Laws of connecting solar cells. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Alternative energy sources
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All silicon solar cells generate an electrical voltage of about 0,5 V. As for the current, it depends on the intensity of the light and on the size of the cell.
Figure 1 shows the characteristics of the solar cell (the current is shown in arbitrary units).
The illumination level of 100 mW/cm2 corresponds to the direct flux of solar radiation at noon. It follows from the characteristic that with an increase in the load current, the voltage at the output of the element decreases until, at a certain current, it drops to zero. This current is called short circuit current. Unlike other power sources, short circuiting a solar cell will not damage it.
To increase the voltage, the solar cells are connected in series. It is clear that in this case the current of the garland is determined by the element with the smallest current.
To increase the current, the solar cells are connected in parallel. In this case, the output voltage is determined by the element with the lowest voltage. Thus, for real applications, solar cells have to be connected as a parallel connection of series strings. This combination is called a battery.
When working with solar panels, they encounter a phenomenon that does not occur when using conventional power supplies. This phenomenon is called reverse bias. Let's assume that there is a set of series-connected solar cells loaded with a resistor. A total voltage is released across the resistor, and current flows through it. If one of the elements is darkened at the same time, then the following will happen. A solar cell that does not produce electrical energy turns into a link with a lot of resistance. Now the entire voltage of the chain is applied not to the load, but to the darkened element. As a result, the element heats up and may fail (explode). To solve this problem, it is necessary to connect a diode in parallel to each element so that it is locked during the operation of the element (Fig. 2).
If now one of the elements is shaded, then the diode parallel to it begins to conduct current around the faulty element. The output voltage of the circuit will decrease, but the shaded element will not fail.
In practice, it is impractical to shunt each battery cell. It is enough to use 4-5 diodes for 1/4 or 1/5 of the battery. Then, when shading, the voltage will decrease by 20-25%.
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