Methodology & data sources

Last updated: November 2026

Every figure on this site comes from a public, openly licensed source. We don't invent numbers, and each local page links to the data behind it.

Sources

• Area boundaries and names: Office for National Statistics, Open Geography Portal (Open Government Licence).
• Solar generation estimates: PVGIS, the European Commission Joint Research Centre's photovoltaic geographical information system. We model 1 kW of panels at the centre of each local authority, south facing, 35° tilt, 14% system losses.
• Installation numbers: MCS Data Dashboard, published by the Microgeneration Certification Scheme.
• Heat pump grants: Boiler Upgrade Scheme statistics, Department for Energy Security and Net Zero, published on GOV.UK (Open Government Licence).
• Housing energy efficiency: Energy Performance Certificate open data, aggregated to area level only. We never publish individual addresses.

Limitations

Our figures are area averages. Your own roof direction, shading, energy use and tariff will change the result, sometimes a lot. Treat our numbers as a starting point for a conversation with a certified installer, not a quote.

Corrections

If you think a figure is wrong, email hello@whatswattworth.com and we'll check it against the source.