Two different sources of value
Electricity used at home avoids buying units at the import tariff. Electricity exported earns the export tariff. Count each generated unit only once: the self-use and export shares together must equal total generation.
Use a site-specific generation estimate
Roof orientation, shading and the system specification affect output. Replace the example with a competent installer’s written estimate. This tool does not infer production from your postcode or assess whether the roof is suitable.
Simple payback has limits
The installation cost divided by net annual benefit gives simple payback. It does not account for finance, panel degradation, inverter or battery replacements, tariff changes or the time value of money. A result is a scenario, not a promise.
Common questions
Is a battery included?
Only through the installed cost, running allowance and self-use share you enter. This is not a battery dispatch model.
Sources & methodology
- Energy Saving Trust: solar panels
Solar savings depend on generation, use at home and export tariffs. No national savings figure is imported.
Checked 8 Oct 2026