Time-of-use tariffs price electricity differently across the day. A heat battery can move some demand into a cheaper period, but the complete tariff and control behaviour decide the result.
The short answer
Match the cheap window to the energy the store needs and its maximum charge power. Then test the expensive rate, standing charge and the rest of the home's consumption. A headline low rate is not an annual bill.
Fixed windows
A repeating cheap period is easier to schedule. Confirm exact times for the meter and account, including clock changes. Seven cheap hours do not help if the store charges slowly and other large loads share the supply.
Dynamic tariffs
Prices can vary daily or half-hourly. Automated controls need a price feed, a demand forecast and an offline fallback. Manual scheduling may be too demanding for everyday use.
Model the whole household
Move only the demand the heat battery can genuinely shift. Refrigeration, cooking and daytime appliances remain in their normal periods. EV and home-battery charging may compete for cheap hours or supply capacity.
Export and solar
If solar charges the heat store, compare the heat value with export income forgone. Tariff interactions can be more important than the store's nominal capacity.
Review after switching
Compare actual half-hourly imports with the design. Look for peak-time boosts and missed cheap windows before assuming the tariff itself is wrong.
Your next step
Export one month of winter half-hourly data. Mark energy the store would move, then price the same profile on the current and proposed tariff.
Sources
Primary and independent references checked by our editorial team.
- Get help with your smart meter — Ofgem Checked 10 Nov 2026
- Economy 7 tariff guidance — Ofgem Checked 10 Nov 2026
- Energy price cap unit rates and standing charges — Ofgem Checked 10 Nov 2026