Battery
How to size a home battery without overpaying for capacity you never use
Bigger is not better. A practical method for matching storage capacity to your actual overnight load, tariff and solar array.
Joe WhitfieldFounder & Lead Engineer 6 min read
Battery capacity is the easiest thing to oversell and the hardest for a homeowner to verify. The right size is the one that cycles fully most days of the year — no more.
Start with your overnight load, not your annual usage
Take your annual consumption, divide by 365, then estimate the share used between sunset and sunrise. For most UK households that is 40–55% of the daily total.
Where a bigger battery does pay
- Time-of-use tariffs with a cheap overnight window you can arbitrage.
- Households with an EV, heat pump or electric hot water.
- Properties with poor grid reliability that want genuine backup capability.
An unused kilowatt-hour earns nothing. Cycles, not capacity, create the return.
We model a year of half-hourly data before recommending a size, which is why our proposals sometimes suggest less storage than the enquiry asked for.
