In Switzerland the available/adequate surface for solar panels deployment is estimated to be 140 km² for roofs and 55 km² for frontages ^[1]. Assuming that 40% of this surface is used for the installation of PV panels with a 25% electric efficiency, then the photovoltaic potential is 25 TWh.

[1] http://www.iea-pvps.org/index.php?id=9&eID=dam_frontend_push&docID=394