UH Solar Cell Research Has Applications for Space Exploration, Clean Cars

HOUSTON — New technologies designed to harness the power of
the sun may hold the key to successful moon colonies, cheaper
and lighter-weight satellites, and cleaner-burning, more
efficient car engines. Solar cells, electronic devices that
convert sunlight into useful electricity, would be an
important resource for powering future industrial bases or
colonies on the moon. Alex Freundlich, research professor
of physics, and Charles Horton, senior research scientist
at the Texas Center for Superconductivity and Advanced
Materials at UH, or TcSAM, are developing methods to
manufacture huge solar cell arrays on the moon using
materials from the lunar soil.

“The raw materials needed to make solar cells are present
in the moon’s regolith,” says Freundlich, who has examined
lunar material to determine whether it contains the necessary
ingredients for making solar cells. He, Horton, Alex
Ignatiev, director of TcSAM, and a team of NASA-JSC and
industry scientists also have used “simulated” moon soil
to determine how to go about manufacturing the solar cell
devices on the moon.

The UH scientists will present talks on three solar cell
research projects during the World Space Congress 2002 Oct.
10-19 in Houston.

“Our plan is to use an autonomous lunar rover to move across
the moon’s surface, to melt the regolith into a very thin
film of glass and then to deposit thin film solar cells on
that lunar glass substrate. An array of such lunar solar
cells could then be used as a giant solar energy converter
generating electricity,” Freundlich says. “These solar
cells would have lower efficiencies compared to devices
currently used on Earth, but by using such a large surface
area, we could eventually generate enough electricity to
supply a lunar base, support lunar manufacturing or
colonies.”

Another possible use for a lunar solar power system would be
to generate electricity to beam back to the Earth for use in
local electric grids. UH physicist David Criswell has spent
20 years developing such a plan.

Freundlich and Horton also are developing solar cells that
are more efficient at converting sunlight to electricity
than those currently used to power orbiting satellites. The
materials used in their advanced solar cells, and the way
those materials are configured, also make them more
resistant to the damaging effects of radiation.

“The best space solar cell technology currently in use
converts only about 28 percent of the sunlight hitting the
device into electricity,” Freundlich says. “By adding a thin
layer of nano-engineered material in these cells we are
capable of boosting solar cell efficiencies to well above
35 percent. These cells potentially would last much longer
because they are much more resistant to being degraded by
radiation from the sun and space.”

One of the most radiation-laden areas surrounding the Earth,
the Van Allen Belts, would be an optimal place to put
orbiting telecommunications satellites, Horton says.
Unfortunately, it’s the worst environment for a satellite.
The radiation there can be 100 times stronger than that
found in geosynchronous orbit, where most satellites operate.

“It takes less fuel to launch a satellite into the Van
Allen Belt region since that area is not as far away as
geosynchronous orbit, so satellites in that closer orbit
would improve on the time it takes signals to be transmitted
around the world,” Horton says. “Using our radiation-hard
technology, satellites could be used closer to the Van Allen
Belt. Also, if this technology were to be used in
geosynchronous satellites, they still would operate at higher
efficiency over a longer period of time that what’s up there
now.”

Freundlich and Horton also are working on a variation of
solar cell technology, called thermophotovoltaics, or TPVs,
which directly convert heat into electricity. While the
concept is not new, the UH researchers say there is a
“renewed interest in an older field.” As an example, the
technology could be used to power deep space exploration
spacecraft in conjunction with a radioactive source to
generate the necessary heat.

The UH scientists are using nanotechnology to change the
structure of existing TPV materials in a way that extends
the amount of infrared radiation the device can convert to
electricity. This modification allows the UH materials to
operate at much higher efficiencies and lower temperatures
than existing TPV technologies.

Because the UH TPVs are much more efficient than those
currently used in the space program, the technology may
increase the longevity and range of deep-space missions,
Horton says.

“The temperature of the heat source for our material needs
to be about 900 to 1000 degrees Celsius to generate useful
electricity. It doesn’t matter what the source of the heat
is,” Horton says. “Using this technology to capture the
heat generated at the heart of the coals in your barbeque
grill, at about 800 to 900 degrees, you could generate
enough electricity to run kitchen appliances. These devices
could operate using the excess heat produced by boilers in
power plants, for example. The energy that is currently
wasted could be recuperated.”

The UH innovations in TPVs also could be used to create
cleaner-burning car engines.

“A car utilizing this technology would still burn gasoline,
but would be powered by TPV-generated electricity,”
Freundlich says. “Because the gasoline would burn and not
explode as in a conventional engine, the gasoline would
burn more efficiently and burn completely, thus producing
much less harmful emissions. Such a car would use less
gas, and you can still use gas stations.”

Also, because the TPVs absorb the infrared radiation from
the engine, the vehicle would be invisible to night
vision, which could be important for military operations,
Freundlich says.

NASA, the state of Texas and private industry have funded
Horton’s and Freundlich’s research.

About the University of Houston

The University of Houston, Texas’ premier metropolitan
research and teaching institution, is home to more than 40
research centers and institutes and sponsors more than 300
partnerships with corporate, civic and governmental
entities. UH, the most diverse research university in the
country, stands at the forefront of education, research
and service with more than 34,400 students.

NOTE TO JOURNALISTS: A publication-quality photo of UH
researchers with a solar cell device is available at
http://www.uh.edu/newsroom/wsc2002/wscfreundlichnhorton102002.html