Solar battery payback calculator
How to calculate whether a UK solar battery improves payback, using extra self-consumption, export income lost and battery cost.
Key takeaways
- Run the solar-only case first, then add the battery as a separate extra.
- The battery earns value by shifting exported solar into later self-use, but it may reduce export income.
- A battery can still be worthwhile for resilience or tariff flexibility, even when pure payback is long.
Use the extra-benefit method
A solar battery payback calculator should answer one question: how much extra annual benefit does the battery create compared with no battery?
The clean formula is battery payback = battery cost divided by extra annual benefit. Extra annual benefit means the additional bill saving after allowing for any export income you no longer receive.
Why blended payback can mislead
If you combine solar and battery into one total cost, the solar panels can make the whole package look healthier than the battery itself. That doesn't mean the battery is bad. It means you need to judge the extra decision separately.
For example, a solar-only system might pay back in a reasonable time. Add a battery, and annual benefit may rise only modestly while the upfront cost rises by several thousand pounds.
What changes the battery result
The battery looks better when evening electricity use is high, import rates are much higher than export rates, and the battery is used regularly. It looks worse when the household already uses plenty of electricity during the day or has a strong export tariff.
Time-of-use tariffs can improve the case, but they add rules. Some households charge the battery from cheap overnight electricity and use it later. Some tariffs have export conditions. Read the terms before assuming the battery can arbitrage every price gap.
What to enter in the calculator
Start with no battery. Enter the solar cost, annual generation, import rate, export rate and realistic self-consumption. Then switch the battery on, add the installed battery cost and choose a cautious uplift.
Try a 10 to 15 percentage-point uplift first. Try 20 to 30 points only if your household use, battery size and tariff make that believable.
- Battery cost: use the installed quote, not a hardware-only price.
- Battery uplift: use percentage points added to self-consumption.
- Export rate: keep it realistic because export income may fall.
- Warranty: check usable capacity, cycle life and backup limits.
Sources checked
- Energy Saving Trust battery storage guideConsumer guidance on home battery costs, storage limits and tariff use.
- Ofgem SEG supplier listCurrent SEG licensee list and annual supplier status.
- Ofgem energy price cap unit ratesCurrent unit-rate context for electricity tariffs.