We replaced our estimates with real data — and the numbers went down

Until now the per-municipality yields in our calculator were static regional estimates, typed in by hand and deliberately set on the low side. We replaced them with data from the European Commission's PVGIS database — one query per municipality, at the town's coordinates.

The result was not what we expected. Not one municipality had been too low. Sarajevo fell from 1,200 to 1,154 kWh/kWp, Mostar from 1,380 to 1,350, Banja Luka from 1,170 to 1,140. Srebrenica fell from 1,195 to 1,064 — 131 kWh, over ten per cent.

Along with the annual yield we got a monthly distribution for each location. Before, the whole country shared one curve. Now Trebinje produces 5.2% of its annual output in December and Srebrenica 4.1% — a difference anyone budgeting for a winter bill will feel.

The data is generated by a script and committed to the repository, so nothing calls PVGIS at runtime: the estimate has to work when the JRC is down, and a climate normal does not change between two deploys anyway.