Page 621 - Environment: The Science Behind the Stories

Basin Ocean
Barrage

Sluice Sluice
gate gate
closed Turbine closed

Basin 1 High tide: Ocean level Basin Ocean
rises while water level
Barrage in basin remains low Barrage
Ocean

Turbine

4 Sluice gates open; 2 Sluice gates open and
water leaves basin Basin water fills basin
and turns turbine
to generate power Barrage Ocean

Sluice Sluice
gate gate
closed closed
Turbine
3 Tide recedes;
water level in basin
remains high

Figure 21.22 We can harness tidal energy by using bulb turbines in concert with the outgoing tide.
At high tide 1 , ocean water is let through the sluice gates, filling an interior basin 2 . At low tide 3 , the basin
water is let out into the ocean, spinning turbines to generate electricity 4 . This technology is used at the new
Sihwa Lake tidal generating station (photo) in South Korea.

vacuum, and its steam turns turbines and then is condensed by Hydrogen
cold water. Because ocean water loses salts as it evaporates,
the water can be recovered, condensed, and sold as desalin- Each of the renewable energy sources we have discussed can be
ized fresh water for drinking or agriculture. OTEC research used to generate electricity more cleanly than can fossil fuels.
has been conducted in Hawaii and elsewhere, but costs remain However, electricity cannot be stored easily in large quantities
high, and so far no facility operates commercially. for use when and where it is needed. This is why most vehicles
rely on gasoline from oil for power. The development of fuel
WEIGHING tHE IssUEs cells and of fuel consisting of hydrogen—the universe’s sim-
plest and most abundant element—shows promise as a way to
yoUR NAtIoN’s ENERGy? You are the president of a nation the store considerable quantities of energy conveniently, cleanly,
size of Germany, and your nation’s congress is calling on you and efficiently. Like electricity and like batteries, hydrogen is
to propose a national energy policy. Your country is located an energy carrier, not a primary energy source. It carries energy
along a tropical coastline. Your geologists do not yet know that can be converted for use at later times and in different
whether there are fossil fuel deposits or geothermal resources places.
under your land, but your country gets a lot of sunlight and a
fair amount of wind, and broad, shallow shelf regions line its
coasts. Your nation’s population is moderately wealthy but is Some yearn for a “hydrogen economy"
growing fast, and importing fossil fuels from other nations is Some energy experts envision that hydrogen fuel, together
becoming expensive. with electricity, could serve as the basis for a clean, safe, and
What approaches would you propose in your energy pol-
icy? Name some specific steps you would urge your congress efficient energy system. In such a system, electricity gener-
ated from intermittent renewable sources, such as wind or
to fund. Are there trade relationships you would seek to estab- solar energy, could be used to produce hydrogen. Fuel cells—
lish with other countries? What questions would you fund your essentially, hydrogen batteries (Figure 21.23)—could then
620 nation’s scientists to research? use hydrogen to produce electrical energy to power vehicles,

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