What would it actually save you, where you live?
Solar output is a fact about a location, not a marketing number. Give us a postcode and we geocode it, model a year of generation at that spot with PVGIS, cap it at the inverter’s AC rating, and value only the share you would use at home — then rank the kits on sale by how fast they pay back there.
What you will get
Your postcode is turned into coordinates, those coordinates are run through PVGIS — the European Commission’s solar yield model — and the resulting annual generation is valued at your own unit rate.
- Orientation and mounting angle are yours to set above, and they matter: a vertical north-facing balcony rail and a 35° south-facing garden frame are barely the same product. System losses 14% — the PVGIS default.
- Generation is capped at the inverter’s AC rating. Panels bigger than the inverter clip on bright days, and we deduct that — most plug-in kits are deliberately oversized, so it is not a rounding error.
- Only the electricity you use at the moment it is generated counts as a saving. Export is not valued.
- No inflation, no export payment, no panel degradation.
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Where the numbers come from. Coordinates from postcodes.io. Annual and monthly generation from PVGIS v5.2, the European Commission Joint Research Centre’s solar model, at 14% system losses — their own default. We call PVGIS server-side only, because PVGIS forbids browser access.
Why the figure is deliberately conservative. Only electricity you use at the moment it is generated counts. Export is worth nothing here. Generation is capped at the inverter, so an oversized array gets no credit for watts the inverter cannot pass. There is no inflation, no export tariff and no degradation in the model. If anything the real figure should beat this one — which is the right way round for a number somebody spends money on.
It is an estimate, not a quotation. Shading, orientation, tilt, weather and your own habits all move it, and none of them are visible from a postcode.