A space solar power station would be located in geosynchronous orbit, which
would cause it to orbit the Earth at the same rate as the Earth revolves around
its axis. It would consist of a large array of solar collectors, perhaps
several square kilometers in area. At geosynchronous orbit, a space solar power
station would remain in sunlight 99 percent of the time, being only in darkness
about an hour an a half per day during the few days around the fall and spring
equinoxes. This is one advantage that a space solar power station has over
ground based solar power, which by definition is in darkness for half the day.
Another advantage of a space solar power station is that, in microgravity, it
is light weight and, in theory, can be as large as one requires. It will also
collect the full spectrum of the sun’s energy and not just the portion that
penetrates the Earth’s atmosphere.
The space solar power station would beam the power via microwaves to a
rectenna, a receiving station on Earth. A rectenna would resemble a mesh of
wires designed to convert microwave energy into electricity. A rectenna, which
would be several square kilometers in area, could be built over farmland, with
livestock and crops being raised safely below it. The electricity converted from
the rectenna would be channeled into the electrical grid.
Safety of the Microwave Transmission
The most controversial aspect of the space solar power station scheme comes
from concern for the safety of people and animals which happen to find
themselves underneath the microwave transmission. Ninety five percent of the
energy of the microwave transmission would be absorbed by the rectenna, the
remainder of which is well below what is considered safe for living beings.
People in airplanes flying through a microwave transmission would be protected
by the metal skin of the aircraft. Experiments in exposing animals to
microwaves have shown no harm over several generations. Research is still
ongoing.