120 Electrical Power Systems Technology
have been made. We are now faced with the problem of finding alterna-
tive sources of energy, and solar energy is one possible alternative source.
The sun delivers a constant stream of radiant energy. The amount of solar
energy coming toward the earth through sunlight in one day equals the
energy produced by burning many millions of tons of coal. It is estimated
that enough solar energy is delivered to the United States in less than one
hour to meet the power needs of the country for one year. This is why
solar energy is a potential source for our ever-growing electrical power
needs. However, there are still several problems to be solved prior to us-
ing solar energy. One major problem is in developing methods for control-
ling and utilizing the energy of the sun. There are two methods for collect-
ing and concentrating solar energy presently in use. Both of these methods
involve a mirror-like reflective surface.
The first method uses parabolic mirrors to capture the energy of the
sun. These mirrors concentrate the energy from the sun by focusing the
light onto an opaque receiving surface. If water could be made to circulate
through tubes, the heat focused onto the tubes could turn the water into
steam. The steam, then, could drive a turbine to produce mechanical en-
ergy. The mirrors could be rotated to keep them in proper position for the
best light reflection.
The second method uses a flat-plate solar collector. Layers of glass are
laid over a blackened metal plate, with an air space between each lay-
er. The layers of glass act as a heat trap. They let the rays of the sun in,
but keep most of the heat from escaping. The heated air could be used to
warm a home.
The first widespread use of solar energy will probably be to heat
homes and other buildings. Experiments in doing this are already under-
way in many areas. To heat a home, a flat-plate collector may be mount-
ed on the part of the roof that slopes in a southward direction. It should
be tilted at an angle to receive the greatest amount of sunlight possible.
The sun would be used to heat a liquid (or air) that would be circulated
through the collector. The heated liquid (air) would be stored in an insu-
lated tank and, then, pumped into the house through pipes and radiators
(air ducts). By adding a steam turbine, a generator, etc., to the solar collec-
tor just discussed, the heat could be used to drive the steam turbine to gen-
erate electrical energy. This solar power system is illustrated in Figure 5-1.
Another major problem in solar heating is in the storage of the heat
produced by the sun. In areas that have several cloudy days each year, an
auxiliary heating system is required. However, solar energy is being used