It’s not the motion of the ocean that matters to Lockheed’s Ocean Thermal Energy Conversion (OTEC) power plant, only the temperature of the water. Lockheed Martin announced yesterday that it is partnering with Beijing-based Reignwood Group to construct a 10MW green power plant that leverages the difference bewteen sun-warmed surface water and icy water from deep below to power a planned low-carbon real estate development on Hainan Island in the South China Sea. It will be the largest commercial OTEC plant ever constructed when it’s finished in 2017.
French physicist Jacques Arsene d’Arsonval first described the theoretic principals of thermal energy production in 1881, though it wasn’t until 1930 that someone built an actual plant in Cuba. OTEC systems typically operate using either a closed or open loop. Closed systems, like the proposed Hainan plant, use a working fluid with a low boiling point, like ammonia, to create steam which drives a turbine (the ammonia is then recondensed using cold water pumped up from the ocean’s depths, hence a closed loop). Open systems on the other hand cycle through seawater vapor as the working fluid.
The primary engineering challenge for these systems revolves around how to wring more energy out of the seawater than it takes to pump it up from the depths. The system is only about 6 per cent efficient under ideal conditions (though most OTEC projects float around 2-3 per cent). But what it lacks in efficiency, OTEC makes up for in endurance. These systems can produce energy 24/7, unlike wind and solar power that are dependent on, well, the wind and sun.
The plants are also location-limited to areas where there is at least a 40 degree water temperature difference year-round (read: the tropics and a thin band of the Atlantic coast) and deep water is fairly close to shore (unless you’re building a floating OTEC platform, in which case you can put it anywhere you please). and to a portion of the Atlantic coast.
The Hainan plant builds off of lessons learned from Lockheed’s previous OTEC plant, which has operated for the last few years in Hawaii with help from Makai Ocean Engineering, the DoE, and the US Navy. “The Navy wants a thriving OTEC industry because they would benefit from it,” Duke Hartman, a spokesman for Makai Ocean Engineering, told Scientific American. Submarines and ships carrying their own OTEC plants would be granted unlimited range, for example.
It will be a while before our oceans are overrun with super subs, however, the technology is still in its infancy. “The biggest obstacle to OTEC is economies of scale,” Hartman said. “You get a lot more bang for your buck if you go bigger.” He estimates that a 100MW plant, the kind the Pentagon hopes to eventually build, would run about $US1 billion.