While most of the green world’s attention is focused on solar and wind power, other ways to gather energy are being studied with less advertisement. This is the case of converting the ocean’s thermal differences into electricity.
Lockheed Martin, who is specialized in building rockets and aircraft engines, is surprisingly taking over this niche of energy production. They spent the last year studying how to make a big and long fiberglass pipe to sink it into the ocean.
Shortly, the process works this way: the lower layers of deep waters are at very low temperature, while the upper ones are at higher temperature. Upper layers of water can heat up a fluid with a low boiling point, such as ammonia or a mixture of ammonia and water. Then, this fluid, boiling at temperatures under 100°C, creates pressure, which is released through a turbine, thus creating motion and electricity. The ammonia is then recycled and cooled by passing it through cold water brought up from the ocean’s lower layers, to be brought back to its original state, ready for boiling. This is, in fact, the challenge to build the whole system: a large pipe, of about 1 km long and 27 meters in diameter, being able to suck cold water at a rate of about 1000 tonnes per second. The technology is called OTEC (Ocean Thermal Energy Conversion).
Robert Cohen, who headed the US federal ocean thermal energy program in the early 1970s, says that, theoretically, they could build a 500 MW OTEC plant in the future. The idea of tapping the ocean’s different thermal layers to generate electricity was first proposed in 1881 by French physicist Jacques d’Arsonval but didn’t receive much attention until the world oil crises of the 1970s. In 1979, a US government-backed partnership that included Lockheed Martin, lowered a cold water pipe from a barge off Hawaii that was part of an OTEC system generating 50 kilowatts of electricity. Two years later, a Japanese group built a pilot plant off the South Pacific island of Nauru capable of generating 120 kilowatts.
The building of such large structures brings the engineers various issues regarding the safety and strength of the materials used. The Indians tried to build a 1 MW ocean thermal plant back in 2003. They attempted to lower an 800-metre cold water pipe into the ocean from a barge in the Bay of Bengal only to lose the pipe in 1100 metres of water. A new pipe met the same fate the following year. “Both times there were some winch problems and it fell to the bottom of the sea,” says Subramanian Kathiroli, director of India’s National Institute of Ocean Technology. “I don’t think we will ever be able to go beyond 5 to 10 MW with present knowledge,” he says.
The Hawaii islands and a strategic military base, located on an island named Diego Garcia, are interested in building such thermal energy systems, because their main source of power comes from diesel, and such a system would be lifesaving and would free them from the energy crisis. And so it would do for the rest of the world, if Lockheed Martin will be able to invent a new generation of cold water pipes, with the $600,000 received from the US Department of Energy.
Ready or not, the Canadians have already implemented a similar system by using the Lake Ontario’s water, but with a slightly different twist: they use the cold water (of about 4°C, at the depth of 80m) to cool down Toronto’s buildings. The pipe they had built has 5 kilometers, going through the city. It is estimated that their natural “air conditioning” system saves about 60MW of electricity from the grid.
Usually, when we speak about alternative energy and generally energy that’s not derived from fossil fuels or nuclear power, we speak about low values. Now, the ocean’s thermal energy conversion only talks big numbers. It may seem viable for an energy-thirsty world.