Constraints and Opportunities

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D. 1.3.1 Institutional

No major institutional constraints to the utilization of OTEC have been identified since the technology is still in its early stages. In the long run, unresolved technological issues, such as the distribution of coproducts, may pose significant institutional constraints. Some uncertainties relative to environmental impact and regulatory issues remain because the required quantitative measurements cannot been made before construction of a pre-commercial plant (i.e., 500 kWJ. The primary environmental issues are on the trajectories, dispersion, and dilution of the seawater effluents and the character and quantity of dissolved gases in the seawater. While these potential environmental impacts must be investigated, it is believed that engineering will provide cost-effective solutions. There is a need for quantitative data to assess what control measures may be appropriate.

A financial constraint is the development of a U.S.-OTEC industry capable of meeting the substantial OTEC market potential. The Japanese have formed an OTEC group called the Ocean Thermal Energy Conversion Association (OTECA) precisely to capture this market. Efforts from the United States could be in the form of: accelerated funding for the current federal program to ensure an operating open-cycle OTEC plant by the mid-1990s; construction of a pre-commercial-sized OTEC plant of 1 MWe net; and continued research required to remove the critical technical impediments to the development of larger-sized plants.

Since OTEC is an emerging technology in its early stages, potential infrastructural constraints are yet to be identified. They may include (1) problems of integrating OTEC plants into island electrical systems, particularly if large OTEC plants are required to achieve economic performance; (2) integrating OTEC fresh-water systems into existing systems, while providing maintenance or emergency storage or backup; (3) integrating cooling systems with hotels, etc., while providing backup capacity; and (4) coastal right-of-way access for large water systems, that will distribute water to users, including return flows to the OTEC plants. Environmental issues may also be involved.

Perceptual constraints for the OTEC technology lie in the perceived risks associated with the reliability and long-term operation of the system. To encourage investments on the early development and market penetration of a capital-intensive technology, demonstration of the reliability of OTEC systems over periods comparable to payback periods-10 years or more-may be required. Significant R.R&D expenditures are required over the next decade to address issues related to scaling, operation, reliability, and performance uncertainties in demonstrations of closed-cycle and open-cycle OTEC systems at pre-commercial sizes.

The discussed constraints limit the development of OTEC technology even in regions where it appears to be economically viable today. The dependency of island nations and regions on imported oil may be prolonged with an increased drain on their economies. Alternately, these regions might become more energy self-sufficient within the next two decades using indigenous resources through accelerated development of OTEC. The Japanese program noted above is developing technology to address these markets.

Institutional decisions on meeting demands for other OTEC co-products, such as desalinated water described elsewhere, will enhance the opportunity for OTEC to penetrate baseload power generation applications.

D. 1.3.2 Performance

The major constraint that remains on the performance of OTEC systems is the lack of operational data for energy production. All other constraints or issues can be resolved through the normal engineering design process-no major breakthroughs are required for the first generation of OTEC plants.

An OTEC system may be divided into three major subsystems: power, seawater, and support facilities. The apparent technical uncertainties in scaling the power and seawater subsystems represent major constraints to elevating OTEC to a viable energy production alternative. These two subsystems also offer the greatest opportunity for performance improvement and cost reduction. Advances in these two areas will yield the needed cost reduction in the third major subsystem, plant and structures. Therefore, in parallel with the construction of a demonstration plant for first-generation plants, to improve the competitive position of OTEC, a research and development (R&D) program must be carried out on innovative turbines for open-cycle OTEC to increase the size limit at least tenfold (from 2.5 MW to 25 MW), on cold water pipe materials and construction, on deeply submerged bottom pumps, and on the viability of innovative power cycles.

The design, construction, and operation of demonstration plants targeted to the identified markets should yield the needed operational data and experience toward commercialization. By the year 2015, a cumulative global market of $13 billion (1989$) could result from intensified R,D&D, including the building of demonstration plants.

D.1.3.3 Additional Values of Cold Water

The described markets do not consider other potential uses of the OTEC cold water. Co-products of OTEC offer unique advantages not provided by any other renewable resource. They not only provide an additional revenue stream, but also provide quality-of-life-enhancing aspects.

To improve the overall economics of the total OTEC system, recent development plans include utilizing the nutrient-rich, pathogen-free, cold water from the deep ocean. Products (in addition to electricity and desalinated water) include mariculture, greenhouses with temperatures controlled by cold water, and use of chilled water for air-conditioning. The entire system of co-products from OTEC has been developing at a faster pace than electricity, primarily because the private sector has been able to attract funding to carry out the pre-commercial work. There is great need, however, to package the total system for specific locations, since the quality and value of many of the co-products are site-specific.

Mariculture. The ability to provide flexible, accurate, and consistent temperature control; high-volume flow rates; and nutrient-rich seawater relatively free of biological and chemical contaminants leads to a natural synergism that can be translated into a marketable product. The cold seawater contains 200 times more nitrates and 20 times more phosphates than surface seawater. Marine life already grown in this environment at the Natural Energy Laboratory of Hawaii (NELH) include salmon, trout, nori (seaweed popular in the Japanese diet), opihi, lobsters, abalone, and both macro and micro algae. The values of these products are high enough that the costs of production can be recovered and profitability ensured—even considering the high cost of the deep-ocean pipeline.

Desalinated Water. The condensate from spent steam in OTEC systems is desalinated water suitable for human consumption and agricultural purposes. The market value of this water in the Pacific islands ranges from $0.40 to $1.60/m3. The revenue from desalinated water is projected to offset the cost of OTEC electricity by as much as 120/kWh in South Pacific islands and 30/kWh in Hawaii.

Air-conditioning/Refrigeration. The deep-ocean cold water can be used as a chiller and in air-conditioning systems. The facilities at the NELH are air-conditioned by passing the cold water through a heat exchanger151. The cold seawater delivered to an OTEC plant is suitable for use in chilled water coils to provide building space air-conditioning. For example, cold water from an OTEC electric power plant, when used to provide cooling, displaces more than 10 times its electric capacity for the air-conditioning load.

Agriculture. Another use of cold seawater is to place an array of cold water pipes on the ground to maintain a cool soil temperature. Atmospheric condensate external to the pipes provide continuous drip irrigation for crop growth. This method has been successful in the growth of cool-weather plants such as strawberries and lettuce at the NELH site.

Figure D-2 illustrates the additional values of cold water. The effective cost of electricity is reduced by the revenues from coproducts-desalinated water, mariculture products, and refrigeration. Depending on the extent to which products other than electricity are included, the electricity cost ranges in 1990 from 220 down to 80/kWh. Thus, QTEC combined with coproducts may be cost effective today for certain markets.

Hawaii a. Water cost is $0.50/m3; equivalent to a credit of 2.7?/kWh.

b. Mariculture offsets cold water pumping power to "effectively" increase plant capacity by 10%.

c. Use of cold \(vater for cooling displaces equivalent plant electric generation capacity to "effectively" double plant yield.

a. Water cost is $0.50/m3; equivalent to a credit of 2.7?/kWh.

b. Mariculture offsets cold water pumping power to "effectively" increase plant capacity by 10%.

c. Use of cold \(vater for cooling displaces equivalent plant electric generation capacity to "effectively" double plant yield.

Electricity (10-MWe OTEC plant)

Electricity + Water2

Electricity + Water + Maricultureb

Electricity (10-MWe OTEC plant)

Electricity + Water2

Electricity + Water + Maricultureb

Electricity + Water + Mariculture + Cooiingc i

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