Harnessing the Oceans’ Thermal Energy
by Sonia Kolesnikov-Jessop, NEW YORK TIMES, May 17, 2010
Generating renewable energy from the ocean through Ocean Thermal Energy Conversion, known as O.T.E.C., has been studied for nearly a century but, although several demonstration plants have been built to prove that the technology works, it has never been put into commercial operation. Now, however, despite the high costs involved, several companies are working toward commercial projects.
O.T.E.C. generates electricity by exploiting the temperature differential between warm surface water and the cold ocean depths. Surface water is pumped through a heat exchanger, where it heats a fluid with a very low boiling point, such as ammonia, which expands as it vaporizes. The vaporized gas drives turbines producing electricity before being piped into a condenser, where cold deep ocean water chills it, returning it to its liquid state. The liquid is then pumped back to the warm water heat exchanger to repeat the cycle.
To work effectively, the technology requires a temperature differential of at least 20 degrees Celsius (68 Fahrenheit). This can be found in large expanses of the tropical oceans. “Every additional degree will help produce 15 percent more energy,” said Philippe Dubau, general manager of Pacific Otec, a subsidiary of Pacific Petroleum, an oil product distributor in French Polynesia, New Caledonia and Vanuatu that has been moving into the renewable energy sector.
According to Kevin Joyce, a renewable energy consultant at Black & Veatch, based in Overland Park, Kansas, one of the more exciting characteristics of the technology is that, unlike most renewable energy sources, it can provide steady, reliable baseload power.
“This would generate electricity 24 hours a day in a predictable and dependable manner,” Mr. Joyce said. “Other renewable technologies with this kind of resource potential, like wind and solar, are intermittent, which means that they need conventional generation to fill the gaps.”
Sometimes, he said, that could mean building additional, fast-response, conventional power plants to kick in with power to the grid when the renewable sources go dark. O.T.E.C., in contrast, “has the ability to avoid those requirements and even displace some of our baseload plants.
“That means that it has more potential for CO2 reduction than many other renewable technologies,” Mr. Joyce said. It also has other advantages. “The technology is compact compared to wind and solar,” he said, adding that it can be “offshore and out of sight.” [Read rest of story]