Environmental Engineering Reference
In-Depth Information
Figure 5.6 Efficiency
cost trade-offs for three generations of photovoltaic solar cells, cost in 2003
US dollars. The categories are I wafers, II thin films, and III
advanced thin films
[55].
-
silicon solar cells. A related form of inexpensive silicon thin-
lm cell is actually a
tandemcell with three different bandgaps based on amorphous Si, semicrystalline Si,
and Si
ciency of these devices has not exceeded 10% and
they are best characterized as type II rather than type III. By far the most common
solar cell is silicon in type I or type II form, followed by CdTe thin-
lm cells.
The goal of grid parity describes the effort to
find solar cell systems cost
competitive with coal- or gas-
red turbine electric power. A consensus view is that
silicon-based products will not reach this goal: crystalline on the basis of cost and thin
films on the basis of ef
ciency. (There may be an opening for crystalline Si cells in
concentrating systems, however, as we mention later in this chapter.) The grid
parity goal assumes the power can be fed into an existing power grid, which avoids
the basic problems of intermittency of sunlight, and variability of power under
weather conditions. A stand-alone solar system would have to provide storage in
massive amounts or connection to a grid so large that the sun is always shining on
some part of it. Storage in a totally solar power gridmight be provided by diversion of
some of the daylight power to hydrogen electrolysis and fuel cell capacity to meet
power demand overnight. A stand-alone renewable power systemmight alternatively
be a combination of solar and wind farms, with the lower power usage at night
provided by wind, using the solar part to bring the total power up to peak demand in
the day.
The leading contenders for grid parity systems appear to be type II thin-lm
cells of CdTe, followed by CIGS cells (copper indium gallium selenium). The First
Solar
Ge alloys. However, the ef
-
lm cells, has a signed agreement
with China to build a 2GW solar cell farm in Ordos City in the Mongolian
desert [56].
The second leading type II thin-
lm cell is CIGS, copper indium gallium selenide.
CdTe and CIGS thin-
lm cells are both more ef
cient and cheaper to produce than
firm, leader in production of CdTe thin-
