Page 608 - Environment: The Science Behind the Stories

Curved reflectors heat Each curved Curved mirrors reflect Field of heliostats focus
liquid in horizontal reflector light onto absorber tube light on central power
tubes focuses light tower
on its own
small receiver
(b) Four methods of concentrating solar power

(a) Solar cooker in India

Figure 21.8 By concentrating solar
energy, we can provide heat and
electricity. Solar cookers (a) focus
solar radiation to cook food. Utilities
concentrate solar power with several
approaches (b) to generate electric-
ity at large scales. At the Solar Two
facility in the southern California desert
(c), hundreds of mirrors reflect sunlight
onto a central receiver atop a power
tower, producing electricity for 10,000
households. (c) The Solar Two power tower facility in California

Concentrating solar rays magnifies energy create electricity. CSP facilities can harness light from lenses
or mirrors spread across large areas of land, and the lenses or
As any mischievous young boy who has killed ants with a mirrors may move to track the sun’s movement.
magnifying glass knows, we can intensify solar energy by CSP facilities need to be located in sunny areas, but they
gathering sunlight from a wide area and focusing it on a sin- have great potential. The International Energy Agency esti-
gle point. This is the principle behind solar cookers, simple mates that just 260 km (100 mi ) of Nevada desert could
2
2
portable ovens that use reflectors to focus sunlight onto food generate enough electricity to power the entire U.S. economy.
and cook it (Figure 21.8a). Such cookers are proving extremely Another study estimated that CSP could fulfill one-quarter of
useful in the developing world. global electricity demand by 2050 if we step up investment. CHAPTER 21 • N E w R ENE wA bl E E NER gy AlTERN AT iv E s
At much larger scales, utilities are using the principle German industrialists and investors have spearheaded an ambi-
behind solar cookers to generate electricity. Concentrated tious effort to create an immense CSP facility in Africa’s Sahara
solar power (CsP) is being harnessed by several methods Desert. In this planned $775-billion project, called Desertec,
(Figure 21.8b) in sunny regions in Spain, the U.S. Southwest, thousands of mirrors spread across vast areas of desert in
and elsewhere. The dominant technology so far is the para- Morocco would harness the Sahara’s sunlight and transmit
bolic trough approach (leftmost diagram in Figure 21.8b), electricity to Europe, the Middle East, and North Africa. Crit-
in which curved mirrors focus sunlight onto synthetic oil in ics of the project—including Hermann Scheer—say it would
pipes. The superheated oil is piped to an adjacent facility be vulnerable to sandstorms and political disputes and would
where it creates steam that drives turbines to generate electric- be less reliable and more expensive than the decentralized pro-
ity. In another approach, numerous mirrors concentrate sun- duction from rooftop panels that feed-in tariffs are promoting
light onto a receiver atop a tall “power tower” (Figure 21.8c). in Europe. Moreover, many people are growing wary of the
From this central receiver, heat is transported by air or fluids environmental impacts that such large-scale developments
(often molten salts) and piped to a steam-driven generator to may pose (see THe SCieNCe BeHiND THe STOrY, pp. 610–611). 607

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