Solar battery cost per kWh (UK, 2026)

Use usable capacity, not the headline capacity

Battery descriptions can show more than one capacity figure. Total capacity is the energy stored across the full battery, while usable capacity is the amount made available in normal operation. The system may keep a reserve rather than regularly emptying every cell completely.

Use the usable kWh figure when comparing prices. If one quote uses total capacity and another uses usable capacity, the resulting price-per-kWh figures are not like for like. Ask the installer to identify the usable capacity explicitly and point to it on the product datasheet.

Capacity is only one part of a quote. Check whether the total includes installation, the battery inverter or hybrid inverter, electrical protection, monitoring, commissioning and warranty cover. A low equipment-only price should not be compared directly with a complete installed quotation.

How to calculate battery cost per usable kWh

Take the total installed battery price and divide it by the usable capacity. For example, a quotation for a battery with 5kWh usable capacity is divided by 5. A quotation for 10kWh usable capacity is divided by 10. The answer is the installed price per usable kWh.

Compare that result with the shared bands: under £300 is unusually low; £300 to £700 is in line with published cost benchmarks; £700 to £900 is above published benchmarks; and more than £900 is high.

Treat the band as a prompt for checking the quote. It does not tell you whether the chosen battery capacity suits your electricity use, solar generation or tariff, and it does not value a particular installation.

Worked example: a 5kWh battery

For 5kWh of usable capacity, the shared bands translate to: under £1,500 unusually low; £1,500 to £3,500 in line with published cost benchmarks; £3,500 to £4,500 above published benchmarks; and over £4,500 high.

To check a real quotation, divide its installed price by 5. Then check whether the result includes every part of the installation. Ask whether the inverter is included, whether any existing solar inverter must be changed and which battery capacity figure the installer used.

A smaller battery is not automatically better value because the final design must fit the household. Equally, a larger battery is not automatically better simply because its price per kWh is lower. The quotation should explain why the proposed usable capacity is suitable.

Worked example: a 10kWh battery

For 10kWh of usable capacity, the equivalent bands are: under £3,000 unusually low; £3,000 to £7,000 in line with published cost benchmarks; £7,000 to £9,000 above published benchmarks; and over £9,000 high.

Divide the quoted installed price by 10 to find the price per usable kWh. If the system is modular, ask whether the total includes every module, the control equipment and commissioning. Also check whether all modules carry the same warranty and whether the warranty describes capacity retention or another measurable condition.

For a solar-and-battery quote with one combined total, the split is less certain. PowerGuardian's checker deducts its configured typical battery allowance before assessing the remaining solar price, and labels the answer clearly as an estimate because the installer has not supplied separate prices.

Questions before you sign

Qualifying residential solar batteries are covered by the zero rate of VAT until 31 March 2027. Get at least three itemised quotes where possible, compare usable capacity and included work, and check each quote before signing.

• What is the usable capacity, and where is it shown on the datasheet?
• Does the price include the inverter, electrical work, monitoring and commissioning?
• What battery and workmanship warranties apply, and who honours them?
• Why is this capacity appropriate for my usage, solar system and tariff?
• Is the installer MCS-certified and a member of RECC or HIES?
• If the deposit exceeds 25%, why is it that high and how is it protected?