Solar energy converters can be loosely grouped into 3 categories:
Photovoltaics is a field of semiconductor technology involving the direct conversion of solar radiation into electricity.
A photovoltaic cell is made of two thin slices of semiconductor (generally silicon) sandwiched together and attached to metal wires.
The top layer contains n-type doped silicon (n-is for negative) that acts as an electron donor and provides an excess of free electrons.
The bottom layer is p-type doped silicon (p-is for positve) with few free electrons and an excess of 'holes' (atoms that have lost an electron) that make it a good acceptor of electrons.
Placing these layers together produces an electric field which prevents electrons travelling from the top layer to the bottom layer. When exposed to sunlight, photons of light knock electrons from the bottom p-layer into the top n-layer. The n-layer with its excess of electrons produces an electric force, pushing the additional electrons away along the metal wire back into the p-layer. This flow of electrical current along the wires is the generated electricity.
Concentrated photovoltaics (CPV)
Concentrating photovoltaics (CPV) is a term used when sunlight is concentrated onto photovoltaic cells (described above) to directly generate electricity.
Many different solar concentrators may be used, often mounted on a solar tracker in order to keep the focal point upon the cell as the sun moves across the sky.
Concentrated Solar Thermal (CST)
Concentrated Solar Thermal systems use lenses or mirrors and tracking systems to focus a large area of sunlight onto a heat transfer system, to heat fluids which drive turbines or heat engines.