Environmental Engineering Reference
In-Depth Information
Science: Using Solar Energy to Generate High-
Temperature Heat and Electricity
Large arrays of solar collectors in sunny deserts can
produce high-temperature heat to spin turbines and
produce electricity, but costs are high.
Several
solar thermal systems
can collect and transform
radiant energy from the sun into high-temperature
thermal energy (heat), which can then be used directly
or converted to electricity. These approaches are used
mostly in desert areas with ample sunlight. Figure 13-32
lists the advantages and disadvantages of concentrat-
ing solar energy to produce high-temperature heat or
electricity.
One method uses a
central receiver system,
called a
power tower.
Huge arrays of computer-controlled mir-
rors called
heliostats
track the sun and focus sunlight
on a central heat collection tower (top drawing in Fig-
ure 13-32).
Another approach is a
solar thermal plant,
in which
sunlight is collected and focused on oil-filled pipes
running through the middle of a large area of curved
solar collectors (bottom drawing in Figure 13-32). This
concentrated sunlight can generate temperatures high
enough to produce steam for running turbines and
Direct Gain
Ceiling and north wall
heavily insulated
Summer
sun
Hot air
Super-
insulated
windows
Warm
air
Winter
sun
Cool air
Earth tubes
Greenhouse, Sunspace, or
Attached Solarium
Summer cooling vent
Warm air
Insulated
windows
Cool air
Earth Sheltered
T rade-Offs
Passive or Active Solar Heating
Reinforced concrete,
carefully waterproofed
walls and roof
Triple-paned or
superwindows
Advantages
Disadvantages
Earth
Energy is free
Need access to sun
60% of time
Flagstone floor
for heat storage
Net energy is
moderate
(active) to high
(passive)
Blockage of sun
access by other
structures
Figure 13-30
Solutions:
three examples of
passive solar
design
for houses.
Quick installation
No CO
2
emissions
Need heat storage
system
Another option is to place plastic
earth tubes
un-
derground where the earth is cool year-round. In this
geothermal cooling system, a tiny fan can pipe cool
and partially dehumidified air into an energy-efficient
house (Figure 13-30, top).* In warm climates, you can
also use high-efficiency heat pumps for air condition-
ing. Toronto, Canada's largest city, cools downtown
buildings by pumping cold water from the depths of
Lake Ontario and passing it through building air con-
ditioning systems.
Very low air and
water pollution
High cost (active)
Very low land
disturbance
(built into roof or
window)
Active system needs
maintenance and
repair
Active collectors
unattractive
Moderate cost (passive)
Figure 13-31
Trade-offs:
advantages and disadvantages of
heating a house with passive or active solar energy.
Critical
thinking: pick the single advantage and the single disadvan-
tage that you think are the most important.
*They work. I used them in a passively heated and cooled office
and home for 15 years. People allergic to pollen and molds
should add an air purification system, but this is also necessary
with a conventional cooling system.
