When Pacific Gas & Electric broke the news six weeks ago that it had signed a deal with Solaren Corp. to buy 200 MW of solar energy from satellites launched into geosynchronous orbit, the idea...
Capturing Ocean Heat
Ocean thermal energy conversion offers a timely renewable alternative.
According to the National Renewable Energy Laboratory, 1 60 million square kilometers (23 million square miles) of tropical oceans daily absorb solar radiation equal in heat content to about 250 billion barrels of oil ( e.g., 1,450 Quads). This is an order of magnitude greater than the expected total U.S. energy consumption through 2030, and twice the projected global energy demand. Even using present maximum estimates for steady-state sustainable energy harvesting 2 ( e.g., 3 to 5 TW, or 90 to 150 Quads), this resource still provides enough clean and non-GHG emitting energy to supply 15 to 20 percent of the global energy demand in 2030.
Ocean thermal energy conversion (OTEC) technologies convert the solar radiation that heats the surface of the ocean into electrical power by exploiting the thermal gradient temperature differences between the surface and the depths. This temperature gradient in the Tropics ( see Figure 1 ) can be 20 degrees C (36 degrees F) or more between the warm surface water and the cold deep seawater, which is sufficient to produce usable power, albeit not very thermodynamically efficiently ( i.e., 3 to 5 percent). It should be noted that lying within the Tropical zone——the area most favorable for OTEC—are some 29 territories and 66 developing nations, as well as portions of Australia and Hawaii, all of which are natural markets for OTEC-generated energy and other side-products.
This enormous resource merits a closer look as policy makers consider alternative technologies for serving future energy demands. Achieving viability, however, will require more supportive and stable regulatory policies as well as funding for research and development.