The following summarizes the availability of the OTEC thermal resource throughout the world:

(1) Equatorial waters, defined as lying between 10 °N and 10 °S are adequate except for the West Coast of South America; significant seasonal temperature enhancement (e.g., with solar ponds) would be required on the West Coast of Southern Africa; moreover, deep water temperature is warmer by about 2 °C along the East Coast of Africa.  (2) Tropical waters, defined as extending from the equatorial region boundary to, respectively, 20 °N and 20 °S, are adequate, except for the West Coasts of South America and of Southern Africa; moreover, seasonal upwelling phenomena would require significant temperature enhancement for the West Coast of Northern Africa, the Horn of Africa, and off the Arabian Peninsula.  The physical factors affecting OTEC site selection, i.e., thermal resource and seafloor bathymetry, greatly restrict the number of desirable sites along the shoreline of major continents, unless some warm seawater temperature enhancement is possible.  The best, land-based, OTEC sites consist of island locations.  The severe constraint of a favorable bathymetric profile, for the practical implementation of land-based OTEC technologies, would be relaxed to a considerable extent with floating OTEC plants.  The potential benefits of OTEC could only be recovered on a large scale through the development of an ambitious floating-plant program, following the initial experimental land-based OTEC phase.


Many other points must be considered when evaluating potential OTEC sites, from logistics to socioeconomic and political factors.  One argument in favor of OTEC lies in its renewable character - it may be seen as the means to provide remote and isolated communities with some degree of energy independence, and to offer them a potential for safe economic development.  Paradoxically, such advantages are often accompanied by serious logistical problems during the plant construction and installation phases.  If an island is under development, it is likely to lack the infrastructure desirable for this type of project, including harbors, airports, good roads and communication systems.  Moreover, the population base should be compatible with the OTEC plant size - adequate personnel must be supplied to operate the plant, and the electricity and desalinated water plant outputs should match local consumption in orders of magnitude.  1 to 10 MW plants would generally suffice in most small Pacific islands, whereas in the case of populous and industrialized countries several of the largest feasible OTEC plants, up to 100 MW, could be considered.

There are at least two distinct markets for OTEC:  (i) industrialized nations and islands; and, (ii) smaller or less industrialized islands with modest needs for power and desalinated water.  Small OC-OTEC plants can be sized to produce from 1 MW to 10 MW of electricity, and at least 1700 m ³ to 3500 m³ of desalinated water per day.  That is, the needs of developing communities with populations ranging from 4500 to as much as 100,000 could be met.  This range encompasses the majority of less developed island nations throughout the world.  Larger CC-OTEC or hybrid cycle plants can be used in either market for producing electricity and water.  For example, a 50 MW hybrid cycle plant producing as much as 62,000 m³ of water per day could be tailored to support a developing community of approximately 300,000 people or as many as 100,000 people in an industrialized nation. 

A study performed for the US Department of State in 1981, identified ninety-eight nations and territories with access to the OTEC thermal resource (20 °C temperature difference between surface water and deep ocean water) within their 200 nautical miles EEZ, exclusive economic zone.  For the majority of these locations, the OTEC resource is applicable only to floating plants.  A significant market potential of up to 577,000 MW of new baseload electric power facilities was postulated (equivalent to 6 percent of present day power consumption by humanity).  In view of the discussion given above, this volume of power production will represent an environmental impact of significant proportion, primarily due to the movement of massive amounts of seawater.  Unfortunately, now as in 1981, there is no commercial size OTEC plant with an operational record available.  This still remains an impediment to OTEC development.