Page 46 - Advances in Renewable Energies and Power Technologies

4. The Solar Cells 19

FIGURE 1.15
The nonideal versus ideal diode IeV curves.

density, the interface recombination current I irc must be considered [14].Itcan be
expressed by

I scr ¼ qAn i v s e V j =nV T (1.21)
where v s is the interface recombination velocity and n is an ideality factor having a
value l. The ideal diode is represented by the rectifier symbol while the general
IeV relation of the diode follows the formula

I ¼ I s e V j =nV T 1 (1.22)
The temperature affects greatly the diode current for fixed diode voltage. The
diode current increases appreciably with the increase in temperature. Keeping the
current constant, the diode voltage decreases almost linearly with temperature.
These temperature variations can be accounted for by the appreciable increase of
I s with temperature.

4. THE SOLAR CELLS
The solar cell is the basic element in a PVarray. It has the vital function of converting
the solar radiation into electricity directly. To perform its function satisfactorily, it
must have the highest possible conversion efficiency. It has to basically carry out
two basic functions:

1. Absorb the incident solar radiation generating at least one hole pair for each
photon.