Energy Underwater

For Taiwan Review www.taiwanreview.nat.gov.tw/

Two ambitious projects aim to harness the power of the sea.

A metal structure stood on the back of a truck at a National Taiwan Ocean University (NTOU) research institute in Taiwan’s northern city of Keelung in late August 2012. The device looked like a cross between a deadly torpedo and a harmless aircraft propeller atop a pyramid-shaped stand, but just before the truck moved off, the dozen or so people nearby photographed and filmed the whole structure much as if it were a local pop star. In fact, the truck was carrying a prototype of an ocean current turbine to its first sea trial, and the scientists who have been perfecting the design hold high hopes that it could one day provide a way out of the island’s precarious energy situation.

Taiwan imports 99 percent of its primary energy resources, a situation that has inspired numerous academic papers on harnessing the energy of the ocean. Recently, support for the development of technology to make the idea a reality has gained momentum, with work beginning in earnest on two such projects: power generation from ocean currents and ocean tides.

In August 2012, the Cabinet-level National Science Council (NSC) announced plans to launch an ocean power pilot plant in the waters near Green Island, just off the coast of Taitung County, eastern Taiwan. The NSC, Taiwan’s main government agency for scientific research, has allotted NT$3 billion (US$100 million) for the pilot plant, which is aimed at generating 30 megawatts of electricity, or enough power for well more than 50,000 households. Depending on the results, the pilot plant, which is expected to begin operation by 2016, could pave the way for a commercial power plant consisting of one or both technologies. A large-scale plant would have the potential to generate an astounding 10 gigawatts of energy, or the equivalent of two nuclear power plants, according to estimates by the NSC.

The turbine prototype developed by NTOU is designed to take advantage of the Kuroshio Current—the name means “black tide” in Japanese, a reference to its dark waters—which runs from the Philippines to Japan along the east coast of Taiwan and is one of the world’s major ocean currents.

“With the right budget, clusters of generators powered by 20-meter-diameter rotors will eventually come into being,” says Kehr Young-zehr (柯永澤), a professor at NTOU’s Department of Systems Engineering and Naval Architecture and the leader of the team that created the ocean current generator prototype. “It all comes down to political will—everything will go smoothly if the government continues to pour funds into the research.”

In terms of energy security, a functioning ocean-based power plant could bring about a huge improvement in Taiwan’s situation. Currently the country’s economy depends on fuel shipped from the Persian Gulf, Africa or mainland China, and if, for any reason, those supplies became unavailable or recorded significant price increases, economic activity in Taiwan would suffer greatly. Neither is nuclear power regarded as a panacea for meeting energy needs. The densely populated island is prone to earthquakes and vulnerable to the threat of tsunamis, and since the nuclear disaster in Japan in March 2011, there has been a groundswell of public support toward creating a nuclear-free Taiwan.

Traditional green energy sources also come with significant drawbacks that limit their usefulness. The wind along the west coast of Taiwan, the island’s industrial heartland, seesaws between slight breezes and typhoon-strength gales. This means that many of the locations where the electricity is needed most are poor choices to set up wind turbines. Moreover, energy from the wind is difficult to store. While solar power seems an obvious choice given Taiwan’s abundant days of sunny weather, just as in the case of wind power, there are profound problems associated with electricity storage. So far, no cost-efficient way has been found to enable solar power, which is harvested in the daytime, to power the many factories in the country that operate 24 hours a day. Making matters even worse is the isolation of Taiwan’s grid. This rules out the possibility of making emergency energy purchases from neighboring countries if local supplies are insufficient, a measure green role model Germany, for instance, is forced to rely on every now and then. While there would still be transportation problems for energy generated in the ocean off Taiwan’s east coast, power supplies from currents or tides would be steady and predictable.

Sea trials for NTOU’s ocean current generator prototype began in August 2012 at Keelung Sill, a shallow ocean area located between the city’s port and nearby Keelung Island. Kehr’s team has worked on the model since about mid-2010. The prototype cost NT$4 million (US$134,000) to build, and prior to its maiden sea launch, had undergone extensive fine-tuning in the university’s enormous cavitation tunnel, a water chamber used to test designs for ship propellers, hulls and, once in a while, torpedoes. Next to the rotor and the magnetic power generator, the most crucial parts are the gears, which increase the revolutions per minute so that the whole device can be kept reasonably small, as well as the tail fin, which enables it to adjust automatically to changes in the direction of the current’s flow. Funding for the prototype came from the NSC.

For its first sea test, a diver attached the prototype to a concrete foundation on the ocean floor at a depth of about 10 meters. It will be a decisively different matter for a pilot plant, however, Kehr says, because he foresees it being set up in much deeper waters just northwest of Green Island. “Functioning as a barrier, Green Island effectively splits the Kuroshio Current in two,” Kehr explains of the chosen location. “The flow’s speed is the highest in the area behind the island, where the two currents unite again and the sea bottom rises up dramatically, confining the flow passage. This phenomenon dictates where the turbines must be placed.”

Deep Down Below

The problem is that the ocean is at least 100 meters deep in the 20-kilometer-long field targeted for the pilot plant, meaning that the generators could not be simply screwed onto a concrete base on the seabed. Instead, they will be moored to the ocean floor with cables and float 25 meters below the surface. In the event of a typhoon, he says, “When the sea’s surface turns too rough, the generators will be lowered further. This can be achieved by altering the buoyancy both through ‘wings’ that work much like landing airbrakes on aircraft, and pumps that either allow sea water into built-in containers or empty them.”

 

When asked about the most difficult part of the plan, Kehr does not have to ponder long. “It’s very challenging to actually fix the cables to the ocean floor,” he says. “Oil pipelines have certain measures, but those are expensive. We still have to find an economical solution.”

Another headache will undoubtedly be maintenance of the power generators. A number of them will eventually be installed in huge metal boxes, or, as Kehr calls them, “bodies,” which could measure dozens of meters in length and width. Sea grass will grow quickly on the bodies, and will have to be scraped off regularly as it would otherwise increase their weight greatly.

Nonetheless, Kehr is obviously confident that the difficulties can be overcome. Once running, the pilot facility alone would easily cover the energy needs of the some 2,000 people of Green Island, who currently rely on diesel fuel, a far more expensive power source than the coal used elsewhere in Taiwan, he says.

That the NTOU project is taken very seriously is also evident by the participation of Wanchi Steel Industrial Co., Ltd., one of Taiwan’s major players in that heavy industry. The company’s engineers have been involved in quite a number of the island’s high-profile projects, such as Formosa Petrochemical Corp.’s No. 6 Naphtha Cracker Plant, the Taiwan High Speed Rail and Taiwan Power Co.’s Fourth Nuclear Power Plant (currently under construction). Wanchi has built a prototype of the bodies that will surround the current power generators; the first sea trials were scheduled for late 2012.

Kehr is enthusiastic about Taiwan’s potential to blaze a trail in developing the needed technology. “The Kuroshio project is totally different from what other countries have been doing,” he says, explaining that although Canada, England and Ireland already have a number of ocean-based power generation plants running, they use tidal power, as opposed to ocean currents. “Whereas tidal power is only good during a few hours a day, current power can be harvested ’round the clock,” Kehr says. “That solves the problem of electricity storage somewhat. The Kuroshio [is part of the North Pacific Ocean gyre that] also runs along Alaska, Japan and the Philippines, yet the position of Green Island as a flow speed enhancer makes it most promising here in Taiwan.”

A second local group searching for energy from the sea is led by Chen Bang-fuh (陳邦富), a professor in the Department of Marine Environment and Engineering at National Sun Yat-sen University (NSYSU) in Kaohsiung, southern Taiwan. Chen’s group, similar to his foreign counterparts, is focusing on tidal power, which can be generated in much shallower waters.

Riding the Tide

Development of the team’s prototype took three years and cost NT$3.5 million (US$117,000), an amount also funded by the NSC. The device looks a little like a very dumpy catamaran floating on the water’s surface, with a 1.2 meter rotor positioned about 2.5 meters underwater between the two hulls. During its first sea trials in the waters off Penghu, an island in the Taiwan Strait, it was not fixed directly to the ocean floor, but anchored to concrete blocks on the seabed. Chen acknowledges that meaningful amounts of energy can only be generated when the tide is going out, but the crucial advantage of the system is that it avoids the prohibitively high construction and operation costs of deep-water designs.

The NSYSU team launched their prototype in early August 2012, around the same time as the NTOU project, but, as it happened, the first sea trial began just one day before Typhoon Tembin battered Taiwan. The results were encouraging, nonetheless, as the prototype passed the ordeal with flying colors, according to Chen. “Taiwan’s first submerged tidal current magnetic generator worked well for at least four days before the turbine was hit by floating timber,” he says. “The tidal current velocity was a little bit more than 0.5 meters per second, leading to output power of around 82 watts.”

While that does not seem like much, Chen says that if the water flow through the device could be increased to 1.5 meters per second—easily achieved with simple changes to the design, according to the professor—output would reach more than 2 kilowatts, which is sufficient to run about 40 household fans.

Testing for both the tidal power and current power prototypes is likely to move to the waters near Green Island later this year.

One issue causing headaches for the NSYSU team is how to protect the rotor from objects such as driftwood without slowing the flow speed. The solution will eventually be some sort of net, but the exact design still has to be worked out, he says. Another challenge is the waterproofing for certain mechanisms. Just as for NTOU’s ocean current power generator, the entire tidal power device would be lowered beneath the surface of the water whenever a typhoon approaches, so any seals would have to be able to withstand increased water pressure.

The scale of power generation is another important factor in whether or not the scheme is commercially viable. “Investors will be attracted from 1 megawatt upward,” Chen says. According to his blueprints, about 25 units producing 10 kilowatts each would be installed in a body, so that a cluster of just a few bodies would make the idea economically feasible. “The NSC envisions that to happen near Green Island by 2030,” he says.

Another issue is the number of highly skilled workers required. A glance at Chen’s team makes it apparent that experts from quite a number of scientific fields must act in concert to achieve such hugely ambitious aims. So far the team has an electrical, a mechanical, a civil and an ocean engineer, a marine physicist and marine architect, among others.

In addition, just because energy produced through ocean power generation is categorized as renewable, that does not mean it is environmentally friendly, says Bruno Walther, an assistant professor of environmental science at Taipei Medical University. According to him, the environmental friendliness of the project will also depend on its scale. “For example, it’s fine if 1 percent of Europe’s North Sea is plastered with wind power generators, as long as they’re not placed right in the middle of migratory birds’ flyways. But if it’s 10 to 20 percent, it’s too much,” Walther says.

He says the same formula is true for ocean current power generators, as the more of them are set up in a certain spot, the more their construction, maintenance and operation will negatively affect the environment. “Just as has been done for wind power, extensive research has to precede the establishment of ocean power plants,” Walther says. For example, studies showed that rotors that spun too fast destroyed large numbers of birds and bats, “but the damage decreased significantly after the speed was adjusted,” he says. “So, will the fish be sucked in and cut into pieces? What will grow on these machines and how will it be removed? These are the questions science has to answer.”

That is by no means to say that Walther is not crossing his fingers as firmly as he can for Kehr and Chen. The technology the two have been working on is promising, and indeed, as water has a much higher density than air, theoretically much more energy could be produced by ocean rotors than wind turbines, he says.

“Power saving in combination with renewable energy are the only measures that can solve our energy problems,” Walther says. “Well, ideally, that would come along with an end to indefinite economic growth.”

In Chen’s eyes, there is another important ingredient to making the dream of environmentally friendly power a reality: passion. “To succeed it is crucial that the scientists involved are happy spending their time developing and fine-tuning the technology needed,” he says. “And if we get commercial ocean power plants running, there will be no more need for nuclear power.”

Copyright © 2013 by Jens Kastner
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