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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 
 
gained.  
 
 
	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 
 
years. 
 
 
	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.