Environmental Engineering Reference
In-Depth Information
Negative
electrode
n-doped
silicon
Boundar
layer
p-doped
silicon
Positive
electrode
Figure 4.11 Solar Cell Structure and Front View of a Crystalline
Silicon Solar Cell
influences. To avoid this, further protection is necessary. Several solar cells with
an edge length between 10 and 21 cm (4-8 inches) are combined in a solar
module for cell protection. Many modules are made up of 32-40 cells; however,
other module sizes with significantly more or fewer cells exist. The front cover
is formed by low-iron glass, which has already been described for the flat solar
thermal collector in Chapter 3. The back cover is made of glass or plastic.
Between the front and rear cover, the solar cells are embedded into plastic. This
material is usually ethylene vinyl acetate (EVA), which is cured at temperatures
of 100°C (212°F) at reduced pressure. This process is called lamination . A
frame is added to the finished modules in some cases. A junction box protects
the contacts from water; bypass diodes are also mounted in this box (see section
headed 'Series connection under inhomogeneous conditions', p143).
Technical data for solar modules are given in Table 4.6.
Thin film modules
Besides crystalline silicon, thin film modules hold promise for the cells of the
future. They can be made of amorphous silicon and other materials such as
cadmium telluride (CdTe) or copper indium diselenide (CuInSe 2 or CIS). Thin
film modules can be produced using a fraction of the semiconductor material
necessary for crystalline modules and this promises lower production costs in
the medium term. Therefore, the development potential of thin film modules is
very high. A disadvantage is the use of toxic materials in some cells; therefore,
the importance of production safety and material recycling will increase in the
coming years. Furthermore, the supplies of certain materials, for example of
tellurium, are restricted, whereas silicon reserves are almost inexhaustible.
However, it is not yet clear which material will dominate future markets. This
chapter will give only a short illustrative description of amorphous silicon thin
film modules because they are the thin film modules with the longest market
history.
The base for amorphous silicon solar modules is a substrate; in most cases
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