Environmental Engineering Reference
In-Depth Information
Manufacturing begins in Michigan, with a half-mile-long, one-foot-
wide roll of stainless steel that is fed through four machines in an automated
system. First, the steel is washed to remove surface dirt.Then two layers of
a reflective coating are applied. Next, layers of amorphous silicon and amor-
phous silicon-germanium alloys are applied to create a kind of triple-decker
sandwich: each layer absorbs a different photon-energy or wavelength of
light (blue, green, or red).The germanium concentration is applied in a gra-
dient to obtain higher efficiency, based on a concept developed by Guha
and confirmed through experimentation.
The long strip is then cut into one-foot lengths, which are shipped to
a plant in Tijuana for final assembly. There, the pieces are joined to form
7-foot-long shingles, which are wired and encapsulated with a plastic pro-
tective coating.
The flexible panels can be mounted on a roof with nails in the same way
that ordinary roofing shingles are attached. The only difference is that a
small hole must be drilled in the roof every 7 feet so that wires can be
dropped from the panels into the building. Then an electrician can hook
the wires up to the building's electrical boxes to channel energy to house
circuits, batteries, or appliances.
Flexible solar shingles went on the market in 1997. United Solar Systems
now holds approximately 160 United States patents on the design, tech-
nology, and production process and has become the world's largest manu-
facturer of roof-mounted solar cells.
While amorphous silicon solar cells are not yet as powerful as conven-
tional crystalline silicon cells (the 13 percent stable energy conversion rate
of United Solar's shingle cells is still less than the 17 percent rate for crys-
talline cells), they are actually more cost-effective, since both their materi-
als and manufacturing costs are far lower than the production costs of
standard solar cells. Moreover, their energy conversion rate is rising, as
United Solar Systems continues to refine and improve the product as well
as to lower its production cost. United Solar Systems holds all the world
records for thin-film solar cells, with an initial cell efficiency of 14.6 per-
cent (the lower stable rate of 13 percent is the effect of light-induced degra-
dation; without hydrogen dilution, the drop in efficiency would be much
greater).The next best rate is from a Japanese company, whose cells have a
stable rate of 10.6 percent.
Flexible solar cells are still prohibitively expensive in communities where
there is an established infrastructure for producing and distributing electri-
