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China Funds Development Of New Tidal Current Energy Devices
China Develops Tidal Current Energy Generators To Help Expand the Countryís Use of Marine Renewables

By Gao Yanbo
Ph.D. Candidate
Dalian Maritime University
Dalian, China

Li Yan
Engineer
and
Ma Changlei
Engineer
National Ocean Technology Center
Tianjin, China


Though the Chinese government has been supporting research on marine renewable energy development and utilization technology since the 1960s, with todayís depleted fossil energy reserves and the threat of climate change, it has never been more important to develop and utilize alternative forms of energy.

In 2000, the Chinese government strengthened support for clean energy from the ocean, setting a goal to develop and use marine renewable energy within the next decade. The government also formulated a renewable energy law and development plan, and Chinaís Ministry of Science and Technology said it considered technical research on marine renewable energy one of the key areas for support.

One type of marine renewable energy that has been of particular interest to China is tidal power. Tidal power generation is similar to wind power generation; the tidal current (moving at about two to four meters per second) rotates a turbine to consistently generate electricity. While some other sources of renewable energy, particularly wind and solar, have been criticized as unreliable, tidal current energy can be regularly predicted many years in advance, allowing it to be easily integrated with other energy sources to reduce fluctuations in supply.

According to the U.N. Convention on the Law of the Sea, China has abundant marine resources under its jurisdiction, with about three million square kilometers of ocean area, 18,000 kilometers of mainland coastline and 14,000 kilometers of island coastline.

Some preliminary studies have been done to determine the theoretic average tidal current power of these marine areas. One hundred and thirty channels in China have been studied, with results suggesting the theoretical average tidal current power of these channels is about 14 gigawatts. The data also suggest that the Zhoushan area and Hangzhou Bay in Zhejiang province have about 50 percent of the nationís tidal current energy resources, since these areas feature many channels with a high-speed, high-volume current. Additionally, the Liaoning, Shandong, Fujian and Taiwan coasts each have roughly 1.1 million to 2.3 million kilowatts of potential tidal power. Such areas with a large number of high-energy channels have higher current velocity and are more suitable for tidal current energy sites.

Compared with conventional energy such as coal, petroleum and natural gas, tidal current energy technology is still at an early stage of development, but prototypes have been tested in China, the U.K., Norway, Canada and elsewhere that have shown promising results.

Forty-kilowatt Wanxiang-II tidal current energy device designed by Harbin Engineering University.


Chinese Tidal Energy Devices
Systematic research on tidal current energy in China began in 1982. Since then, researchers have made considerable progress in the development of tidal current energy generators.

One of the earliest devices to be developed was the 70-kilowatt floating vertically oriented tidal current energy generator Wanxiang-I, designed by Harbin Engineering University and completed in January 2002. The device consists of a ship-shaped pontoon carrier, turbine, mooring system, electric generator and control system. The turbine is housed inside the pontoon carrier, which is anchored to blocks on the seafloor to hold the device in place. The turbine has two rotors on a vertical axis with adjustable-angle blades. The main-axle output port connects with a hydraulic pressure and control system that converts mechanical energy into continuous pressure, which drives the generator. The tidal current generating station serves the functions of battery-charge control, preventing overcharging, paralleling control and related protective functions.

Wanxiang-I was installed in Guishan, China, in an area 40 to 70 meters deep and 100 meters from the coast, and it has since been providing power to a small area. This deployment has shown the Wanxiang-I infrastructure to be successful and easily installed and maintained.

Then, in November 2005, Wanxiang-II, a 40-kilowatt bottom fixed vertical-axis tidal current energy plant, was installed in the tidal channel between Gaoting on Daishan Island in Zhejiang province and Duigangshan Island, China.

Wanxiang-II has two H-shaped rotors with adjustable-angle blades and a vertical axle. It consists of a cabin, a pontoon, a cone, a caisson and riggers.

The device differs from Wanxiang-I in that it is located on the seabed to avoid damage from typhoons, and it transports power to shore through seabed cables, where the power is converted and regulated to be used for a lighthouse. It can float to the surface when it requires maintenance. In the years since its deployment, Wanxiang-II has been proven to have improved energy conversion efficiency over Wanxiang-I.

Harbin Engineering University later collaborated with Ponte di Archimede International Co. (Messina, Italy) to develop a 250-kilowatt device based on the companyís Kobold vertical-axis turbine. The design has been completed, and the new device will be installed in coastal Zhejiang.

Other recent Chinese tidal energy devices have used horizontally oriented turbines. While this design is more efficient at producing energy, it has the drawback that the turbineís direction must be changed according to the tide.

Five-kilowatt tidal current energy device designed by Zhejiang University.

Northeast Normal University developed a one-kilowatt underwater horizontal-axis turbine to provide supplemental energy for underwater monitoring equipment. The device includes a mooring system, generator and flexible shaft. The transform efficiency of the horizontal-axis turbine is higher. In order to improve efficiency during reversed tidal current, the design features a flexible shaft, providing variable pitch.

In addition, Zhejiang University designed a five-kilowatt stationary horizontal-axis turbine with a fixed base. The prototype was successfully tested in Daishan in 2005. Zhejiang University also developed a 25-kilowatt tidal current energy conversion prototype. They have made progress in developing methods to aid in sealing and lubricating the device, as well as preventing debris from winding around the turbine.

Conclusions
As the world seeks new means of powering itself to reduce dependence on fossil fuels and carbon pollution, the Chinese government has held a leading role in the development of marine renewable energy, particularly tidal power.

Chinese academic institutions are developing strong new designs to harness Chinaís vast tidal energy resources, and many of these devices already demonstrating their worth in the water. Though major challenges remain to be solved, such as sealing the device, avoiding corrosion, preventing floating debris from winding around the turbine blade and automating the alignment of the turbine based on flow direction, a new era in the development of Chinese marine renewable energy is on the horizon.


Acknowledgments
This article was funded by grant No. 908-02-09-01-03 from Chinaís State Oceanic Administration.

Additional thanks go to the crews of the research vessels that contributed to this project.



Gao Yanbo is a Ph.D. candidate at the institute of environmental science of Dalian Maritime University. She has been researching marine monitoring technology at the National Ocean Technology Center since she received her M.S. in geology in 1996.

Li Yan is an engineer at the National Ocean Technology Center of China. She received her bachelorís degree in 2004 and masterís degree in marine biology from the Ocean University of China in 2007.

Ma Changlei received his M.S. in marine monitoring technology from the National Ocean Technology Center. He has worked as an engineer focusing on marine strategy since 2003. His research interests include the application and integration of oceanographic sensor platforms.




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