Environmental Engineering Reference
In-Depth Information
thermal farms. Further to the plan for Ordos City are biomass operations, fueled by
organic materials like wood chips and straw for 0.31GW, and 70MW from hydro
storage, a load-balancing technology that uses off-peak power to pump water to a high
reservoir from which it can be released to turn turbines at peak demand periods.
First Solar is likely to build a plant in China to make thin-
lm solar panels.
According to the article, the 2 GW solar farm as built in China is likely to cost
signif-
cantly less than the $5
-
$6 billion if it were built in the United States. It is
commented that the CdTe solar cells of First Solar are less ef
cient than the standard
crystalline silicon solar cells made by companies like Suntech, but they are signif-
icantly less expensive to build. First Solar has also recently agreed to provide 1.1 GW
to two California utilities from three big solar farms. It is commented in this article
that the Chinese project is atypical of large solar projects, which have generally been
awarded to solar thermal technology, which deploys mirrors to heat a liquid to create
steam that drives an electricity-generating turbine, rather than to straight photovol-
taic projects. It is pointed out in this comparison that the straight photovoltaic
projects generally have fewer environmental impacts, such as requiring cooling
water, and can be brought online faster than solar thermal plants.
Basic forms of CdTe cell construction are shown in Figure 6.15. The junction is
between n-type CdS and p-type CdTe.
CdTe is a direct bandgap material with high absorption of light of energy beyond
the bandgap about 1.45 eV. Although Cd is toxic, the devices contain thickness of only
a fewmicrometers of CdTe and the toxic material is encapsulated to as not to present
an external hazard. The material is very favorable it seems from the point of view of
cost of fabrication. It appears that CdTe cells are leaders in the competition for large
and cost-competitive photovoltaic installations.
Figure 6.15 Two types of CdTe solar cells [81].
In both cases, the structure is built starting from
the glass substrate, and methods including CSS
(closed space sublimation) and chemical bath
deposition are used to deposit succeeding
layers. In these devices, the CdTe film is
1.5
m in thickness, is deposited using CSS
especially for large-area devices, and is subject
to an anneal with CdCl
2
or other Cl- containing
compound to promote grain growth after
fabrication. Device efficiencies are in the range
10
3
m
-
16%, panel record efficiency is 12.8%.
-
