Photovoltaic (solar electric) modules are clean, safe and efficient devices that have long been considered a logical material for use in buildings. Recent technological advances have made PVs suitable for direct integration into building construction. PV module size, cost, appearance and reliability have advanced to the point where they can function within the architectural parameters of conventional building materials. A building essentially provides free land and structural support for a PV module, and the module in turn displaces standard building components. These systems should be the first markets for BIPV products in the commercial buildings, and should remain an important high-end market for the foreseeable future. PV can be integrated into the sides of buildings, replacing traditional glass windows with semi-transparent thin-film or crystalline solar panels. These surfaces have less access to direct sunlight than rooftop systems, but typically offer a larger available area. In retrofit applications, PV panels can also be used to camouflage unattractive or degraded building exteriors.