Page 607 - Environment: The Science Behind the Stories

Solar Energy roofs, and walls, or can be used in portable blocks. Plant-
ing vegetation around a building to buffer the structure from
The sun releases astounding amounts of energy by convert- temperature swings is another passive solar approach. Passive
ing hydrogen to helium through nuclear fusion (p. 574). The solar approaches are an important component of sustainable
tiny proportion of this energy that reaches Earth is enough to buildings (pp. 364–368). By heating buildings in cold weather
drive most processes in the biosphere, helping to make life and cooling them in warm weather, passive solar methods
possible on our planet. Each day, Earth receives enough solar conserve energy and reduce energy costs.
energy, or energy from the sun, to power human consumption Active solar energy collection makes use of devices to Curved reflectors heat Each curved Curved mirrors reflect Field of heliostats focus
for a quarter of a century. On average, each square meter of focus, move, or store solar energy. We can use such technolo- liquid in horizontal reflector light onto absorber tube light on central power
Earth’s surface receives about 1 kilowatt of solar energy—17 gies to heat water and air in our homes and businesses. One tubes focuses light tower
times the energy of a lightbulb. As a result, a typical home has common method involves installing flat plate solar collectors on its own
enough roof area to meet all its power needs with rooftop pan- on rooftops. These panels generally consist of dark-colored, small receiver
els that harness solar energy. However, we are still in the pro- heat-absorbing metal plates mounted in flat glass-covered (b) Four methods of concentrating solar power
cess of developing solar technologies and learning the most boxes. Water, air, or antifreeze runs through tubes that pass
effective and cost-efficient ways to put the sun’s energy to use. through the collectors, transferring heat from the collectors to
the building or its water tank (Figure 21.7). Heated water can
be stored for later use and passed through pipes designed to (a) Solar cooker in India
We can collect solar energy using passive release the heat into the building.
or active methods Over 200 million households worldwide heat water with
solar collectors. Only 1.5 million of these are in the United
The simplest way to harness solar energy is through passive States, and most of these are used for swimming pools. Active
solar energy collection. In this approach, buildings are solar heating is used more widely in China and in Europe,
designed to maximize absorption of sunlight in winter and to where Germans motivated by feed-in tariffs installed 200,000
keep the interior cool in the heat of summer. Installing south- new systems in 2008 alone. Because solar heating systems do
facing windows maximizes the capture of winter sunlight. not need to be connected to an electrical grid, they are useful
Overhangs shade windows in summer, when the sun is high in in isolated locations. In Gaviotas, a remote town on the high
the sky and when cooling, not heating, is desired. plains of Colombia in South America, residents use active
Passive solar techniques also use materials that absorb solar technology for heating, cooling, and water purification.
heat, store it, and release it later. Such thermal mass (of straw, This shows that solar energy need not be confined to wealthy
brick, concrete, or other materials) often makes up floors, communities or to regions that are always sunny.

(c) The Solar Two power tower facility in California
1 Sunlight shines on flat
plate solar collector

4 Flat plate solar collector, warmed
by sun, heats fluid in pipe

5 Heated fluid flows to water
tank, where pipes transfer
heat to water in tank

Flat plate Hot water
solar collector Water to tap Figure 21.7 Solar collectors can
provide heating. Systems for heating
tank 6 Boiler heats water vary in design, but typically
water as 1 sunlight is gathered on a flat
needed when plate solar collector, until a controller
solar energy is
2 switches on a pump 3 to circulate
2 Controller senses Controller not available fluid through pipes to the collector.
when collector is Boiler The sunlit collector heats the fluid
warm enough
4 , which flows through pipes 5 to
a water tank. The hot fluid in the pipes
transfers heat to the water in the tank,
and this heated water is available for
the taps of the home or business.
3 Pump switches on, Pump Cold water Generally an external boiler 6 kicks in
circulating fluid supply to heat water when solar energy is not
606 through system available.

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