Analysis of the OTEC cycle indicates that equatorial OTEC plant ships slowly "grazing" on warm surface water at 1/2 knot could continuously generate more than 5 megawatts-electric (MWe) of net electric power per square kilometer of tropical ocean. The electricity generated would be converted to chemical energy on board the plant ship by electrolyzing water into hydrogen and oxygen. ..... Engineering studies indicate that OTEC plant ships designed to produce 100 to 400 MWe (net) of electricity (which is between 10 and 40 percent of the output of a large conventional power plant) would be the optimum size for commercial operation.
The U.S. Department of Energy (DOE) sponsored engineering designs that were developed between 1975 and 1982 by industrial teams under the technical direction of the Johns Hopkins University Applied Physics Laboratory (APL). Designs are available for a 46-MWe pilot OTEC plant ship that would produce 15 metric tons per day of liquid hydrogen (or 140 metric tons per day of liquid ammonia) in a conventional chemical plant installed on the OTEC vessel. It would use the same synthesis process that produces ammonia on land but would eliminate the costly methane-reforming step of that process.
An APL conceptual design is available for a 365-MWe commercial OTEC plant ship that would produce 1,100 metric tons per day of liquid ammonia. Used as a motor vehicle fuel, this could replace approximately 150,000 gallons of gasoline. If operating experience confirms the utility of this conceptual design, 2,000 OTEC ammonia plant ships could supply enough ammonia fuel per day to match the total daily mileage of all the automobiles presently in the United States. If these plant ships were distributed uniformly over the tropical ocean, an area of about 60 million square kilometers, they would be spaced 175 kilometers apart
Competitiveness and financing. OTEC systems are "low" technology. Operating temperatures and pressures are the same as those in household air conditioners. About two-thirds of the required OTEC system components and subsystems are commercially available. Another 10 to 15 percent need to be scaled up and optimized for OTEC use, which adds some cost unpredictability. Only the cold water pipe construction, platform attachment, and deployment will require new types of equipment and procedures. If we assign l00 percent cost uncertainty to these items, the overall investment uncertainty of the OTEC system is around 15 to 25 percent. This relatively low uncertainty permits cost estimates to be made with reasonable confidence.
The ultimate sales price of fuel from OTEC plant ships depends on the cost to amortize plant investment (including construction costs) over plant life, plus operation and maintenance costs, including shipping to consumers. For a range of scenarios, the cost of OTEC-ammonia delivered to U.S. ports is estimated to vary from $0.30 to $0.60 per gallon (in 1995 dollars). Adjusting for the lower mileage per gallon of ammonia, this would be equivalent to gasoline costing $0.80 to $1.60 per gallon. These estimates are strongly dependent on assumed interest rates, amortization times, and whether tax credits and other subsidies that are available to gasoline users would be available to ammonia producers as well.
The seven-year DOE R&D program provided positive answers to doubts about OTEC. It demonstrated at a reasonable scale that the OTEC concept for ocean energy production is technically feasible. The next step was to have been construction of a 40-MWe (nominal) pilot plant that would provide firm cost and engineering data for the design of full-scale OTEC plant ships. Planned funding for this step was canceled in 1982 when the Reagan administration, with different energy priorities from those of the Carter administration, took office. Since l982, government support of OTEC development has been undercut further by the drop in oil prices that has reduced public fears of an oil shortage and its economic consequences, as well as by the opposition of vested interests that are committed to conventional energy resources.
Lack of support for OTEC research is part of a general lack of interest in energy alternatives designed to address fundamental problems that will not become critical for several decades. If and when the need for measures to forestall energy shortages and/or severe environmental effects from present energy sources becomes evident, the long lead times needed for the costly transition from fossil fuels to sustainable energy resources may prevent action from being taken in time to be effective. It is prudent to renew OTEC R&D now.
At present, the external costs of energy production and consumption are not considered in determining the charges to the user. Considering all stages of generation, from initial fuel extraction to plant decommissioning, it has been determined that no energy technology is completely environmentally benign. The additional costs associated with corrosion, health impacts, crop losses, radioactive waste, military expenditures, employment loss subsidies (tax credits and research funding for present technologies) have been estimated to range from 78 to 259 billion dollars per year. Excluding costs associated with nuclear power, the range is equivalent to adding from $85 to $327 to a barrel of fuel oil, increasing the present cost by a factor of 4 to 16. As a minimum, consider that the costs incurred by the military, in the USA alone, to safeguard oil supplies from overseas is at least $15 billion corresponding to adding $23 to a barrel of fuel - equivalent to doubling the present cost. Accounting for externalities might eventually help the development and expand the applicability of OTEC, but in the interim the future of OTEC rests in the use of plantships housing closed (or hybrid) cycle plants transmitting the electricity (and desalinated water) to land via submarine power cables (and flexible pipelines).
Conventional power plants pollute the environment more than an OTEC plant would and, as long as the sun heats the oceans, the fuel for OTEC is unlimited and free. However, it is futile to use these arguments to persuade the financial community to invest in a new technology until it has an operational record.
In short, the key breakthrough now required for OTEC/DOWA is no longer technological or economic, but the establishment of confidence levels in funding agencies to enable building of a representative-scale demonstration plant. Given that demonstrator, the early production plants will be installed predominantly in island locations where conventional fuel is expensive, or not available in sufficient quantity, and where environmental impact is a high priority. Both simple OTEC and OTEC/DOWA combined plants will feature, depending on the particular requirements of each nation state.
MicroHydro wrote:As I understand it, electricity generation efficiency from small temperature differentials is pretty poor.
The Tuapo geothermal plant in New Zealand produces mainly steam heat energy for local heating, with electricity as a trace byproduct.
The arguments for the viability of Pacific OTEC have been mainly:
1) Cold water to provide cheap air conditioning
2) Fresh water (through condensation)
So if one was doing OTEC primarily for electricity production, what would be the cost/kwh? Does someone think that OTEC electricity would cost less than the offshore wind cost of $0.05/kwh?
Microhydro wrote:For generation of hydrogen (or ammonia), the varying nature of wind power doesn't matter. That is probably why the 2003 Imperial College study on future aviation fuel for the UK mentioned hydrogen from offshore windfarms. With OTEC plants very capital intensive and high maintenance (corrosion of heat exchanger) and requiring plastic (oil based) pipes, I see a very limited future for OTEC as an electricity or fuel source.
Andy wrote:if we get serious about alternative energy OTEC providing countries like Jamaica, Cuba, Puerto Rico Dom. Republic, Haiti etc. with 40 - 50% of their electricity needs and also supplemental fresh water, coastal AC, mariculture sufficient for a significant fraction of protein needs etc.
Ammonia from natural gas costs 33500 cubic feet of natural gas per ton. At $9/ thousand cubic feet for natural gas, the feedstock cost is $300/ton of ammonia or about $42/BOE ammonia
I can see why the World Bank and venture capitalists haven't jumped on this bandwagon.
Microhydro wrote:If
EnergySpin wrote:For what it's worth there is a web site with OTEC news. I found it a few days ago. Those guys are bitter
bjelkeman wrote:EnergySpin wrote:For what it's worth there is a web site with OTEC news. I found it a few days ago. Those guys are bitter
What us bitter? Nahhh....
It is just part of our chosen editorial style really.
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