Prototype of a thin film photovoltaic solar cell. This is made by applying thin coatings to a substrate of aluminium. The coatings are copper indium selenide and cadmium sulphide, each coat being about 5 microns thick. Thin film technology means that the cells are far easier to make than the silicon cells currently being used, and so have a considerable cost advantage. Cells of this type show an efficiency of around 10%, comparable to silicon wafer cells.