for each energy source to my home for each month (rounded to 0dp so it might not equal to 100 when summed)
| Aug 2022 | 45% | 48% | 7% |
| Sep 2022 | 36% | 55% | 6% |
| Oct 2022 | 28% | 56% | 16% |
| Nov 2022 | 12% | 54% | 36% |
| Dec 2022 | 8% | 37% | 56% |
| Jan 2023 | 11% | 43% | 46% |
| Feb 2023 | 18% | 52% | 30% |
| Mar 2023 | 20% | 46% | 35% |
| Apr 2023 | 35% | 46% | 19% |
| May 2023 | 46% | 43% | 11% |
| Jun 2023 | 50% | 43% | 6% |
| Jul 2023 | 47% | 42% | 11% |
Month
Solar%
Battery%
Grid%
It shows how the battery storage makes up close to half my home's consumption on average with the rest seesawing between solar and grid depending on the time of year.
I have given some serious thought to getting another battery. In the winter months, we average about 25kWh per day. Another 8.2kWh battery would definitely mean I'm running off battery during peak time for at least 9 months of the year and cover most of the day and evening during the coldest months. However, the difference between the off and on peak prices for my just renewed Octopus Go rates are less than previously, so the offset savings are less. Plus I was quite lucky with battery prices as they seem to have gone up by at least 50% since last year. My ideal solution would be to have an EV capable of supplying my home.
Hope that's been interesting and useful to a few of you.
Edit: to answer a couple questions popping up
- our home is in South Derbyshire.
- we do not have an export tariff. I mistakenly assumed it had to be combined with my import but I just learnt that is not the case and will be looking into it. I have data for the amount I currently exported and if I had set it up we would have earned around £130 (at a rate of 12p per kWh)
