The Telegraph 8 Jan 08;
As Gordon Brown steers Britain towards a nuclear future, Dominic Michaelis, Alex Michaelis and Trevor Cooper-Chadwick suggest we turn to the oceans instead.
The French inventor Georges Claude is largely forgotten today; if he is remembered at all, it is as the creator of the neon lamp. Yet one of his projects from the 1920s could resolve the global energy crisis - by harnessing the power of the oceans.
It may sound like science fiction, but Ocean Thermal Energy Conversion (OTEC) is an idea whose time has come. It is based on the work of Jacques-Arsène d'Arsonval, a 19th-century French physicist who thought of using the sea as a giant solar-energy collector.
The theory is very simple: OTEC extracts energy from the difference in temperature between the surface of the sea (up to 29C in the tropics) and the waters a kilometre down, which are typically a chilly 5C. This powers a "heat engine": think of a refrigerator in reverse, in which a temperature difference creates electricity.
Claude's efforts to develop a practical version of d'Arsonval's concept had to be abandoned due to poor weather and a lack of funds.
But a modern equivalent would meet much of the world's energy needs, without generating polluting clouds of carbon and sulphur dioxide. It could also produce vast quantities of desalinated water to be shipped to parched areas of the world such as Africa.
There are two basic versions of the technology. The first operates in a "closed cycle", using warm surface water to heat ammonia, which boils at a low temperature. This expands into vapour, driving a turbine that produces electricity. Cold water from the depths is used to cool the ammonia, returning it to its liquid state so the process can start again.
The "open cycle" version offers the added benefit of producing drinking water as a by-product.
Warm seawater is introduced into a vacuum chamber, in which it will boil more easily, leaving behind salt and generating steam to turn a turbine. Once it has left the turbine, the steam enters a condensing chamber cooled by water from the depths, in which large quantities of desalinated water are produced - 1.2 million litres for every megawatt of energy.
A 250MW plant (a sixth of the capacity of the new coal-fired power station that has just won planning permission in Kent) could produce 300 million litres of drinking water a day, enough to fill a supertanker. Using electrolysis, it would also be possible to produce hydrogen fuel.
Such a vision is far removed from the first OTEC plant, constructed by Claude in 1930 in Matanzas Bay, Cuba, where the sea plunges to great depths close to the shore. After several failures - including the loss of two of the pipes used to suck up cold water from the sea - Claude produced 22,000 watts of electricity from this early prototype.
This is a very small amount, enough to heat five well insulated houses. But it confirmed that his calculations worked, and that both electricity and drinking water could be produced by the sea.
When a later version was installed on a converted boat in Brazil, Claude found a use for this desalinated water: he froze it to make ice, a valuable commodity at the time. The boat, however, was damaged in a storm and the project abandoned.
Similar difficulties have beset the many subsequent attempts to turn principle into practice, but with oil at $100 a barrel, and with pressure growing to arrest the effects of climate change, the conditions are right for OTEC to make a comeback.
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In fact, there is no need to stop at OTEC as the sole technology. If you are going to build an offshore platform, it makes sense to harness its space to create an "energy island" - a facility that uses a variety of alternative energies, such as wind, wave and solar, to generate enough power to pump the huge quantities of water from the sea and run the vacuum pumps of the OTEC plant.
Not only would these "islands" be self-sufficient, but several could be linked to generate energy outputs of around 1,000MW, rivalling the output of a typical nuclear plant. The cost, according to our models, would be roughly double that of a nuclear power station.
This might seem expensive, but an OTEC plant would not involve the waste-treatment or astronomical decommissioning costs of a nuclear facility. Also, it would offset its expense through the sale of the desalinated water.
This is in addition to the other advantages: carbon-free energy production and no generation of heat. In fact, the plants would cool the seas and oceans by the same amount as the energy extracted from them.
The energy islands would mainly be built from reinforced concrete, using corrosion-resistant metals, but they would come in different sizes and with different functions: some would be simple energy-generating platforms, while others would be larger installations, linked to the land by cable, along which the electricity could be distributed (this would involve superconductors, materials that lose all resistance to electricity when cooled, minimising energy loss in transmission).
And energy generation would not be their only function. Larger islands could support fish farms that used the plankton pumped up along with the cold seawater, as well as pods for heliports, greenhouses, accommodation and maintenance areas, facilities for producing sea salt and harbours and mooring for supertankers.
These tankers would collect the desalinated water or the hydrogen produced by electrolysis, which could both be shipped to energy- and water-scarce parts of the world, just as natural gas is piped from Siberia to Western Europe.
These hydrogen fuel cells could soon be used to power cars, trucks, boats, factories and aircraft, helping to establish a clean hydrogen economy. A model for this is Iceland, where hydrogen for fuel cells is being generated by electrolysis using cheap geothermal energy. On this basis, Iceland expects to become emissions-free by 2020.
We also have a clear idea where to build these powerful islands. For the system to function, the gap between the surface and the depths must be at least 20C.
Maps of the oceans show which waters contain the necessary temperature gradients -and China, India and Brazil, the three countries projected to have the greatest economic and population growth this century, and therefore the most pressing energy requirements, all have OTEC potential.
In April in New York, international agencies, national and state governments, environmental groups and industry associations are sponsoring the most substantive global conference on renewable marine power for years.
Here is one fact that should help delegates to focus minds on what is possible: 50,000 energy islands could meet the all world's energy requirement while providing two tons of fresh water per person per day for its six billion inhabitants. That would be a legacy of which Georges Claude could be proud.
• Dominic Michaelis is an architect and engineer. He and his architect son Alex are developing the energy island concept with Trevor Cooper-Chadwick of Southampton University.
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