Annual generation
Request a site-specific estimate based on the proposed equipment, orientation and shading. Two roofs with the same panel capacity can produce different annual outputs. The calculator deliberately asks for generation rather than inventing it from the property location.
Use at home and export
Separate generated electricity used in the home from electricity exported. Value each share using the appropriate tariff and avoid counting the same units twice. A battery may change timing and losses, but this simple calculator does not simulate its operation.
Installation and ongoing costs
Include the agreed installation total and an annual running allowance. Ask about warranties and likely replacement components. A simple payback calculation cannot capture every future expenditure or the cost of financing the purchase.
Test a less favourable scenario
Reduce generation or self-use, change the tariffs and compare the result. The purpose is to see which assumption your outcome depends on most. A precise-looking number should never be taken as a guaranteed return. Use the Energy Saving Trust guidance alongside a written installer proposal.
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