IF the price of oil is too high, island nations could look to a source of energy that they have in abundance — seawater.

Ocean Thermal Energy Corporation (OTEC) of Lancaster, Pennsylvania, plans to build the Caribbean's first commercial plant to exploit differences in ocean temperatures to generate electricity in the Bahamas.

The company hopes to start construction of the project, currently in the design phase, by the fourth quarter of 2012 and to have it in operation by 2015, producing up to 10 megawatts of power.

A second plant of similar size would follow in the Bahamas while the company is in discussions with the Caymans about a third.

“Everybody's struggling with the cost of power and it's only going to get worse,” said Jeremy Feakins, OTEC's chairman and CEO.

The project would cost between US$150 million and US$185 million, Feakins said.

“We're keeping our plants in the 10 to 15MW range,” he said. “We'll be using off-theshelf components, greatly minimising construction risk.”

A pipe would be built along the seabed from the shore to a depth of about one mile, sucking up cold water like a straw.

This water, up to 20ºC below the surface temperature, would be put through a heat exchanger to condense ammonia, the operating fluid.

The liquid ammonia would then go through a heat exchange with surface water, turning it back into a gas but at a much high pressure so that it could drive the turbine and generate electricity.

The cold water would have several other uses after passing through the heat exchange.

Current plans call for it to be piped around the Baha Mar resort on New Providence, Bahamas, a type of air conditioning already used, in summer, by Toronto, with water drawn from Lake Ontario.

The company is also looking at growing strawberries and grapes on the island by running pipes through the soil to cool and irrigate it. Deep-sea water is particularly good for agriculture because it is nutrient rich yet pathogen free.

And it would be possible to use some of the energy to power desalination plants to provide drinking water. This would leave it with almost no waste water to return to the sea.

Another option would be to inject the waste water into on-shore wells from which it would gradually seep into the sea.

The idea of using ocean heat differentials to make electricity was first proposed by Jacques Arsene d'Arsonval, a French physicist, in 1881. One of his students built a plant in Cuba in 1930.

But it has received little attention since because other fuels were cheaper. Much of the practical research was conducted on Hawaii, where a demonstration plant was built after the oil price spikes of the 1970s.

“The US government has put billions of dollars behind the research over the years,” said Feakins.

In theory, ocean thermal energy becomes commercially viable when oil is around US$60 per barrel. With the Saudis promising to put a floor under the price of crude at US$100, and Goldman Sachs forecasting a 2012 peak of US$150, it looks as if the technology's time may have come.

One of the problems with ocean thermal energy is that to scale up would require larger undersea pipes, and the largest currently available is just 2.5 metres in diameter, said Feakins. “That's enough for a 50MW plant.”

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