Power Generation - Hydrogen and Fuel Cells: Advances in Transportation and Power - page 197

Solar concentrators contract the solar radiation from a relatively
large area onto a small area. A parabolic mirror of four feet in diameter
covers an area of 4 pi, or 12.57 square feet (1.17 square meters). This sur-
face area is measured on a plane and is slightly less than the surface area
of the curved mirror. If the sun is about 20% down from peak strength,
its strength should be about 800 watts per square meter. Then the total
amount of energy striking the mirror is almost 1,000 watts.
SOLAR GROWTH
The sun's output is abundant and free, but it is also diffuse. Its po-
tential as a resource has not always been welcomed. In 1985, the old Cen-
tral Electricity Generating Board in England stated that large-scale elec-
tricity generation from solar power had the disadvantages of high cost,
large demands on land area and in the United Kingdom (U.K.) low levels
of solar radiation. British Nuclear Fuels, stated that 150 square km of solar
panels would be needed to produce as much energy as a typical nuclear
power station.
But, the sun's energy can be harnessed in various ways. Buildings
can capture and retain the sun's warmth using passive solar heating. Solar
collectors or panels can be added to buildings to generate power.
Freiburg, Germany, probably has more solar energy projects than
anywhere in Europe. The city has a 65 page guide topic of examples rang-
ing from solar powered parking meters to the solar heated headquarters
building of the International Solar Energy Society.
Solar thermal power plants concentrate the sun's heat to raise steam
and drive generators. During the 1970s oil crises, several were built in
the southwestern United States. Five are operated by the Kramer Junction
Company (KJC) in California's Mojave Desert. These plants have rows of
parabolic trough reflectors covering an area of more than 405 hectares. The
troughs reflect the sun's rays onto a network of steel tubes containing a
fluid which is heated up to 390°C. This fluid is pumped through heat ex-
changers to produce steam for generator turbines with an total output of
150-MW.
Photovoltaics are adaptable and do not need deserts or cloudless
skies. The application of PV systems to buildings shows that solar electric-
ity can now be produced without needing any extra land. Arrays of PV
modules can be designed into new buildings or added to old ones. Build-