The information about solar energy potential on our website should be used as a rough guide. The solar radiation analysis is an automatic calculation and is no substitute for expert advice. It is an estimate of the output when the entire roof area is used. The effective output may deviate from the values calculated automatically.

The amount of electricity generated from a photovoltaic system depends on the surface area available, solar radiation, and the efficiency of the solar panels used. The roofs used in our calculation come from swisstopo’s buildings dataset, which shows how much sunlight a roof receives both during the course of the day and over the entire year. This takes into account shade cast by terrain, buildings and vegetation You can find further information in the final report on the solar energy potential analysis (available in German only).

Sonnendach.ch is based on buildings data that is regularly collected and updated by swisstopo. This data is derived from aerial photographs and updated on average every six years. It may therefore take some time before new buildings or converted buildings are visible on our website.

Data on solar energy potential is updated once a year for all buildings available. It is not updated for new buildings or converted buildings not yet included in swisstopo’s buildings dataset. The current status of the data can be seen in the metadata.

Yes, sonnendach.ch takes into account how terrain, buildings and vegetation cast shadows on roof surfaces by calculating a far horizon, a mid-distance horizon and a near horizon for each roof surface. Shade cast by distant mountains as well as by nearby objects such as trees or houses is also taken into account. Terrain and surface models with a spatial resolution of 50cm are used for the calculation.

Sonnendach.ch calculates solar potential per roof. The solar potential of several roofs can be added together. A specialist should be consulted for more complex analyses.

Sonnendach.ch is based on buildings data regularly collected and updated by swisstopo. Building geometries are recorded per building; plot boundaries are not taken into account.

Swisstopo records building geometries at a level of detail that does not take into account roof details such as chimneys or small roof dormers. For this reason, smaller roof elements are usually missing from sonnendach.ch, which is why a reduction factor is applied for chimneys and roof dormers when calculating solar energy potential.

The data is available as open government data at opendata.swiss.