Battery Capacity (kWh) explained
Battery capacity is measured in kilowatt-hours (kWh) and represents the maximum amount of energy the battery can store when fully charged. It's the primary specification to look at when choosing a solar battery.
How to size your battery:
- The average UK home uses 8–12 kWh of electricity per day
- Most of this evening/night demand (4–8 kWh) is what you want the battery to cover after solar generation ends
- A 5 kWh battery provides moderate coverage; 10 kWh covers most evening demand for a typical home
Important: the usable capacity is less than the nominal capacity. A battery rated at 10 kWh might have a usable capacity of 9.0–9.5 kWh after accounting for its maximum depth of discharge.
Common residential battery capacities:
- 5–6 kWh: entry level, suits 1–2 person households or homes with high daytime self-consumption
- 9–10 kWh: the most common size, suits most 3–4 bedroom homes
- 13–15 kWh: large family homes, EV owners, or off-grid aspirations
Oversizing your battery is wasteful — a battery that's rarely fully discharged will have a very long payback period. Use your actual evening consumption data to size correctly.