What could you actually save?

The calculator below gives a range, not a single number, on purpose. Solar economics depend on so many variables — weather, tariff, household behaviour, export rate — that any single-figure estimate is misleading. We err toward honesty even if it makes the answer less satisfying.

The three levers that determine your savings

Yieldis how much electricity your panels actually generate, measured in kilowatt-hours per kilowatt-peak (kWh/kWp) per year. In the UK, this depends heavily on where you are and how your roof is oriented. South-facing roofs in Cornwall might yield 1,050 kWh/kWp annually; north-facing roofs in Scotland might yield 650 kWh/kWp or less. The regional yield data in this calculator comes from PVGIS, the European Commission's photovoltaic tool.

Self-consumptionis the share of your generated electricity you actually use yourself, rather than exporting to the grid. This is the single biggest variable in determining whether solar is financially worthwhile. If you're home during the day, have high daytime loads (washing machine, dishwasher, heat pump), or have an EV you charge during the day, your self-consumption rate is high — and your savings are correspondingly larger. If you work away from home all day, you'll export most of your generation at the export rate (currently 4–15p/kWh depending on your supplier), rather than saving on import at 24–28p/kWh. The difference in outcome is significant.

Tariff is what you currently pay per unit. Savings calculations for solar are extremely sensitive to your import rate. Someone on a time-of-use tariff (like Octopus Agile) who can schedule loads to match solar generation will see different numbers from someone on a flat-rate tariff. The calculator handles both.

Before the numbers, here's the first big variable: where you live. UK yield varies by roughly 40% between the sunniest South West and the least-sunny far North of Scotland.