ANALYSIS OF HYDROKINETIC TURBINES

PROJECT SUMMARY REPORT

ANALYSIS OF HYDROKINETIC TURBINES

Submitted To

The 2012-13 Academic Year NSF AY-REU ProgramPart of

NSF Type 1 STEP Grant

Sponsored ByThe National Science Foundation

Grant ID No.: DUE-0756921

College of Engineering and Applied ScienceUniversity of Cincinnati

Cincinnati, Ohio

Prepared By

Joe Tscherne, 5th Year Senior, Aerospace EngineeringJarred Wilhite, 4th Year Junior, Aerospace Engineering

Dr. Karman N. GhiaREU Faculty Mentor

Aerospace EngineeringUniversity of Cincinnati

January 7 – April 19, 2013

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Goals & Objectives of Project

Currently the subject of renewable, low-cost energy is of great interest across the world. As use of burning fossil fuels keep increasing, and the current reservoirs are depleting, there is a major effort to find sustainable energy for the future. Utilizing natural currents of our oceans and rivers is one of the possible sources of energy. The ocean currents are energized by the Earth’s natural gravitational and tidal forces; therefore there is a virtually limitless source. Hydrokinetic turbines would take advantage of this source of energy, and convert these natural current’s kinetic energy into useful mechanical work. The background for these devices, their many challenges, current practices, and future potential will all be examined.

A turbine is defined as a rotary mechanical device which functions by taking energy from a fluid flow and converting the energy into electricity or other useful power. A wind turbine is powered by air and uses the wind to rotate. It converts the kinetic energy from the wind into mechanical energy. A hydrokinetic turbine works in a similar manner, but instead uses the natural currents in the ocean and rivers in order to rotate. It extracts kinetic energy from the currents and converts the energy into electricity. Since water has a higher density than air, it also has greater kinetic energy than air. Therefore, hydrokinetic turbines have the ability to generation of greater kinetic energy than the corresponding wind turbines, which means more energy produced per turbine. A hydrokinetic turbine is also known as a tidal turbine, current turbine, or wave turbine.

Hydrokinetic turbines have the potential to be a very useful and promising source of clean, renewable energy and it appears it should have minimal impact on the environment. These turbines are arranged carefully to form a farm. Thus, the typical farm house a large number of turbines to harness abundant energy from oceans and rivers and this energy is converted to electrical energy to power homes, buildings, and even entire cities. Different farm arrangements will be discussed in further detail later in this report.

The goals for this project are; i) to increase our knowledge and understanding of the engineering technology related to turbines, ii) To educate ourselves on the current practices and future of hydrokinetic

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turbines currently being used in different parts of the world, iii) To instill the importance of this technology upon others, iv) To promote future research into the field of hydrokinetic turbines, and v) To familiarize ourselves with aerodynamic concepts that are involved with the operation of hydrokinetic turbines.

The analysis of hydrokinetic turbines is such a vast topic. There are so many aspects of hydrokinetic turbines that one can study, for instance the best turbine arrangement for optimal power output, the best location to place the turbines, the environmental impact of the turbines, and so on. An individual could spend years conducting research on hydrokinetic turbines and could still not know everything about them. Since we were given a limited time frame to research this topic, we aimed to gain a basic understanding of the function of these turbines and to get a general idea of the potential power output they could produce.

Research Tasks Undertaken

Since this project relies heavily on research and acquiring information on hydrokinetic turbines, the Internet was the main resource that was used throughout this project. Various websites like the UC Library website, Google Scholar, and Aerospace Database were used to find information on the hydrokinetic turbines. Zhisong Li, a former doctoral student of our mentor Dr. Karman Ghia, wrote his doctoral thesis on hydrokinetic turbines. This thesis is entitled, “Advanced Computational Modeling for Marine Tidal Turbines,” and it was one of our main sources of scientific information for this project.

Figure 1: Joe Tscherne finding information on hydrokinetic turbines on the Aerospace Database website

There are many types of challenges that come with the installation of hydrokinetic turbines. One of the main issues is with the actual location of the turbine. It needs to be placed in relatively shallow water, preferably a depth of less than 500 feet, to keep the cost of installation and the production of electrical power to a minimum. The farther underwater they are placed, the more difficult it becomes for construction as well as maintenance, which can also be considered one of the major challenges. This location will also need steady, predictable current to pass through it at all times to make the turbine a reliable energy source. Ideally this current would need to travel at about 4 knots.

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Figure 2: Joe Tscherne has found a very interesting piece of information that will benefit the project

Figure 3: Joe Tscherne explaining his findings to his research partner, Jarred Wilhite

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Another issue with construction and operation underwater is the environmental impact the tidal current farm may have. This could come in the form of disrupting the marine life in terms of their migration patterns, causing certain species to simply stop traveling the paths where turbines occupy. It could also alter locally the actual natural current flow of the ocean or river the turbine is located. This would be harmful not only to marine life but have an impact farther down the current path as well, i.e. the ocean the river flows out to or another part of the globe the ocean current flows to.

Figure 4: Jarred Wilhite watching a video on how hydrokinetic turbines function

A third issue is that the components of the turbine being exposed to saltwater may have a corrosion factor over a long period of time underwater. Though this is not considered a priority issue; the turbines can be constructed from corrosion-proof materials if the environmental impact of corroding parts is found to be great. This would also include the leaking of mechanical fluids such as oil into the river or ocean, which obviously needs to be avoided at all costs.

Methodologies and Results

There are two types of wind turbines and hydrokinetic turbines, and they are horizontal axis and vertical axis turbines. Horizontal axis turbines need to be aligned with the wind and they use a yaw system. Horizontal axis turbines are often elevated high off the ground to obtain greater wind speed. Vertical axis turbines are always aligned with the wind, and only need a “boost” in order to start. The design of vertical axis turbine makes the installation lower to the ground. This allows for easy maintenance, but also slower wind speed. Similar issues also prevail for hydrokinetic turbines.

An analysis of the power production by turbines was done by focusing on the fluids they are powered by, in this case wind and water. This was accomplished through the turbine power equation, as shown below:

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As the density of water is substantially greater than the density of air, it will play a great impact in the energy production comparison between wind powered and water powered turbines. A comparison of these can be seen in the table below:

The table shows two typical turbines one would find for applicable use. It can be seen that the water powered turbine needs far less area in contact with the fluid to provide essentially the same amount of power. This is important because the blades of hydrokinetic turbines cannot be very large due to the pressure from the water above pushing down on them.

The rate of energy usage by the typical American household can range anywhere from 17 kWh/day (Maine) to 43 kWh/day (Tennessee). This brings about an average of 30 kWh/day for the average household. Looking at the previously studied wind turbine, it can be seen that the 1.2 mW of power it produces can theoretically provide 40 homes with electricity. If this turbine was put into a farm formation (x50) it would be possible to supply 2000 homes. This is in an ideal case and will not technically be correct due to energy losses by flow disturbances and energy loss through transferring, but for this study we will assume theoretical output. Comparing this to the water powered turbine, it will provide a few more homes due to the power production (1.2 mW vs. 1.12 mW). However, if the blades of the water powered turbine were doubled in size from 5m to 10m, the increase in energy production is very substantial. This would cause it to jump from 1.12 mW to 4.5 mW, and in a farm configuration provide power for up to 7500 homes. Again, this is in an ideal setting with maximum power production from every turbine, which will generally not be the case.

A lack of predictability has been problem in the past with natural alternative energy forms. This is especially true with wind turbines since the wind often changes direction and it does not blow constantly. If the hydrokinetic turbines are placed in a river or ocean with a current that constantly flows, there will never be a problem of having periods of low energy generation. This holds true even if the current is moving relatively slowly. For these reasons, reliability and predictability are the main advantages of using hydrokinetic turbines for sources of energy. Hydrokinetic turbines also have the potential to minimize both visual and noise pollution. These turbines will clearly be located underwater, which means they will be located in areas where few people would be affected by their presence. They will not cause a problem of noise pollution or excessive, disruptive noise that is often caused by wind turbines.

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Expensive deployments and constructions are likely to be involved when building tidal turbine facilities, since it is difficult to build such a structure underwater and the cost is high due to a challenging environment. Because of this, it is important to figure out the most cost effective means of deployment, which is to locate several turbines together in a farm configuration, which will minimize some of the costs, such as cabling and servicing. However, grouping turbines together poses problems. For example, the wake of the upstream turbines may interfere with downstream turbines, which will reduce the amount of overall energy produced by the farm. In addition, the turbulence caused by the wake of turbine in the first row will result in a decrease of energy produced by turbines in subsequent rows. When installing a cluster of turbines in a turbine farm, certain spacing between the turbines must be maintained in order to optimize power output. Spacing depends on the terrain, current direction and speed, turbine size, etc.

Dr. Li (2012) evaluated multiple turbine configuration layouts in his doctoral thesis, and here we have focused on two of them for this project. The first layout is a configuration with four rotors which resembles a parallelogram shape. The second layout is a configuration in which the rotors are in a slanted line formation. In his thesis, Dr. Li recommended the latter layout, which is why it was studied for this project. Also, the parallelogram configuration was investigated since it was easiest to compare to the slanted line configuration. The turbine rotors in the diagrams are separated in terms of rotor diameter, D. To get an idea of the distance between the rotors, the SeaGen tidal turbine has two axial flow rotors with diameters of 15-20 meters.

Figure 1: Turbine Arrangement in Parallelogram Configuration 7

As can be seen from Figure 1, the parallelogram layout has a leading rotor in the row upstream, two rotors in the middle row, and one in the downstream row. Each row is separated by five rotor diameters and three rotor diameters in the y-direction between the axes of the two rotors in the middle row. Each of the two rotors rotates at 1.5 rad/s while the downstream rotor rotates in the opposite direction at -1.2 rad/s.

Figure 2: Turbine Arrangement in Slanted Line Configuration 7

The second configuration is shown in Figure 2, and is in a slanted line formation, which can be seen as a small segment of a large arced layout. Each turbine is separated by 5.28 rotor diameters in the x-direction, and 1.5 diameters in the y-direction between the axes of the rotors. Each rotor spins in the same direction at 1.5 rad/s. As previously mentioned, Dr. Li recommended this arrangement. If the turbines are placed close to each other in a clustered manner, channel blockage will become an issue. When the rotors operate, they create a wake, which is highly turbulent. The rotor that is positioned in the wake of another rotor will be compromised by upstream wake turbulence. It will also produce more

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X+

Y

X+

Y

turbulence behind itself. In his thesis, Dr. Li stated the following, “An arced layout may be able to get rid of the adverse side of a blockage channel and benefit from some favorable factors.” The arced layout will create a situation in which two of the three rotors can take energy from an overall faster stream than the inflow. This layout also prohibits any rotor from working under the low-momentum and turbulent wakes, which come from the rotors in the preceding rows in the turbine farm.

The following table lists tidal power stations that have been in operation as of August 2010. Each of these stations uses hydrokinetic turbines.

Station Capacity (MW)

Turbines Country Location Year Commissioned

Jiangxia Tidal Power Station

3.2 1 x 500KW 1 x 600KW 3 x 700KW

China East China Sea 1980

La Rance Tidal Power Station

240 24 x 10MW France Rance River Brittany, France

1966

Sihwa Lake Tidal Power Station

254 10 x 25.4MW

South Korea Sihwa Lake, Gyeonnggi Province

2011

Strangford Lough SeaGen

1.2 1 x 1.2MW United Kingdom

Strangford Lough, Northern Ireland

2008

Proposed

The following table lists tidal power stations that are in the proposal stage.Station Capacity

(MW)Turbines Country Location Proposed

Construction Time

Garorim Bay Tidal Power Station

520 20 x 26 MW South Korea Garorim Bay N/A, but gov’t approved

Gulf of Kutch Project

50 1 x 50 MW India Gulf of Kutch 2012-13

Minas Basin Project

5,000+ 128 Canada Bay of Fundy N/A

Roosevelt Island Tidal Energy

Project

1.05 30 x 35 KW United States New York 2013-End of 2014

Severn Estuary Project

8,640 --- United Kingdom

England & Wales N/A, need to find funding for

project

Conclusions

Hydrokinetic turbines will aid in production of the energy supplied by natural currents in our oceans, and can provide much greater electrical production due to the increased density of water, compared with air. In a farm type arrangement, it can provide a quality energy source for smaller towns and cities. Hydrokinetic turbines show great promise to be a part of the move towards cleaner, sustainable, green energy for the future. Though this form will not be completely relied upon for energy production in the near future, they will help curb the burning of fossil fuels and contribute a small portion to the larger effort. This is similar to the way wind turbines are viewed now in the energy grid.

The subject of hydrokinetic turbines is very broad, and we have touched on several different aspects of it at various depths of detail. Through this work we were able to accomplish our set goals at the beginning of this study, though for a much more thorough understanding of the topic, one could spend years conducting scientific research.

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References

[1] Bahaj, A. S. and Myers, L. E. (2003). “Fundamentals applicable to the utilization of marine current turbines for energy production.” Renewable Energy. 28(4), 2205-2211.

[2] McDermott, M. (2008). “SeaGen Tidal Turbine Begins Full Operation in Northern Ireland.” Treehugger, <http://www.treehugger.com/renewable-energy/seagen-tidal-turbine-begins-full-operation-in-northern-ireland.html> (Dec. 19, 2008)

[3] (2008). “Tidal turbine features composite rotors.” Reinforced Plastics, <http://www.reinforcedplastics.com/view/1648/tidal-turbine-features-composite-rotors/> (May 5, 2008)

[4] van Zwieten, J., Driscoll, F. R., Leonessa, A., and Deane, G. (2006) Design of a prototype ocean current turbine-Part I: mathematical modeling and dynamics simulation. Ocean Engineering. (33).

[5] Wang, J., Piechna, J., Muller, N. (2011). “A Novel Design and Preliminary Investigation of Composite Material Marine Current Turbine.” The Archive of Mechanical Engineering. 355-366.

[6] Wang, J., Piechna, J., Muller, N. (2011). “A Novel Design and Preliminary Investigation of Composite Material Marine Current Turbine.” The Archive of Mechanical Engineering. 28(4), 355-366.

[7] Li, Z. (2012). “Advanced Computational Modeling for Marine Tidal Turbines,” dissertation, submitted to the University of Cincinnati, at Cincinnati, OH in partial fulfillment of Doctor’s Degree of Aerospace Engineering.

[8] Moll, Eric. "How Many Watts of Power Does the Average House Use Per Day?" EHow. Demand Media, 08 Oct. 2010. Web. 01 Apr. 2013. <http://www.ehow.com/facts_7308930_many-house-use-per-day_.html>.

[9] "Tidal Stream Generator." Wikipedia. Wikimedia Foundation, 29 Mar. 2013. Web. 01 Apr. 2013. <http://en.wikipedia.org/wiki/Tidal_stream_generator>.

[10] "Tidal Power." Wikipedia. Wikimedia Foundation, 31 Mar. 2013. Web. 01 Apr. 2013. <http://en.wikipedia.org/wiki/Tidal_power>.

[11] "Tide Turns for Turbines." - IEEE Spectrum. N.p., n.d. Web. 01 Apr. 2013.

[12] "Annapolis Tidal Power Station." Global Greenhouse Warming. N.p., n.d. Web. 01 Apr. 2013.

[13] "5 Largest Tidal Power Projects Proposed for a Green Future." Greendiary Greendiary Lets Go Green and save the Environment for a Sustainable Future. N.p., n.d. Web. 01 Apr. 2013.

*[14]"Jiangxia Pilot Tidal Power Plant - MHK." Jiangxia Pilot Tidal Power Plant - MHK. N.p., n.d. Web. 01 Apr. 2013.

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