What size solar battery do I need for a typical UK home?

For a typical UK home using 8-10 kWh per day with a 4 kWp solar panel system, a 5-10 kWh battery is usually ideal. If you're out at work all day (low daytime usage), a larger battery captures more surplus solar for evening use. If you work from home and use most solar directly, a smaller battery may suffice. The key is matching the battery to your surplus solar — there's no point buying a 13.5 kWh battery if you only generate 4 kWh of surplus per day.

What are common solar battery sizes available in the UK?

Popular UK home battery options include the GivEnergy 2.6 kWh and 5.2 kWh (stackable), GivEnergy All-in-One 13.5 kWh, Tesla Powerwall 2 at 13.5 kWh, SolaX Triple Power at 5.8-11.6 kWh, and Fox ESS HV systems from 2.56-10.4 kWh. Most can be stacked or combined to increase capacity. GivEnergy and Tesla are the most popular brands installed by UK solar companies.

How much does a solar battery cost in the UK?

Solar battery costs in 2025-2026 are approximately £400-600 per kWh of capacity, fully installed. A 5.2 kWh GivEnergy system costs around £2,500-3,000 installed. A 13.5 kWh Tesla Powerwall 2 costs approximately £6,000-8,000 installed. Prices are falling as the market matures. VAT on solar batteries is 0% when installed alongside solar panels.

What is self-consumption and why does it matter?

Self-consumption is the percentage of your solar generation that you use yourself, rather than exporting to the grid. Without a battery, typical self-consumption is 30-50% — the rest is exported for just 4-15p/kWh via the Smart Export Guarantee. With a battery, self-consumption rises to 70-90%, meaning you use your free solar energy instead of buying electricity at 24-30p/kWh. The bigger the gap between your import and export rates, the more a battery saves.

Can I charge my solar battery from the grid at off-peak rates?

Yes, if you have a time-of-use tariff like Octopus Agile, Octopus Go, or Intelligent Octopus. These tariffs offer cheap overnight electricity (often 7-10p/kWh) which you can use to charge your battery, then discharge during peak hours when the rate is 24-35p/kWh. This 'tariff arbitrage' can save an additional £200-400 per year on top of your solar savings. Your battery inverter needs to support scheduled charging.

How long does a solar battery last?

Most home solar batteries have a warranty of 10-12 years or a specified number of charge cycles (typically 6,000-10,000 cycles). At one cycle per day, that's 16-27 years of use. In practice, lithium-ion batteries degrade to about 70-80% of their original capacity after 10 years. Tesla Powerwall 2 is warranted for 10 years at 70% capacity. GivEnergy offers a 12-year warranty.

Solar Battery Storage Calculator

Size a home battery for your solar panel system based on daily electricity usage, daytime consumption patterns and tariff rates.

Solar Panel System Size

Total kWp of your solar array

Daily Electricity Usage

Check your smart meter or bill (UK avg ~8-10 kWh)

Daytime Usage (while sun shines)

How much electricity you use during daylight hours

Electricity Import Rate

Your current electricity unit rate

Smart Export Guarantee (SEG) tariff

Receive payment for exported solar electricity

Export Rate

SEG export rate (typical 4-15p/kWh)

Time-of-use tariff (e.g. Octopus Go)

Cheap overnight rate for grid charging

How We Calculate This

This calculator estimates the optimal battery size for your solar panel system based on your electricity consumption patterns, system size and tariff rates.

How battery sizing works

The recommended battery size is based on the rule of thumb:

Battery size ≈ Daily usage × (1 - Daytime usage fraction) × 0.8

This sizes the battery to cover approximately 80% of your evening and overnight electricity needs using stored solar energy. The calculation is also capped by your actual daily solar surplus — there's no point having a battery larger than what your panels can fill.

Solar generation

UK solar panels generate an average of ~2.5 kWh per kWp per day across the year (more in summer, less in winter). A 4 kWp system generates approximately 10 kWh per day on average.

Self-consumption

Without battery: Typically 30-50% of generation is self-consumed
With battery: Typically 70-90% of generation is self-consumed

Savings calculation

Daily saving = Stored energy × (Import rate - Export rate). Each kWh stored saves you the difference between what you would have paid to import it and what you would have received for exporting it. With time-of-use tariffs, additional savings come from charging at off-peak rates and discharging at peak rates.

Important notes

This calculator provides estimates based on annual averages. Actual performance varies significantly by season, weather and individual usage patterns. Battery savings are highest in summer when solar generation peaks and lowest in winter.

Frequently Asked Questions

Related Calculators

U-Value Calculator

Calculate the U-value of wall, floor and roof constructions.

Insulation Thickness Calculator

Determine the insulation thickness needed to meet UK Building Regulations.

Heat Loss Calculator

Calculate room-by-room heat loss for heating system sizing.

Cavity Wall Insulation Calculator

Estimate cavity wall insulation quantities and potential savings.

Loft Insulation Calculator

Calculate loft insulation rolls needed for your loft area.

Last updated: February 2026

All calculations are estimates. Verify with your supplier.