Three things set the size, and the smallest one wins: your consumption, your roof area, and your connection capacity. Most households hit consumption first — because, as the net-metering guide explains, producing much more than you use is not rewarded.
How much roof you need
Budget about 5 m² per installed kilowatt, gaps included. Of a pitched roof roughly 75% is usable, of a flat roof about 55% — because on a flat roof the rows must be spaced so they don't shade each other.
What one kilowatt produces
This is not one number across the country. The spread between the sunniest and least sunny municipality in our data is over 300 kWh per kilowatt per year — nearly a third. The figures come from the European Commission's PVGIS database, for a 35° south-facing plane.
| Municipality | kWh/kWp | Elevation |
|---|---|---|
| Trebinje | 1,373 | 282 m |
| Čapljina | 1,365 | 148 m |
| Ljubuški | 1,360 | 97 m |
| Neum | 1,358 | 68 m |
| Čitluk | 1,357 | 228 m |
| Stolac | 1,354 | 60 m |
| Mostar | 1,350 | 67 m |
| Tomislavgrad | 1,322 | 906 m |
| Posušje | 1,319 | 648 m |
| Široki Brijeg | 1,316 | 265 m |
These figures assume a south-facing roof at 35°. East or west costs about 13%, north far more, and permanent shade from a chimney or tree can cost more than orientation does. The calculator accounts for all three.