The only eco-friendly source of "base power," that is, power that (unlike solar or wind) is available at a constant rate whenever you need it, is geothermal. This lack of reliability makes green power a hard sell, and the Oak Ridge National Laboratory might have an answer: seawater.
Really, it's not the seawater itself that ORNL is interested in: it's the temperature difference between water up near the surface, and water thousands of feet down. Wherever you've got a temperature difference somewhere, it's theoretically possible to harvest energy from that system, and the bigger the temperature difference the more energy you can extract. One handy place where this would work is out in the ocean, especially in the tropics, where seawater near the surface can be 70 or 80 degrees, and just 40 degrees a couple thousand feet down.
That 30 or 40 degree difference is enough to boil ammonia, use it to drive a turbine to produce power, and then condense the ammonia again to start all over. There's no fuel necessary, no waste products, and the slightly colder water that's dumped back into the ocean apparently has no effect on the environment. ORNL figures that offshore power stations have the potential to generate between three and five terawatts of power in tropical latitudes, which is more green energy than is produced by the entirety of the United States of America.
The secret to doing this efficiently enough to make it cost effective and worthwhile is a stupendous heat exchanger, and ORNL has come up with a doozy: graphite foam. This stuff has a ton of surface area, and it's a very efficient heat conductor, which is exactly what you need in an exchange system. ORNL estimates that using this stuff could either half the cost or double the efficiency of any heat-based power source, which covers not just these seawater plants, but traditional power plants (coal, nuclear, etc) as well.
If ORNL has its way, a demonstration version of this seawater energy project should be up and running in Hawai'i sometime this spring.
ORNL, via SimplyGreen
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