Structural solar panels. This building has panels of photovoltaic cells (solar panels, banded) built into its south-facing outside wall. The panels form an integral part of the building's structure; this was the first such building in Europe. The rest of the wall is occupied by tinted windows. More solar panels are incorporated into the roof. Solar panels convert the rays of the sun into electricity that helps power the building. This is the Solarzentrum (Solar Centre), Freiburg, Germany. It was completed in 1993 and is used as offices.