Very Small Steps for Mankind
Electricity from space remains a powerful idea.
By Seth MaSia
Seth Masia is managing
editor of SOLAR TODA Y.
Last May, physicist John Mankins set up a portable
concentrating photovoltaic array at 10,000 feet
( 3,050 meters) atop Haleakala on Maui. He attached
a microwave antenna and beamed 20 watts of the captured
power 92 miles (148 km) across the Alenuihaha Channel
to Mauna Loa on Hawaii. The receiving rectenna managed
to scavenge only about 0.0002 watt, but Mankins, a 25-year
veteran of NASA, said the test demonstrates the viability of
power transmission from space.
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at 2. 45 gigahertz — at which frequency the atmosphere is
transparent — could beam the power to a ground station
at about 83 percent efficiency. And you could put your
stadium-sized rectenna close to where you need the power.
The problem, of course, is the cost of launching a solar array
large enough to provide utility-scale power. For the price of
a gigawatt station in space, you could probably build 400
gigawatts in the Sahara or Mojave.
Roger Lenard of Heliosat Inc. thinks he can lick the
cost problem. Lenard is a former
U.S. Air Force fighter pilot who
later worked on Star Wars projects. He’s devoted to the idea of
energy independence. He knows
a lot about launch vehicles, orbiting nuclear reactors, solar collectors and energy beams. He notes,
for instance, that a broad low-intensity microwave beam is preferable to a tightly focused laser
because the laser can be mistaken
for a weapon. Heliosat’s project
is based on a concentrating solar
thermal turbogenerator, where
the receiver heats an argon-heli-um fluid and a specially designed
vacuum-facing radiator functions
as the condenser. A 1-megawatt
unit might weigh 1,500 kg ( 3,300
lb), so it might be boosted to low
earth orbit with a reusable launch
vehicle. From there, the station
would be hoisted electrically up a 3,700-km ( 2,300-mile)
orbiting tether and catapulted to geosynchronous earth
orbit (GEO), 36,000 km ( 22,240 miles) out. Once he
has a couple of powersats up and can draw on unlimited
free electricity, Lenard thinks he can reduce the cost of
a GEO launch from more than $20,000 per kilogram to
something under $500 per kilogram. Then he can gang
his concentrating turbogenerators together in gigawatt
formations. If all that technology comes together, and if
fossil fuels are burdened by a carbon tax, Lenard figures he
can sell power for market rates.
Cohen hasn’t done all the math. Even if putting stuff into
space doesn’t make sense, he still likes the idea of microwave power transmission. What if you didn’t need to string
cables to send solar power from Nevada to Chicago? “
Wireless transmission has lots of terrestrial uses,” he says. ST
an artist’s conception of a
concentrating solar turbogenerator, beaming power
to earth via a microwave
antenna.
The orbiting solar power station, or solar power satellite,
was dreamed up in 1968 by Peter Glaser, who patented
the idea in 1973. Since then, NASA, the Pentagon and the
Department of Energy have run several feasibility studies.
It’s an attractive idea for folks who want an unlimited source
of electricity, potentially untied to a terrestrial footprint. If
you want a lot of power at a forward base in Afghanistan,
on a ship at sea or at an oil shale processing site in a remote
corner of Utah, wouldn’t it be great to just summon it from
the sky?
Solar pioneer and longtime Acciona executive Gilbert
Cohen loves the concept. In theory, he points out, a solar
collector above the atmosphere has access to twice the
solar flux as the same collector on earth. If it sees the sun
24 hours a day, you get six or eight times the daily power
collection as a ground station. In theory, a microwave beam
