Solar PV & Battery Calculator
Size a PV array and battery from how much electricity you use, or switch to backup mode to see how long a battery will run a load in a power cut.
Last reviewed
Sizing from usage
The array size follows from how much of your yearly consumption you want to cover and how much a kilowatt-peak generates on your roof:
UK specific yield is roughly 900 to 1000 kWh per kWp each year for a good south-facing roof, less for east/west or shaded aspects. The suggested battery stores the slice of daily use that falls in the evening and overnight, when the panels are not generating.
Backup runtime
In backup mode the runtime is simply the usable energy in the battery divided by the load it has to carry:
The load also has to sit within the inverter's continuous output, and the system has to be wired to provide a backup supply in the first place, which not all installations are.
Reference
For a fuller commercial treatment, including tariffs and payback, see dedicated tools such as LoadSense's solar & battery feature. The figures here are a quick first pass, not a financial or MCS design.