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Broadstairs Solar BatteryBroadstairs, Thanet, Kent · CT10 07763 100477

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What size solar battery do I need?

Last reviewed 7 October 2026. Written for Broadstairs, Kent. Figures are estimates, not quotes.

Short answer. Most homes do well with 5 to 10 kWh. Choose the size from the power you use once the sun goes down, not from the size of your roof. A bigger battery costs more and often adds little extra saving.
White wall-mounted home battery beside a consumer unit with neat grey conduit on a brick garage wall
In this guide

What kWh means

A kWh is one unit of electricity, the unit on your bill. A 5 kWh battery holds 5 units. The Energy Saving Trust says a typical home battery is about 10 kWh.

A simple rule

Work out what you use between about 5pm and midnight. A home using 3,000 kWh a year uses about 8 kWh a day, and perhaps 4 to 5 kWh of that in the evening (our assumption). A 5 kWh battery covers that. A 10 kWh battery would often sit half empty.

The price gap is real. We estimate £2,750 to £4,750 for 5 kWh against £5,000 to £8,750 for 10 kWh, and our model adds only about £60 a year for the extra 5 kWh on a cheap overnight tariff.

When a bigger battery helps

  • An electric car or heat pump drives high evening use.
  • A large family, or someone working from home, uses a lot by day.
  • You want longer backup in a power cut.
  • You are on a time-of-use tariff and use a lot at peak times.

Match the solar to the battery

A small array with a big battery will rarely fill it, especially in winter. A sensible pairing is 4 to 4.5 kWp of panels with 5 to 10 kWh of battery. We size it from your bills.

Questions people ask

Is 5 kWh enough?

For many homes, yes. If your evening use is under 5 kWh, a bigger battery will not be used fully.

Can I add a second battery later?

Sometimes, if the model stacks. Ask before you buy. A later install will carry 5% VAT after 31 March 2027.

Does battery size change the VAT?

No. The 0% rate applies whatever the size, until 31 March 2027.

Want numbers for your own home? Try the estimator or ask for a free quote.

Sources

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