Photovoltaic Power - Wind and Solar Power Systems - page 28

FIGURE 3-14

Lens concentrating the sunlight on small area reduces the need of active cell material. (Source:
Photovoltaic Fundamental, DOE/NREL Report DE91015001, February 1995.)

3.3.6 Concentrated Cells

In an attempt to improve the conversion efficiency, the sunlight is concen-
trated into tens or hundreds of times the normal sun intensity by focusing
on a small area using low cost lenses ( Figure 3-14 ) . The primary advantage
is that such cells require a small fraction of area compared to the standard
cells, thus significantly reducing the pv material requirement. However, the
total module area remains the same to collect the required sun power. Besides
increasing the power and reducing the size or number of cells, such cells
have additional advantage that the cell efficiency increases under concen-
trated light up to a point. Another advantage is that they can use small area
cells. It is easier to produce high efficiency cells of small areas than to produce
large area cells with comparable efficiency. On the other hand, the major
disadvantage of the concentrator cells is that they require focusing optics
adding into the cost.
The annual production of various pv cells in 1995 is shown in Table 3-1 .
Almost all production has been in the crystalline silicon and the amorphous
silicon cells, with other types being in the development stage. The present
status of the crystalline silicon and the amorphous silicon technologies is
shown in Table 3-2 . The former is dominant in the market at present and the
latter is expected to be dominant in the near future.