Photovoltaic Systems

The history of PV's dates back to 1839. Solar Electric or Photovoltaic Systems convert some of the energy in sunlight directly into electricity. Photovoltaic (PV) cells are made primarily of silicon, the second most abundant element in the earth's crust, and the same semiconductor material used for computers. When the silicon is combined with one or more other materials, it exhibits unique electrical properties in the presence of sunlight. Electrons are excited by the light and move through the silicon. This is known as the photovoltaic effect and results in direct current (DC) electricity. PV modules have no moving parts, are virtually maintenance-free, and have a working life of 20 - 30 years.

There are three basic categories of photovoltaic systems with several types in each category.

• Crystalline Photovoltaic Materials flat plate collectors are the most developed and prevalent type in use today. These include single crystal silicon and polycrystalline silicon which is either grown or cast from molten silicon and later sliced into its cell size. They are then assembled onto a flat surface; no lenses are used.
• Thin Film systems are inherently cheaper to produce than crystalline silicon but are not as efficient. They are produced by depositing a thin layer of photovoltaic material to a substrate like glass or metal. This group includes amorphous silicon like the kind found in calculators and watches.
• Concentrators use much less of a specialized photovoltaic material and employ a lens or reflectors to concentrate sunlight on the photovoltaic cell and increase its output. They can be produced more cheaply than either of the other type due to the reduced amount of expensive PV material. But they can only use direct sun, so they must track the sun precisely and do not work when it is cloudy.