Page 42 - Solar Power in Building Design The Engineer's Complete Design Resource

12 SOLAR POWER SYSTEM PHYSICS

POLYCRYSTALLINE PHOTOVOLTAIC SOLAR CELLS

In the polycrystalline process, the silicon melt is cooled very slowly, under controlled
conditions. The silicon ingot produced in this process has crystalline regions, which
are separated by grain boundaries. After solar cell production, the gaps in the grain
boundaries cause this type of cell to have a lower efficiency compared to that of the
monocrystalline process just described. Despite the efficiency disadvantage, a number
of manufacturers favor polycrystalline PV cell production because of the lower man-
ufacturing cost.

AMORPHOUS PHOTOVOLTAIC SOLAR CELLS
In the amorphous process, a thin wafer of silicon is deposited on a carrier material and
doped in several process steps. An amorphous silicon film is produced by a method
similar to the monocrystalline manufacturing process and is sandwiched between
glass plates, which form the basic PV solar panel module.
Even though the process yields relatively inexpensive solar panel technology, it has
the following disadvantages:

■ Larger installation surface
■ Lower conversion efficiency
■ Inherent degradation during the initial months of operation, which continues over
the life span of the PV panels

The main advantages of this technology are

■ Relatively simple manufacturing process
■ Lower manufacturing cost
■ Lower production energy consumption

Other Technologies

There are other prevalent production processes that are currently being researched and
will be serious contenders in the future of solar power production technology. We
discuss these here.
Thin-film cadmium telluride cell technology In this process, thin crystalline
layers of cadmium telluride (CdTe, of about 15 percent efficiency) or copper indium
diselenide (CuInSe , of about 19 percent efficiency) are deposited on the surface of
2
a carrier base. This process uses very little energy and is very economical. It has
simple manufacturing processes and relatively high conversion efficiencies.

Gallium-arsenide cell technology This manufacturing process yields a highly
efficient PV cell. But as a result of the rarity of gallium deposits and the poisonous