Andrew Thompson Ultra-Small Scale Hydroelectric as a Supplemental Energy Source Faculty Mentor: Daniel Maynes, Department of Mechanical Engineering For centuries water has been used as a source of power; from the middle ages where waterwheels were used for simple mechanical tasks to the 21st century where large hydroelectric power plants supply megawatts of electricity to the power grid. In recent decades developing and remote regions in Tibet, Laos, Uganda and parts of Latin America, have begun using small scale hydroelectric generators to provide electricity to their areas. With the rising concerns of greenhouse gas emissions, developed nations have also begun to look into ‘small scale hydro.’1 Where there is a sufficient water supply these small scale generators possess several advantages over other forms of alternative energy. First, hydroelectric power generation is generally highly efficient (between 70% and 90%). The output is very predictable; it is very simple to calculate the power output from flow rate and available head. They can be very inexpensive to install and maintain; the necessary equipment is usually locally available. Because of their simplicity, small scale hydro is environmentally benign and long lasting.2 The impetus behind this project was to apply the concepts of small scale hydro to the production of hydroelectric energy by placing small turbines inside of a water main and using the preexisting plumbing to turn the turbine to supplement the energy needs of a home or business. There are two main parameters that characterize small scale hydro independent of the type of turbine used. These are head and flow rate with flow rate being the most important factor in the production of power. Head, also known as pressure head, is defined as the height of a column of fluid necessary to develop a specific pressure3, representing the potential energy in a column of water. Flow rate is the volume of water moving through an area in a certain time and can be determined either by multiplying the cross-sectional area of the pipe by the velocity of the water moving through it, or by using a flow meter. Using these parameters the theoretical power that can be generated is2 found by multiplying the head, flow rate, density of the fluid, gravitational acceleration, and efficiency. This is the maximum amount of power at a certain efficiency that can be produced by a column of water. There are two types of turbines that were used in this project, impulse and axial. Impulse turbines are characterized by water impinging on buckets or vanes and are optimized for operation at low specific speeds (high head/low flow). An axial turbine is essentially a propeller and is optimized at high specific speeds (low head/high flow).4 These turbines were mounted on a hydraulic table that provided 23 m of head and connected to a tube flow meter with a 15 gpm capacity. The turbine shaft was connected to a torque sensor and an encoder that output data to a LabView VI to measure torque and angular velocity. These values were multiplied together to determine the power. It was found that the theoretical maximum amount of power that could be produced by an ultra-small scale hydro generator was about 70 watts. Though this is not a large amount of power, it could be used to charge a battery bank and supplement a home’s power usage. It was also found that this power would come at a pressure loss, which in a residential situation would be unacceptable. Though there is a large amount of head for this application, it is more important to have a large amount of flow. When water was actually run through the turbines an insignificant amount of power was produced (a maximum of 0.8 watts), possibly due to misalignment of the interface between the shaft and the torque sensor, misalignment of the shaft in the bearings (for the axial flow turbine), ‘water braking,’ water not impinging on the correct part of the axial turbine, and because of the size of the turbines not enough torque could be generated. It is apparent from this project that ultra-small scale hydroelectric generation is not a practical means to produce power in a residential context because of the low amount of flow and its intermittency. To be practical, a turbine should be placed in a stream of running water that can provide a large amount of flow and an adequate amount of head. The turbine also needs to be of a size that can generate the torque necessary to turn a generator. With these requirements met, small scale hydro could produce the power necessary to power a home. 1. Micro-Hydro Power, Knowledge and Information Services, The Schumacher Centre for Technology and Development, Bourton Hall, Bourton-on-Dunamore, Rugby Warwichshire, UK. 2. A Guide to UK Mini-Hydro Developments, (January, 2005), British Hydropower Association. 3. Sybil P. Parker, Editor and Chief, McGraw Hill Dictionary of Science and Engineering, (1984), McGraw Hill Book Company. 4. Munson, B.R., Young, D.F., Okiishi, T.H. (2006) Fundamentals of Fluid Mechanics, Fifth Edition. John Wiley and Sons. For more information, the author is invited to request a copy of the full report from the author.
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