[thedoc (OP)]

Wilf James  asked the Naked Scientists:
   
Dear Chris,

In your recent podcast about using waste heat you had a question about using thermo-electricity to extract energy from the heat differential between to top and the bottom of the sea.

I can't remember the details but there was a project to get energy in a different way many years ago.

Then the idea was to use the cold water from the bottom of the sea at around 4 degrees C to provide cooling for a turbine system that worked under low pressure to make use of the fact that warm water taken from the sea surface will boil under low pressure. I heard that the organisation that tried this idea could not make it economic although such an idea was theoretically possible.

Another idea I came across years ago was the use of a Tilley type lamp as a heat source combined with a dozen iron/copper thermocouples arranged with their hot ends in a ring near the lamp mantle with their cold ends in a finned radiator. The power available from this setup was alleged to be enough to run a portable radio.

With my best wishes

Wilf James

What do you think?

[yor_on]

I don't think that would work, and btw, where is that Geezer when one needs one?
We need some serious engineering ingenuity here.

[syhprum]

Unfortunately thermoelectric generators at present have a considerable lower conversion efficiency than mechanical ones such as turbines or Stirling engines.
This is recognised by satellite builders who are developing Stirling engines for use in long distance space vehicles.

[CliffordK]

As always, there is a good wikipedia article on the thermal gradient generators.

http://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion

The low pressure generator that you described is one method, and can also be utilized to produce fresh water.

The Japanese plant, for example, produces about 120KW of energy, uses 90KW, and has a net of only 30KW.  I.E. in the grand scheme of things, a relatively small amount of net power generation.  There are a few 1MW to 10MW plants being planned.

[MikeS]

I think Wilf summed it up in the original question.  Deep ocean thermo generators are possible but uneconomic.