The direct conversion of solar radiation into electricity by the interaction of light with the electrons in a semiconductor device or cell. Solar PV cells are constructed from semiconducting materials that use sunlight to separate electrons from atoms to create an electric current. Modules are formed by interconnecting individual cells. Monocrystalline modules typically are slightly more efficient but relatively more expensive than multi-crystalline silicon modules, although these differences have narrowed with advances in manufacturing and technology. Thin film solar PV materials can be applied as flexible films laid over existing surfaces or integrated with building components such as roof tiles. Building-integrated PV (BIPV) generates electricity and replaces conventional materials in parts of a building envelope, such as the roof or facade. Solar photovoltaic-thermal (PV-T) is a hybrid system which includes solar thermal collectors mounted beneath PV modules to convert solar radiation into electrical and thermal energy. The solar thermal collector removes waste heat from the PV module, enabling it to operate more efficiently.