Designing Prototype Tidal Current Turbines in Taiwan

Since the island has limited energy resources, developing renewable energy projects is an imperative for the government of Taiwan.  Although it has a few on-shore wind turbines, ocean-based renewable energies are an obvious alternative since the country is surrounded by the Pacific Ocean.  This line of thinking has secured National Science Council funding for Tsai et al. (2010) to begin the design and testing of prototype tidal current turbines.  The team plans to conduct field tests between Keelung Harbor and Keelung Island because of the high speeds that currents achieve while traveling over Keelung Sill.  Tsai et al. are primarily focused on designing blades, with an ideal camber and pitch, and turbines, which will move automatically to take advantage of the changing direction of currents.  Once a prototype is designed, the will test for the design’s dynamic response to irregular waves and winds, non-uniform currents and typhoon conditions.  If they are successful, Taiwan will be closer to its goal of increasing renewable energy to 10% of total capacity by 2025.—Juliet Archer
          Tsai, C., Doong, D., Kehr, Y., Li, H., Ho, C., Kuo, N., Huang, S., Lo, Y., Lee, H., 2010.  A pilot project on ocean energy generation by tidal currents on the northern coast of Taiwan.  Oceans 2010 IEEE – Sydney, 1–5.

     

          Cheng-Han Tsai and colleagues at the National Taiwan Ocean University and Minghsin University of Science and Technology have undertaken five related projects in order to install a 3 kW current generator on Keelung Sill and to better understand the dynamic responses of tidal energy converters.  The first three projects aim to simulate and assess the tidal current power surrounding Taiwan and especially that of the Keelung Sill area.  To accomplish this challenging task, Tsai et al. use a numerical model, in situ measurements and satellite images.  In order to simulate tides numerically, the model used a finite difference method[1] to solve control equations.  In addition, a vertically integrated continuity equation and equations of motion in x and y directions were used along with a hydrostatic equation[2] that determined pressure at depth z.  To measure water velocity, the model averaged volume transport over depth.  The numerical model shows that strong currents are present at Keelung Sill.  However, the model is likely an underestimation of current velocity because it shows a maximum velocity of only 1.0 m/s in a 24-hour cycle. 
          In order to verify their model, the Tsai et al. are conducting in-situ measurements of the currents at Keelung sill three times, for at least one month each.  The velocity is measured by deploying Aquadopp Profilers (at depths of 10m, 15m, and 20m) in addition to an Aquadopp (at 5m) and a RCM-7 current meter (at 20m).  These instruments are deployed at five different sites on Keelung Sill during each testing period.  Preliminary measured results show that the current speed in this area can be as high as 2.2–2.4 m/s depending on the depth, 15–20 m, respectively.  These early results confirm the team’s suspicion that the numerical model underestimated current speed.  From these measurements the power (in Watts) of the current can be calculated, using velocity, an efficiency coefficient, the water density and the blade sweep area. 
          The third project of Tsai et al. is to determine water depth, tidal elevation, and tidal energy around Keelung Sill using high frequency satellite images.  The scientists will use a Formosa-2 satellite that has a sun-synchronous orbit.  The images will be used to calculate temporal-variable water depth, which can then be compared to the in-situ data.  This information will also be used to estimate tidal elevation and energy.  Developing a tidal current turbine is the fourth project presented in this paper.  The team’s objective is to find the ideal configuration of blade camber and pitch so that the turbine will produce the maximum power output, based on the current speed.  The team also plans on designing a turbine that moves, on its own, in response to a current’s change in direction.  If Tsai et al. succeed, the turbine will always face into the current and therefore maximize its power production.  Before testing on-site, the power generation capacity of the design will be tested at the National Taiwan Ocean University’s cavitation tunnel. 
          The last project planned is the assessment of the dynamic response behavior of the new turbine.  This project will begin with the installation of the team’s 3 kW turbine design at Keelung Sill.  The scientists are interested in this topic because there are few data available on the response of turbines to the forces of winds, waves, and currents.  Their hypothesis is that the blade will experience the most load variations.  The team is especially interested in the effect of extreme forces, present during typhoon conditions, on the blades and structure of turbines.  This information is pertinent because of their government’s goal of increasing renewable energy production and its emphasis on ocean-based renewable energies.  If ocean current energy production is to be a viable option for Taiwan, then turbine designs must withstand typhoon conditions[3].  Although these on-going projects are not complete, significant results are expected based on the ambitious goals and detailed plans that have been laid out in this paper.     
Other Sources
American Meteorological Society.  “Glossary of Meteorology.”  Accessed February 12, 2011.  http://amsglossary.allenpress.com/glossary/browse?s=h&p=36
Central Weather Bureau of Taiwan.  “Meterology Encyclopedia.”  Accessed February 13, 2011.  http://www.cwb.gov.tw/V6e/education/encyclopedia/ty015.html
Wikipedia. “Finite difference method.” Last modified December 31, 2010.  Accessed February 12, 2011.  http://en.wikipedia.org/wiki/Finite_difference_method


[1] “Finite-difference methods approximate the solutions to differential equations using finite difference equations to approximate derivatives” (Wikipedia)
[2] “The form assumed by the vertical component of the vector equation of motion when all Coriolis, earth curvature, frictional, and vertical acceleration terms are considered negligible compared with those involving the vertical pressure force and the force of gravity” (American Meteorological Society)
[3] An average of three to four typhoons hit Taiwan each year. (Central Weather Bureau of Taiwan)

One thought on “Designing Prototype Tidal Current Turbines in Taiwan

  1. This was a very enjoyable blog entry for me as a first time visitor. I was an anthropology/environmental studies student during the Carter administration. That administration was very environmentally friendly, and encouraged research into several projects (i.e. wind, solar, geothermal, tidal). I remember at that time, that some generators were placed in the Gulf Stream, but because of their fixed position and lengthy blade shafts, too many of the blades broke due to shifts in the current direction and velocity.

    Though I would someday love to see the whole Eastern U.S. supplied with power from the Gulf Stream, I am happy to see that tidal/current technology is being studied and developed in Taiwan where I once lived for two and a half years.

    I enjoy your blog, and will subscribe. Thank you.

    Like

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