Researching Urban Wind Turbines
by
Clare Cui
Mechanical Engineering Major
The Ohio State University
(513) 375-9407
cui.163@osu.edu
Prepared for
Wind energy researchers everywhere
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.
March 11, 2013
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INTRODUCTION
Statement of Problem
Human 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.
Objective
This 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 Turbines
Wind 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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PROPOSAL
The Purpose
In 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.
Drawbacks
Unfortunately, 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 Research
Despite 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 & EXPERIENCE
I 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.
BUDGET
Several 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.
CONCLUSION
Global 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/windbasics/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/windbasics/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.