How the calculation works
The savings come from tariff arbitrage: charging your battery when electricity is cheap (overnight) and using that stored energy when rates are high (daytime).
For example, with Octopus Go you pay 7p/kWh overnight and 29p/kWh during the day. Every kWh you shift saves you 22p. A 10kWh battery cycled daily saves around £800 per year.
The calculator assumes 90% round-trip efficiency (typical for modern lithium batteries) and daily cycling. Your actual savings depend on your usage patterns.
UK tariffs that work with batteries
| Tariff | Off-peak | Peak | Savings/kWh |
|---|---|---|---|
| Octopus Go | 8p | ~28p | 20p |
| Intelligent Octopus Go | 7p | ~29p | 22p |
| Economy 7 | ~10p | ~28p | 18p |
| Octopus Flux | ~17p | ~34p | 17p |
Rates vary by region and change over time. Check your latest bill for your exact rates, or log into your energy account.
What size battery do I need?
5kWh is good for flats, smaller homes, or if you're out during the day. Covers 3-4 hours of typical evening usage.
10kWh is the sweet spot for most 3-4 bedroom homes. Covers most daytime and evening usage without running out.
There's no point going bigger than your daily usage—you won't be able to cycle the full capacity, which reduces your return on investment.
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Pre-configured batteries for UK tariffs. No solar required.