Visualizing Environmental Science

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.

1. What is active solar energy? passive solar
   energy?


2. What are the advantages of producing
   electricity by solar thermal energy? using
   hydrogen and photovoltaic (PV) solar cells?


3. 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.