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How Photovoltaics Work
From Light to Electricity

As solar power becomes increasingly popular, more and more solar panels can be seen on the roofs of homes and businesses alike. These solar panels employ one of the most environmentally friendly methods for producing electricity: “photovoltaic”. The term photovoltaic, or PV, is used to describe something that creates electricity when exposed to sunlight. Solar panels, or PV modules, are made up of several solar cells. Each cell is comprised of materials which have photovoltaic properties.

Functional principle of photovoltaics Source: Solarpraxis AG

Photovoltaic technology is actually quite simple:

Electricity can be produced by solar cells whose principal component consists of a semiconductor that is typically made of silicon. A semiconductor consists of a material that cannot be classified as an isolator or a conductor and whose electrical properties can be influenced by adding foreign substances (doping). The solar cells comprise two adjoining semiconductor layers that are equipped with separate metal contacts and have each been doped, thus creating an “n” layer (n = negative) with a surplus of electrons and below that, a “p” layer (p = positive) with an electron deficiency. Due to the difference in concentration, the electrons flow from n into the p area, thus creating an electrical field, or “space charge zone”, inside the semiconductor structure.

The Photovoltaic Effect

The upper “n” layer in a solar cell is so thin that the photons from sunlight can penetrate it and can only discharge their energy to an electron once they are in the space charge zone. The electron that is activated in this manner follows the internal electrical field and thus travels outside of the space charge zone and reaches the metal contacts of the “p” layer. When an electrical load is connected, the power circuit is closed: the electrons flow across the electrical load to the solar cell’s rear contact and then back to the space charge zone. This effect is called the “photovoltaic effect” (derived from ‘‘Phos’’, the Greek word for light and the name of the physicist Alessandro Volta). An inverter, the “heart” of the system, converts the direct current (DC) produced by the solar cells into alternating current (AC).

From the Cells to the Module

The sun radiates approximately 1000W per square meter, so a 10 x 10 cm solar cell is exposed to nearly 10 watts of radiated power. Depending on the quality of the cell, it can produce an electrical output of 1 - 1.5 watts. To increase the output, several cells are combined and connected to a PV module. The connection of several PV modules is also referred to as a PV array. You can learn more about photovoltaics using the menu bar on the upper right-hand side.

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