Ocean energy

Predictions revisited

Ocean energy for free

or As close as you’ll get to perpetual motion

Hearing of the success with a submersible powered entirely by the differences in temperature at different ocean depths brings a feeling of déja vu. A press release of from NASA’ s Jet Propulsion Laboratory (JPL) quotes engineer Jack Jones:

While not a true perpetual motion machine, since we actually consume some environmental energy, the prototype system … can continuously monitor the ocean without a limit on its lifetime imposed by energy supply.

SOLO-TREC deployed for an endurance test. Photo: NASA/JPL/US Navy/Scripps Institution of Oceanography

JPL’s partner in the project is the Scripps Institution of Oceanography at the University of California San Diego. The robotic vehicle’s name is SOLO-TREC, an acronym for the Sounding Oceanographic Lagrangrian Observer Thermal RECharging submersible. It heralds a new generation of robotic vehicles for virtually endless ocean monitoring for climatic studies, marine biology, exploration, and no doubt military uses too. Funding comes from the Office of Naval Research.

The vehicle has ten tubes around it filled with a waxy material that expands mightily in warm water near the surface and shrinks in the cold water down below, driving a hydraulic motor for power generation. In recent months, SOLO-TREC has made 3-4 dives a day to 500 metres, producing enough power to keep its batteries charged, control its buoyancy, and operate its instruments and communications.

In “Spaceships of the Mind”, a 1978 TV series that I scripted and fronted for the BBC’s producer-director Dick Gilling, we talked centrally about the idea, then being strongly touted, to build settlements in space to relieve the human pressure on planet Earth. But the geochemist Harrison Brown of Caltech, himself a prolific writer on “futures”, intervened to advocate man-made islands floating on the oceans. As he explained:

In the tropics it is quite possible to extract energy from the oceans by making use of the temperature differential between the deeper waters and the waters of the surface. The potential power available is ample to supply a large city for all of its needs. In addition, the deeper waters are filled with plant nutrients – phosphates and nitrates – and if these are contained then one can grow photosynthetic matter, marine plants, and permit fish, shellfish and so forth to feed upon them. This would provide a great deal of food. And indeed one could easily see a very self-sufficient city out in the ocean, which would be a lot loss expensive than an orbiting city up in space – and I suspect a lot more comfortable.

In Brown’s scheme it was a matter of pumping up deep-lying water and using the temperature difference with the surface water to generate power for the pumps and everything else. Although ocean energy is “free”, that’s only in the sense that solar, tidal, hydro and wind power are free. Heavy engineering is required, and the thermodynamics of ocean power are poor because of the small temperature differences.

As a result “ocean thermal energy conversion” has been slow to progress since French physicists began toying with the idea more than 100 years ago and built the first 22-kilowatt plant in Cuba in 1930. But interest continues in the USA, Japan and India, so it may be only a matter of time before ocean gigawatts confound the Malthusians — if need be, decades or centuries from now, on the same kind of timeline as those settlements in space. Meanwhile little SOLO-TREC cheers the spirits, telling us that the natural world is much richer than most people seem willing to know.

References

NASA/JPL press release 5 April 2010

Spaceships of the Mind” BBC-TV 3X50min, produced and directed by Dick Gilling, scripted and presented by Nigel Calder, 1978

Spaceships of the Mind by Nigel Calder, BBC, Viking, etc. 1978.

The Challenge of Man’s Future by Harrison Brown, Viking 1954

The Next 100 Years by James Bonner and Harrison Brown, Viking 1957

Wikipedia http://en.wikipedia.org/wiki/Ocean__energy_conversion

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