- Joined
- 27 Jan 2008
- Messages
- 27,400
- Reaction score
- 3,307
- Location
- Llanfair Caereinion, Nr Welshpool
- Country
I have 6 kW solar, 5 kW inverter, and 6.4 kWh battery, and I use around 12 kWh per day. I have an Octopus EV supply tariff, 8.5p/kWh 00:30 to 05:30 rest of time 30.51p/kWh and had the solar just over 2 years, since moving to Octopus get paid 15p/kWh for export and standing charge 68.34p per day.
So summer I was exporting loads, up to 900 kWh per month, but now into winter, and the solar is down, last year December was the lowest at 97 kWh, this month 173 kWh but the question is what size battery?
I can fit 1 to 4 batteries, at 3.2 kWh each, at the moment have 2 so 6.4 kWh, but 10% reserved for UPS, so 5.76 kWh useable. To last the day in winter I would need to double battery size, I have 14 solar panels, there is room for 18, but the cost of scaffold etc, means really stuck with 14 panels, and the batteries have a limited life, so don't want to go too big. The inverter covers all, but when having a shower, and for such a short time, not worth an upgrade, so only the batteries are really in question.
End of April, I will have a whole year with export, although the panels were fitted early September 2023, British Gas never paid me for export, so not got a full year of data yet. So far this year, we are about net-zero, which includes the standing charge, so we have produced more than we have used, but winter means yesterday ran out of battery 11:30 pm, day before 6:15 pm, Wednesday 7 pm Tuesday 10 pm, so back to Sunday when the battery lasted the whole day.
But summer, we are still gaining, charging a battery at 8.5p and getting 15p but with some losses 6 p per kWh is not really going to pay for another battery. So it does not seem a financially viable idea to get an extra battery. Over £1000 so not cheap, and looking at around 12 years life.
But maths was never my good point, maybe I have got it wrong, however the other question is how long will they pay 15p per kWh for?
So is it worth getting a third battery? Or should I go for four? I see you-tube videos of people with massive batteries, have I got it wrong? At what point is the battery size right?
I see problems with oversize solar arrays, there is a limit on how much the grid and take, but a battery is not generation, is there a limit?
So summer I was exporting loads, up to 900 kWh per month, but now into winter, and the solar is down, last year December was the lowest at 97 kWh, this month 173 kWh but the question is what size battery?
I can fit 1 to 4 batteries, at 3.2 kWh each, at the moment have 2 so 6.4 kWh, but 10% reserved for UPS, so 5.76 kWh useable. To last the day in winter I would need to double battery size, I have 14 solar panels, there is room for 18, but the cost of scaffold etc, means really stuck with 14 panels, and the batteries have a limited life, so don't want to go too big. The inverter covers all, but when having a shower, and for such a short time, not worth an upgrade, so only the batteries are really in question.
End of April, I will have a whole year with export, although the panels were fitted early September 2023, British Gas never paid me for export, so not got a full year of data yet. So far this year, we are about net-zero, which includes the standing charge, so we have produced more than we have used, but winter means yesterday ran out of battery 11:30 pm, day before 6:15 pm, Wednesday 7 pm Tuesday 10 pm, so back to Sunday when the battery lasted the whole day.
But summer, we are still gaining, charging a battery at 8.5p and getting 15p but with some losses 6 p per kWh is not really going to pay for another battery. So it does not seem a financially viable idea to get an extra battery. Over £1000 so not cheap, and looking at around 12 years life.
But maths was never my good point, maybe I have got it wrong, however the other question is how long will they pay 15p per kWh for?
So is it worth getting a third battery? Or should I go for four? I see you-tube videos of people with massive batteries, have I got it wrong? At what point is the battery size right?
I see problems with oversize solar arrays, there is a limit on how much the grid and take, but a battery is not generation, is there a limit?
