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 Summary: "
Electricity From the Sun--Where do we Stand?" With
trilingual summary
Unlimited electrical energy throughout
the world--that's the promise of using arrays of silicon solar cells
to directly convert sunlight into electricity, a technology known as
photovoltaics. Such a cell produces a low d-c voltage. Connecting
multiple cells in series-parallel groups, then connecting their
output to an inverter producing alternating current, allows a
photovoltaic system either to serve as an isolated generator or to
be directly connected into the utility grid.
Such systems are being used in
developing nations, where utility grid power is unavailable, to
operate pumps, light school buildings, support agriculture, and
otherwise improve living conditions.
Much larger installations (with outputs
in the megawatt range) have been installed in industrialized
countries, most often as heavily-subsidized experimental projects.
Such efforts have supported development of new types of cells such
as those using "thin film" crystalline silicon.
Solar cells alone represent only part
of the system cost. The inverter, controls, and backup battery or
generator (for operation at night or in overcast weather) add
significant expense.
Consequently, the cost of photovoltaic
energy remains prohibitive in most areas where alternatives exist.
In the United States, the Department of Energy continues to support
photovoltaic research with $75 million to $100 million annually. The
goals are an equipment cost approaching $1 per peak watt of output,
and an energy cost of $0.08 to $0.10 per generated kilowatt hour.
Both goals have proven difficult to achieve.
One obstacle continues to be the low
value of energy conversion efficiency--the percentage of solar
energy that the cell can turn into electrical output. Instead of the
30% to 40% efficiency needed, figures have ranged between 5% and 20%
for many years.
Nevertheless, the market for
photovoltaic equipment continues to grow at from 15% to 35% per
year. Worldwide, the total solar power generating capacity now
exceeds 2000 megawatts.
From
"Electricity From the Sun--Where do we Stand?" ...by
Richard L. Nailen, EA Engineering Editor -
published in Electrical Apparatus August 2004
© 2004
Barks Publications, Inc. All Rights Reserved.
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