inside ases | chair’s corner
Protecting the Space Frontier
Solar power satellites promise carbon-free electricity, 24/7. At what cost?
By JOHN REYNOLDS,
John reynolds, Faia,
is chair of the american
Solar energy Society
Board. Contact him at
provide most of
power, isn’t that
quality of solar?
Ihave recently seen two concepts for solar satellites
designed to beam electricity to Earth, 24 hours a day,
seven days per week, using microwave transmission.
One example would use Peter Glaser’s 1968 idea of solar
power satellites (SPS), large space stations covered in photovoltaic (PV) panels. A rival concentrating solar option
uses orbiting thermal generators and mirror arrays (see
SOLAR TODAY, March, page 18).
What’s not to like about solar 24/7? The SPS answers
the pro-fossil and pro-nuclear arguments that solar is
undependable, seasonal and diurnal. An SPS generates no
noxious gases in operation, heats no rivers and leaves no
On the other hand, an SPS intercepts solar radiation
that was not headed for our planet. It therefore adds more
heat to a climate that seems to be producing too much heat
already. An SPS will burn enormous quantities of rocket
fuel to send all that gear skyward. What about maintenance?
How will we repair the holes punched in a mile-wide collector by orbiting debris?
Perhaps worse, an SPS may spawn attempts to mine the
moon or asteroids for raw materials, rather than send them
from Earth. Not content with despoiling our own planet
with extractive technologies, we then would visit destruction on other worlds. Ben Bova, the science fiction novelist
and past president of the National Space Society, recently
noted that “Americans are a frontier people at heart. We
have a frontier that begins a scant hundred miles overhead
and contains more riches of energy and raw materials than
the Earth can provide.”
In “An Energy Fix Written in the Stars” ( Washington
Post, Oct. 12), Bova wrote, “Microwave transmitters are…a
well-developed technology. There’s one in almost every
kitchen in the nation, in the heart of our microwave ovens.
Some people worry about beaming gigawatts of microwave
energy to the ground. But the microwave beams would be
spread over a wide area, so they wouldn’t be intense enough
to harm anyone. Birds could fly through the thinly spread
beams without harm. Nevertheless, it would be best for the
receiving stations to be set up in unpopulated areas: say, the
deserts of the American Southwest.”
Even if the beams are thinly spread and not harmful and
we, nevertheless, locate receiving stations as far as possible
from population centers, won’t those stations be competing for land with concentrating solar power-generating
stations? And adding miles of transmission lines to the
ongoing risk of microwave transmission? I heard similar
arguments when nuclear power was being touted as “
eventually too cheap to meter, no harmful radiation, perfectly
safe.” I asked Bova why he favored a remote location. He
56 June 2009 SOLAR TODAY
replied: “Although there is no immediate danger to health
from the microwave beams of solar power satellites, the
long-term effect of such exposure is mostly unknown. That,
plus the possible effects of microwaves on electronic and
electrical equipment, make it prudent to keep the receiving
antenna farms in unpopulated areas. Of course, there is also
the fact that we are a litigious society, and people might sue
for the nuttiest reasons (or just because they oppose SPS)
if the receivers were anywhere near them.”
The demonstrated efficiency of microwave power transmission is so very small (of 20 watts sent, just 0.0002 watt
was received in a test in Hawaii) that an Earth-bound array
seems a far safer investment.
Plenty of renewable sources already produce power
24/7. In the American Solar Energy Society-sponsored
study “Tackling Climate Change in the U.S.” ( ases.org/
climatechange), researchers calculated that biomass can
produce 355 terawatt-hours (TWh), or 8. 3 percent of
America’s projected 2030 grid needs, and geothermal
potential is 395 TWh, 9. 2 percent of 2030 grid requirements. And 24/7 hydropower already produces up to 16
percent of our grid needs, depending on droughts and purchases from Canada.
In addition, there’s ocean energy: tidal, wave power and
ocean thermal. Tidal energy (it’s lunar in origin) waxes and
wanes, with absolutely predictable precision, twice daily.
Wave power peaks in the winter, nicely balancing the annual variation in solar flux reaching terrestrial collectors.
These alternatives are not squeaky clean. Biomass has
big implications for forest ecosystems and agriculture.
Geothermal bores and steam lines place some scars in the
landscape. Ocean energy operates in an exceptionally harsh
environment, and the effects on ocean ecosystems are only
beginning to be researched. The fishing industry isn’t happy
about hydropower or ocean power.
Our daytime use of electricity greatly exceeds nighttime
use. If uninterrupted ground-based renewables can provide
most of our nighttime power, isn’t that sufficient to compensate for the diurnal quality of solar? That depends partly
on the degree of our transition from gasoline to electricity
for transportation. Our future electric vehicles will charge
in parking lots below PV arrays by day. But they will also
charge in the carport overnight.
Energy storage is a key ingredient for renewable energy
sources by night. With efficient batteries, or with efficient
renewable production of hydrogen, we can store daytime solar production for nighttime consumption. That’s
clearly preferable to electricity from nuclear, natural gas,
oil or coal — and to solar satellites glowing brightly in
the night sky.