Scientists and engineers around the world are striving to develop new sources of energy. One source, ocean thermal energy conversion, has virtually unlimited potential. It is based on techniques that exploit heat produced by solar energy that may, in turn, be used to produce fuel and electricity. This book reviews the status and background of this promising technology. William H. Avery is the leading expert in this field, and his co-author Chih Wu is an authority on heat engine performance. Together they describe the workings of an OTEC power plant and how such a system might be implemented as part of a futuristic national energy strategy. The book is the only detailed presentation of basic OTEC technology, its testing and improvement. It is based on extensive development initiatives undertaken internationally during the period from 1974 through 1985. The book offers a thorough assessment of the economics of OTEC in comparison with other energy production methods. It will be of interest to a wide range of professionals in energy research, power and mechanical engineering, and to upper-level undergraduate students taking courses in these fields.

The historical development leading to the proposal by Claude to generate power by producing steam in flash evaporation of warm seawater has been discussed in Chapter 2. In this chapter, the thermodynamic fundamentals of the open-cycle concepts are discussed, leading to a detailed review of state of the art and commercial prospects of the process. There are several variations on the standard OTEC open-cycle (OC) system. The three major variations are “hybrid cycle” (Bartone, 1978), “mist lift cycle” (Ridgway, 1977), and “foam lift cycle” (Beck, 1975; Zener et al., 1975). These are advanced concepts that offer certain attractive features and are being investigated. The three cycles will be discussed in Sections 5.3, 5.4, and 5.5, respectively. The standard OTEC open cycle is discussed in the following. The modest but nearly steady temperature difference that exists between the warm surface water and the much colder water at great depth in some tropical regions of the world has attracted the attention of many thermodynamicists from the time that these temperature differences were first observed. From the thermodynamicist’s view, any significant temperature difference can be used to produce power. The open or Claude cycle is the forerunner of various OTEC cycles. The open cycle refers to the use of seawater as the working fluid. A schematic diagram of the system, which comprises a flash evaporator, vapor expansion turbine and generator, steam condenser, noncondensables-removing equipment, and deaerator, is shown in Fig. 5-1 (Chen, 1979). The cycle is a basic Rankine cycle for converting thermal energy of the warm surface water into electrical energy. In the cycle, the warm seawater is deaerated and then passed into a flash evaporation chamber, where a fraction of the seawater is converted into low-pressure steam. The steam is passed through a turbine, which extracts energy from it, and then exits into a condenser. This cycle derives the name “open” from the fact that the condensate is not returned to the evaporator as in the “closed” cycle. Instead, the condensate can be used as desalinated water if a surface condenser is used, or the condensate is mixed with the cooling water and the mixture is discharged back into the ocean.

The financial analyses presented in Chapters 7 and 8 indicate that commercial development of OTEC will have a significant impact on the economics of U.S. energy production and use. Two scenarios for commercial development are examined in this section: 1. Development of OTEC methanol capacity sufficient to replace all U.S. gasoline produced from imported oil. 2. Development of OTEC ammonia capacity sufficient to replace all gasoline used in U.S. transportation. Commercialization of this option implies a project goal to produce methanol plantships with enough total methanol capacity to replace the gasoline used in the United States that is now produced from imported petroleum, 47 billion gallons of gasoline in 1990 (DOE/EIA, 1990). This would require a total of 427 200-MWe plantships, each producing 199 million gallons of methanol per year (1.8 gallons of methanol give the same automobile mileage as 1 gallon of gasoline. We assume financing based on an initial nominal plant investment of $960M (1990$) and an eighth plant investment of $664M. With repeated manufacture, the cost will be reduced to $438M for the 427th plantship, assuming that an experience exponent of 0.93 applies for all production of identical plantships after the first three. The average plant investment for the total production is then $507M. If financial support is maintained to complete the program, the year 2020 is a reasonable target date for achieving the full fuel production capacity. This implies construction of OTEC plantships at an average rate of 17 per year after commercial production is established. This rate could be accommodated in U.S. shipyards with feasible modifications to satisfy specific OTEC requirements. The U.S. shipbuilding facilities are discussed in Section 4.1. In addition to the investments required for OTEC, methanol automobiles must be in production, and distribution systems for methanol must be installed. The associated costs must be included in the financial analysis. Offsetting these costs are the savings resulting from: 1. Large improvements in the U.S. balance of trade through elimination of oil imports. 2. Tax receipts accruing from reinvigorated U.S. shipbuilding and associated manufacturing industries. 3. Economic benefits of stabilized world fuel prices.

As in other branches of technology, the understanding of the physical and chemical principles underlying the operation of heat engines followed long after such systems were in commercial use. Apparently both the ancient Egyptians and Chinese were able to use steam or combustion gases to do work in special applications; however, the first practical use of a heat engine was the steam-driven piston engine for pumping water from mines, invented in 1698 by the Englishman Thomas Savery. This was followed by a better device invented in 1712 by Newcomen and further developed by Smeaton, which was widely adopted for mining operations in the tin mines of Cornwall and the British coal mines. In 1763, James Watt invented his greatly improved steam engine, which laid the foundation for the industrial revolution based on steam power. Interesting accounts of these developments are presented in Fenn (1982) and Callendar and Andrews (1958). By 1800, there were nearly 500 engines of Watt’s design emplaced throughout England for pumping water, working metal, or other uses. Steam use in ships was successfully demonstrated by Fulton on the Hudson River in New York in 1807. Railroad transportation based on steam-driven locomotives was introduced by Stephenson in 1812 following small beginnings in 1801 by Trevithick. As the steam engines of Newcomen were manufactured and installed, their performance was measured by the amount of water that could be pumped to a given height per bushel of coal burned. The heating value of the coal being used was approximately 1 million Btu per bushel. The data of Table 2–1 show how the thermal efficiency of steam engines improved with time. It is interesting to note that the industrial revolution began with engines of less than 1% efficiency and blossomed with the development of Watt’s engine of 2.7% efficiency. Watt and his predecessors related the performance of their engines in pumping water to what could be accomplished by horses engaged in the same task. An average value of the power capability of a horse was estimated by Watt, who established the unit of one horsepower as the power needed to raise 33,000 pounds 1 foot in 1 minute.

Innovative technologies such as OTEC achieve commercial development when potential investors decide that the return on the investment will repay the estimated development costs plus a profit, with an acceptably low risk of cost overruns. Industrial experience shows that the estimated cost to complete development of a new technology generally increases as development proceeds from the conceptual design through pilot development, demonstration, field testing, and final commercial manufacture (Merrow et al., 1981). The ratio between final cost and initial design estimate is strongly dependent on the extent to which the manufacturing process employs already developed equipment, procedures, and facilities. New projects that require “high technology” for their success, such as jet engines or nuclear power plants, have been characterized by large underestimates of the final costs, whereas the costs of projects that are firmly based on existing technology, such as the development of “supertankers,” have been accomplished well within the usual industrial uncertainty margin of ± 15 to 20%. The accuracy of the estimate is also strongly dependent on the thoroughness of the systems engineering evaluation that is done before development proceeds. Commercial applications of OTEC have been proposed in three principal categories. The first includes OTEC power plants mounted on floating platforms that would generate 50- to 400 MWe (net) of onboard electric power. The need to minimize plant size makes it mandatory to use closed-cycle OTEC for these applications. The second category includes land-based or shelf-mounted plants designed to supply power in the 50- to 400-MWe range to municipal utilities. Either open- or closed-cycle systems could be suitable. The third category comprises small (5- to 20-MWe) land-based or shelf-mounted OTEC plants designed for island applications where electric power generation, mariculture, fresh-water production, supply of cold water for air-conditioning systems, and fuel production could be combined to offer an economically attractive OTEC system despite the relatively high cost of power for small OTEC installations. Open-cycle OTEC plants may be the preferred choice for the third category. The estimated investment costs of installed complete OTEC systems, measured in dollars per kilowatt of net OTEC electric power generated, differ significantly among the three categories.