Page 69 - Advances in Renewable Energies and Power Technologies

42 CHAPTER 1 Solar Cells and Arrays: Principles, Analysis, and Design

characteristics. At 20 C, the short circuit current of the module I sc ¼ 730 mA, the
open circuit voltage of the module ¼ 22 V, the maximum power P m ¼ 12 W, and the

module efficiency ¼ 12%. At 60 C, I sc ¼ 770 rnA, V oc ¼ 18 V, P m ¼ 10 W, and
h ¼ 10%. From the figure, we see further that I sc increases slightly with temperature,
V oc , P m , and h decrease with temperature. This behavior is similar to that of the solar
cells, which is expected because the parallel connection is a current multiplication
process while the series connection is a voltage multiplication process. The open cir-
cuit voltage per cell V oc /cell ¼ 22/n e ¼ 22/36 ¼ 0.61 V, and the short circuit current
per cell I sc /cell ¼ 730/n s ¼ 730/6 ¼ 122 mA. These values are in very close agree-
ment with those of the single cell.

5.5 THE SOLAR CELL ARRAY
The array is composed of solar modules connected according to certain configura-
tion to satisfy the voltage, the current, and the power requirement. If the array
voltage is V a , the array current is I a , and the array power is P a , one can determine
the number of the modules required and their circuit configuration. As an example,
using the modules with the characteristics given in Fig. 1.36, we can design an array
with V a ¼ 120 V, I a ¼ 4 A, and an output power w0.5 kW peak. The number of
modules connected in series ¼ 120 V/m ¼ 120 V/20V ¼ 6 and the number of mod-
ules strings connected in parallel ¼ 4A/I m ¼ 4/0.7 ¼ 6. Then the total number of
the modules ¼ 6 6 ¼ 36 modules. A protection diode may be commented in series
with the array to allow the passage of the current to the load only and prevent the
back current.

5.6 THE FLAT PLATE MODULES
Solar cells must be encapsulated to protect them against environmental effects and to
give them mechanical support for easy handling [32]. The terrestrial modules must
be hermetically sealed against the moisture. The following requirements must be
satisfied by the encapsulation:
1. rigidly support the mechanically weak solar cells
2. hermetically seal the solar cells against moisture
3. transparent for the solar radiation
4. withstand the environmental effects such as: (1) temperature cycling, (2) wind
forces, (3) rain and hail fall.
5. remain reliable for long times to be economically feasible (more than 10 years)
6. as cheap as possible
7. relief temperature cycling leading to thermomechanical stresses on solar cells
and interconnectors between them
8. have large area efficiency.
9. conduct the heat of the solar cells.
10. easily fabricated by simple processes.