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BOUNTY FROM THE SEA |
John Pina Craven is escorting a public television crew around what he calls his garden of delights. "What we have here is the capacity to change nature," he proclaims. Bounding through the garden with the energy of a man half his 71 years, he shows off lustrous eggplants, giant garlic, bulging zucchini and voluptuous crimson tomatoes. "We've grown more than a hundred varieties of vegetables, herbs, fruits and flowers here," he says. "And just taste these strawberries!" Grinning, he plucks a luscious sample for each visitor.
Craven has brought forth this cornucopia in an area that seems incapable of sustaining scrub brush, let alone a plethora of beautiful crops. Situated in a desert on the Big Island of Hawaii, the garden is shoe-horned between the Pacific Ocean on one side and an utterly barren expanse of hardened lava on the other. Almost nothing lives on the lava flows, which look like sheets of shattered black glass. This is obviously no ordinary garden. And Craven is no ordinary gardener.
He is, in fact, a lawyer, ocean engineer and former chief scientist for the U.S. Navy. He is also the founder of the Natural Energy Lab of Hawaii. It is here at the lab that Craven has created his garden of delights. The secret to its success - the "capacity to change nature" - lies not far offshore. Cold Pacific seawater, pumped up from a depth of about 2,000 feet, runs through plastic pipes laid in the garden rows, chilling the soil and fooling the temperate plants into performing as if they're in Illinois or California while they bask in the year-round, tropical sunlight. Moisture from the hot, humid air condenses on the pipes and irrigates the plants, drip by steady drip.
Between the sea and the garden, the chilly water participates in another feat: the production of electrical power. By a process known as ocean thermal energy conversion, or OTEC, warm seawater piped to a power plant produces steam that drives a turbogenerator to produce electricity. The piped-in cold water then recondenses the steam and afterwards is available for other uses - like cooling and watering the roots of strawberries and other crops.
OTEC has been under development here at Keahole Point for more than 20 years. It has cleared significant technological hurdles, and its supporters now say it has proved to be a viable, though not yet commercially competitive, alternative energy source. Along the way an array of unexpected spin-off benefits has evolved, including air conditioning, fresh water production, aquaculture and cold-water agriculture. The possibility of converting the vast store of energy in the oceans into usable power has inspired global-scale dreams. Some promoters of ocean energy envision shore-based OTEC plants throughout the tropics, producing power and water for rapidly growing coastal populations. Other visionaries see the beginnings of a new energy economy in a flotilla of floating OTEC plants that could use their electrical output to produce fuels such as methanol, ammonia and liquid hydrogen, helping to liberate the world from dependence on fossil fuels.
But Craven is fixed on the present: He believes that the spin-off uses of deep, cold seawater are available right now for small-scale sustainable development, especially in Third World tropical countries. "All you really need to get it going," he says, "is a pipe, a pump, and a pond. "
Ironically, Craven's small-is-beautiful ethic has been honed from a lifetime of work on much bigger projects, all involving ocean technology. During a 20-year civilian science career with the U. S. Navy, he worked on such projects as the Polaris missile, the first nuclear-powered submarine and the Man in the Sea program, in which researchers conducted experiments in manned underwater labs. He also helped draft the first arms control treaty between the United States and Soviet Union; supervised development of deep-sea vehicles for search, rescue and salvage; and assisted in the recovery of both a hydrogen bomb lost by the United States and a U.S. nuclear submarine that had sunk.
When the era of big budgets for naval oceanographic research and development ended in the late 1960s, Craven left the Navy and headed for Hawaii. Appointed dean of marine programs at the University of Hawaii and marine affairs coordinator for the governor's office, he became the state's czar of ocean technology.
The foreign oil crisis of the 1970s was then in full swing, spurring development of alternative energy sources. Hawaii, which depended on imported oil for about 90 percent of its energy needs, had much to gain by getting into the act. Craven became interested in OTEC when two University of Hawaii researchers proposed to resurrect a scheme for ocean thermal energy conversion that had been tested in Cuba in 1930 by French engineer Georges Claude. Craven told them to find the best site in Hawaii. They chose undeveloped Keahole Point because its steep drop-off close to shore was ideal for bringing cold water up from the depths. Then, in 1974, Craven convinced the state to establish the Natural Energy Laboratory of Hawaii there.
In its essence, OTEC is a way of using solar energy collected by the surface waters of the tropical oceans as they are heated by the rays of the sun. The amount of energy collected by the tropical oceans is unimaginably huge, far greater than the energy needed to fuel civilization. "If you put floating OTEC plants on the oceans and extract all the energy possible, without changing ocean temperatures more than one degree Fahrenheit, you could extract about 10 to the 13th power watts of electricity," says oceanographer Tom Daniel, science director at the energy lab. "That's enough to supply all of humankind's current energy needs," he says. "None of the alternatives - not wind power, not wave energy, nor photovoltaics - can compete." Moreover, the ocean is an energy storage system that's available 24 hours a day.
Lured by an energy source that just keeps going and going, engineers and scientists at the natural energy lab plunged into OTEC research and development, primarily to ease Hawaii's oil addiction and, secondarily, for eventual commercial export. To make an OTEC plant work, there must be at least a 68-degree temperature difference between surface and deep ocean water. That difference is available within 25 degrees of latitude of the equator, so OTEC could be developed around the Gulf of Mexico, many island nations and coastal areas of Central and South America, Africa, and Asia.
OTEC is actually a remarkably simple in concept. There are two basic systems: an open-cycle and a closed-cycle. In an open-cycle system, warm surface water is drawn into a vacuum chamber. Under low pressure in the chamber, the seawater, which is at about 77 degrees, boils and vaporizes into steam. The steam then turns the turbine's blades of a generator to make electricity. Cold water drawn into the plant from the depths of the ocean is fed into a condenser, where it turns the steam back into water. This condensed water has been distilled in the process, which means that it's free of salt and other impurities. In other words, one side benefit of the open-cycle system is desalinated water, which can be used for drinking. Meanwhile, the cold water that was used to condense the steam is available for other purposes. One example is the cold-water agriculture of Craven's garden. The cold water can also be channeled into aquaculture ponds where fish, seaweed and a host of other commercial products can be raised.
The closed-cycle system differs from its open-cycle sibling in that the warm ocean water is not used directly to power the generator. Instead, it is used to vaporize another fluid, such as ammonia. No vacuum chamber is needed, because at atmospheric pressures, ammonia vaporizes at relatively low temperature. The fast-moving vapor turns the generator to make electricity, and is then cooled and converted back into a liquid by the cold seawater circulating through the condenser. In 1979, the energy lab launched Mini-OTEC, a closed-cycle system built partly with corporate support. Mounted on an offshore barge, it had a net electrical output of 15 kilowatts - enough to supply power to five to 10 homes. This was the first OTEC experiment to produce more power than it consumed. (Electricity is required to operate the pumps that draw the water from the ocean.) The following year the U.S. Department of Energy launched OTEC 1. Based on a Navy tanker off the west coast of the Big Island of Hawaii, this plant tested components for both closed-cycle and open-cycle systems. Soon afterward a Japanese electric utility produced net power with a land-based, closed-cycle OTEC plant on the South Pacific island of Nauru, until a typhoon damaged the facility in 1982.
Proving the feasibility of OTEC was one thing, but designing and building a land-based system with a steady, respectable power output was quite another. The science of OTEC is not overly complex. But due to the inherent low efficiency of the process, enormous volumes of water are required to generate profitable amounts of power. This means mega-sized pumps, pipelines, heat exchangers and other components to accommodate all that water. It also means that all of the parts must operate at peak efficiency. As a result, much of the last 20 years at the energy lab has been dedicated to increasing the efficiency of the technology.
Finding the best method of installing OTEC's arteries, the seawater pipelines, was a big challenge. At first, small pipelines were draped over the shoreline to bring in the water. When the lab's needs expanded, requiring intake of greater quantities of water, engineers blasted trenches in the lava shoreline to hold pipelines up to 40 inches in diameter. Since 1988, two of these pipelines have been sucking up a total of 11,300 gallons per minute of warm surface water. Meanwhile, cold-water pipes more than 7,000 feet long deliver up to 17,100 gallons per minute from a depth of 2,000 feet. A pipeline system now under construction will more than double the seawater intake at the energy lab, bringing in enough to run a one-megawatt OTEC plant. A commercial-scale plant, however, would need to be on the order of 50 to 100 megawatts. A 100 megawatt plant would use up to 10 million gallons of cold water per minute and a similar quantity of warm water. The cold water pipeline would have to be about 33 feet in diameter.
If seawater is the blood of an OTEC plant, then evaporators and condensers are its lungs. Key to efficient performance, these components must be corrosion-resistant and very large by industrial standards. The years-long search for an ideal design and construction material has recently produced a breakthrough that will significantly cut expenses: aluminum evaporators and condensers that cost about 85 percent less than the original titanium prototypes. (A 100-megawatt OTEC plant using titanium evaporators and condensers would require one-quarter of the U.S. annual consumption of the rare metal, and would likely be far too expensive to operate profitably.)
The engineers also faced another serious problem: the coating of heat-exchanger parts by microscopic algae and bacteria from the warm surface water. They solved it by adding a benign amount of chlorine to the warm water flowing into the power plant. While the energy lab was overcoming engineering obstacles, Craven and his colleagues were dreaming up secondary uses for the cold, deep seawater. As Craven tells it, "We started with an experiment to grow the seaweed nori and found that it grew at unbelievable rates," increasing in weight by as much as 55 percent a day. Soon, other aquaculture projects sprang up. Among the list of products that have been raised successfully are kelp, spirulina algae, sea vegetables, mushrooms, abalone, shrimp, lobsters, salmon, flounder, tilapia, cold-water trout, and oysters (both edible and pearl-producing), Many of these have evolved into commercial enterprises, with production facilities using cold seawater on the 800-acre Hawaii Ocean Science and Technology park adjacent to the tab.
These businesses have an unqualified advantage over other aquaculture projects. The deep water is virtually free of bacteria and other pathogens. Moreover, it's rich in dissolved nutrients such as nitrates, silicates and phosphates. As a result, the aquaculturalists at Keahole Point are able to grow uncontaminated cultures and to control precisely the water temperatures in their tanks simply by adding warm or cold seawater.
The chilly water has proven to be "clean, cool cash," as Craven puts it, in other ways as well. In the early 1980s one of the energy lab tenants, tired of sweltering in his office, rigged up an air conditioner using cold seawater and an old car radiator. The idea spread like news of free beer on a crowded beach. Not long thereafter, water from the Pacific depths was providing air conditioning for many of the buildings around the lab.
In conventional air conditioners, a power-hungry compressor is needed to pressurize the refrigerant that does the cooling. With seawater cooling, you don't need a compressor. In the simplest system, cold water is sent through a loop that runs throughout the building, thereby cooling the air directly. The system installed at the energy lab uses about one-fifth the power needed by conventional systems; at larger scales the energy savings could be even greater. Engineers estimate that a cold-water system employing a one-meter diameter pipeline could provide air conditioning to thousands of homes on a hot day, using only 500 watts of electrical power. By comparison, it would take 5 megawatts of power to provide the same amount of cooling using conventional air conditioners. In addition, the use of seawater would reduce the heating of urban environments caused by air conditioners that exhaust warm air into the atmosphere.
Since only cold water is needed, the region of potential application extends far beyond the tropics. "Large areas of the industrial world, such as the West coast of the U.S. could use it to realize huge savings in energy costs, carbon-dioxide generation, and the restoration of the microclimates of major cities," Craven contends.
Of all the promising uses for cold seawater that have emerged at Keahole Point, cold-water agriculture is undoubtedly the most surprising. It started in the mid-1980s. After returning from a trip to Spain, botanist Sanford Siegel, Craven's friend, told him that vineyards there were able to flourish in otherwise barren coastal locations thanks to cold seawater that was percolating up into the fractured rock beneath the soil. Siegel and Craven wondered whether it might be possible to grow temperate crops in the tropics if cold water pipes were placed adjacent to plants or at root depth to induce condensation and create a temperate microclimate. Craven found a researcher, Martin Vitousek, to experiment with a quintessentially temperate food: strawberries.
Vitousek's well-watered but uncooled control plants managed to grow, but their fruit tasted sour. Plants that were drip-irrigated by condensation forming on the cold seawater pipes, however, produced lusciously sweet strawberries. Vitousek turned the project over to Craven, who later left the plants untended for several months. When he returned he found that the seawater-chilled plants were smothering the pipes with new growth.
After additional experiments with lettuce, brussel sprouts and other temperate crops were successful, Craven concluded that it was the temperature difference between root level and the ground surface - about 31 degrees on a hot day - that accounted for the plants' rapid growth and superior flavor. The blazing sun kept the environment hostile to pests, and the few weeds that invaded were weak and shallow-rooted. As a result, pesticides and herbicides weren't needed. The experiments have since blossomed into a cooperative organic gardening project, in which volunteers cultivate more than a hundred plant varieties, growing, in many cases, up to three crops a year.
With the addition of cold-water organic agriculture, OTEC "was starting to look like a total system," Craven says. In 1990 he left his administrative post at the energy lab and soon afterward started the Common Heritage Corporation to promote and market cold seawater systems. Coastal areas of less-developed countries are his prime focus. He is currently advising energy developers in Haiti, Malta, the Cape Verde Islands and a group of South Pacific islands. His vision is to provide energy, fresh water and food to rapidly growing coastal populations. Since Craven's departure, the Natural Energy Lab of Hawaii, long acknowledged as the world headquarters for OTEC development, has been forging ahead on development of ever-larger OTEC facilities. A plant opened in 1994 is now generating as much as 65 kilowatts of net power and producing desalinated water from the plant's steam. A new 50-kilowatt, closed-cycle plant, which will test new aluminum evaporators and condensers, was scheduled to start operating in June 1996. Daniel is helping developers assess potential OTEC sites in Okinawa and the Philippines, and he is fielding inquiries from Madras, India, Taiwan, the Virgin Islands and elsewhere. But despite the advances, it's still an open question as to when OTEC might be ready to plug into the power grid.
OTEC has faced the uphill struggle common to most promising alternative energy schemes: competition with oil. While the oil economy continues to receive government subsidies, OTEC is not receiving as much financial support as it once did. Federal funding became endangered as soon as oil prices stabilized in the late 1970s. The Reagan and Bush administrations routinely scrapped funding for OTEC from their energy budgets. Nevertheless, Congress and the Hawaii legislature have continued to support OTEC on a project-by-project basis, and corporations have also played a role. But Daniel says "there's never been a long-term commitment in funding or a development plan for OTEC, and that's hurt our progress." He points out that in 20 years, only $300 million has been spent on OTEC research. By comparison, he says nuclear fusion research has been funded at much more than $400 million per year.
Without strong potential for profit, banks and utilities are reluctant to fund OTEC research. At today's oil prices, an OTEC plant would take 20 years to break even, and only if it could go without major overhauls, Daniel says. If it lasted 30 years, the plant would provide a 30 percent return on the capital invested. It's not yet clear whether a large plant can go so long without major breakdowns.
Engineers such as Luis Vega, a project director at the energy lab, believes that a 5-megawatt plant operated for five years would provide the kind of solid demonstration that could attract investors for a 50-megawatt plant. At that scale, he believes the profits would flow in. But also at that scale, the economic benefits of the spin-off uses of cold seawater become a proverbial drop in the bucket.
It's this hard reality that appears to separate Craven's vision for self-sufficient, sustainable development from the goal of large-scale OTEC development. (Craven calls it the "PC approach versus the mainframe approach.") And perhaps it comes down to this: Will OTEC, purely as an electrical power source, be developed to serve the energy needs of the industrialized world? Or will energy from the ocean offer an environmentally benign option for less-developed areas to catch up? The best of future worlds just might include both options.
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