Types of PV technologies
There are essentially two types of PV technology, crystalline and thin-film. Crystalline can again be broken down into two types:
Monocrystalline cells - These are made using cells cut from a single cylindrical crystal of silicon. While monocrystalline cells offer the highest efficiency (approximately 18% conversion of incident sunlight), their complex manufacturing process makes them slightly more expensive.
Polycrystalline cells - These are made by cutting micro-fine wafers from ingots of molten and recrystallised silicon. Polycrystalline cells are cheaper to produce, but there is a slight compromise on efficiency (approximately 14% conversion of incident sunlight).
Thin film PV is made by depositing an ultra thin layer of photovoltaic material onto a substrate. The most common type of thin-film PV is made from the material a-Si (amorphous silicon), but numerous other materials such as CIGS (copper indium/gallium diselenide) CIS (copper indium selenide), CdTe (Cadmium Teluride), dye-sensitised cells and organic solar cells are also possible.
Types of PV systems
Grid connected PV systems
These systems are connected to a broader electricity network. During the day, the solar electricity generated by the system is either used immediately or sold off to electricity supply companies. In the evening, when the system is unable to supply immediate power, electricity can be bought back from the network.
Off grid PV systems
These systems are used in isolation of electricity grids, and may be used to power radio repeater stations, telephone booths and street lighting. There is also a growing market for mobile PV in the boat and caravan leisure market. Off Grid (also known as Stand-Alone) PV systems also provide invaluable and affordable electricity in developing countries, where conventional electricity grids are unreliable or non-existent.