Direct Solar Energy 449
Flow of negatively charged
electrons provides electricity
H 2 2H++ 2e
Air
(oxygen)
Fuel
(hydrogen)
Electrolyte
solution Electrodes
H 2 O
© Kimimasa Mayama/©Corbis
© Kim Kulish/Corbis
Adapted from Henrichs, RA
Energy: Its Use and the
Environment
, 2nd Edition. Philadelphia: Harcourt
publishers (2002).
c. Fuel cells can be
adapted to many
applications.
a. These experimental fuel cells combine hydrogen and oxygen
to create electricity.
b. Cross section of a fuel cell.
whereas hydrogen offers a convenient way to store so-
lar energy as chemical energy. It can be transported
by pipeline, possibly less expensively than electricity is
transported by wire.
Production of hydrogen from PV electricity currently
has a relatively low efficiency (perhaps 10 percent),
which means that very little of the solar energy absorbed
by the PV cells is actually converted into the chemical en-
ergy of hydrogen fuel. Low efficiency translates into high
costs. Scientists are working to improve this efficiency
and make solar-generated hydrogen fuel commercially
viable.
We face other challenges besides high costs if we are
to replace gasoline with hydrogen as a transportation fuel.
First, we would need to develop a complex infrastructure
(such as hydrogen pipelines) to provide hydrogen to ser-
vice stations. Because hydrogen
is extremely volatile, it must be
stored, handled, and transported
very carefully. Another challenge
is developing fuel cells for mo-
tor vehicles that are inexpensive,
safe, and allow the vehicle to
drive a long distance without the
need to refuel.
A fuel cell is an electrochemical cell similar to a bat-
tery (Figure 18.6). Fuel cells represent the most promis-
ing way to use hydrogen.
Whereas batteries store a fixed amount of en-
ergy, fuel cells produce power as long as they are
supplied with fuel. Fuel cells are available to power
everything from cell phones to city buses. While fuel
cells are currently more expensive than other energy
sources, the cost has dropped from $275 per kW ca-
pacity in 2002 to just $51 per kW in 2010. For most
applications (including automobiles) however, they re-
main very expensive.
- What is active solar energy? passive solar
energy? - What are the advantages of producing
electricity by solar thermal energy? using
hydrogen and photovoltaic (PV) solar cells? - How do fuel cells work?
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fuel cell A device
that directly converts
chemical energy into
electricity. A fuel cell
requires hydrogen
and oxygen from
the air.