A 10-MW ocean thermal energy conversion (OTEC) pilot plant is being planned off the coast of southern China by global security and aerospace firm Lockheed Martin and Beijing-based cleantech firm the Reignwood Group. The companies announced an agreement in mid-April to develop the pilot plant to fully power a planned resort community, and if it comes to fruition, the project could pave the way for more efficient and cheaper plant designs using the technology.
OTEC plants generally generate electricity by exploiting the ocean’s thermal gradients—temperature differences of 36F or more between warm surface water and cold deep seawater—to drive a power-producing cycle. According to the U.S. National Renewable Energy Laboratory (NREL), 23 million square miles of tropical seas absorb an amount of solar radiation equal in heat content to about 250 billion barrels of oil—a tenth of which could supply 20 times the power needs of the entire U.S. on any given day.
The possibilities offered by OTEC have been considered for more than a century. The technology was first proposed as far back as 1881 by a French physicist, and several prototypes have been tested intermittently since the first experimental 22-kW low-pressure turbine was deployed in 1930. In the 1990s, the Pacific International Center for High Technology Research operated a 210-kW open-cycle OTEC plant at the Natural Energy Laboratory of Hawaii (Figure 3), and India unsuccessfully tested a floating 1-MW floating OTEC plant near Tamil Nadu in 2002. No commercial plants exist, however, Lockheed Martin’s own history with OTEC began in 1970s, when it developed a floating mini-OTEC plant (50 kW) that ran for three months. In 2007, Lockheed began developing specialized composite piping for obtaining cold water using a $1.2 million grant from the U.S. Department of Energy (DOE). And in 2009, following a $8.1 million contract with the U.S. Navy, the company continued to develop a 10-MW OTEC pilot plant in Hawaii, which included creating a robust interface between the platform and cold water piping. That project was apparently cancelled after the Navy deemed the project too costly.
|3. A hot-and-cold reality. Lockheed Martin and the Beijing-based Reignwood Group have agreed to develop a 10-MW ocean thermal energy conversion (OTEC) plant that would exploit the ocean’s thermal gradients to fully power a new resort community in southern China. Conceptualized in the 1880s, OTEC’s many benefits are shadowed by the high costs and risks associated with seawater systems. This image shows researchers laying a cold-water pipe at Keahole Point, Hawaii, in the early 1990s. The pipe supplied cold water for an OTEC experiment at Hawaii’s Natural Energy Laboratory—a 210-kW project that has been billed as the largest net-producing OTEC system tested. Courtesy: A. Resnick|
According to NREL, cost is the most significant reason the technology has failed to reach larger scale, despite the investigation of many potential thermodynamic cycles to reduce overall costs. The estimated capital cost for OTEC in 2011 ranged from $10,000/kW to $15,000/kW, and the majority of costs are linked to seawater systems, the research lab says.
However, the technology’s potential benefits are lucrative, Lockheed says. Not only can OTEC serve as a baseload power source that is renewable, OTEC power can also be used to produce hydrogen (via electrolytic processing of freshwater) and ammonia, which can be shipped to areas not close to OTEC. The system can also include freshwater production by flash evaporating the warm seawater and condensing the subsequent water vapor using seawater.
Once a proposed plant is developed and operational in China, Lockheed and Reignwood plan to use the knowledge gained to improve the design of the additional commercial-scale plants—of up to 100 MW—to be built over the next decade.
—Sonal Patel is POWER’s senior writer.