Skip to main content

Using the ocean to run a heat engine

Ocean thermal energy conversion diagram and applications. (Image: National Renewable Energy Laboratory)

In 1976, science fiction writer Jerry Pournelle published a Galaxy magazine article titled How Long until Doomsday? It was written partly in response to The Club of Rome's downer of a book called The Limits to Growth, which saw economies going forward as severely resource-limited. One way out of our energy dilemma, according to Pournelle, was to harness the heat being harvested by the ocean. The Gulf Stream, he pointed out, had 75 times the energy being used at the time in the United States.

The way to extract that energy is called ocean thermal energy conversion (OTEC). An OTEC device has three major components, an evaporator, a turbine, and a condenser. Warm ocean water is used to heat vaporize ammonia or perhaps Freon or its equivalent. The gas drives a turbine to generate electricity. The gas is then cooled in the condenser by cool ocean water pumped from the deeps. As long as you can generate more electricity than you need to operate the pumps, the energy is free, courtesy of the Sun that warms the shallow water. Best of all, this type of energy does not add carbon to the atmosphere or even heat to the planet, since it uses the heating that is already occurring.

A side benefit, potentially, is the use of the nutrient-rich deep water in aquaculture. Another possibility is to use the excess cold water in the air conditioning of buildings. Sea water or cold lake water is already used in at least five different ongoing projects, the oldest one initiated in 1986. OTEC might also be used to drive desalination plants to generate potable water.

OTEC is not at all a theoretical idea; Georges Claude (who also invented neon), developed a working system off the coast of Havana in 1929, which generated about 20 kilowatts.

The Defense Department is actively interested in the use of OTEC to supply energy to its island bases. Lockheed Martin and Makai Ocean Engineering have collaborated on the designs of a 100 megawatt OTEC facility. Currently, the concept is being tested at the Natural Energy Laboratory of Hawaii on the big island. In 2003, Ocean Thermal Energy Corp. also designed an 8.3 megawatt OTEC project for the U.S. naval base on the island of Diego Garcia, in the Indian Ocean, though the plant has yet to be built.

In Pournelle's original article, he advised using the OTEC generated to hydrolyze water to obtain hydrogen. Hydrogen can be used as pollution-free energy source: hydrogen combines explosively with oxygen. Hydrogen, in theory, could be transported by pipeline, like natural gas. 

The use of fracking, of course, has recently created a bonanza of natural gas in the United States, as well as petroleum, in Texas and North Dakota. Unfortunately, this boomlet diminishes the economic impetus to consider other non-polluting energy sources like OTEC. As the planet continues to warm, we will surely regret it, if we do not develop obvious, technologically feasible, alternative energy sources.  

Learn more about getting energy from our oceans in this video from a recent AAAS Cutting Edge event.

Representative Image Caption
Ocean thermal energy conversion diagram and applications. (Image: National Renewable Energy Laboratory)
Blog Name


Steven A. Edwards, Ph.D.

Related Scientific Disciplines