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Sci Tech

Ocean Thermal Energy Conversion can slow climate change.

By       Message Dominic Michaelis     Permalink
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We are desperately looking for water on Mars, but are ignoring that water on Earth. Seas and oceans, on average 3.5 kilometers deep, can supply us with all the energy we need, prompting us to switch from the climate-changing fossil and nuclear economies to a clean ocean-energy economy, in the form of ocean thermal energy conversion, OTEC.

The idea of energy from the oceans originated from the fertile imagination of Jules Verne in 1869.

Twelve years later, in 1881, the French physicist d'Arsonval (1851-1940) patented the idea of using the large difference of temperatures at the surface of some warm seas and that of water 1000 meters lower, to generate electricity.

In the d'Arsonval patent, the working fluid, ammonia, is contained in a closed circuit, which is known as Closed-Cycle Ocean Thermal-Energy Conversion, or CC-OTEC.

The surface temperature makes the ammonia boil and become a gas under pressure, sufficient to power a turbine generating electricity. The ammonia gas is then condensed back to its liquid state in a condenser, cooled by cold water piped up from the depth of 1000 metres.

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A younger colleague of d'Arsonval's, the French chemist Georges Claude (1870-1960), developed an OTEC variant where the seawater itself is the working fluid. It is evaporated under vacuum, and so loses its saline components, now providing both electricity and invaluable desalinated water.

Because the working fluid is not in a closed circuit, this cycle is known as Open-Cycle Ocean Thermal-Energy Conversion, or OC-OTEC.

Dr Luis Vega took the bases of these earlier inventions, and from 1993 to 1998 set up a 210-kW land-based CC-OTEC test facility with an OC-OTEC parallel test facility in Hawaii, where he was able to confirm system designs, workings and efficiency figures. This seminal work should be recognized, as it took proven OTEC into the 21st century.

Unlike many other renewable-energy resources that are variable, OTEC delivers electricity with or without desalinated water continuously all year round, using no fuel.

OTEC is now economically competitive in its closed-cycle mode with offshore wind farms costing on average $5600/kW (NREL), compared to $4000/kW for 100-MW OTEC plant (Dr Vega).

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It is competitive with large desalination plants in its open-cycle mode.

A $1bn reverse-osmosis desalination plant expected to supply 120,000 m3/day in San Diego would be matched by a 51-MW OC-OTEC plant supplying the same and costing twice the cost of CC-OTEC at $8000/kW, a total of $408M, less than half the cost of the reverse-osmosis plant.

Dr Paul Curto, previously NASA chief technologist, wrote in OpEdNews on 12/15/2010:

"OTEC is a true triple threat against global warming. It is the only technology that acts to directly reduce the temperature of the ocean (it was estimated one degree Fahrenheit reduction every twenty years for 10,000 250 MWe plants in '77), eliminates carbon emissions, and increases carbon dioxide absorption (cooler water absorbs more CO2) at the same time. It generates fuel that is portable and efficient, electricity for coastal areas if it is moored, and possibly food from the nutrients brought up from the ocean floor. It creates jobs, perhaps millions of them, if it is the serious contender for the future multi-trillion-dollar energy economy."

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Dominic Michaelis was educated in England and in France, going to Trinity College, Cambridge as a major scholar, to read Architecture and Engineering, his thesis, in 1964 being a solar house and a floating solar village. He then went to (more...)

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Ocean Thermal Energy Conversion can slow climate change.