Battery storage for solar panels has moved from a niche addition to a mainstream consideration for UK domestic solar installations. The economics have shifted because the Smart Export Guarantee (SEG) rates paid for exported solar electricity are significantly lower than the retail price of grid electricity — meaning every unit of solar-generated electricity you consume yourself is worth more than every unit you export. A battery stores daytime generation for evening use, improving self-consumption and with it the financial return. Whether the battery's cost is justified depends on household consumption patterns, system size, and the battery's usable capacity.
What a Battery Does — and Does Not — Change
A solar battery does not increase the amount of electricity your panels generate. It changes when you consume it. Without a battery, generation that exceeds household demand at the time it is produced is exported to the grid. With a battery, that excess charges the battery and is consumed in the evening or overnight when the panels are not generating. The improvement in self-consumption depends on the household's consumption profile: a household that uses most of its electricity in the evening benefits most from battery storage; a household where someone is home during the day and runs appliances while the panels are generating benefits less, because much of the generation is already self-consumed.
"A well-sized battery on a 4kWp solar system can increase self-consumption from around 30–40% (without storage, for a typical working household) to 70–80%. At current electricity prices, this is the difference between saving around £400–500 per year and saving £700–900 per year, depending on consumption and tariff. The battery needs to last long enough for that additional saving to repay its cost — at current prices, a quality 10kWh battery system costs £3,000–£5,000 installed."— Energy Saving Trust — Solar Battery Storage Guide
Capacity — How Many kWh Do You Need?
A typical UK household consumes 8–12 kWh of electricity during the evening and overnight (5pm to 8am). A battery sized to cover this entirely would need 8–12 kWh of usable capacity. In practice, domestic batteries are sized 5–15 kWh: a 5kWh battery covers a partial overnight load; a 10kWh battery covers a full overnight load for most households. Larger batteries (15kWh+) are worth considering for households with an EV being home-charged or with above-average consumption. Usable capacity (the proportion of the nominal capacity that can actually be cycled) varies between battery chemistries — lithium iron phosphate (LFP) batteries typically have 90%+ usable capacity; older lithium cobalt or NMC chemistries may have lower usable proportions.
Leading Battery Systems and Warranties
The UK domestic battery market is led by a small number of established systems: GivEnergy, SolarEdge Energy Bank, Tesla Powerwall, Growatt, and Solis are the most commonly specified. All are compatible with the major solar inverter brands. Battery warranties are typically 10 years or a cycle count, with a guaranteed retained capacity at end of warranty (usually 70–80% of original capacity). The warranty term matters — a battery that degrades to 60% of original capacity in year 7 is delivering significantly less self-consumption than it was at installation, and its payback calculation needs to reflect this degradation curve.
"The battery warranty conversation is one installers should be having with every customer but often do not. A 10-year warranty with a 70% end-of-warranty capacity guarantee sounds reassuring, but it means the battery could be at 70% capacity at year 10 — and then what? Most LFP batteries are expected to last 15–20 years in a domestic cycling application, but the warranty period is shorter than the useful life. Asking the installer what the expected capacity is at year 15 — and whether there are any expansion options — is a reasonable question."— Which? — Solar Battery Storage Reviews
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