Do solar batteries work in winter?
They work, but in December there is little spare sun to put in them. We followed 20 homes with solar panels and a 9.5 kWh battery through a whole year, month by month. Left to itself, the battery saved the average home £3.75 in December. Planned every half hour, £29.42. Here is why, and what it means for your own battery this winter.
In winter the panels make a third of what the house uses.
A battery left to itself only stores sun the house doesn’t need at that moment. In December that came to about 2.2 kWh a day, less than a quarter of what a 9.5 kWh battery holds. Most of the battery sat empty.
4 kWp of panels, the average home
- December: 147 kWh made, 572 kWh usedAbout 4.7 kWh of sun a day, and about half of it went straight into the house.
- July: 712 kWh made, 373 kWh usedNearly five times December’s sun, and 522 kWh of it spare for the battery or for export.
- November to February: 703 kWh made, 2,181 kWh usedMay to August: 2,557 kWh made, 1,471 kWh used.
Left to itself, the battery all but stops in winter. Planned, it keeps saving.
What the battery saved each month against the same home with no battery, on Agile with Outgoing Octopus’s fixed export rate, the cheapest tariff for these homes without a battery.
| Month | Sun made | House used | Saved, left to itself | Saved, planned by Orza |
|---|---|---|---|---|
| October 2025 | 272 kWh | 470 kWh | £6.13 | £57.27 |
| November | 190 kWh | 494 kWh | £7.43 | £33.10 |
| December | 147 kWh | 572 kWh | £3.75 | £29.42 |
| January 2026 | 181 kWh | 589 kWh | £8.91 | £29.54 |
| February | 185 kWh | 526 kWh | £4.95 | £20.36 |
| March | 414 kWh | 562 kWh | £22.24 | £45.76 |
| April | 572 kWh | 421 kWh | £10.67 | £45.59 |
| May | 603 kWh | 385 kWh | £15.78 | £16.26 |
| June | 599 kWh | 349 kWh | £14.61 | £30.26 |
| July | 712 kWh | 373 kWh | £15.60 | £29.21 |
| August | 643 kWh | 364 kWh | £25.50 | £29.80 |
| September | 436 kWh | 380 kWh | £35.42 | £64.76 |
The average of 20 homes with a 9.5 kWh battery and 4 kWp of panels facing south, 1 October 2025 to 30 September 2026. Saved is against the same home, panels and tariff with no battery. Standing charges are left out, and no limit was put on export.
- November to February, left to itself: £25.04Four months of winter, between them less than September alone. With little spare sun, a battery that only stores sun sits nearly empty.
- November to February, planned: £112.42More than the four summer months planned, £105.53. With little sun to store, the planned battery fills from the grid in the cheapest hours instead, and uses that charge when it is worth more.
- The best months were spring and autumnEnough sun to store, and prices that still move a lot through the day.
On a tariff with a cheap night, winter is when a battery earns most.
The same homes and battery, November to February against May to August. On Octopus Go a night rate a fraction of the day rate makes every winter night worth filling for.
Saved over four months, average home
- Go, nothing paid for export: £224.22 in winter, £159.04 in summerLeft to itself: £89.43 and £151.28.
- Flux: £160.67 in winter, £179.35 in summerBetween £36.95 and £47.20 every month of the year. Left to itself: £64.46 and £76.01.
- Agile with Outgoing Octopus: £112.42 in winter, £105.53 in summerLeft to itself: £25.04 and £71.49.
Before the clocks go back.
What battery owners ask as the days get shorter, answered from the same year where it can be.
All our guidesShould I charge my battery from the grid in winter?
If your tariff has cheaper hours, yes. That is where most of the planned battery’s winter saving came from. On a single rate tariff that is the same price all day, filling from the grid saves nothing, and a battery has little to do until spring.
Does my battery still charge from solar in winter?
A little. In December these panels made about 4.7 kWh a day. The house used about half as it was made, which left about 2.2 kWh a day to store, on a bright day more and on a dull one next to nothing.
Does the cold hurt a battery?
Batteries charge more slowly when they are very cold, which is why makers give a range of temperatures to keep them in. A battery indoors or in a garage usually stays within it. We didn’t model temperature here.
Are these real homes?
Their electricity use is: real households’ smart meter readings, from Low Carbon London (UK Power Networks, CC BY 4.0), moved to 2025 to 2026 a whole number of weeks so a Thursday stays a Thursday. The panels and battery are modelled, on a south facing roof in London, with the weather that came. The prices are the ones Octopus published for North West England.
Is a battery worth it if it does so little in winter left alone?
Over a whole year, planned, the same battery saved the average home £435 against having none. What that means over a battery’s life.
What does Orza cost?
Nothing during the beta, and no card is needed to join.
Keep your battery working through the winter.
Free during the beta. Connect in a few minutes, and start in Monitor only.