Environmental Engineering Reference
In-Depth Information
5.6
The Possibility of Space-Based Solar Power
The idea of putting solar converters in space, and beaming the power to reception
areas on earth, by microwaves or by lasers has been discussed [58] for decades. One
possible scheme, based on concentrating mirrors, a heliostat in space, is sketched
in Figure 5.7 [59].
The conceptual heliostat design of Figure 5.7 (one of the
five designs proposed in
the cited report) is envisioned to be stationary at 22 700 miles above a location on
earth. Tilting of the primary and secondary mirrors optimizes power collected by the
energy converter during the 24 h cycle. The size of this system is large: to make a
suitably collimated beamat 5.8GHz, the satellite transmitting antenna would have to
be about 500m in diameter, powered by a phased array transmitter, and would
require a 7.5 km diameter rectifying antenna rectenna on earth. The power density
at this receiving antenna would not be dangerous, but this expensive system would
provide only 1.2GW on earth. The system would have to be assembled in space, as
was the International Space Station (ISS), which, in a LowEarthOrbit, LEO, cost $130
billion. This would suggest more than $100/W cost, 100 times larger than on-earth
solar or wind installations. Electric power usage inAmerica is on the order of 500GW,
so the Heliostat Power Satellite device indicated in Figure 5.7 would be a relatively
Figure 5.7 Heliostat conceived for
geosynchronous earth orbit [59]. A sketched
system of focusing mirrors, photovoltaic or
thermal energy converters, and transmitter(s)
to earth, placed in geosynchronous earth orbit at
altitude 36 000 km (22 370mi). In Ref. [59], this
figure
1DOF
means
one degree of freedom.
One such power satellite could equally serve any
North American city, providing power almost
continuously, but requiring a dedicated
rectifying antenna of 7.5 km diameter on earth,
assuming a 500m phased array transmitting
antenna on the satellite, and delivering 1.2GW
on earth. The cost of this system is likely to be
more than $100 billion, corresponding to $100/
W. The transmission frequency is 5.8 GHz,
corresponding to wavelength 5.2 cm. This band
transmits well through clouds and even light
rain.
