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The structure and operation of the solar cell
How do solar cells
In solar cells and panels (batteries) solar cells to produce an electrical current is used the energy of the sun - solar radiation power per square meter is about 1350 Watts.
The principle of operation of the solar cell
The structure of a simple solar cell and the basic principle of his actions following. Take an ordinary semiconductor - two plates attached to each other. They are made of silicon with the addition of each of these specific impurities derived elements through which the desired properties: the first plate has an excess of the valence electrons for the second, on the contrary, they are not sufficient. As a result, in the semiconductor layer has a layer of negatively charged and positively charged, ie layers «n» and «p».
On the border of contact of these plates is the barrier layer area. This layer prevents the transfer of excess electrons from the layer of «n» in a layer of «p», where the electron lacking (missing electrons space called holes). If you connect to a similar semiconductor external power supply ("+" to "p" and "-" to the «n»), the external electric field will cause electrons to overcome the closing zone and through the conductor current flows.
Something similar happens when solar radiation on the solar cell. When a photon of light enters the layers of «n» and «p», it transfers its energy to release electrons (located on the outer shell of the atoms), and in their place there is a hole. Electrons with energies received freely overcome the barrier layer and the semiconductor layer is transferred from «p» layer in «n», and the holes, by contrast, move from layer «n» in a layer of «p».
This transition of electrons, their area «p» to «n» and holes of «n» field to «p» also contribute to electric fields of positive charges, located in the zone of «n» conductor and negative - a «p» zone that if draws in, one - electrons, the other - the hole. As a result, a layer of «n» acquire an additional negative charge and «p» - positive. The result of this phenomenon is the appearance of a semiconductor potential difference (voltage) between the two plates close to 0.5 V.
The strength of the electric current, which can generate a solar cell varies in proportion to the number of photons captured by the surface of the photocell. This rate, in turn, also depends on many other factors, the light emission intensity, the photocell area, time of operation, efficiency of the device. It also depends on the temperature (at its increase, the conductivity of the photocell drops significantly).
That's why you need to remember the following: solar cells (photovoltaic cells, batteries) are not able to be very powerful, they can not operate in a continuous mode (through a natural day and night), in order to stabilize the main parameters - current and voltage - there is a need to use additional devices (stabilizers, batteries, etc.).
But as an extra source of power they can be used perfectly in those places where only small capacity and there is no possibility to connect urban elektromagistrali. When combining the work of the solar cell and the electric battery get fully autonomous power supply system. This system can be used in areas with good solar illumination and demand for small electric capacity.
The structure of the solar cell
In the image shown above, it is seen that the top layer of p-n junction, which has an excess of electrons, connected with the metal plates. These plates serve as the positive electrode, and light passing adding additional rigidity to the element. The lower layer in the solar cell structure has a deficiency of electrons, it is adhered to a solid metal plate performs the function of the negative electrode.
It is believed that ideally, the solar battery is close to 20% efficiency. However, in practice, according to experts www.sun-battery.biz site it is approximately equal to only 10%. Efficiency solar cells for some more some less. Basically this depends on the technology, which is formed by pn junction. The most frequently used and have the highest efficiency solar cells fabricated from a single crystal or a polycrystalline silicon. Moreover, the second from the relative cheapness are becoming more common.
What type of solar cell design concerns can be determined with the naked eye. Monocrystalline are exclusively black and gray, and a model based on a polycrystalline silicon allocates blue surface. Polycrystalline solar cells are made by casting, they were cheaper to produce. However, in polymers, and single-crystal plates have one drawback - the solar cell structure on the basis of their lack of flexibility that is needed in some cases.
This situation changed with the appearance of an amorphous silicon solar cell 1975 godu active element of which is from 0.5 to 1 micron thickness and provides it with flexibility. The thickness of conventional silicon cells up to 300 mm. However, although the property of amorphous silicon to absorb the light, which is about 20 times higher than that of conventional silicon solar cell efficiency of this type does not exceed 12%. it can reach 17% and 15% respectively for mono and polycrystalline embodiment.
The material from which the plates are made to affect the characteristics of solar cells.
Pure silicon wafers in the production of practically no use for solar batteries. Most often, as an additive for the production of the plate, which produces a positive charge, boron is used, and for negatively charged plates - arsenic. Besides them in the manufacture of solar batteries are increasingly used components such as arsenide, gallium, copper, cadmium telluride, selenium, and others. Thanks to them, solar cells become less sensitive to extremes of ambient temperatures.
Most solar energy can accumulate, are so-called system. Given that solar cells produce electricity only if direct sunlight or light, at night or on a cloudy day, they become virtually useless. With systems for all different solar cells. They are equipped with a battery capable of accumulating an electric current in the afternoon, when the solar battery produces it, and at night the stored charge can be given to consumers.