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Components |
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Photovoltaics use crystalline
silicone cells (about three inches across) connected in a series with
solder and foil and placed under glass to form a panel. Arrays of
panels range in size from one foot square to two-by-four feet square
and only a few inches thick. Panels are rated based on their electrical
output under Standard Test Conditions (1,000 watts/m{\fs16\up62} insolation
and cell temperature of 25 Celsius/77F). Power is stored in dry-cell
batteries for output at night or on cloudy days. Panels and batteries
need protection from voltage extremes, and inverters are required
to operate AC appliances since solar panels produce a DC current.
Site-specific insolation, PV-cell output, battery characteristics
and load requirements must all be coordinated for an effective system
(Sorvig, p. 30). |
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![](figure1.jpg) |
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Figure 1: Transformation
from sunlight into energy (www.fsec.ucf.edu/-pv/pvs_s1.htm) |
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Silicon is the most popular solar-cell
material for commercial applications because it is readily abundant
(it is the second most common element in the Earth's crust). To be
useful in solar cells, however, silicon must be refined to 99.9999%
purity. In the case of single-crystal silicon, the entire structure
is grown from the same or a "single" crystal; its molecular
structure is therefore uniform. This uniformity is ideal for efficiently
transferring electrons through the material. |
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Semi-crystalline silicon,
on the other hand, consists of several smaller crystals or grains
separated by "boundaries." These boundaries impede the
flow of electrons and encourage them to recombine with holes; they
therefore reduce the power output of the cell. Semi-crystalline
silicon is much cheaper to produce than single-crystalline silicon,
however, so researchers are working on ways to minimize the effects
of the grain boundaries. |
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![](2PVcells.gif) |
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![](thincell.gif) |
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Thin film cells are a newer technology
that, unlike crystalline cells, are not produced by slicing silicon
crystals or blocks into thin wafers, and can be made with elements
other than silicon. Thin film cells are formed by depositing a liquidized
semiconductor material directly onto plastic, glass, or stainless
steel substrate. Silicon, copper indium diselenide, or cadmium telluride
are the semiconductor materials most commonly used in thin film technology. |
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