perm filename SOLAR[L,VDS] blob sn#250517
filedate 1976-11-27 generic text, type C, neo UTF8
COMMENT ⊗ VALID 00002 PAGES
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One interesting application of solar power is that of an orbiting
solar-power station that would beam energy to earth by microwaves. This
station is the concept of Dr. Peter Glaser. He has proprosed that the station
be placed in a geosynchronous orbit, about 23,000 miles high, and have the
energy which is collected and concentrated by the satellite beamed down to a
fixed spot on earth to a ground station. He feels that with continued research
in the field, power from space has the potential to provide an economically,
environmentally, and socially acceptable option to providing a large percentage
of the future world energy needs.
The major reason for having a satellite solar power station, (SSPS), rather
than a ground based solar station is because of the fact that a space station has
almost a 24 hour infall of sunshine--only 72 minutes of darkness when the orbiting
satellite is briefly overshadowed by the earth around the time of the equinoxes.
To prevent these losses, Glaser has proposed two synchronous satellites spaced 21
degrees apart, which could cover for eachother during those specific times. Glaser
has designed the SSPSs to have an output which will produce up to 15,000 MW on earth.
A 15,000 MW producing SSPS would provide approximately the amount of energy that the
city of New York would need in the year 2000.
The solar energy conversion into electricity will be done by the photovoltaic
process, using the single-crystal silicon solar cells, which have a working efficiency
of around 11%. The single-crystal gallium arsenide solar cell might be desirable to
use someday,if they can be developed for large scale use,because of their smaller
thickness and 18% efficiency. The individual solar cells will be arranged in
solar arrays, with mirror coatings which will reflect only the useful part of the
solar spectrum which can be used in the photovoltaic process. The solar arrays will
be symmetrically arranged, each array being about 5 km by 5 km. The high cost of the
silicon is a major drawback to the solar cells. In l965, the cost was about $175/W--
the price will have to be lowered to about $1/W before any economic success can be
The wavelength of the beam chosen was a 10 cm length, a microwave length,
because of the large amounts of power that could be transmitted with minimum losses
in the ionosphere and atmosphere, and with little environmental and biological effects.
The transmission efficiency (the ratio of the DC power output at the receiving antenna
on earth to the DC power input at the transmitting antenna) is about 70%. The antenna
are large--the transmitting antenna is about 1 km in diameter, whereas the receiving
antenna is about 7 km in diameter. About 90% of the transmitted energy is intercepted.
The concept of this sounds great...to obtain power with a fuel cost of nothing,
and, without a lot of the pollution effects. However, like most everything, this
satellite solar power station has many big setbacks...the number one being cost.
It has been estimated that a satellite of 10 million kilowatts would have a cost of
$23.4 billion, which includes the cost of the ground receiver. This is quite an enor-
mous price to pay, and the lifetime of one of these stations is only about thirty
The huge weight of the station seems to be almost the biggest problem encountered.
A station which could produce 5,000 MW of earth power would weigh about 25 million
pounds. Glaser is dependent upon the advancement of the present space shuttle program,
which must be designed for high-volume transport of payloads to low Earth orbit, and a
high-performance low Earth orbit to synchronous orbit transportation for final assembly
and deployment. About 500 launches would be required to deliver the parts of the
25 million pound station to synchronous orbit. At transportation costs of about
$100/lb, we can see where enormous costs come into the SSPS program.
By increasing the conversion efficiency of the solar cell to 18% to 20%,
by dropping the present 14lb/KW weight of the solar battery to only 2lb/KW, using
lightweight mirrors to concentrate the sunlight on the batteries, and other such
improvements,it has been predicted that a hundredfold decrease in solar battery array
costs are possible. Many people seem to believe that the formidable costs of the
SSPS which are run across now might be lowered substantially enough within the next
twenty years so as to compete competitively with the fossil and nuclear power plants.
This, of course, is yet to be seen. Much research will be needed.
Along with the economic problems, the SSPS system is also running across
some possible biological problems. Just how much harm might be done to the life
on earth with these microwave beams being shot down to earth? A major problem is
that there is controversy on the acceptable standard for microwave exposure. A better
understanding of the effects of microwaves on the human body need to be obtained. In
the U.S., the microwave level exposure limit is 10 mW/square cm, whereas it is only
.01 mW/square cm in the Soviet Union. By providing a guard ring for the antennas,
it seems possible to keep the level of exposure to the people at below the .01 mW/
square cm level, though.
Other effects might be interference wwth electronic equipment, medical
instrumentation, and electro-explosive devices. What the effects of the beam upon
flying birds will be is still not known. Another unfortunate effect might be in the
potential for radio frequency interference. The frequency band which is ideally
suited for the SSPS operation is already in heavy use by the communications industry.
Thus, agreement on frequency assignments will have to be made. A final problem
which will have to be analyzed is that of the effects of adding these huge amounts of
microwave heat into the earth's atmosphere.
There is a lot of work ahead for this SSPS project. But, as in the past,
technological advancements have proved to be feasible. At one point, the idea that
man could be put on the moon was scoffed at. In the same light, we just might surprise
ourselves and find that in the year 2000, we will have numerous SSPS stations floating
around in outer space, supplying much of our energy needs. Because of the shortage
of fossil fuels, the undesirability of using coal for fuel because of the pollution
effects, and the uncertainty in using nuclear power because of the possible radiation
effects, the idea of using solar power is certainly promising.