Researching Urban Wind Turbines

by

Clare CuiMechanical Engineering Major

The Ohio State University(513) 375-9407

cui.163@osu.edu

Prepared forWind energy researchers everywhere

March 11, 2013

Abstract: The purpose of this proposal is to suggest further research into the area of urban wind turbines. While there has

been considerable research and implementation of wind turbines in rural areas, the growth of the urban area in recent years suggests that mounting small turbines on buildings may be beneficial to city areas. There are concerns with turbulence, wind noise, and public health and approval, however, so more

information and research is still needed on urban wind turbines.

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INTRODUCTIONStatement of ProblemHuman impact on climate change has been an ongoing issue for several of the past decades. In the realization that society is increasing the velocity of global warming, there has been an urgency to find alternatives to the combustion of fossil fuels, excessive waste, and other environmentally-harmful activities – in other words, a need to reduce the “carbon footprint.”

Carbon and other greenhouse gas emissions perpetuate global warming because their quantities trap the sun’s heat when it is reflected back by the earth. This causes a slow but steady rise in temperature over time, as seen in Figure 1 from [1]. While global warming may be a natural occurrence, humans have played a large part in speeding up the process. Therefore, it is possible – and necessary – to slow down its impact by putting further research and development into more efficient, powerful green technologies.

Figure 1 : A graphical representation change in temperature from 1860 to 2000 from [1]. Clearly, there has been an increase in positive deviation over the last half of the 20th century.

ObjectiveThis proposal will provide some background information on the function and advantages of wind turbines. It will then detail the benefits of implementation of wind turbines and provide support for why further research should be done on urban wind turbines. The proposal will also take into account the negative aspects of urban wind turbines and then propose ways to further research this technology.

Background on Wind TurbinesWind turbines harness energy in a fairly standard way. According to [2], Typical wind turbines are freestanding and at heights of 80 feet or greater. When the wind passes over the blades of the turbine, it generates a force that allows the blades to spin, which, in turn, causes a shaft in the gearbox to turn. The gearbox accelerates a speed of maybe 30 revolutions per minute by a multiple of more than 1,000. The velocity generated by the gearbox spins magnets inside coils of copper wires in order to create an induced electric current. The current flows from the turbine, down to the ground, and out to the electric grid. As seen in Figure 2 from [3], each part of the wind turbine plays a significant role in the success of the power-generating instrument.

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Figure 2 : The different components of the typical wind turbine. Some of the key parts are: rotor blades, gear box, high-speed shaft, and generator. [3]

The wind turbine has several advantages. Economically, it can be seen in [4] that wind energy is completely free and naturally occurring, eliminating transportation and mining costs completely. Wind turbines also “promote cost-effective energy production,” reducing costs to as little as 2.5 cents. Wind turbine projects create many jobs, about 30% more jobs than coal plants and 66% more than nuclear power plants, on a per unit of energy generated basis. On the environmental side, wind turbines put out no pollution, resulting in “clean” energy. They take up very little space, having minimal effect on crops or livestock grazing. Lastly, wind turbines preserve resources, such as water, because they are almost completely run by the wind.

There are two different types of wind turbines in use today. One is the more common one, called the Horizontal Axis Wind Turbine (HAWT) and the other is the Vertical Axis Wind Turbine (VAWT). Though these turbines have the same purpose, there are some differences in the advantages between the two. According to [5], HAWTs have greater efficiencies and are more powerful due to their longer blade length. VAWTs, on the other hand, do not depend on the direction of the wind and can therefore afford to be installed closer to the ground than HAWTs. They have lower efficiencies but have lower wind start up speeds and make less noise. Both types are used in society today, and examples can be seen in Figure 2 below, also from [5].

Figure 3: A comparative picture depicting a Horizontal Axis Wind Turbine and Vertical Axis Wind Turbine from [5]. Though used for the same purpose, the turbines’ designs suit different environments.

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PROPOSALThe PurposeIn the present day and time, urban cities are expanding and take up more space than ever. Therefore, it is prudent to incorporate energy-saving technology into the city environment as much as possible. While technologies like solar panels and hydraulic generators are used, it would be even more cost-effective and spatially frugal to find a way to implement wind turbines in the urban area.

There are several other benefits to urban wind turbines. In [6], it is seen that, because urban wind turbines can be installed for specific homes in the city, owners of the turbine experience direct savings from the turbine itself. Not only this, but there are possibilities of selling excess electricity generated by the turbine, resulting in even a profit for the individual. Companies like Green Choice give discounts to customers who give their surplus energy back to the grid. Clearly, urban wind turbines can be implemented to become a source of income in addition to benefiting the environment.

However, not enough research has been done on urban wind turbines. According to [7], the research experiments that have been conducted are unsatisfactory in that they do not provide for error nor are very reproducible. Researchers have only been able to create graphs of turbine power specific only to their areas, so “there is a need for rigorous research into effective power curves for small-scale wind turbines, which analyses the error associated with the use of effective power curves for multiple locations.” Every urban location is different, with different building placement and heights, as well as different wind patterns. Along with location research, further optimization of blade rotor design and energy generation techniques needs to be accomplished.

DrawbacksUnfortunately, there are several complications to having urban wind turbines. As seen in [8], wind turbines are known to be noisy and potentially harmful to human beings. Large turbines cause significant health problems, like difficulty sleeping, nausea, cognitive dysfunction and more. This is largely attributed to sound and electromagnetic waves generated by the turbine as well as poor power quality in the wires. Wind turbines are also a definite concern for nearby wildlife. Though urban environments have significantly less animal diversity in the area, birds are threatened by turbines because of their flight patterns. Wind turbines in an urban environment are also a lot less efficient due to wind turbulence, according to [9]. This comes about from various variables like roof shape, building height, and the urban layout. Based on problems with local nature and location-based efficiency, one additional issue is that placement of urban wind turbines is very particular and is not always viable based on certain environments.

Suggestions for Further ResearchDespite adversity to urban wind turbines, there are certain measures that can be taken to reduce or even eliminate some of the drawbacks. First of all, wind turbulence and inconsistencies can be partially remedied with the use of vertical-axis turbines. Since these kinds of turbines take in wind from every direction, they would be able to best harness more unpredictable wind directions. Another improvement may come from innovating the generator of the wind turbine.

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The University of Bristol in [10] has developed a permanent magnet generator that has a direct drive. These small wind turbines are more “suitable for the urban environment,” as they are silent, compact, and low maintenance. Already, this would eliminate some of the cons of urban wind turbines. Small turbines would have little to no impact on human health and would not be a loud distraction in the urban environment. The next step would be to determine a way to harness even more of the wind’s power, as current VAWTs are not nearly as efficient as HAWTs due to decreased blade length.

One problem mentioned earlier was the lack of control of errors. One definitive way to check variables would be to model wind conditions and city scenarios on the computer. In [9], computer simulation found that, when isolating factors, high rise buildings with vaulted roofs were more ideal for mounting wind turbines. However, this study also found that a wind turbine height of 1.3 times the height of the building was also required for optimal power. This is definitely not an ideal situation, so further research would need to be done in order to compensate for the lack of height of urban wind turbines.

Figure 4 : Wind velocity pathlines show that the greatest velocity is located at the top of the building, from [9].

In addition to those mentioned, there are some additional suggestions for future research on urban wind turbines in the future. Because wind patterns vary in any city, a good first step would be to analyze cities throughout the US that average from roughly 12 mph to 27 mph on a yearly basis – according to [6], this is around the wind speed that urban wind turbines need in order to function well. Then, tests would need to be performed on different locations throughout the city, as well as data collected on the wind patterns of that city. If possible, general guidelines for turbine placement should be formed so that research can be replicated in other urban areas with similar success levels.

On the topic of the wind turbine itself, durability and longevity would definitely be a focus point in improving wind turbines. Because of turbulence and the occasional wind storm, urban turbines would have to be able to take the battering of the urban wind. Another high point of concern would be the power. Data found in [6] shows that VAWTs only produce about 10 kW of energy based on the speeds given earlier, which is very low compared to HAWTs and could definitely

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use improving. Since the urban wind speed cannot be changed, it is up to the researchers to design urban wind turbines that make the most of the wind that is available.

QUALIFICATIONS & EXPERIENCEI am a first year mechanical engineering student at The Ohio State University. As a student, I am enrolled in the Fundamentals of Engineering Honors (FEH) program at Ohio State. In FEH, we have done a laboratory experiment on power generation of a wind turbine due to a wind tunnel, so I am familiar with wind technology.

BUDGETSeveral expenses will need to go into the research for urban wind turbines. These will include researcher salaries, data collection, modeling of turbines, implementation of experimental models, insurance, maintenance, and report development. The estimated total cost would be about $1 million dollars.

CONCLUSIONGlobal warming is a growing concern in the world today. In addition to its growth, urban environments continue to expand. If society is to accommodate these changes, there must be a way of incorporating green technology with the city. Urban wind turbines are definitely a feasible solution for this due to their free, clean energy. However there are some problems that still need to be faced before these products can be put into mass production. In addition to accounting for error and reproducibility, researchers in the wind industry must still optimize the efficiency of vertical axis wind turbines and find the best kind of placement for them in the urban environment, taking all the variables into account in the process. Hopefully, in the future, urban wind turbines will be able to reach a point where they can be installed on buildings with long term success.

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REFERENCES[1] J. Vallenga. (2013). Global Warming and Climate Change. [Online]. Available:

http://www.cheaperpetrolparty.com/Global_Warming.php[2] K. Greene, “Wind Turbines,” Pop. Science, vol. 259, no. 5, p. 83, Nov. 2001.[3] (2013). How Do Wind Turbines Work?.[Online]. Available:

http://www.windpowersavings.com/how-do-wind-turbines-work/14/.[4] (2012). Why Wind Energy?. [Online]. Available:

http://www.windustry.org/wind-basics/why-wind-energy[5] Wind Power. [Online]. Available: http://www.energygroove.net/windpower.php.[6] J. Cace, E. ter Horst, K. Syngellakis, M. Niel, P. Clement, R. Heppener, E. Pelrano. (2007

February). Wind Energy Integration in the Urban Environment. [Online]. Available: http://www.urban-wind.org/pdf/SMALL_WIND_TURBINES_GUIDE_final.pdf

[7] S.L. Walker. (2011, April 4). Building mounted wind turbines and their suitability for the urban scale –A review of methods of estimating urban wind resource. [Online]. Available: http://www.sciencedirect.com.proxy.lib.ohio-state.edu/science/article/pii/S037877881100110 1

[8] M. Havas, D. Colling. (2011). Wind Turbines Make Waves: Why Some Residents Near Wind Turbines become Ill. [Online]. Available: http://journals.ohiolink.edu/ejc/pdf.cgi /Havas_Magda.pdf?issn=02704676&issue=v31i0005&article=414_wtmwwsrnwtbi

[9] I. Abohela, N. Hamze, S. Dudek. (2012, October 2). Effect of roof shape, wind direction, building height, and urban configuration on the energy yield and positioning of roof mounted wind turbines. [Online]. Available: http://journals.ohiolink.edu/ejc/pdf.cgi/Abohela_Islam .pdf?issn=09601481&issue=v50inone_c&article=1106_eorswdpormwt

[10] J.D. Booker, P.H. Mellor, R. Wrobel, D. Drury. (2010, March 2). A compact, high efficiency contra-rotating generator suitable for wind turbines in the urban environment. [Online]. Available: http://journals.ohiolink.edu/ejc/pdf.cgi/Booker_J.D.pdf?issn=0960 1481&issue=v35i0009&article=2027_achecgwtitue

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APPENDIX I: ANNOTATED BIBLIOGRAPHY[1] J. Vallenga. (2013). Global Warming and Climate Change. [Online]. Available:

http://www.cheaperpetrolparty.com/Global_Warming.php

Vallenga details the causes and effects of global warming. Greenhouse gases, volcanic eruptions, and an increase in solar activity are a few examples of how global warming has come about. There are, however, actions that society can take to reduce greenhouse gases, which include simply turning off lights, make technology more efficient, etc. This article was used to explain why there is such a need for green technology in the current time and day.

[2] K. Greene, “Wind Turbines,” Pop. Science, vol. 259, no. 5, p. 83, Nov. 2001.

This article details how a wind turbine works in a step-by-step process. The wind pushes the rotors, and this motion is accelerated by the gearbox. This is then converted to electricity by the generator and sent to the electric power grid. This was helpful for explaining how a wind turbine worked as a pretext for the reader, prior to getting into more detailed explanations for optimizing urban wind turbines.

[4] (2012). Why Wind Energy?. [Online]. Available: http://www.windustry.org/wind-basics/why-wind-energy

This is an elaboration of the many advantages and disadvantages of wind turbines. Advantages are broken up into economic, social, and environmental categories. This was helpful in explaining why wind turbines are a viable source of green energy and worth pursuing as a research topic.

[6] J. Cace, E. ter Horst, K. Syngellakis, M. Niel, P. Clement, R. Heppener, E. Pelrano. (2007 February). Wind Energy Integration in the Urban Environment. [Online]. Available: http://www.urban-wind.org/pdf/SMALL_WIND_TURBINES_GUIDE_final.pdf

This guide for small urban wind turbines provides detailed accounts of several versions of vertical axis wind turbines. It also provides some background information on the differences between HAWTs and VAWTs and details how VAWTs may be profitable in the future. This was very helpful in explaining some of the improvements that need to be made to urban wind turbines as well as supporting research for them.

[8] M. Havas, D. Colling. (2011). Wind Turbines Make Waves: Why Some Residents Near Wind Turbines become Ill. [Online]. Available: http://journals.ohiolink.edu/ejc/pdf.cgi /Havas_Magda.pdf?issn=02704676&issue=v31i0005&article=414_wtmwwsrnwtbi

This study explains some of the problems that humans have experienced living near large wind turbines. Headaches, pains, and irritability are all caused by emitted sound and electromagnetic waves from the turbines as well as poor power quality are a result of this. This was useful in the development of goals for future urban wind turbine research.

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[9] I. Abohela, N. Hamze, S. Dudek. (2012, October 2). Effect of roof shape, wind direction, building height, and urban configuration on the energy yield and positioning of roof mounted wind turbines. [Online]. Available: http://journals.ohiolink.edu/ejc/pdf.cgi/Abohela_Islam .pdf?issn=09601481&issue=v50inone_c&article=1106_eorswdpormwt

This study isolates different factors that might influence wind turbine performance. These include but are not limited to: building height, roof type, proximity of neighboring buildings. These calculations were performed on a computer, giving a more idealistic approach than normal conditions would. This was used to suggest how to perform further research of urban wind turbines.