Technology of solar photovoltaic cells. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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Solar photovoltaic systems are easy to handle and do not have moving mechanisms, but the photovoltaic cells themselves contain complex semiconductor devices similar to those used for the production of integrated circuits. The basis of the operation of photocells is the physical principle in which an electric current arises under the influence of light between two semiconductors with different electrical properties that are in contact with each other. The combination of such elements forms a photovoltaic panel or module.

Photovoltaic modules, due to their electrical properties, generate direct rather than alternating current. It is used in many simple battery powered devices. Alternating current, on the other hand, changes its direction at regular intervals. It is this type of electricity supplied by energy producers, it is used for most modern appliances and electronic devices. In the simplest systems, direct current from photovoltaic modules is used directly. In the same place where AC is needed, an inverter must be added to the system, which converts DC to AC.

The modern production of solar cells is almost entirely based on silicon. About 80% of all modules are made using poly- or single-crystal silicon, while the remaining 20% ​​use amorphous silicon. Crystalline photovoltaic cells are the most common and usually have a blue tint with a sheen. Amorphous, or non-crystalline - smooth in appearance and change color depending on the angle of view. Monocrystalline silicon has the best efficiency (about 14%), but it is more expensive than polycrystalline silicon, which averages 11% efficiency. Amorphous silicon is widely used in small devices such as watches and calculators, but its efficiency and long-term stability are much lower, so it is rarely used in power applications.

The photocell is a "sandwich" of silicon - the second most common substance on Earth. Ninety-nine percent of modern solar cells are made from silicon (Si), and the rest are built on the same principle as silicon solar cells. A certain substance is applied to one layer of silicon, due to which an excess of electrons is formed. This results in a negatively charged ("N") layer. On the other layer, a lack of electrons is created, it becomes positively charged ("P"). Assembled together with conductors, these two surfaces form a photosensitive electron-hole junction. It is called a semiconductor because, unlike an electric wire, it conducts current in only one direction - from negative to positive. When exposed to the sun or other intense light source, a direct current of approximately 0,5 volts is generated. The current strength (amps) is proportional to the light energy (number of photons). In any photovoltaic system, the voltage is almost constant, and the current is proportional to the size of the photovoltaic cells and the intensity of the light.

Photovoltaic cells are made from ultra-pure silicon, mixed in precise proportions with some other substances. The ultra-pure silicon substrate from which solar cells are made is very expensive. The amount of ultra-pure silicon needed to make one 50 W photovoltaic module would be enough for the integrated circuits of about two thousand computers. In addition, aluminum, glass and plastic are present in solar cells - inexpensive and reusable materials.

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