444 CHAPTER 18 Renewable Energy ResourcesPROCESS DIAGRAM
- Distinguish between active and passive solar
heating and describe how each is used. - Contrast the advantages and disadvantages
of photovoltaic solar cells and solar thermal
electric generation in converting solar energy
into electricity. - Explain how fuel cells work.
T
he sun produces a tremendous amount of
energy, most of which dissipates into space.
Only a small portion is radiated to Earth.
Solar energy differs from fossil and nuclear
fuels in that it is always available; we will run out of solar
energy only when the sun’s nuclear fire burns out. To
make solar energy useful, we must collect it.Direct Solar Energy
LEARNING OBJECTIVES
In most cases, we must also transform solar energy
from light and heat into other useful forms, usually
electricity or biomass.Heating Buildings and Water
In active solar heating, a series of
collection devices mounted on a
roof or in a field gather solar en-
ergy. The most common solar col-
lection device is a panel or plate
of black metal, which absorbs the
sun’s energy (Figure 18.1). Ac-
tive solar heating is used primar-
ily for heating water, either foractive solar
heating A system
of putting the sun’s
energy to use in
which collectors
absorb solar energy
and pumps or
fans distribute the
collected heat.(^2) Sunlight enters the solar
panels and warms liquid
flowing through pipes to
a heat exchanger.
(^3) Each solar panel is a
box with a black metal
base and glass
covering.
(^4) In the heat exchanger,
the fluid heats water,
which then moves into a
hot water storage tank.
(^5) A backup heater
runs on electricity or
natural gas and
keeps the water hot.
(^1) Solar panels are
mounted on the roof
of a building.
Solar collector
or panel
Pump Heat Pump Backup heater
exchanger
Cold water
in
Hot water
out
Hot water
tank
Where do you use hot water at home?
How is it heated?
Think Critically
444 CHAPTER 18 Renewable Energy Resources
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