Methodology
How we measure roofs.
Every figure on Solarable comes from the same place: a measured read of the actual roof, or — where that's impossible — an estimate that says so. This page is the full method, for anyone who wants to check us.
The aerial read
Roof outlines, roof areas and the sun-intensity overlays are measured from aerial solar data (via the Google Solar API). For each building that means the roof's usable sections, their pitch and direction, and the sunlight landing on every square metre across a year. Each building page's imagery date is published in the downloadable datasets. Solar data includes data from Google.
What "capacity" means
Capacity assumes 400 W panels on every measurable roof section — a full-roof theoretical figure, before structure, loading, shading from plant, planning, or the lower output of poorer-facing sections. Some large roofs are membrane or retractable structures where standard racking wouldn't apply; read those as "if it were a solid deck". A real project starts with a commercial solar assessment — always.
Generation figures and ranges
Generation is the modelled range for that specific roof, scaled to full capacity; where a page shows a single figure it is the midpoint of that range, marked with ~. Yield (kWh per kW of panels a year) uses the same midpoint. Irradiance-based models slightly flatter hot climates — panels lose output as they heat — so sunny-country figures give a little of that sun back in practice.
Cross-checks
We test our numbers against independent models. NREL's PVWatts lands within 11% of our yield at 15 of the 16 World Cup host grounds (within 2% at four of them, our source reading slightly higher; Estadio BBVA wasn't part of that pass). At the 17 British grounds first measured, roof-specific yields sit 8–21% below PVGIS's optimal-tilt figure at every site — conservative in the right direction. Two independent models, and ours agrees with both everywhere we can check.
When we estimate instead
Where aerial solar data doesn't cover a building, we publish a deliberately wide estimate from the building's outline — roughly half a flat roof usable, about 0.13 kWp per usable square metre — and label it "estimated from outline". A handful of famous grounds get special handling: where the building database splits a stadium into separate stands we sum the stand readings and say so ("sum of the stands"), and where most of a roof is missing from the database entirely we hand-measure the stand area from the satellite and publish a wide band ("outline estimate").
What we refuse to publish
Buildings we can't measure honestly are left out rather than guessed. Every candidate runs through a quality gate that rejects mis-resolved buildings, partial reads of famous roofs, and capacity figures that don't match the building's extent. Where a building sits out — a stadium with pre-construction imagery, say — we name the gap instead of inventing a number. Seat counts and similar published facts are the only inputs we don't measure ourselves.
Homes-equivalent and CO₂
"Homes' worth of electricity" uses Ofgem's typical annual household consumption (2,700 kWh). CO₂ figures use the grid-offset factor supplied with the solar data. Both inherit the ranges above — treat them as scale, not accounting.
Seen enough method?
Check your own roof.
Enter your house number and postcode — we'll read your roof from above: direction, usable space and sunlight, with a Solarable Score. Free, about a minute, no account.