Optimizing Wind Power Generation

The provided content includes various studies, research papers, and books related to wind power installations, renewable energy, climate change, air pollution, and energy security policy. The sources cover topics such as the aerodynamics of wind turbines, design considerations for different turbine concepts, and the evaluation of shrouded micro-wind turbines. Additionally, the content includes information on small-scale wind turbine systems, fault ride-through strategies for doubly fed induction generator-based wind turbines, and experimental studies on diffuser augmented horizontal axis tidal current turbines. The sources also explore the potential benefits and challenges of using wind energy to mitigate climate change and promote sustainable development.

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ANALYSIS AND COMPARISON OF A CUSTOM CONSTRUCTED SMALL-SCALE WIND
AUGEMENTATION DEVICE WITH A WIND-GUIDE ATTACHEMENT TO IMPROVE
WIND POWER GENERATION
(May 2017)
Bhavana Kashibhatla, B.Tech., JNTU
Chairman of Advisory Committee: Dr. Ulan Dakeev

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CHAPTER - 1
INTRODUCTION
Wind energy is one of the most reliable and abundant sources of renewable energy on this
planet. The humankind has used it for centuries as there are estimates that people were using this
type of energy as far as 4,000 years ago. In the year 1700, it was employed by the king of
Babylon for irrigation purposes (Ackermann & Kuwahata, 2013). The wind was also for
grinding grain by several farmers. It is also surprising to note that one of the earliest windmills
had the vertical axis of rotation. The people use braided mats or sails for rotating these windmills
across the vertical axis. These windmills had an operational advantage as they were independent
of the direction of the wind.
History of Wind Power
The wind power was initially utilized by humans in the form of irrigation pumping, sailboats
and garn milling. The history of wind power can easily be tracked back to the ancient 6,000
years ago. The sails, ships and sailboats were used on the Nile River though its water, in Egypt.
The earliest known use of wind power was represented by the sailboats. Although as per today’s
standard, it is considered to be a rudimentary use of wind but the technology impacted the
development of the current sail-type windmills (Hansen, M. O., 2015). The first documented
proof of the existence of such mills dates back to 12th century. However, the ability to study the
wind power across the horizontal axis was the first to measure in the 20th century (Kuwahata
et.al, 2013).
There are two types of wind turbines. One is built with high speed and is intended to generate
electricity whereas the other one is built for low wind speeds (Wahab et al. 2008). The major

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components of Wind turbines include a rotor with a set of blades with a rotor hub which is seen
to deflect the airflow by creating a force on the blades. Due to this, a torque is produced on the
shaft and the rotor is seen to rotate around the horizontal axis attached with a generator and a
gearbox. All this is present inside the nacelle present with other important electrical parts with
the tower end. Electricity is generated moving down from the tower to the transformer which is
then converted from voltage (usually 700V, 33000V for countrywide grid, 240 V for the personal
use). The core windmills are termed as horizontal axis wind turbine (HAWT) and the vertical
axis wind turbine (VAWT). The windmills using the horizontal axis of rotation are relatively
new as compared to vertical axis ones.
United States and Wind Power
Due to increasing high-energy costs, the government and the people are becoming highly
concerned towards global warming, pollution and feel financially strapped at the same time
(Bollen, Hers & Zwaan, 2010). With around 30 percent of the total world reserves, the United
States have a vast coal supply (Hook & Aleklett, 2010). The annual production of United States
is almost twice as compared to India and lacks only behind China (Hook & Aleklett, 2010). But
it has been noticed that the US reserves are concentrated only in few states and have
considerably decreased from 29.2 MJ/kg 23.6 MJ/kg in the period of 1950-2007 due to
movement of subbituminous western coals by US (Hook & Aleklett, 2010). The production of
one kilowatt hour (kWh) of electricity from coal is seen to produce 1kg of Carbon Dioxide
(CO2), more than 200 grams of waste amounts of several metals and ash, seven grams of
nitrogen oxides, sulfur oxides and particulates are released such as Methane (CH4), hydrogen
sulfide (H2S), hydrocarbons ethane (C2H6), etc. (Stracher & Taylor, 2004).

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Benefits of Wind Power
According to Klingenberg (1996), CO2 levels were around 345,000 parts per billion in 1996 as
compared to 290,000 parts per billion decades ago (Graedel & Crutzen, 1989). According to the
U.S. Department of Energy, 2013, the dependency of the fossil fuels can be reduced using the
wind energy as there is no emission of greenhouse gases. Although the generation of electricity
is not just one cause of increasing CO2 level in the atmosphere but it contributes to a major share
of CO2 emission (Graedel & Crutzen, 1989). Therefore, the reduction of greenhouse gases in the
atmosphere can be done by environmentally friendly electricity generation using wind power.
The tunnel attachment of the wind has the ability of capturing low speeds of the winds especially
at the lower altitudes which might lead to deduction in the wind turbines and will lead to over
improvement of the efficiency. A vital step can be taken by the wind power in the field of
renewable source for production of energy. The current status of wind energy is promising. The
fourth edition of Global Wind Energy Outlook claimed that the wind energy constitutes 3.5% of
global electricity production. The share in power generation is estimated to reach 12% by the
year 2020 (Kuwahata et.al, 2013). At the end of the year 2012, the total global production of the
Wind Energy was 282 Giga Watts showing an increase of 44% from the year 2011 (Kuwahata
et.al, 2013). The installation of wind energy had reached its peak during the year 2012, but after
the same year, the total production of wind power generation has decreased due to several
reasons. In fact, the installation of wind energy for electricity generation falls to 18.7% which is
the lowest in the past two decades.
The United States has also gained the global momentum, and the growth rate in the
country was estimated to be around 27.9% during the year 2012. The total electricity produced in
the United States from wind energy was 140 terawatt-hours constituting the 3.5% of the total

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energy produced from entire sources (Armentrout & Armentrout, 2009). The US Department of
Energy (DOE) has accelerated its efforts to install wind and water power generation capability of
the country. The DOE also issues loans and guarantees to install wind electricity generation. The
DOE has estimated to supply 20% energy from the wind generation by the year 2030
(Armentrout et.al, 2009).
Adoption of Wind Energy
The main concerns for adoption and investments in the renewable energy technologies
along with agreeing to the implementation policies for their support include environmental,
security and economic concerns. The primary objectives for the adoption of wind energy on the
global scale include the reduced risk from rising and volatile energy costs, energy security and
decreased carbon emissions and other pollutants. One of the primary reasons for the adoption of
wind energy worldwide is the fact that it is a highly environment-friendly source of energy. It is
also estimated that in future conventional sources of energy such as fossil fuels might run out.
The world has to look for alternate sources of energy to meet the energy demands of the future
generations (Crossley, 2000).
The most important factor towards the adoption of the Wind Energy as energy production
source as it is the cleanest forms of energy. The use of wind power as a source of power ensures
that there is no emission of carbon dioxide and other harmful gasses into the atmosphere and thus
it is safer to use as compared to fossil fuels and nuclear power stations. The main concern,
however, is to increase the output and efficiency of wind energy generation keep the costs under
check.

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The wind power generation will be able to meet the increasing demand of the energy felt
worldwide. The adoption of wind power can be beneficial in enhancing the diversity in the
supply market of the energy and help in securing long-term sustainable supplies of the energy.
The emission of local and global atmospheric emissions will be reduced. Furthermore, in order to
meet the specific demands of the energy services new commercially attractive options would be
available along with creating tremendous job opportunities. The production of renewable energy
especially from the sustainable natural sources is seen to contribute to the sustainable
development and considers the needs of the future generation. Wind power will promise out to
be the best alternative and the most suitable supplement towards the traditional energy sources
especially in the developing countries. According to the studies, wind energy has made the
considerable amount of contribution to the field of grid power installed capacity and can easily
emerge out to be one of the options for mitigating pollution (Dincer, I., 2000). Due to wind
power being environmental friendly and renewable in nature, wind energy can be converted to
electricity.
Wind Power and Augmentation
The primary challenge being faced by the urban wind energy is the lower mean speed of the
wind especially in the urban environment owning to the increased roughness in the surface of the
free streams and reduction in the heights of the wind turbines on being installed. The incoming
wind is seen to encounter higher turbulence intensity which is seen to be next to the lower mean
wind speed. However, the harvesting of the wind turbines can take place in the well sited
acceleration of the flows. This can result in over 70 percent of the increase in power.
The wind turbines and its performance can be increased using a plethora of methods.
According to Phillips (2003), a myriad of research has been performed in the field of power

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augmentation of the wind turbines. Some of the famous examples of these attempts in power
augmentations are cylindrical obstruction concentrators, tip vanes on the rotor blades, diffusers
in which the rotor is located and vortex type augmentation devices. According to him, the
diffuser augmented wind turbines were considered to be the best suitable action amongst all.
The building and maintaining of the large scale wind shrouding is seen to be expensive
however, its proper use can act as a great source of renewable energy providing an incentive for
methods that can improve the technology (Foote, 2011). According to a study by Dakeev (2014),
a cone shaped wind guide system is present in the shrouding system which results in over 60
percent of the power outcome with respect to the traditional bare wind turbine. Studies like
Dakeev (2010) and Kosasih & Tondelli (2012) suggested that the wind augmentation devices are
seen to influence the generation of power significantly.
Various research also revealed that the shroud having an angle of 30 degrees will connect to
the wind turbine and will lead to delivering of an improved power efficiency and performance as
compared to the augmentation devices installed at various angles and positions. A study
calculated that the shroud must accelerate the wind speed by 2.1 factor where the power output
will be augmented by almost three times.
It has been stated by the Betz Law that no wind turbine would be able to capture over 59.3
percent of the kinetic energy present in the wind. Around 80 percent of Betz limit is seen to be
achieved by the utility scale wind turbines at their highest peak. According to Hansen, 2000,
when the wind turbine is enclosed within the shroud, the power generation is seen to be
improved beyond the Betz limit.

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The intended objective of this study is to develop an augmented wind device which can improve
the efficiency of the small-scale experimental wind turbines. Testing of the wind turbine with the
help of shroud and cone might facilitate in increasing the air flow to the turbine and thus increase
the overall efficiency. The performance of the device at various speeds and output powers will be
examined numerically and experimentally. The power output of the wind turbine will be
compared using shrouded wind turbine using cones with the turbines which are not using the
cones.
Purpose of the study
The purpose of this study is to build and test a wind augmentation device that might improve
power generation of an experimental small-scale wind turbine. Testing of the wind turbine with
the shroud and a cone may allow the incoming airflow from the wind turbine for a greater output.
The performance of the shrouded wind turbine will be experimentally and numerically
investigated at various wind speeds as well as power output. Furthermore, the power output
parameter will be compared between shrouded wind turbine with a cone and a shrouded wind
turbine without a cone.
Significance of the study
The significance of this study was to investigate the optimal design for wind augmentation
devices to increase the power output at the outlet. Many countries are adapting renewable energy
to counteract the process of global warming. Among all the renewable energies wind is the
fastest-growing renewable energy source. Wind energy is actually a form of solar energy. Wind
energy will not produce greenhouse gas during conversion unlike with biomass.

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Definition of terms
Anemometer- An instrument for measuring the speed of the wind
Shroud- A cover around the wind tunnel.
Summary
The purpose of this thesis is to investigate the optimal design for wind augmentation devices
to increase the power output at the outlet. Additionally, a cone is introduced into wind tunnel to
investigate if there is a significant difference when the cone had been introduced. Furthermore, I
would like investigate by changing the distance of the cone in the tunnel would increase the
power efficiency or not

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CHAPTER 2
LITERATURE REVIEW
Various endeavors have been made in order to make the best of the all the natural
resources provided to us for generating energy. Various projects have been performed for
increasing the efficiency of the power generation and the main concern being the increasing of
throughput of the wind present in the tunnel and on concentrate fully on the turbine and its
blades. As various limitations have been seen in the efficiency of a conventional wind turbine.
Therefore, various augmentation has been performed for overcoming the weaknesses of the wind
tunnel.
A dynamic wind shroud has to be built with sensors that can help in determining the
optimal relationship between the angle wind shrouding adjusts and wind velocity owning to the
constantly changing velocities of the wind and to establish better generation of power. A critical
factor for increasing the power generation and its efficiency is to determine the optimal design of
the wind augmentation. The study aims to build and test a wind augmentation device which can
be used in improving the efficiency of the power generation in the experimental small-scale wind
turbine.
The wind turbine when tested along with the shroud and a cone helps in allowing the
incoming airflow coming directly from the wind turbine in order to generate a greater output.
The study first discusses the various types of wind turbines present and then focuses on the mall-
scale wind augmentation device for increasing the efficiency of the wind power. The wind
turbines can be divided into sub sections and can be classified on the basis of various criteria.

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Classification or Types of Wind Turbines
The classification of the wind turbines is done on three main parameters. These parameters
are:
1. On the basis of orientation of axis of rotation (Crossley, 2000).
2. The component of aerodynamic forces which are responsible for its rotation (Crossley,
2000).
3. The basis of energy generation capability (small, medium or large) (Crossley, 2000).
Vertical Axis Vs Horizontal Axis Turbines
There are mainly two kinds of wind turbines when they are classified on the basis of axis of
rotation. As their name suggests, the vertical type of the wind mills rotate perpendicular to the
ground known as the vertical axis wind turbine (VAWT) while the horizontal type rotates
parallel to the ground known as horizontal axis wind turbine (HAWT). Currently there are three
popular designs of wind mills (ERIKSSON, BERNHOFF, & LEIJON, 2008).
1. Savonius VAWT.
2. Curved Blade VAWT.
3. Straight Blade VAWT.
Savonius rotors typically have two or half drums attached to the central shaft in the opposite
directions and are seen to function similar to those water wheel that utilize drag forces. Curved
blade VAWT consists of two or more curved blades attached to the central vertical shaft. At last,
the Straight Blade VAWT has variable pitch angles (LEIJON et.al, 2008). In the horizontal axis

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of rotation, the rotor shaft rotates parallel to the ground. The electric generator is attached to the
turbine rotor via primary and secondary shafts.
It is seen that the VAWTs function quiet near to the ground and not present in the nacelle as
compared to the HAWTs and are beneficial in enabling the proper placement of heavy
equipment like the generator and gearbox. However, as the winds are seen to have lower speed at
the ground level, less amount of power is generated. VAWTs are seen to be more advantageous
that the HAWTs as they are packed closely and are present inside the wind farms allowing more
amount of space. VAWTs are omnidirectional, quiet and generate low amount of force on the
support structure. Further they can be implemented on the structures present at height and can be
controlled easily (Riegler, H., 2003).
Whereas the Horizontal Axis Wind Turbines are seen to be positioned at the right direction
so as to work in the most efficient manner. The HAWTs that are positioned away from the
direction of the wind are termed as the downwind turbines due to their location with respect to
the towers and are then pushed in an appropriate orientation.
Large Vs Small Scale Wind Turbines
Generally, the wind turbines can also be divided on the basis of their intended application
and rated capacity. The definitions of Large and Small scale wind turbines are not clearly
elaborated in the literature present on the wind energy. Small scale wind turbine was defined by
its capacity to meet the demands of individual households. The capacity of the small wind
turbines is less than 50 kW size and sometimes are as large as 250 kW (these are designed for

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agricultural, residential, industrial applications, small commercial etc.) and are aimed at
providing energy to the end user for offsetting grid power and its use.
Small scale wind turbine was defined by its capacity to meet the demands of individual
households. The problem is the fact that the energy demand of a family varies with respect to
time and place. The average energy demand of an American home is 10 kW while for the
European houses this requirement is decreased to 4 kW. This requirement reduces to 1 kW in
China (Howard, 2012). Based on the energy demands from a small scale wind turbine following
types can be shortlisted.
1. Micro-scale Wind Turbines (μSWT) having a rotor diameter of ≤ 10 cm.
2. Small-scale wind turbine (SSWT) having rotor diameter of ≤ 100 cm.
3. Mid-Scale Wind Turbine (MSWT) having rotor diameter of ≤ 5m.
Whereas the large wind turbines are seen to have the capacities in the range of 660 kW to 1,800
kW (1.8 MW). These are typically designed for generating electricity in the power plants. These
are used for deploying the wind farms and can be used for providing wholesale bulk electricity
production and can be delivered to the local transmission network.
Definition of Terminologies
There are some basic terminologies related to wind mills and wind energy which are defined in
this section:
1. Wind Generator: It is a device which is responsible for capturing wind force for
providing the rotational motion. This is responsible for producing power along with
the wind alternator or generator.

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2. Wind Turbine: It is a machine which is responsible for capturing the wind force and
is also called as the Wind Generator in cases where it is used for production of
electricity.
3. Leading Edge: it’s the point located at the front of air foil, this point has the
maximum curvature.
4. Trailing Edge: it located at rear end of air foil, having maximum curvature.
5. Chord Line: Line connecting the leading edge and trailing edge.
6. Chord Length (c): Simply the length of chord line.
7. Suction Surface: upper surface of airfoil. The main attributes attached to this surface
are higher velocities and lower static pressures.
8. Pressure Surface: lower surface of an airfoil having lower velocity and high static
pressure.
9. Maximum Thickness: it is regarded as maximum thickness of an airfoil measured in
perpendicular to the chord line.
10. Setting Angle: The angle between the plane of the rotation of the blade and the blade
Chord is known as setting angle. It is also called the blade or the Pitch angle. The
blade with is carved along with the Twist can have various setting angles at the Tip as
compared to the Root.
11. Shaft: The part of the turbine which rotates continuously and is present in the center
of the wind generator is called the shaft. It is responsible for transferring the power.
12. Tower: the structure of the wind generator which is responsible for supporting it is
called the tower. It is usually situated at the top and high in the air.

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13. Torque: The turning force of the generator which is also equal to the force times
radius.
Apart from the nomenclature of the airfoil there are some terminologies related to the wind
turbine. These are:
1. Power Coefficient: it is a measure to determine the efficiency of the wind turbine which
is used by the wind power industry. Power Coefficient can be defined as the ratio of
electric power been generated by the wind turbine and the total amount of wind power
being flowing at the certain wind speed in the blades of the turbine. It is used for
representing the combined efficiency of the components of the wind power system which
includes the shaft, gear train, turbine blades, power electronics and generators. It is
defined as amount of mechanical power produced by the wind turbine compared to the
available wind energy (Kadar, 2013).
2. Betz’ Law: This law is used to calculate maximum mechanical power produced by the
turbine while placed in an open wind flow. The law states that even most of the efficient
turbines can extract only 59.7% of the total kinetic energy of the wind as 100 percent of
the wind energy generation is impossible due to the structure and mechanism of the wind
turbines to convert the wind energy into 100 percent of the kinetic energy (Kadar, 2013).
3. Torque Coefficient: it is used to calculate the shaft torque produced by the wind turbine.
High value of torque coefficient allows the wind to operate at lower wind speed.

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λ = speed ratio of the turbine.
a. Shrouded Turbines
In past few years, it has been concluded that the output power and efficiency of the wind turbines
can be improved with the help of shrouded turbines compared to bare turbines. The shrouded
tidal turbines are one of the revolutionary idea in the tidal stream technology where the turbine is
seen to be enclosed in the venture shaped vent duct and produces atmosphere with low amount of
pressure in the turbine. This helps the turbine to operate at high amount of efficiency as
compared to the traditional turbine where the volume of flow is seen to be increased over the
turbine.
One of the most advanced designs of the wind turbines is known as diffuser augmented wind
turbine (DAWT) (Ohya & Karasudani, 2010). It is also known that these turbines can extract
more output power from the same geometry as compared to the conventional designs of the wind
turbines. According to estimates, two-fold power augmentation can be achieved by using two
wing profiled rings mounted on the rotor. The DAWTs offer various advantages as compared to
the traditional turbines which include factors like minimal top speed, increased augmentation,
rotor diameter for increasing the rounds per meter and is less yaw sensitive as compared to the
HAWTs.
The shrouded wind turbine can improve the efficiency by 1.7 times compared to simply
bared turbines. The terms shrouded, ducted, and turbine enclosed in a diffuser. The energy
confined in a tidal current is directly related to density and area of cross-section. The cube
velocity can be derived using the following equation.

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The energy is converted into velocity by using the tidal current, and thus the power generated
in the horizontal axis tidal current turbine is dependent on the current speed. The velocity to gain
maximum efficiency should be around 2 m/sec. However, the global tidal velocity available
ranges close 1 m/s. To obtain efficient output power from such low velocity, a bigger turbine
system is needed (Karasudani et.al, 2010). The installation of larger turbine system is not cost-
effective, and thus the velocity can be increased by using diffuser augmented tidal turbine. The
diffuser augmented tidal turbine is highly famous among the researchers due to the following
aspects:
 Better spatial coherence
 Less sensitive to turbulence
 Better resistant to fatigue
 Less sensitive to jaw
 Same power generation at lower torque
 Lower fluctuating blade loads
 Enhanced mass flow
 Higher possible rotational speed, so reduced gear ratio
 Less noise
 Reduction of tip losses (Nasir Mehmood, Z. L., & Khan, J., 2012).

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The diffuser, in this case, acts as devices to increase the tidal speed and operates on a
principal that a minimum increase in the speed can result in increased output power of the
turbine. The diffuser augmented turbine produces same output power with a relatively small
diameter compared to the naked turbines. Thus the installations of diffuser augmented turbines
are more efficient economically compared to conventional turbines (Karasudani et.al, 2010).
Although the high cost of DAWTs counter balance its benefits due to high cost of material,
transportation, fabrication and installation. Furthermore, the DAWTs are seen to be highly
susceptible to the effects from environment like the temperature fluctuations, windborne
particulates etc. Due to the flow separation, the diffusers are also seen to encounter aero elastic
instabilities.
There are several advantages to the installation of the diffuser augmented wind turbines.
These can be summarized in the following points:
1. The diffuser augmented wind turbines can extract more energy compared to
conventional wind turbines. These turbines are more efficient as compared to
conventional turbines due to their increased flow manipulation and removal of tip losses
(Toshimitsu, 2012).
2. The sound pollution caused by using this type of turbines is far less than the
conventional turbines (Toshimitsu, 2012).
3. Weed growth a problem faced by the conventional turbines can be eliminated by the
use diffuser augmented wind turbines (Toshimitsu, 2012).
4. The diffusers can be manufactured using low-cost materials. The current cost to
benefit ratio of these turbines can result in developing more efficient diffusers in the
future (Toshimitsu, 2012).

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However, there are some limitations related to the use of diffuser augmented wind
turbines which can be summarized in the following points:
1. To gain high efficiency from the turbines, small clearance should be present between
shroud and blade tip. These require manufacturing and installations of very complex
shapes which are very expensive and complicated (Toshimitsu, 2012).
2. The inner and outer profiles of the shrouds are tough to fabricate (Toshimitsu, 2012).
3. The diffuser augmented turbines operate at higher RPM which can cause vibration
issues.
4. The diffuser augmented turbines have more drag as compared to the conventional
turbines and thus require additional support structure (Toshimitsu, 2012).

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