Sea’s got the power – Alternative Energy

Sea’s got the power – Alternative Energy – Special Earth Day Action Issue: Make Waves

Ben P. Stein

Someday soon you may light up your life with energy from the sea. To make it happen, scientists are tapping the plentiful, hot-n-cold seawater of the tropics.

Few coastal spots in the United States receive more sunshine than Keahole (KAY-ah-HO-lay) Point. Located onm the westernmost edge of Hawaii’s largest island, Keahole is not only a beachgoer’s dream. To some scientists, it’s an ideal spot to make “clean” energy. Each day, the tropical seas surrounding Hawaii’s Keahole Point absorb vast amounts of heat energy for the sun. Scientists at Keahole’s Natural Energy Laboratory of Hawaii (NELH) are using the heated water, taken from the ocean surface, and much cold water form the deep sea nelow, to make electricity. Theyc all their method OTEC, short for ocean thermal energy consersion. With today’s technology, the scientists say, OTEC can be expanded to generate all the electricity the world needs–with little or no pollution.


Whenever you flip on the lights or turn on your TV, you’re using electricity. Most comes from power plants that burn fossil fuels, such as oil and coal. But Earth’s supplies of oil and coal won’t last forever. Some experts predict that we may run out in the next few hundred years. Anither drawback: Burning these fuels to generate electricity produces pollutants that lead to acid rain and possibly global warming. So scientists are looking for alternative energies–ones that are clean and won’t run out.

It’s hard to think of anything more abundant than ocean water, which covers two-thirds of Earth’s surface. And the water that runs an OTEC plant is never used up. It’s continually recycled. The best part: Once some outside electricity gets the OTEC machinery started, the electricity produced by the ocean water keeps it running.

Check out the diagram above to see how the Hawaii plant works, First, pipes collect water form two ocean depths: one near the surface, where the water can be as warm as 27 [degrees] C (about 80 [degrees] F, bath water); the other 600m below, where the water is a chilly 6 [degrees] C (43 [degree F).

The warm water enters a vacuum chamber, where the air pressure is very low. The drop in pressure lowers the water’s boiling point from 100 [degrees] C (212 [degrees] F) to about 27 [degrees] C (80 [degrees] F). So the warm water at the surface boils and turns to steam.

The steam then passes through a turbogenerator, spinning its fanlike blades. The generator converts the spinning mechanical energy to electrical energy. The electricity can then be sent through power lines to light up buildings and homes.

The leftover steam enters two condensing chambers cooled by the cold water pipes. As the steam’s temperature drops, it condense back to liquid form and is discharged.


Hawaii’s small experimental OTEC plant cranks out more than 200,000 watts of electricity, says Tom Daniel, chief scientist at NELH. That’s enough to power more than 600 color TVs at a time. Substract the power needed to keep the plant running, and you still have enough lefts to run some 150 TVs. Scientists are now designing a larger OTEC plant that can produce one million watts of total energy. Such plants, says Daniel, could suppy power to several hundred tropical coastal locations that now depend on costly oil imports for energy.

And if OTEC plants were put on enough ships throughout the world’s oceans, he adds, they could produce 10 terawatts (or [10.sub.13] watts) of energy–enought power to supply the entire world.

And added benefit: The cold seawater that runs through OTEC can be used for a variety of other projects, including air-conditioning, agriculture, seafarms, and gardens.


Yet, cool as it sounds, OTEC does have some drawbacks. Like many other alternative energy projects, says Nelson Ho, chairperson of the Sierra Club’s Hawaii chapter, OTEC may look harmless when tried at one small experimental plant. But when you expand the technology for large-scale use, unexpected problems can appear.

For instance, after cold water runs through one OTEC cycle, it is warmed to about 10 [degrees] C–too warm to be reuse in the other OTEC process, but colder than Hawaii’s tropical surface waters. Returning this cold water (25,00 liters per minute in Hawaii to the coastal surface could harm some sea creatures. Tropical corals, for instance, die off quickly below 18 [degrees] C NELH’s Daniel admits.

Another concern is that the cold deep-sea water is very rich in dissolved nutrients. Says Daniel, “That could cause lots of algae to grow at the surface” because the nutrients act as fertilizer for these microscopic plant-like organisms. An increase in algae could use up the water’s oxygen supply and kill fish.

Finally, there’s the cost. Much of OTEC’s machinery including the massive pipes that collect deep-sea water, is very expensive. The OTEC technology may turn out to be too costly for those less-developed tropical countries most likely to benefit from it.

So before OTEC becomes a reality, there’s a lot more work to be done: studying its ecological effects and looking at ways to cut cost, for instance. In the meantime, we should explore other energy alternatives, including solar, wind, and geothermal power (see SW 11/5/93, p. 14). Even more important, says the Sierra Club’s Ho, we should find ways to conserve energy (see p. 23). That means using less hot water, cutting down air conditioner use, and maybe even air-drying your hair. And when you’re finished reading this magazine, don’t forget to turn off the lights.

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