Reducing the Cost of Energy by Reducing Overall Cost of the System
Researchers at Cleveland State University (CSU), an urban school in Cleveland, Ohio, have designed a wind tower system that is aligned with the small distributed wind energy systems initiative of Energy Efficiency and Renewable Energy of the US Department of Energy. The patented system is designed to facilitate the conversion of wind energy into useable electricity at locations where the wind speed is relatively low, and where conventional wind turbines do not yield significant amounts of electrical power. One of the goals of this research project at CSU is to reduce the cost for generating electricity via reducing the overall cost of the system. As a result of the unique modular attributes of the design the system can be scaled up along its vertical axis, while at the same time keeping its footprint and the size of its individual turbines unchanged for different targeted power ratings.
By Dr Majid Rashidi, Cleveland State University (CSU), USA
The cylindrical wind-deflecting structure shown in Figure 1 increases the wind speed in its vicinity, where the four turbines are installed. This in turn will result in a lowering of the cut-in wind speed for the turbines. The design configuration of Figure 1 can be retrofitted onto a silo or a water tower. The turbines shown in Figure 1 are 2 metres (about 6.5 feet) in diameter and are capable of turning (yaw) about the vertical axis of the cylinder. A double-worm-gear reducer actively turns the turbines around the cylinder in order to direct them into the prevailing wind. The diameter of the cylinder shown in Figure 1 is about 9 metres (about 29.5 feet). A fifth turbine, not shown in Figure 1, has been installed on the same rooftop, far from the cylinder, so that it is not affected by the cylindrical wind-deflecting structure. The purpose of the fifth turbine is to have a reference stand-alone turbine with a base-line performance, in order to examine the effect of the wind-deflecting structure on the performance of the other four turbines.
Features of the Wind Tower
The unique features of this wind tower are as follows:
In Figure 2, the far right graph (light blue) is the power curve of a stand-alone turbine which received no wind speed augmentation. The four other graphs to the left of the stand-alone power curve are those for the same type of turbines when installed near a cylindrical wind-deflecting structures of 5, 15 and 35 feet (approximately 1.5, 4.5 and 10 metres) in diameter respectively. As shown in Figure 2, when a typical standard wind turbine is installed near a cylindrical wind-deflecting structure, its power generation capability reaches its maximum rated capacity at a lower natural wind speed when compared with the same turbine installed in a standard manner on a mast. For example, consider a turbine installed near a cylinder having a diameter of 15 feet (about 4.5 metres). The power curve for this case is shown in red in Figure 2. In this case when the natural wind speed is about 18 mph (29 kph), the turbine will produce about 1580 watts, whereas the same turbine with a customary installation on a mast (light blue font) produces only 580 watts.
Experimental Results
Figure 3 shows a comparative performance of the turbines in Figure 1 obtained experimentally. This figure is a bar-graph depiction of the average powers for the months of June to October 2009. In this figure, P1, P2, P3 and P4 are the average power outputs generated by the four turbines installed around the main cylindrical wind-deflecting structure of Figure 1, while P5 is the average power generated by the fifth reference turbine which is not affected by the cylinder. As shown in Figure 3, the four turbines of the CSU wind tower have consistently outperformed the reference turbine (no. 5).
The computational results of this work have revealed that a cylindrical wind-deflecting structure increases the wind speed by an average factor of 1.56 by the time the airflow reaches the wind turbines installed near the cylinder. For example, when the natural wind speed is about 10 mph (16 kph), a cylindrical wind-deflecting structure increases the wind speed to about 15.6 mph (25kph). Since the power contained in a stream of wind is proportional to the cubic exponent of its speed, the increased factor of 1.56 in wind speed results in an increase factor of about 3.8 in the wind power reaching the turbines. The experimental results, obtained from CSU’s wind tower prototype, validate the computational results. The experimental and computational results of the research at CSU have shown that when a turbine is installed next to a round structure, the turbine’s electrical energy output is increased. This arrangement also results in a lowering of the cut-in wind speed for the turbine. The wind tower designed at CSU may be retrofitted to existing cylindrical structures such as a silo and/or a water tower. In the case of active water towers, the generated electric power can simply be stored in the water tower, in the form of gravitational potential energy, by pumping water into the elevated reservoir.
A group of students at the Business and Engineering colleges of CSU have formed a company to commercialise the wind tower system. Their marketing strategy is to first implement the technology on farms where cylindrical structures, such as silos and/or water towers, are already integral parts of the infrastructure. Using these pre-existing cylindrical structures, the installation cost will mostly be spent on the equipment and components for retrofitting the turbines.
Biography of the Author
Majid Rashidi, PhD, PE is the Betty L. Gordon Distinguished Professor of the Mechanical Engineering Department, and Chair of the Engineering Technology Department at Cleveland State University in Cleveland, Ohio. His area of research includes machine design, dynamics of gear-trains, and fluid–solid interactions in machinery. He holds eight US patents, four of which relate to wind-power-harnessing systems.{/access}
Researchers at Cleveland State University (CSU), an urban school in Cleveland, Ohio, have designed a wind tower system that is aligned with the small distributed wind energy systems initiative of Energy Efficiency and Renewable Energy of the US Department of Energy. The patented system is designed to facilitate the conversion of wind energy into useable electricity at locations where the wind speed is relatively low, and where conventional wind turbines do not yield significant amounts of electrical power. One of the goals of this research project at CSU is to reduce the cost for generating electricity via reducing the overall cost of the system. As a result of the unique modular attributes of the design the system can be scaled up along its vertical axis, while at the same time keeping its footprint and the size of its individual turbines unchanged for different targeted power ratings.By Dr Majid Rashidi, Cleveland State University (CSU), USA
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The Cleveland State University (CSU) wind tower system design concept focuses on the use of cylindrical wind-deflecting structures to increase wind speed as the stream of wind approaches the turbines. Figure 1 shows a picture of the first fully functional proposed wind tower, fabricated and installed on the rooftop of the Planet Service Building located on the CSU campus.The cylindrical wind-deflecting structure shown in Figure 1 increases the wind speed in its vicinity, where the four turbines are installed. This in turn will result in a lowering of the cut-in wind speed for the turbines. The design configuration of Figure 1 can be retrofitted onto a silo or a water tower. The turbines shown in Figure 1 are 2 metres (about 6.5 feet) in diameter and are capable of turning (yaw) about the vertical axis of the cylinder. A double-worm-gear reducer actively turns the turbines around the cylinder in order to direct them into the prevailing wind. The diameter of the cylinder shown in Figure 1 is about 9 metres (about 29.5 feet). A fifth turbine, not shown in Figure 1, has been installed on the same rooftop, far from the cylinder, so that it is not affected by the cylindrical wind-deflecting structure. The purpose of the fifth turbine is to have a reference stand-alone turbine with a base-line performance, in order to examine the effect of the wind-deflecting structure on the performance of the other four turbines.
Features of the Wind Tower
The unique features of this wind tower are as follows:
- Able to be retrofitted to existing cylindrical structures such as water towers and silos.
- Suitable for use in urban areas with low wind speed regimes (5 to 6 miles per hour (mph), 8 to 10 kilometres per hour (kph)).
- Boosts the capacity of standard rooftop wind turbines by a factor of 3 to 4 times.
In Figure 2, the far right graph (light blue) is the power curve of a stand-alone turbine which received no wind speed augmentation. The four other graphs to the left of the stand-alone power curve are those for the same type of turbines when installed near a cylindrical wind-deflecting structures of 5, 15 and 35 feet (approximately 1.5, 4.5 and 10 metres) in diameter respectively. As shown in Figure 2, when a typical standard wind turbine is installed near a cylindrical wind-deflecting structure, its power generation capability reaches its maximum rated capacity at a lower natural wind speed when compared with the same turbine installed in a standard manner on a mast. For example, consider a turbine installed near a cylinder having a diameter of 15 feet (about 4.5 metres). The power curve for this case is shown in red in Figure 2. In this case when the natural wind speed is about 18 mph (29 kph), the turbine will produce about 1580 watts, whereas the same turbine with a customary installation on a mast (light blue font) produces only 580 watts.
Experimental Results
Figure 3 shows a comparative performance of the turbines in Figure 1 obtained experimentally. This figure is a bar-graph depiction of the average powers for the months of June to October 2009. In this figure, P1, P2, P3 and P4 are the average power outputs generated by the four turbines installed around the main cylindrical wind-deflecting structure of Figure 1, while P5 is the average power generated by the fifth reference turbine which is not affected by the cylinder. As shown in Figure 3, the four turbines of the CSU wind tower have consistently outperformed the reference turbine (no. 5).
The computational results of this work have revealed that a cylindrical wind-deflecting structure increases the wind speed by an average factor of 1.56 by the time the airflow reaches the wind turbines installed near the cylinder. For example, when the natural wind speed is about 10 mph (16 kph), a cylindrical wind-deflecting structure increases the wind speed to about 15.6 mph (25kph). Since the power contained in a stream of wind is proportional to the cubic exponent of its speed, the increased factor of 1.56 in wind speed results in an increase factor of about 3.8 in the wind power reaching the turbines. The experimental results, obtained from CSU’s wind tower prototype, validate the computational results. The experimental and computational results of the research at CSU have shown that when a turbine is installed next to a round structure, the turbine’s electrical energy output is increased. This arrangement also results in a lowering of the cut-in wind speed for the turbine. The wind tower designed at CSU may be retrofitted to existing cylindrical structures such as a silo and/or a water tower. In the case of active water towers, the generated electric power can simply be stored in the water tower, in the form of gravitational potential energy, by pumping water into the elevated reservoir.
A group of students at the Business and Engineering colleges of CSU have formed a company to commercialise the wind tower system. Their marketing strategy is to first implement the technology on farms where cylindrical structures, such as silos and/or water towers, are already integral parts of the infrastructure. Using these pre-existing cylindrical structures, the installation cost will mostly be spent on the equipment and components for retrofitting the turbines.
Biography of the Author
Majid Rashidi, PhD, PE is the Betty L. Gordon Distinguished Professor of the Mechanical Engineering Department, and Chair of the Engineering Technology Department at Cleveland State University in Cleveland, Ohio. His area of research includes machine design, dynamics of gear-trains, and fluid–solid interactions in machinery. He holds eight US patents, four of which relate to wind-power-harnessing systems.{/access}
