Imari riding the wave of the future in ocean thermal energy technology

Unlike solar and wind power output, there is a renewable energy source that is not at the mercy of the weather and can supply electricity around the clock.

Called ocean thermal power energy conversion, it harnesses the temperature difference between frigid deep seawater and warm surface water to produce electricity.

Full-scale practical application of the technology is still years away, however.

Tokyo-based Xenesys Inc. has been working on the technology for many years. It set up a plant on a vast tract of land facing Imari Bay in 2007, and remains far ahead of its rivals overseas in developing the system as an alternative energy source.

Xenesys selected Imari because Saga University’s Institute of Ocean Energy, the leader in the research of ocean thermal energy conversion in Japan, is situated here.

The concept of generating power through thermal energy conversion was first mooted in the 19th century.

In resources-poor Japan, leading electronics companies got interested in ocean thermal energy conversion technology after the “oil shocks” of the 1970s sent crude oil prices soaring.

The momentum faded after Japan weathered the higher oil costs.

But Haruo Uehara, an engineer and former president of Saga University, continued with the research.

Xenesys saw promise in the technology and decided to pursue it by collaborating with researchers at the university.

The basic principle of producing power using the ocean thermal technology conversion process is similar to that at thermal or nuclear power plants.

Water from the ocean’s depths is pumped to cool fluids with a low boiling point, such as ammonia, and then vaporized with the use of warm surface water. The vapor expands and spins a turbine coupled with a generator, producing electricity.

The biggest challenge facing the university’s system in putting the technology into a practical use was how to achieve a surplus of power.

It had none, after subtracting the power needed to run the system from the amount that was generated.

Xenesys realized that to efficiently spin a turbine it needed to expand the gap in pressure in the condenser and the vaporizer.

Its answer was to design the titanium-made interior of the condenser and vaporizer, where seawater and cooling fluids come into contact, in the pattern of scales of a fish.

The resulting fine, concavity and convexity on the surface created whirlpool, which made it easier for warm water and cold water to efficiently conduct their temperatures to working fluids.

The company also found a way to cut electricity used to pump seawater by significantly improving the flow of seawater through the condenser and vaporizer, leading to the production of surplus power.

That put Xenesys ahead of its rivals in the United States and Europe.

Its technology has been in great demand.

The company delivered a heat exchanger for its ocean thermal energy conversion system to a research institute in India, and also set up joint ventures in Kuwait and Tahiti.

It began demonstrating the system in Kumejima island in Okinawa Prefecture in 2013 after winning an order from the prefectural government.

In the experiment, the system generates enough electricity to power 50 households.

Water pumped from the depths is rich in minerals and also used for shrimp farming in Okinawa Prefecture and to make skin-care products.

Shunji Sakurazawa, who leads the Xenesys design and development team, remains upbeat about the future of the technology despite a recent decision by utilities to curb their purchase of power from generators of renewable energy sources.

“We have been steadily preparing ourselves to spread our sails as soon as the time becomes more favorable,” he said.




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