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All
Charged Up
Fuel
cells fall into five major categories, based on the type of
electrolyte used. Each medium works best at different temperatures,
using various sources of hydrogen, ranging from pure hydrogen
to hydrogen-rich compounds like cooking-oil, wax or alcohol.
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| Helios
in flight. |
At
AeroVironment, Inc., headquartered in Monrovia, CA, mechanical
engineer Catherine Mohr works to design the most appropriate
fuel cell for the company's flying wing called Helios,
The 250-foot-long plane is intended to fly high up in the
Earth's atmosphere for months at a time, replacing costlier,
higher-maintenance satellites circling the planet today.
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"There is no such thing as a free lunch," says mechanical
engineer Catherine Mohr. "That should be the second law
of thermodynamics."
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Such
a vehicle must fly for months without requiring a single re-fueling.
In the case of Helios, solar energy, a fuel cell and a tank
of water are the answer. During the day, solar energy collected
by panels on Helios' wings runs the airplane's electric motors.
But extra energy gathered by the plane's oversized solar panels
is used to separate the stored water into hydrogen and oxygen
gases. Overnight, the fuel cell uses these gases to power
the plane. The resulting wastewater is collected, and the
whole process begins again in the light of dawn.
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| These
solar cells collect the energy that powers the plane during
the day. |
The
configuration works for Helios, but, as Mohr points out, "there
are a lot of trade-offs associated with choosing the right
energy storage and power source for the right application."
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Photo:
AeroVironment, Inc.
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