How Much Battery Storage Do I Need?

Updated June 2026

The goal isn’t to store all your electricity — it’s to store enough to avoid buying at peak prices. Here’s how to land on a sensible number.

Step 1: Know your daily usage

Check a recent bill or smart meter for your average daily kWh. UK homes typically use 8–15kWh/day, more with an EV or electric heating.

Step 2: Estimate your peak-hour share

How much of that do you use during expensive peak hours (roughly late afternoon to evening)? For many homes it’s 50–70%. That peak-hour energy is what a battery lets you buy cheaply overnight instead.

Step 3: Size to the shiftable load

Add ~20% headroom to your peak-hour usage. For example, a home using 10kWh/day with 60% in peak hours wants to shift ~6kWh, so an ~7kWh usable battery is a good fit. Try the battery sizing calculator for your numbers.

With solar vs without

• With solar: also size for storing daytime surplus to use in the evening — you may want a little more capacity.
• Without solar: size purely for off-peak arbitrage — there’s no point storing more than you can charge in the cheap overnight window. A 3.6kW battery fills ~11kWh in a 6-hour window.

Don’t forget power (kW)

Capacity (kWh) sets how long it runs; power (kW) sets how much it can deliver at once. For whole-home backup you want higher power — see our all-in-one batteries, where models like the Powerwall 3 lead on output.