Space solar power is a concept which involves building solar collection stations in space that would literally tap into nature's fusion reactor, the Sun, and transmit that energy to Earth. The energy thus collected is limitless and without pollution.
The idea of getting energy from the Sun has been around for a number of
decades. People are familiar with solar power calculators, solar powered
traffic lights, and other devices. Ground based solar power has a number of
problems, however. The Sun emits untold amounts of energy, a hundred and seven
five thousand terawatts (i.e. a 175 thousand trillion watts) of which strike
the Earth’s upper atmosphere. Unfortunately much of that energy is reflected
back into space, is absorbed by such things as dust and water vapor, or is used
to generate photosynthesis in plants. Ground based solar is a very poor
technology for powering a modern, industrial society. The surface area of solar
cells that would be necessary to run an industrial plant or an office building
would be enormous and in most cases unworkable. Fortunately there is another
way to tap into the boundless energy of the sun.
The Birth of Space Solar Power
In 1968, Peter Glasser, at Arthur Little, published a paper suggesting that
solar collectors placed in geosynchronous orbit around the Earth would be able
to collect solar energy and beam that energy down to collectors on the Earth’s
surface known as rectennas. In 1974, Glasser discovered and patented a method
of transmitting energy from the solar collectors to the ground using
microwaves.
Around the same time, NASA became interested in the concept, due in part to
the energy crisis then afflicting the world. NASA, either directly or through
aerospace contractors, financed studies of space solar power. However, by the
early 1980s, when energy prices began to ease, the concept was put on the back
burner.
Meanwhile, Gerard K. O’Neil, then a professor of physics, popularized the
subject of space solar power in his classic book, The High Frontier. O’Neil’s
idea was that space settlements, which he envisioned as being huge, free flying
structures where people would live on the inside of cylinders that rotated to
provide the semblance of gravity, would become economically viable by building
space solar power stations and selling the power to Earth. To make the plan
even more viable, these stations would be built out of materials mined on the
Moon or from asteroids, thus obviating the expense of lifting building material
from the Earth’s surface.
Due to advances in technology and the increase in energy prices, interest in
space solar power has revived to a certain degree. The world uses 13 terrawatts
of energy per year at the present time. In about fifty years, that amount is
estimated to increase to 30 terrawatts. Some people believe that space solar
power is one solution to finding that needed energy, without causing pollution.
How Space Solar Power Works
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.
Lunar Based Solar Power
The University of Houston
at Clear Lake’s
Dr. David Criswell has come up with an interesting variation of the space solar
power scheme. Instead of building the space solar power stations in
geosynchronous orbit, he proposes to build them on the lunar surface. An
advantage of this approach is that the challenges surrounding the building of
large structures in microgravity are avoided. Also, many of the materials for
building solar collectors, primarily silicone, are already on the Moon and
available for exploitation. The main disadvantage of the Criswell approach is
that the microwave power has to be transmitted to Earth via a series of relay
satellites. Also, the Moon has a four week day and night cycle, making it
necessary to build redundant solar collector stations on both the near side and
the far side of the Moon.
The Advantages of Space Solar Power
Space solar power does not require fuel for it to operate, unlike virtually
every other form of energy production, including oil, coal, natural gas, and
even nuclear and fusion. Space solar power does not create air or water
pollution nor does it create radioactive byproducts. Once the cost of building
a space solar power station is completed, the only expense is maintenance which
can be amortized over a long life cycle, lasting two or even more decades.
There exists some economic analysis that suggests that space solar power would
be competitive with other, more conventional forms of energy, even leaving out
the intangible pollution and health costs associated with, for example, oil and
coal. Space solar power can be one of the solutions to meeting civilization’s
energy needs in the future.