Tools
Calculators and tools
Free tools that run in your browser and show their working. Change any input and see what moves, then read the formula underneath.
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Plug-in solarSavings calculator See what a plug-in kit could take off your bill, and how fast it pays for itself. Open the tool
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Plug-in solarState rules map Check the plug-in solar rules for your US state or the UK. Open the tool
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Backup powerBattery size calculator Tick what you need in a power cut and see how big a battery it takes. Open the tool
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Backup powerPower station finder Find out how long a power station runs your fridge, router or CPAP. Open the tool
How our tools work
Nothing you enter leaves your device: the maths runs in your browser and isn't stored. Each tool lists its assumptions, such as the 85% efficiency we allow for inverter losses, so you can judge the result yourself. Rules and product specs behind the tools are checked against their original sources, and the date of the last check is on each page.
How we research