What a solar battery actually does
A solar battery stores surplus electricity generated by your panels during the day, making it available for use in the evening when generation has stopped. Without a battery, surplus generation is exported to the grid at SEG rates (typically 4–15p/kWh). With a battery, you consume that surplus yourself later in the day, displacing grid imports at 24–30p/kWh.
The financial benefit comes from the difference between the export rate you forego and the import rate you avoid. If your SEG rate is 12p/kWh and your import rate is 28p/kWh, storing and self-consuming one kWh is worth 16p more than exporting it.
Most domestic batteries also enable time-of-use tariff optimisation: charging from the grid at cheap overnight rates (5–10p/kWh on Octopus Go or similar) and discharging during expensive peak periods. This is separate from solar self-consumption and can add significantly to the financial case.
Common UK battery products and costs
The most widely installed home batteries in the UK are: GivEnergy (various sizes 2.6–13.5 kWh, strong app, competitive pricing), Tesla Powerwall 3 (13.5 kWh, integrated inverter, premium pricing), SolarEdge Energy Bank (paired with SolarEdge inverter), Enphase IQ Battery (modular, paired with Enphase microinverters), and Sonnen eco (German, premium build quality, high price).
Installed costs for a quality 5–10 kWh battery system including compatible hybrid inverter where needed range from £4,000 to £9,000. Battery-only retrofits to an existing solar installation (adding a battery to a system with a string inverter) add complexity and cost, as many string inverters are not battery-compatible without additional hardware.
New installations combining solar and battery from the outset are generally more cost-effective than retrofitting. If battery storage is a likely future addition, specify a hybrid inverter at installation even if you do not add a battery immediately.
Payback period — the honest numbers
A 10 kWh battery that self-consumes 2,500 kWh per year that would otherwise have been exported saves approximately 2,500 × 16p = £400/year in the solar self-consumption benefit alone. At £6,000 installed, payback on this basis is 15 years — which is close to the battery warranty period (most manufacturers offer 10–15 years or 4,000–6,000 cycles).
Add time-of-use arbitrage (charging from cheap overnight grid electricity), and the combined annual benefit may reach £600–£900 for a household on an appropriate tariff with an EV or high evening consumption. This reduces payback to 7–10 years, which is within the warranty period and makes the investment financially rational.
For households without EVs, without high evening consumption, and on a flat-rate tariff, the battery payback currently exceeds the warranty period. The financial case strengthens significantly if electricity prices rise or SEG rates fall (both of which reduce the cost of not having a battery).
When a battery is clearly worth it
An EV charging from overnight cheap-rate electricity substantially improves the battery economics. A heat pump that runs in the evening consuming stored solar also improves the case. High evening household consumption (large families, home offices, air conditioning) means more of the stored electricity is actually used rather than wasted at full battery.
Households planning to go fully electric — replacing gas boiler with heat pump, adding EV — are the strongest candidates for solar-plus-battery. In this scenario the battery is a central component of a complete household energy transition rather than a marginal financial optimisation.
For existing solar owners who feel they are "giving away too much to the grid", a battery diverter (immersion diverter) is a much cheaper first step at £200–£400 installed. If after deploying a diverter you still see significant export, a full battery becomes more justifiable.