Fixed, Capped and Variable Tariffs: Which Ones a Home Battery Can Use
- Ofgem's price cap covers standard variable tariffs, not fixed tariffs.
- A flat price per kWh gives a battery little to do unless you store your own solar.
- Time-of-use and dynamic tariffs create the price gap a battery needs.
- Smart tariffs need a smart meter.
- Check your tariff type before you size or buy a battery.
A home battery earns its keep from price differences. Some tariffs offer almost none, others offer a lot, so the tariff you are on matters as much as the battery you buy.
Three families of tariff
Most households are on one of three kinds of tariff. A fixed tariff holds the unit rate for a set period. A standard variable tariff follows the Ofgem price cap, which changes every three months. A time-varying tariff, such as a time-of-use or dynamic tariff, charges different prices at different times of day.
Ofgem says on its page about the energy price cap that the cap protects standard variable tariffs, not fixed tariffs, business contracts or heat networks. That tells you which tariffs the cap applies to, but not which suit a battery.
Flat tariffs: fixed and capped
On a fixed or capped tariff the price per kWh is the same at every hour of the day. A battery cannot buy cheap and use dear, because there is no cheap period. The remaining value comes from solar: storing the surplus you would otherwise export, and using it later instead of importing at the full rate.
If you have no solar and are on a flat tariff, a battery has very little to save. We cover that in home battery without solar panels.
Time-varying tariffs
Time-of-use and dynamic tariffs give a battery its price gap. As the Energy Saving Trust notes, these tariffs need a smart meter, and owners of home batteries can charge when electricity is cheap and use it later. Our smart meters and half-hourly settlement guide explains how half-hourly data is used.
The risk on the other side is price swings. A tariff that follows wholesale prices can be very cheap one hour and costly the next. If you cannot or do not want to manage that, automation inside the battery software helps, as described in AI smart charging explained.
Check the small print
Some time-varying tariffs are tied to a specific battery, charger or heat pump. Make sure you can still leave the tariff without losing a discount you were counting on.
How to match tariff and battery
Work through three questions before you buy:
Find your tariff type
Check whether you are on a fixed, standard variable or time-varying tariff, and the unit rate and standing charge.
Check what your meter allows
Smart tariffs need a smart meter. Ask your supplier what is available at your address.
Test the savings with your own numbers
Enter your rates and use into the home battery calculator, and compare a flat-rate case with a time-varying one.
Common questions
Does the price cap apply to fixed tariffs?
No. Ofgem says the cap covers standard variable tariffs, not fixed tariffs.
Can I use a battery on a fixed tariff?
Yes, but with a flat price the saving mainly comes from storing your own solar, not from buying cheap and using later.
Do I need a smart meter for a smart tariff?
Yes. The Energy Saving Trust says time-of-use tariffs need a smart meter.
Which tariff is best with a home battery?
It depends on your use, solar and appetite for price swings. A time-varying tariff gives a battery more to work with, but test it with your own figures first.
Related guides
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