sonnendach.ch: the suitability of every roof surface
The Swiss Federal Office of Energy, together with swisstopo and MeteoSwiss, has calculated for every building in Switzerland how much sun falls on the individual roof surfaces. sonnendach.ch rates each surface by suitability, from low to excellent, and states the annual solar irradiation and the possible electricity yield. The basis is the pitch, orientation and size of the roof surface as well as the local climate.
What determines suitability
- Orientation: south yields the most; east and west each deliver around a fifth less, but in the morning and evening respectively. For self-consumption, an east-west layout often makes sense.
- Pitch: on the Swiss Plateau, the optimum is around 30 degrees. On flat roofs, the panels are mounted on raised frames.
- Surface: chimneys, roof windows and dormers reduce the usable area.
- Shading: the point that sonnendach.ch only roughly represents, and which is decisive in winter.
Shading: what the 3D model adds
SunPlot overlays sonnendach.ch on the 3D model of the address and, alongside it, calculates the cast shadows with the terrain, the mountains, the neighbouring houses and the trees every 10 minutes throughout the year. So you can see whether a roof with good suitability disappears behind the mountain in December, or whether a row of trees shades the southern half in the afternoon. The shadow-hours map shows it for every spot on the roof.
From potential to installation
sonnendach.ch and the shadow report are the preliminary check. Designing the installation, its economic viability with self-consumption and feed-in tariff, subsidies and the permit are matters for an installer or an energy advisory service. With the report, you go into that conversation with the right questions: which roof surface first? Is east-west worth it? What does the tree cost you in winter?
Short answers
How do I find out whether my roof is suitable for solar?
With sonnendach.ch from the Swiss Federal Office of Energy. It rates every roof surface in Switzerland by suitability and states the solar irradiation and possible yield. SunPlot shows it on the 3D model of the address and adds the shading from mountains, neighbouring houses and trees.
Does sonnendach.ch take the shadow of trees into account?
Only roughly. That is why SunPlot additionally calculates the cast shadows from the 3D model with the trees from the laser point cloud and the neighbouring buildings, every 10 minutes throughout the year. The shadow-hours map shows which parts of the roof are shaded in winter.
Is an east-west roof bad for solar?
No. East and west together deliver less peak output than south, but spread over the day, which often suits self-consumption better. sonnendach.ch lists both surfaces separately.