A trick that exploits the difference in temperature between seawater near the surface and deep down could supply the world with cheap green power

In this age in which we are trying to free ourselvels from the oil dependence the ocean have been studied many times as a tremendous and limitless potential energy reserve. Wave buoys or Tidal power are two different ways to draw this energy from the ocean but they are still far from being really effective but there is a third way, less acquainted by the public opinion but which is much closer to be effective and could really change the world of alternative energy: the OTEC, that stands for Ocean Thermal Energy Conversion.
On the smallest scale this kind of technology is already installed and working, the actual challenge is to size it up in order to create huge plants able to produce up to 500 Mega Watts each one! The plants consits in floating offshore platforms sending electricity to onshore grids via submarine cables.
To understand how OTEC works look at the diagram below.
Warm surface water heats a fluid with a low boiling point, such as ammonia or a mixture of ammonia and water. When this "working fluid" boils, the resulting gas creates enough pressure to drive a turbine that generates power. The gas is then cooled by passing it through cold water pumped up from the ocean depths via massive fibreglass tubes, perhaps 1000 metres long and 27 metres in diameter, that suck up cold water at a rate of 1000 tonnes per second. While the gas condenses back into a liquid that can be used again, the water is returned to the deep ocean.
The challenge is to create those massive fibreglass tubes and to protect them form the energy of the currents.
However if you want to know more about this incredible technology, its history that started back in the 19th century and why Lockheed Martin, a rocket science company and aerospace giant, has received 600.000$ by the US Department of Energy to develop a new generation of cold water pipes, the better thing you can do is reading this comprehensive article by Phil Mckenna on NewScientist:
Plumbing the oceans could bring limitless clean energy