464 CHAPTER 18 Renewable Energy Resources
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Indirect Solar Energy 450- Biomass is plant and animal material used as fuel. Biomass fuel—
materials such as wood, fast-growing plant and algal crops, crop
wastes, sawdust and wood chips, and animal wastes—is burned
to release energy. Biomass fuels can be solid, liquid, or gas. - Wind energy is electric energy obtained from surface air currents
caused by the solar warming of air. Restricted primarily to areas
with consistent winds, wind power is a clean and cost-effective
source of energy. Wind turbines can kill birds and bats, and some
people find their appearance unpleasant. Hydropower is a form
of renewable energy that relies on flowing or falling water to
generate electricity. Hydropower is highly efficient, but the dams
built in traditional hydropower projects can greatly disrupt the
natural environment and displace local residents.
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Other Renewable Energy Sources 456- Geothermal energy is the use of energy from Earth’s
interior for either space heating or generation of electricity.
Deep geothermal energy uses high-temperature heat from
Earth’s interior. Ground-effect heat pumps take advantage of
constant but relatively low temperatures just below Earth’s
surface. Tidal energy is a form of renewable energy that
relies on the ebb and flow of the tides to generate electricity.
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Energy Solutions: Conservation
and Efficiency 458- Energy conservation is using less energy—for example, by
reducing energy use and waste. Energy efficiency is using
less energy to accomplish a given task—for example, with
new technology. Examples of energy conservation measures
that reduce gasoline consumption include carpooling and
lowering driving speeds; energy efficiency measures include
designing and manufacturing more fuel-efficient automobiles. - Households can conserve energy in many ways, including by
keeping vents and refrigerator coils clean, replacing inefficient
light bulbs and appliances, and adjusting thermostats.
Summary
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Direct Solar Energy 444- An active solar heating system collects solar energy and
then relies on pumps or fans to distribute heat. Passive solar
heating systems distribute heat using mechanical devices. - A photovoltaic (PV) solar cell is a wafer or thin film of solid-
state materials, such as silicon or gallium arsenide, that is
treated with certain metals in such a way that it generates
electricity when solar energy is absorbed. Manufacturing PVs
requires toxic industrial chemicals, but PVs generate electricity
with no pollution and minimal maintenance. PVs are limited
by their low efficiency and by the amount of land needed for
their large-scale use. The cost of PV’s is much lower than it
was three decades ago and continues to fall. Solar thermal
electric generation is a means of producing electricity in
which the sun’s energy is concentrated by mirrors or lenses
onto a fluid-filled pipe; the heated fluid is used to generate
electricity. Solar thermal energy systems are efficient and
provide significant environmental benefits; but they are only
now becoming more cost-competitive with fossil fuels. - Fuel cells convert chemical energy into electricity; a fuel cell
requires hydrogen fuel and oxygen (from the air).
Key Terms
active solar heating 444
biomass 450
cogeneration (CHP) 460
energy conservation 458
energy efficiency 458
fuel cell 449
geothermal energy 456
hydropower 454passive solar heating 445
photovoltaic (PV) solar cell 445
solar thermal electric generation 447
wind energy 452James P. Blair/NG Image Collection✓✓THE PLANNER