UK Home Battery Storage
Battery Sizing
Calculator
Not just "what size?" — but "what will it actually do for me?" Choose your goal, enter your details, and get a clear recommendation with trade-off analysis.
What do you want your battery to do?
Minimise Bills
Charge cheap overnight, discharge during expensive peak hours to cut your electricity bills.
Cover Peak Usage
Size a battery to cover your evening peak demand — cooking, TV, EV charging, avoiding peak rates.
Maximise Solar
Store excess solar generation and use it after dark instead of exporting to the grid.
Emergency Backup
Keep essential loads running during a power cut for a set number of hours.
Your Energy Usage
Annual consumption and usage pattern — used to estimate daily demand.
Annual electricity usage
?
Check your energy bills or smart meter. UK average: ~3,500 kWh/yr
kWh
Daytime electricity usage
?
Share of usage during daylight hours (roughly 8am–6pm)
Minimise Bills — Details
Your tariff determines how much you can save by charging off-peak.
Electricity tariff
?
Peak-period energy usage
?
Electricity used during your peak period (e.g. 4pm–11pm). Tip: ~40–60% of your daily usage. Daily usage = annual ÷ 365.
kWh
Desired battery coverage
?
How much of your peak demand should the battery cover?
Solar system size
?
Your solar system size (kWp). Check your MCS certificate or inverter label.
kWp
Backup duration required
?
How long should your battery cover a power cut at average household load?
Your Results
Best-value size
—
nearest standard size
Usable energy
—
at 90% depth of discharge
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Estimated daily energy flow
Assumptions DoD: 90% Round-trip efficiency: 90% Optimised for: bill savings
Recommendations are rounded to standard battery product sizes (5, 10, 13.5, 20 kWh) and assume 90% depth of discharge and 90% round-trip efficiency. Annual saving estimates use illustrative UK tariff rates (28p/kWh peak, 7.5p/kWh off-peak) and are indicative only. Actual performance varies by product, usage pattern, and temperature. Consult a qualified MCS-accredited installer for a site-specific assessment.