Solar panel savings calculator

Annual generation is estimated as your system size (kWp) multiplied by a location-specific "kWh per kWp per year" figure sourced from PVGIS, the European Commission Joint Research Centre's solar resource database, then adjusted for roof orientation if you've refined the estimate. A well-positioned system in southern England typically generates around 850–1,050 kWh per kilowatt-peak installed; sunnier locations generate more.

Self-consumption — the share of generated electricity you use directly rather than exporting to the grid — is assumed at 30% without a battery and 65% with one, based on typical UK domestic usage patterns. These are fixed assumptions, not calculated from your own usage, since actual self-consumption depends heavily on when you're home and what you run during daylight hours. Adding a battery lets you use more of what you generate rather than exporting it at a lower rate, which is why it increases the assumed self-consumption share.

Payback period is only shown once you enter an installation cost — it's simply that cost divided by the estimated annual saving. It's a simple estimate: it doesn't account for electricity price inflation, panel degradation over time, or maintenance costs, all of which would shift the real-world figure.

Shading from trees, chimneys, or neighbouring buildings can significantly reduce output and isn't modelled here — if shading is a factor, treat the result as an upper estimate. Electricity rates shown are regional averages; your actual saving will depend on your supplier's import and export tariff. This tool gives a planning estimate, not a substitute for a site survey and quote from an installer.