About Photovoltaics

About Photovoltaics | Solar Energy | Typical System | Energy Production

Anyone who has used a modern mathematical calculator can grasp the concept of photovoltaics (PV). It is simply the process of converting energy from the Sun into electricity that can power everything from household appliances and lights to commercial buildings and power plants.

In precisely the same way as the small solar cells on hand-held calculators eliminate the need for batteries, PV can provide the world with a clean, reliable source of electricity and reduce our reliance on ever-depleting fossil fuels.

The PV technology of the 21st century makes it possible. It employs layers of micro-fine crystalline silicon to convert ordinary sunlight into small electrical charges. This process is then multiplied thousands of times over to create, smaller than ever before, modules and systems that can generate enough electricity to power entire towns.

It's important to note that PV is different from the solar thermal energy used for heating or in hot water production. A single PV cell consists of two or more thin layers of semi-conducting material, most commonly crystalline silicon. When the silicon is exposed to light, small electrical charges are generated and conducted away by metal contacts as direct current (DC).

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In order to maximize energy collection and conversion, single cells are connected together and housed in a module. These modules are the building blocks of the PV systems and are, in turn, connected together to generate usable volumes of electricity. In some instances, an inverter is also used to convert low voltage DC into higher voltage AC power.

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 recrystallized 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-sensitized cells and organic solar cells are also possible.

Types of PV Systems

PV technology was first applied in space, by providing electricity to satellites. Today, PV systems can be used to power just about anything on Earth. PV systems operate in two basic forms.

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 the developing countries, where conventional electricity grids are unreliable or non-existent.