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Coral reefs: Tomorrow's renewable power stations?

Professor's tiny but tough turbines capture energy of breaking waves

Professor Tsumoru Shintake's sketch of his envisioned wave power system (Courtesy of Tsumoru Shintake)

TOKYO -- Japan and other maritime countries may not have to look far for their affordable, stable alternative energy source of the future. It might be lapping at their shores.

A professor in Okinawa hopes he has found the answer in the waves that break over coral reefs surrounding the southern islands. Tsumoru Shintake of the Okinawa Institute of Science and Technology Graduate University is attempting to harness the power of the surf by installing turbines on the reefs.

The cost-effective method he has in mind could even help make for more picturesque coastlines.

Soon, Shintake intends to start testing a prototype wave energy converter. The contraption, completed in October, features five propellers measuring 35cm in diameter. If the device ever makes it into practical use, a large number would be deployed.

The prototype converter is compact enough for easy transport. (Courtesy of Okinawa Institute of Science and Technology Graduate University)

When the converter is affixed atop a coral reef or other structure, a sophisticated neodymium magnet mechanism keeps water out of the propeller shaft and helps it withstand the waves.

The idea of using wave energy is not new, but so far most projects have failed to reach commercialization partly because of the difficulty of creating cheap, durable equipment. Researchers like Shintake are forging ahead because, if all goes according to plan, wave power would be more efficient than wind turbines.

"While wind power generation requires large turbines, [waves] can generate a sufficient amount of electricity even with small [turbines]," Shintake said. This is "because the energy density of waves is 100 times greater than that of wind." 

If the trial proves successful, Shintake said he plans to produce more converters, possibly next year, to conduct another experiment that would be closer to actual use.

He said the small converter will help keep installation costs low. Mass production would also slash the device's price. If the per-unit cost can be reduced to 1 million to 2 million yen ($8,894 to $17,788) or lower, Shintake said the electricity generation cost would range between 5 and 10 yen per kilowatt-hour.

That would make the system competitive with thermal or nuclear power.

No natural reef? No problem

Shintake's concept relies on "reef breaks" -- reefs that obstruct waves, causing them to break and curl before crashing down.

Waves that break over coral reefs tend to travel long distances while maintaining their shape, making them ideal for surfers. This reminded Shintake of something from his background as a physicist working with electron microscopes. The waves, he said, are "similar to a type of wave called 'soliton' in physics" -- a wave that keeps its shape and velocity.

Reef breaks offer a couple of benefits, when it comes to tapping wave energy. The first is the waves' high speed -- 5 to 6 meters per second. The second is that the waves flow in one direction. These factors allow for a stable supply of energy compared to waves farther offshore.

Still, the converters do not need an actual reef to function. 

Shintake pointed to the concrete blocks that dot Japan's coastline, serving as tsunami defenses. These blocks, he suggested, could be moved a little farther out to act as "artificial reefs." The waves that surge over them could be used for electricity.

This plan, he added, "kills two birds with one stone, because it can also improve the scenery around the coasts."

Relocating those concrete blocks, of course, would require substantial public works spending. This might be feasible in some places, but not everywhere.

In any case, similar blocks could also be an option for Pacific island states and other countries looking for an alternative to carbon-emitting thermal power plants. 

Rough road

In recent years, European countries like Britain and Spain have been actively pursuing wave power systems to help combat global warming. But some attempts have highlighted just how difficult it can be.

U.K. company Pelamis Wave Power's electricity generation system was expected to be the first commercial endeavor. But a trial launched off the coast of Portugal in 2008 was scrapped a few weeks later due to technical issues.

The system, named Pelamis, was designed to generate electricity when long, snakelike devices flex and bend in the waves.

In Japan, the New Energy and Industrial Technology Development Organization, or NEDO, in 2015 ran a wave energy test at the Port of Sakata in Yamagata Prefecture.

NEDO's generation system, set up on an existing revetment, works by rotating turbines using the airflow created by the undulations of the ocean surface. The trial was successful, reaching a maximum output of 13 kilowatts.

Hopes remain high in the West, too. Ocean Energy Europe estimates the global capacity of marine energy -- power generated from waves, tides and other marine resources -- will reach 3.6 gigawatts by 2020 and nearly 200GW by 2050. The latter figure would be enough to meet about 15% of the electricity needs in the 27 EU member countries.

The association contends that marine energy will eventually become one of the main renewables, alongside solar and wind power.

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