MadSci Network: Earth Sciences

Re: Are the chemicals used to manufacture solar cells enviornmentally friendly?

Date: Sun Dec 17 17:45:03 2000
Posted By: Adrian Popa, Director Emeritus, Hughes Research Laboratories
Area of science: Earth Sciences
ID: 975284001.Es


Depending on the application that silicon solar cells are used for, different coatings are
applied to protect them from the weather on the earth’s surface and to protect them from
solar radiation when used on spacecraft. These coatings are usually made in the form of a
glass (silicon dioxide) film about 250 micrometers (100 microinches) thick. Also, to
improve their efficiency for gathering light energy, solar cells often have antireflection
coatings placed on the surface of the glass film. These antireflection coatings are a few
micrometers (a few microinches) thick and are made from polymers (plastics).

In general, solar cell manufacturing is similar to the manufacturing of silicon integrated
microcircuits (ICs) and similar precautions must be taken to protect the environment from
the manufacturing byproducts. One major environmental issue that has been raised about
the manufacturing and large scale use of solar cells is the great amount of energy required
to generate the heat to form the large number of silicon wavers required to make an array
of solar cells. Most solar cells used today use more energy in the manufacturing process
than the electrical power (energy) that they will generate over their operating lifetime.
However, this is a somewhat simplistic argument and is highly dependent on the
application. For example; when you compare the total energy that would be consumed to
deliver power to a network of remote emergency radio telephones placed along the
thousands of miles of highways, solar cell powered devices are probably more energy
efficient and certainly are more cost efficient.

Determining the total energy costs and environmental impact for any given application
is a very complex problem which our nation, and the other industrial nations,
will have to face in the 21st century.
Meanwhile, to reduce the manufacturing costs (including energy) of solar cells, significant
progress is being made in the development of large solar cell arrays formed by depositing
thin silicon films on metal and ceramic substrates in place of the expensive silicon
wafers now being used.

Best regards, Your Mad Scientist
Adrian Popa

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