Last updated: September 2026
UK Solar Battery Guide
In Britain, a battery changes what rooftop solar can do: it turns midday surplus into evening power, lets you buy cheap overnight electricity on time-of-use tariffs, and keeps the lights on in a power cut. But batteries are the most expensive part of a home solar setup, and UK winters are unforgiving. This guide covers sizing, tariffs, export payments and the winter reality check.
What a battery actually does for you
A home battery earns its keep three ways:
- Raising self-consumption. Without a battery, a UK home self-consumes ~30–40% of its solar. A well-sized battery lifts that to 60–80%, and each extra self-consumed kWh is worth the ~25–30p you would have paid to import it.
- Time-of-use arbitrage. Charge the battery overnight at ~7p/kWh (Octopus Intelligent Go / Economy 7 style tariffs) and discharge it during the ~30p/kWh evening peak — even with no solar at all. This works all winter, when solar contributes little.
- Backup power. With EPS (emergency power supply) wiring, a battery keeps essentials running in an outage — valuable in rural areas, though it adds cost.
Sizing: the golden rule
Size the battery to your evening and overnight consumption, not to your solar array:
- Check your smart meter or bill: a typical UK home uses 8–12 kWh/day total, with ~40–60% falling in the evening/overnight window.
- 5 kWh suits low users or flats; 10 kWh is the sweet spot for a typical 3-bed home; 13–15 kWh for high users, heat pumps or EVs.
- Oversizing wastes money: a battery that rarely fills or empties fully earns nothing on its idle capacity. One full cycle per day is the economic ideal.
- Check the usable capacity (not nominal) and the continuous power rating — a 10 kWh battery limited to 3 kW output cannot run a 7 kW shower and the oven together.
Time-of-use tariffs: the battery's best friend
2026's standout tariffs for battery owners:
- Overnight EV tariffs (~7p/kWh, 00:30–05:30): charge the battery (and the car) dirt-cheap, then coast through the morning on stored energy.
- Agile-style dynamic tariffs: half-hourly prices that sometimes go very low — or even negative — when wind is strong. Automation (via the battery's app or a platform) captures this without you watching prices.
- Peak rates (~30–35p/kWh, 16:00–19:00): this is the spread your battery arbitrages. A 10 kWh daily cycle on a 23p spread saves ~£2.30/day or £840/year before efficiency losses (~10%).
Crucially, arbitrage works in winter too — December's short days barely dent a strategy built on cheap overnight charging.
Export: the Smart Export Guarantee
Under the Smart Export Guarantee (SEG), retailers must pay you for exported electricity. Standard SEG rates are modest (~3–5p/kWh), but:
- Octopus Flux and similar smart tariffs pay ~15p/kWh or more for exports — worth switching to if you regularly export.
- With a battery, you can choose: export at peak for maximum SEG income, or self-consume to avoid 30p imports. Self-consumption usually wins unless your export rate is exceptional.
The winter reality check
A 4 kWp south-facing UK system produces roughly 3,400–3,800 kWh/year, but the distribution is brutal:
- June: ~400 kWh — the battery cycles fully, exports flow.
- December: ~100 kWh — barely 3 kWh/day. The battery will sit mostly empty of solar.
Winter is when time-of-use arbitrage carries the economics: the battery earns its keep by shifting cheap overnight grid electricity into the expensive evening peak. Size and model your battery for year-round value, not summer abundance — and do not expect meaningful solar self-sufficiency from November to February.
Costs and payback
- Battery prices 2026: roughly £500–800/kWh installed for AC-coupled units — a 10 kWh system typically £5,000–8,000 installed.
- VAT: 0% VAT applies to batteries installed alongside solar (and in most cases standalone domestic battery installs too, since the 2024 extension).
- Payback: 8–12 years for a well-used battery on a good time-of-use tariff — longer if it only stores solar and sits idle in winter. The solar panels themselves typically pay back in 6–9 years; evaluate the battery separately.
- Warranty: look for 10-year / 6,000-cycle warranties with ≥70–80% capacity retention.
Frequently asked questions
What size battery do I need for a UK home?
10 kWh suits a typical 3-bed home; 5 kWh for low users, 13–15 kWh for heat pumps or EVs. Size to your evening/overnight consumption so the battery cycles fully once a day.
Is a battery worth it without solar panels?
It can be: on a time-of-use tariff, overnight charging at ~7p and evening discharge avoiding ~30p gives a 10 kWh battery roughly £800/year of value. Solar on top improves the case further.
How much does a home battery cost in the UK in 2026?
Roughly £500–800 per kWh installed — so £5,000–8,000 for a typical 10 kWh system, with 0% VAT on domestic installs.
What happens to my solar battery in winter?
Solar input collapses (a 4 kWp system makes ~100 kWh in December vs ~400 in June). Winter value comes from time-of-use arbitrage: charging cheap overnight and avoiding peak imports.
What is the Smart Export Guarantee?
The UK scheme requiring electricity retailers to pay small generators for exported power. Standard rates are ~3–5p/kWh, but smart tariffs like Octopus Flux pay ~15p/kWh.
Size your system with our UK solar battery sizing calculator — consumption, tariffs and winter production built in.
This guide is for information only and is not professional financial advice.