Robert Cohen
OTEC technology can continuously generate electricity from the solar radiation converted into heat by the earth's major oceans. For this purpose, OTEC power plants employ the temperature differences between warm surface water and cold water pumped from a depth of about 1000 meters. In a "closed cycle" plant, the warm water (via an "evaporator") warms and evaporates a working fluid (probably ammonia). The expanding vapor drives a turbogenerator, and the spent vapor is cooled and liquefied (via a "condenser") by cold seawater, then recirculated. In an "open cycle" plant, seawater is used as the working fluid and is evaporated under a partial vacuum.
Besides removing the daily intermittence of solar radiation, the ocean thermal resource acts as a concentrator of solar radiation in that -- analogous to a hydropower plant -- an OTEC power plant pools the thermal energy collected over extensive ocean areas. OTEC power can be generated on land, transmitted to shore by submarine electrical cable, or be used at sea on plantships for manufacturing energy-intensive fuels (such as hydrogen) or other products. Ultimately, OTEC could become a major energy supplier for a global hydrogen economy.
Attractive early OTEC electrical markets are found in land-based locations where OTEC-derived electricity can be generated on shore and substituted for presently oil-derived electricity. Such U.S. OTEC markets include Guam, Hawaii, Puerto Rico, and the Virgin Islands, and there is a large, near-term OTEC electrical market in many developing countries having access to the major oceans. A Science Applications International Corp. study report by Dunbar (Potential for ocean thermal energy conversion as a renewable energy source for developing nations, 1981) documents many attractive early markets where OTEC-derived electricity could be substituted for presently oil derived electicity or used to expand the electrical supply. That report indicates that there are about 60 developing nations -- including Brazil-- with access to a viable ocean thermal energy resource within their exclusive economic zones. The Dunbar study also identified about 30 territories of developed nations -- such as Puerto Rico, Tahiti, and the Virgin Islands -- which are similarly situated. For each megawatt of existing oil-derived electricity replaced by OTEC generation, about 40 barrels per day of oil would be conserved. An early market penetration of some 50,000 megawatts could be achieved in such locations, amounting to a daily global savings of 2 million barrels of oil. Also, likely coproducts of OTEC plants and of OTEC technology have considerable potential in developing countries. They include coastal cooling, fresh water production, mariculture, solar ponds, and bottoming cycles.
Technological, economic, and institutional aspects of OTEC power plants are described by R. Cohen (Energy from the ocean, Phil. Trans. R. Soc. Lond. A 307, 405-437, 1982). Suitable temperature differences are widely available in tropical and sub-tropical regions, thus offering a very large resource base. The paper describes how ultimately, OTEC-derived energy-intensive products -- such as hydrogen -- have the potential for supplying a considerable fraction of global energy needs. Economically viable commercial OTEC power plants are projected to lie in the range of 5 MWe to 500 MWe.
Several industrial nations (the United States, Japan, and France) have invested to date about $250 million in OTEC research and development. This know-how is in the form of study reports, individual experience, and hardware resulting from an extensive and intensive activity by many organizations in industry, government laboratories, and elsewhere. Expertise regarding OTEC technology is available from those countries for transfer to developing nations that can exploit the ocean thermal resource and thereby reduce their oil consumption and environmental degradation. Some of the relevant legal, institutional and financial aspects of OTEC have been examined in a study by the American Society of International Law (Ocean thermal energy conversion -- legal, political and institutional aspects, ASIL, Lexington Books, 1977).
Although OTEC systems have not yet reached a commercial stage, closed-cycle components and sub-systems are readily available at known costs and limited risk, as are the technologies for deriving coproducts (such as fresh water production, coastal cooling, and mariculture) needed for making a prototype 5 MWe OTEC system economically viable, assuming 50-50 cost sharing. OTEC-related "bottoming cycles" can extract up to about 10% additional electrical energy from the warm-water effluents of existing fossil and nuclear power plants.
In the following sections, FY'93, FY'94, and FY'95 funding levels are recommended for a revitalized U.S. ocean energy program. There are four ocean energy resources other than the ocean thermal resource; they are waves, tides, currents, and salinity gradients. Tides have relatively modest global resource potential compared to the others, and the technology to harness tides is relatively well known. However, there are significant domestic and global resources in the other three areas and some promising federal studies to develop technologies to harness those resources were conducted in the late 1970s. Accordingly, a revived research and development program on technology and resource assessment relating to waves, currents, and salinity gradients is recommended and included in the last section.
DOE This recommendation
FY92 FY93 FY93 FY94 FY95
$0.0 0.0 2.0 8.0 17.0
This federal funding would provide a 50-50 cost-sharing demonstration to develop a prototype, closed-cycle, land-based, 5 MWe OTEC commercial electric plant sited in a U.S. state or territory such as Guam, Hawaii, Puerto Rico, or the Virgin Islands. Such a plant is estimated to cost a total of about $50 million. Plant output would include one or more coproducts such as fresh water, coastal cooling, and mariculture. This system size would be sufficient to be economic and to project credible cost/performance estimates for larger commercial systems, and the project would provide an attractive opportunity environment in which industry would share the technical and economic risks. Industry would be attracted to this project by the large potential electrical market in many developing countries where OTEC-derived electricity would substitute for presently oil derived electricity.
2) OTEC Bottoming Cycles DOE This recommendation
FY92 FY93 FY93 FY94 FY95
$0.0 0.0 1.0 3.0 6.0
Develop OTEC systems to extract about 10% more electrical energy from existing thermal power plants (coal and nuclear) by using their warm-water effluents. Costs to be shared 50-50 with the power producer.
3) OTEC Coastal Cooling Systems DOE This recommendation
FY92 FY93 FY93 FY94 FY95
$0.0 0.0 1.0 3.0 6.0
Develop OTEC coastal cooling systems that pump cold ocean water to greatly reduce electricity presently used for air conditioning coastal buildings (such as resort hotels and commercial structures). Costs to be shared 50-50 with the building owners.
RESEARCH ON COST-EFFECTIVE OTEC COMPONENTS AND SUBSYSTEMS
R&D on OTEC Components & Subsystems DOE This recommendation
FY92 FY93 FY93 FY94 FY95
$0.0 0.0 1.0 2.0 4.0
These funds would support research on improved cold-water pipe design and deployment; development of improved designs, techniques, and analyses for achieving efficient heat transfer; research on turbine-powered water pumps and open-cycle turbines; environmental studies, including fluid-dynamical modelling of optimum discharge of warm and cold water effluents; and resource assessment for ocean thermal and coastal cooling applications.
R&D ON ALTERNATIVE OTEC POWER SYSTEMS
R&D on Alternative OTEC Power Systems DOE This recommendation
FY92 FY93 FY93 FY94 FY95
$2.0 0.0 1.0 2.0 4.0
Systems analyses on alternative OTEC power system concepts, such as the open cycle and steam lift pumps, including experimentation using seawater.
R&D ON WAVES, CURRENTS, AND SALINITY GRADIENTS
R&D on Energy from Waves, Currents, DOE This recommendation
and Salinity Gradients FY92 FY93 FY93 FY94 FY95
$0.0 0.0 1.0 3.0 5.0
Resource and environmental assessment and research on technologies to harness waves, currents, and salinity gradients.
TOTAL OCEAN ENERGY FUNDING DOE This recommendation
FY92 FY93 FY93 FY94 FY95
$2.0 0.0 7.0 21.0 42.0
* * * * * * *
NOTE: The same revitalized ocean energy R&D program was also recommended to Secretary Hazel R. O'Leary in the following fax message:
July 22, 1993
Madam Secretary:
This is to call your attention to the need to correct a serious oversight in DOE's FY'94 budget request; namely, the absence of proposed funding for the ocean energy program area.
I'm in a position to provide a relatively unique perspective on this subject, since I changed careers in 1973 and joined the budding federal solar energy program, where I was assigned to organize the original ocean energy program. Subsequent to taking early retirement from DOE in 1981 I worked in the private sector on OTEC studies sponsored by Alcan International and by the Taiwan Power Company. From 1985-1990 I was a Senior Program Officer at the Energy Engineering Board of the National Academy of Sciences, working on energy-policy studies.
In my opinion, a revitalized ocean energy program is desirable from all of the standpoints you advocate:
In particular, the United States should not overlook the development of ocean thermal energy conversion (OTEC) technology, which is one of only several candidates for ultimately becoming a major global energy source. Meanwhile, there are promising near-term OTEC markets in many developing countries where oil is being used to generate electricity and where OTEC can become an economic substitute. Further, U.S. development of OTEC technology will provide us an export technology to help satisfy the demand abroad. There are similar near-term markets in U.S. island locations. From the standpoint of mitigating adverse global climate change, note that closed-cycle OTEC plants can be operated using ammonia as a working fluid and without liberation of carbon dioxide.
Attached is a proposed budget for the sort of revitalized ocean energy program that I recommend for your consideration. Note that in the late 70s the annual federal ocean energy budget reached about $40 million.
Sincerely,
Robert Cohen
Attachment: Recommended Ocean Energy funding levels by line item