Environmental Engineering Reference
In-Depth Information
global warming because it does not emit CO
2
—as long
as the hydrogen is not produced from fossil fuels or
other carbon-containing compounds.
So what is the catch? Three problems arise in turn-
ing the vision of widespread use of hydrogen as a fuel
into reality.
First,
hydrogen is chemically locked up in
water and in organic compounds such as methane and
gasoline.
Second,
it takes energy and money to produce
hydrogen from water and organic compounds. In
other words,
hydrogen is not a source of energy—it is a
fuel produced by using energy. Third,
fuel cells are the
best way to use hydrogen to produce electricity, but
current versions are expensive.
T rade-Offs
Geothermal Energy
Advantages
Disadvantages
Very high efficiency
Scarcity of
suitable sites
Moderate net
energy at
accessible sites
Depleted if used
too rapidly
Lower CO
2
emissions than
fossil fuels
CO
2
emissions
Moderate to high
local air pollution
Low cost at
favorable sites
Noise and odor
(H
2
S)
T rade-Offs
Low land use
Hydrogen
Low land disturbance
Cost too high
except at the most
concentrated and
accessible sources
Moderate
environmental impact
Advantages
Disadvantages
Can be produced
from plentiful
water
Not found in nature
Figure 13-44
Trade-offs:
advantages and disadvantages of
using geothermal energy for space heating and to produce
electricity or high-temperature heat for industrial processes.
Critical thinking: pick the single advantage and the single dis-
advantage that you think are the most important.
Energy is needed
to produce fuel
Low
environmental
impact
Negative net energy
Renewable if
produced from
renewable energy
resources
CO
2
emissions if
produced from
carbon-containing
compounds
x
H
OW
W
OULD
Y
OU
V
OTE
?
Should we greatly increase our
dependence on geothermal energy to provide heat and to
produce electricity? Cast your vote online at http://biology
.brookscole.com/miller11.
No CO
2
emissions if
produced from
water
Nonrenewable if
generated by
fossil fuels
or nuclear power
Good substitute
for oil
High costs (but may
eventually come
down)
13-7
HYDROGEN
Competitive price
if environmental
and social costs
are included in cost
comparisons
Science: Can Hydrogen Replace Oil?
Some energy analysts view hydrogen gas as the
best fuel to replace oil during the last half of this
century.
When oil is gone or when the remaining oil costs too
much to use, how will we fuel our vehicles, industry,
and buildings? Many scientists and executives of ma-
jor oil companies and automobile companies say the
fuel of the future is hydrogen gas (H
2
). Figure 13-45
lists the advantages and disadvantages of using hy-
drogen as an energy resource.
When hydrogen gas burns in air or in fuel cells, it
combines with oxygen gas in the air to produce non-
polluting water vapor. Widespread use of hydrogen as
a fuel would eliminate most of our current air pol-
lution problems and greatly reduce the threats from
Will take 25 to 50
years to phase in
Easier to store than
electricity
Short driving
range for current
fuel-cell cars
Safer than
gasoline and
natural gas
No fuel distribution
system in place
Nontoxic
Excessive H
2
leaks
may deplete ozone
in the atmosphere
High efficiency
(45-65%) in fuel cells
Figure 13-45
Trade-offs:
advantages and disadvantages of
using hydrogen as a fuel for vehicles and for providing heat and
electricity.
Critical thinking: pick the single advantage and the
single disadvantage that you think are the most important.
