Store the right amount

Battery storage savings calculator

Explore the value of moving energy from a cheaper charging period to a more expensive one. This model includes charging losses and limits savings to the energy you use.

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Make it your scenario

The starting values are examples. Replace them with your bills or installation proposal.

Usable battery capacity · kWh

Use usable capacity, not the nominal label.

Energy you could shift each day · kWh

Demand that would otherwise use higher-rate grid electricity.

Capacity reserved for backup · %

Reserved energy is unavailable for normal daily savings. Backup also needs suitable hardware.

Round-trip efficiency · %

Allows for electricity lost while charging and discharging.

Available charging power · kW

Input power available to the battery, after other loads. Use the lower of the charger and supply limits.

Charging window · hours per day

Hours at this power and charging price. For solar, use equivalent hours of available surplus, not daylight hours.

Charging energy cost · p/kWh

For solar charging, use the export payment you give up. For grid charging, use the off-peak import rate.

Import rate avoided · p/kWh

The rate you would otherwise pay when using the stored energy.

Equivalent full-use days per year

Allow for seasonal solar output, holidays and days with less available energy.

Full installed battery cost · £

Include the inverter, gateway and installation work relevant to your quote.

Put the result in context

Compare complete battery proposals

Read the guide ↗

The working, made visible

How this tool works

Daily delivery is the smallest of shiftable demand, capacity after reserve, and charging power × hours × round-trip efficiency. Charging energy = delivery ÷ efficiency. Annual benefit = full-use days × (avoided import cost − charging energy cost). The capacity figure is treated as deliverable usable energy before your chosen reserve.

What to allow for

One daily cycle at constant available charging power is modelled. The result excludes degradation, standby consumption, finance, servicing and tariff changes. Instantaneous discharge power, variable solar surplus and shared EV charging can further restrict use. This does not specify a battery or guarantee backup.

Energy Saving Trust: battery storage ↗