UNIT IV

WIND ENERGY
History:
Wind power has been used as long as humans have put sails into the wind. King
Hammurabi's Codex (reign 1792 - 1750 BC) already mentioned windmills for generating
mechanical energy. Wind-powered machines used to grind grain and pump water,
the windmill and wind pump, were developed in what is
now Iran, Afghanistan and Pakistan by the 9th century Wind power was widely available
and not confined to the banks of fast-flowing streams, or later, requiring sources of fuel.
Wind-powered pumps drained the polders of the Netherlands, and in arid regions such
as the American mid-west or the Australian outback, wind pumps provided water for
livestock and steam engines.

The first windmill used for the production of electric power was built in Scotland in
July 1887 by Prof James Blyth of Anderson's College, Glasgow (the precursor
of Strathclyde University). Blyth's 10 metres (33 ft) high, the cloth-sailed wind turbine
was installed in the garden of his holiday cottage at Marykirk in Kincardineshire and was
used to charge accumulators developed by the Frenchman Camille Alphonse Faure, to
power the lighting in the cottage,[25] thus making it the first house in the world to have its
electric power supplied by wind power. Blyth offered the surplus electric power to the
people of Marykirk for lighting the main street, however, they turned down the offer as
they thought electric power was "the work of the devil." [25] Although he later built a wind
turbine to supply emergency power to the local Lunatic Asylum, Infirmary and
Dispensary of Montrose, the invention never really caught on as the technology was not
considered to be economically viable

Across the Atlantic, in Cleveland, Ohio, a larger and heavily engineered machine
was designed and constructed in the winter of 1887–1888 by Charles F. Brush.[27] This
was built by his engineering company at his home and operated from 1886 until 1900.
[28]
 The Brush wind turbine had a rotor 17 metres (56 ft) in diameter and was mounted
on an 18 metres (59 ft) tower. Although large by today's standards, the machine was
only rated at 12 kW. The connected dynamo was used either to charge a bank of
batteries or to operate up to 100 incandescent light bulbs, three arc lamps, and various
motors in Brush's laboratory.

With the development of electric power, wind power found new applications in
lighting buildings remote from centrally generated power. Throughout the 20th century
parallel paths developed small wind stations suitable for farms or residences. The 1973
oil crisis triggered the investigation in Denmark and the United States that led to larger
utility-scale wind generators that could be connected to electric power grids for remote
use of power. By 2008, the U.S. installed capacity had reached 25.4 gigawatts, and by
2012 the installed capacity was 60 gigawatts. Today, wind-powered generators operate
in every size range between tiny stations for battery charging at isolated residences, up
to near-gigawatt sized offshore wind farms that provide electric power to national
electrical networks.

Wind Power:
Wind power or wind energy is the use of wind to provide the mechanical
power through wind turbines to turn electric generators and traditionally to do other
work, like milling or pumping. Wind power is a sustainable and renewable energy, and
has a much smaller impact on the environment compared to burning fossil fuels.

Wind farms consist of many individual wind turbines, which are connected to

the electric power transmission network. Onshore wind is an inexpensive source of
electric power, competitive with or in many places cheaper than coal or gas plants.
Onshore wind farms also have an impact on the landscape, as typically they need to be
spread over more land than other power stations and need to be built in wild and rural
areas, which can lead to "industrialization of the countryside" and habitat loss. Offshore
wind is steadier and stronger than on land and offshore farms have less visual impact,
but construction and maintenance costs are higher. Small onshore wind farms can feed
some energy into the grid or provide electric power to isolated off-grid locations.

The wind is an intermittent energy source, which cannot make electricity nor
be dispatched on demand. It also gives variable power, which is consistent from year to
year but varies greatly over shorter time scales. Therefore, it must be used together with
other electric power sources or storage to give a reliable supply. As the proportion of
wind power in a region increases, more conventional power sources are needed to back
it up (such as fossil fuel power and nuclear power), and the grid may need to be
upgraded. Power-management techniques such as having dispatchable power sources,
enough hydroelectric power, excess capacity, geographically distributed turbines,
exporting and importing power to neighboring areas, energy storage, or reducing
demand when wind production is low, can in many cases overcome these
problems. Weather forecasting permits the electric-power network to be readied for the
predictable variations in production that occur.

In 2018, wind supplied 4.8% of worldwide electricity, with the global installed wind
power capacity reaching 591 GW. Wind power supplied 15% of the electricity consumed
in Europe in 2019. At least 83 other countries are using wind power to supply their
electric power grids.

What is wind energy?

Wind energy (or wind power) refers to the process of creating electricity using the wind,
or air flows that occur naturally in the earth’s atmosphere. Modern wind turbines are
used to capture kinetic energy from the wind and generate electricity.

There are three main types of wind energy:

 Utility-scale wind: Wind turbines that range in size from 100 kilowatts to several
megawatts, where the electricity is delivered to the power grid and distributed to
the end user by electric utilities or power system operators.

 Distributed or "small" wind:  Single small wind turbines below 100 kilowatts that
are used to directly power a home, farm or small business and are not connected
to the grid.
  Offshore wind: Wind turbines that are erected in large bodies of water, usually
on the continental shelf. Offshore wind turbines are larger than land-based
turbines and can generate more power.

How wind turbines work

When the wind blows past a wind turbine, its blades capture the wind’s kinetic energy
and rotate, turning it into mechanical energy. This rotation turns an internal shaft
connected to a gearbox, which increases the speed of rotation by a factor of 100. That
spins a generator that produces electricity.

Typically standing at least 80 meters (262 feet) tall, tubular steel towers support a hub
with three attached blades and a “nacelle,” which houses the shaft, gearbox, generator,
and controls. Wind measurements are collected, which direct the turbine to rotate and
face the strongest wind, and the angle or "pitch" of its blades is optimized to capture
energy.

A typical modern turbine will start to generate electricity when wind speeds reach six to
nine miles per hour (mph), known as the cut-in speed. Turbines will shut down if the
wind is blowing too hard (roughly 55 miles an hour) to prevent equipment damage.

Over the course of a year, modern turbines can generate usable amounts of electricity
over 90 percent of the time. For example, if the wind at a turbine reaches the cut-in
speed of six to nine mph, the turbine will start generating electricity. As wind speeds
increase so does electricity production.

Another common measure of wind energy production is called capacity factor. This
measures the amount of electricity a wind turbine produces in a given time period
(typically a year) relative to its maximum potential.

For example, suppose the maximum theoretical output of a two megawatt wind turbine
in a year is 17,520 megawatt-hours (two times 8,760 hours, the number of hours in a
year). However, the turbine may only produce 7,884 megawatt-hours over the course of
the year because the wind wasn’t always blowing hard enough to generate the
maximum amount of electricity the turbine was capable of producing. In this case, the
turbine has a 45 percent (7,884 divided by 17,520) capacity factor. Remember—this
does not mean the turbine only generated electricity 45 percent of the time. Modern
wind farms often have capacity factors greater than 40 percent, which is close to some
types of coal or natural gas power plants.

Windmills vs. Wind Turbines

Sometimes people use the terms “windmill” and “wind turbine” interchangeably, but
there are important differences. People have been using windmills for centuries to grind
grain, pump water, and do other work. Windmills generate mechanical energy, but they
do not generate electricity. In contrast, modern wind turbines are highly evolved
machines with more than 8,000 parts that harness wind's kinetic energy and convert it
into electricity.

What is a wind farm?

Oftentimes a large number of wind turbines are built close together, which is referred to
as a wind project or wind farm. A wind farm functions as a single power plant and sends
electricity to the grid.

How wind energy gets to you

The turbines in a wind farm are connected so the electricity they generate can travel
from the wind farm to the power grid. Once wind energy is on the main power grid,
electric utilities or power operators will send the electricity to where people need it.

Smaller transmission lines, called distribution lines, collect electricity generated at the
wind project and transport it to larger "network" transmission lines, where the electricity
can travel across long distances to the locations where it is needed. Finally, smaller
distribution lines deliver electricity directly to your town, home or business.
WIND POWER BENEFITS
Wind energy is a source of renewable energy. It does not contaminate, it is
inexhaustible and reduces the use of fossil fuels, which are the origin of greenhouse
gasses that cause global warming. In addition, wind energy is a “native” energy,
because it is available practically everywhere on the plant, which contributes to reducing
energy imports and to creating wealth and local employment.
For these reasons, producing electricity through wind energy and its efficient
use contributes to sustainable development.
Wind energy does not emit toxic substances or contaminants into the air, which
can be very damaging to the environment and to human beings. Toxic substances can
acidify land and water ecosystems, and corrode buildings. Air contaminants can trigger
heart disease, cancer and respiratory diseases like asthma
Wind energy does not generate waste or contaminate water—an extremely
important factor given the scarcity of water. Unlike fossil fuels and nuclear power plants,
wind energy has one of the lowest water-consumption footprints, which makes it a key
for conserving hydrological resources.

Wind energy benefits

 Renewable energy

 Inexhaustible

 Not pollutant

 Reduces the use of fossil fuels

 Reduces energy imports

 Creates wealth and local employment

 Contributes to sustainable development

HOW MUCH ELECTRICITY IN THE ENTIRE WORLD IS CREATED FROM THE
WIND?
Wind energy currently supplies around 2.5% of global electricity consumption. The
industry projections show that, with the support of an adequate policy, the capacity will
double in 2015 and again at the end of this decade.
 

WHICH COUNTRIES ARE LEADERS IN IMPLEMENTING WIND ENERGY AT THE

GLOBAL LEVEL?

Wind energy is present in a total of 79 countries; 24 of them have more than 1,000
megawatts (MW) installed. In terms of megawatt accumulation, the five main markets
are China, USA, Germany, Spain and India.
Spain has been one of the pioneering countries and leaders in exploiting wind to
produce electricity. Thirty years after installing the first wind turbine in the country, Spain
has achieved becoming the first country in the world in which wind energy is the main
source of electricity for an entire year (2013, with 20.9% of total production), which also
establishes it as an advanced country in technological solutions that allow integrating
wind energy into the grid. With nearly 23,000 MW installed at the close of 2013, Spain is
the second-most European country in operating wind energy after Germany (34,250
MW), and the fourth in the world, after China (91,424 MW) and the USA (61,091 MW) 

Wind turbines have some negative effects on the environment

Modern wind turbines can be very large machines, and they may visually affect the
landscape. A small number of wind turbines have also caught fire, and some have
leaked lubricating fluids, but these occurrences are rare. Some people do not like the
sound that wind turbine blades make as they turn in the wind. Some types of wind
turbines and wind projects cause bird and bat deaths. These deaths may contribute to
declines in the population of species also affected by other human-related impacts. The
wind energy industry and the U.S. government are researching ways to reduce the
effect of wind turbines on birds and bats.
Most wind power projects on land require service roads that add to the physical effects
on the environment. Producing the metals and other materials used to make wind
turbine components has impacts on the environment, and fossil fuels may have been
used to produce the materials.

Site Selection for Wind Turbines:

Winds are caused by heating of atmosphere due to solar heating. There are two types
of wind i.e. planetary winds and local winds.

 Four types of site are considered suitable. These are :

 Plane land sites
 Hill tops sites
 Sea- shore sites
 Off-shore shallow water sites.

The main considerations in selection of site for WECS are based on its technical
feasibility, economics, social environment & other considerations some of the important
criteria for selection of site are.

a) Located where the high average wind velocities available are in the range of 6 m/s to
30 m/s throughout the year since power developed is proportional to cube of wind
velocity.

b) The WECS must be located for away from cities and forests since the buildings and
forests offer resistance to the air movement. There should be notall structures in 3 km
radius from the installation.

c) The wind farms are located in flat open areas, deserts , seas, shores and off shores
site since wind velocities are of high in these locations.

d) Historical data of wind mean wind speed must be collected for average velocities
during the year to select the site for availability of wind velocities needed for installation
of wind farms.
e) Ground surface should have high soil strength to reduce the cost of foundation.

f) If small trees or vegetation exists at a particular location then it would need to

increase the height of tower since any obstruction reduce the wind velocity. It causes
the increase in cost of installation.

g) It should be installed away from localities so that the sound pollution caused by wind
mills does not affect the habitants in near areas.

h) The minimum wind speeds at the selected site must be higher than 3.5 to 4.5 m/s
which is the lower limit at which the present wind energy conversion system starts
turning. It is called as cut-in-speed. Upto this speed no power will be generated by the
system.

Building a wind turbine is far more than simply a matter of finding a field or
mountaintop where the wind is blowing and plopping one down. Engineers give a great
deal of attention to finding the proper site for a wind turbine. The main factor they
consider is the average speed of the wind over an extended time. Using a wind-cup
anemometer, engineers take extensive measurements of wind speed over a long time.
Wind Speed

Wind speed measurements have to be precise. If engineers overestimate the amount of

wind, the power output of the turbine can be reduced considerably. If, for example, wind
is believed to average 10 miles (16 kilometers) per hour but is only 9 miles (14
kilometers) per hour, the power output of the turbine is reduced 27 percent. If the wind
speed is only 8 miles (13 kilometers) per hour, the power output is 41 percent less than
expected. If the wind speed is higher than believed, power output increases. If the wind
speed is 11 miles (18 kilometers) per hour, the power generated increases 33 percent.
If the wind speed is much higher than expected, the equipment may be too small and
too fragile for the site.

Turbine Height
In general, wind turbines should be sited well above trees, buildings, and other
obstacles. When the wind flows over an obstacle like a building or a tree, the wind is
slowed down and turbulent air is created, and if a wind turbine is located in this zone of
turbulence, the result will be poor energy production and increased wear and tear on the
turbine. One way to get above the zone of turbulence is to put the wind turbine on a tall
tower.

Other Considerations
When looking for a place for a wind turbine, engineers consider factors such as wind
hazards, characteristics of the land that affect wind speed, and the effects of one turbine
on nearby turbines in wind farms. The following factors are important:

• Hill effect. When it approaches a hill, wind encounters high pressure because of the
wind that has already built up against the hill. This compressed air rises and gains
speed as it approaches the crest, or top, of the hill. Siting wind turbines on hilltops takes
advantage of this increase in speed.

• Roughness, or the amount of friction that Earth's surface exerts on wind.

Oceans have very little roughness. A city or a forest has a great deal of roughness,
which slows the wind.

• Tunnel effect, or the increase in pressure air undergoes when it encounters a solid
obstacle. The increased air pressure causes the wind to gain speed as it passes
between, for example, rows of buildings in a city or between two mountains. Placing a
wind turbine in a mountain pass can be a good way to take advantage of wind speeds
that are higher than those of the surrounding air.

• Turbulence, or rapid changes in the speed and direction of the wind, often caused by
the wind blowing over natural or artificial barriers. Turbulence causes not only
fluctuations in the speed of the wind but also wear and tear on the turbine. Turbines are
mounted on tall towers to avoid turbulence caused by ground obstacles.

• Variations in wind speed. During the day, winds usually blow faster than they do at
night, because the sun heats the air, setting air currents in motion. In addition, wind
speed can differ depending on the season of the year. This difference is a function of
the sun, which heats different air masses around Earth at different rates, depending on
the tilt of Earth toward or away from the sun.

• Wake. Energy cannot be created or destroyed. As wind passes over the blades of a
turbine, the turbine seizes much of the energy and converts it into mechanical energy.
The air coming out of the blade sweep has less energy because it has been slowed.
The abrupt change in speed makes the wind turbulent, a phenomenon called wake.
Because of wake, wind turbines in a wind farm are generally placed about three rotor
diameters away from one another in the direction of the wind, so that the wake from one
turbine does not interfere with the operation of the one behind it.

• Wind obstacles, such as trees, buildings, and rock formations. Any of these obstacles
can reduce wind speed considerably and increase turbulence. Wind obstacles such as
tall buildings cause wind shade, which can considerably reduce the speed of the wind
and therefore the power output of a turbine.

• Wind shear, or differences in wind speeds at different heights. When a turbine blade
is pointed straight upward, the speed of the wind hitting its tip can be, for example, 9
miles (14 kilometers) per hour, but when the blade is pointing straight downward, the
speed of the wind hitting its tip can be 7 miles (11 kilometers) per hour. This difference
places stress on the blades. Too much wind shear can cause the turbine to fail.
 CHARACTERISTICS OF WIND ENERGY:

Advantages of Wind Power

 Wind power is cost-effective. Land-based utility-scale wind is one of the lowest-

priced energy sources available today, costing 1–2 cents per kilowatt-hour after the
production tax credit. Because the electricity from wind farms is sold at a fixed price
over a long period of time (e.g. 20+ years) and its fuel is free, wind energy mitigates the
price uncertainty that fuel costs add to traditional sources of energy.
 Wind creates jobs. The U.S. wind sector employs more than 100,000 workers, and
wind turbine technician is one of the fastest growing American jobs. According to
the Wind Vision Report, wind has the potential to support more than 600,000 jobs in
manufacturing, installation, maintenance, and supporting services by 2050.
 Wind enables U.S. industry growth and U.S. competitiveness. New wind
projects account for annual investments of over $10 billion in the U.S. economy. The
United States has a vast domestic resources and a highly-skilled workforce, and can
compete globally in the clean energy economy.
 It's a clean fuel source. Wind energy doesn't pollute the air like power plants that
rely on combustion of fossil fuels, such as coal or natural gas, which emit particulate
matter, nitrogen oxides, and sulfur dioxide—causing human health problems and
economic damages. Wind turbines don't produce atmospheric emissions that cause
acid rain, smog, or greenhouse gases.
 Wind is a domestic source of energy. The nation's wind supply is abundant and
inexhaustible. Over the past 10 years, U.S. wind power capacity has grown 15% per
year, and wind is now the largest source of renewable power in the United States.
 It's sustainable. Wind is actually a form of solar energy. Winds are caused by the
heating of the atmosphere by the sun, the rotation of the Earth, and the Earth's surface
irregularities. For as long as the sun shines and the wind blows, the energy produced
can be harnessed to send power across the grid.
 Wind turbines can be built on existing farms or ranches. This greatly
benefits the economy in rural areas, where most of the best wind sites are found.
Farmers and ranchers can continue to work the land because the wind turbines use
only a fraction of the land. Wind power plant owners make rent payments to the farmer
or rancher for the use of the land, providing landowners with additional income.

 Clean energy 

Wind energy is one of the cleanest energy sources. Generating energy using wind
turbines does not emit any greenhouse gases. 

It is true that the manufacturing, transportation, and installation of wind turbines does
release some pollution. However, it is nowhere near the level of emissions released
from burning fossil fuels. 

Because the actual production of energy does not have any greenhouse gas emissions,
it is considered a source of green energy.

 Renewable

Wind energy is a renewable energy resource, meaning that the source of energy is not
depleted when it is used. So, as we use wind energy we don’t decrease the amount of
wind available. 

This is not the case for non-renewable energy sources, like oil and natural gas. As we
use fossil fuels, we reduce the amount that is available to be used in the future. 
 Space-efficient 
Wind turbines can’t be placed too close to one another, which is what makes solar
farms so large. The wind turbines themselve, however, don’t take up that much space. 

The space in between each turbine can be used for things like farming, which is why
wind farms are popular in rural areas. Plus, each turbine has the potential to produce a
lot of electricity - enough to power approximately 2,500 homes. 

 Low-cost energy 
Although wind turbines have high upfront costs, the energy they produce is cheap. This
is for a few reasons, one being that you don’t have to pay for any fuel for the turbines.
Wind is free! Turbines also have relatively low operating costs once they are erected,
and need little maintenance.

When you consider the upfront investments and cost of operations and maintenance
over the lifetime of the turbine, studies show wind energy costs about $0.029 per
kilowatt hour. 

That is much cheaper than coal, which comes out to about $0.036 per kilowatt hour
when you consider the cost to build and operate coal power plants. 

 Promotes job growth 

The wind industry is seeing rapid growth year after year. Between 2010 and 2018, the
amount of installed wind capacity in the U.S. more than doubled, creating enough wind
energy production to power over 30 million homes. This growth has created the
opportunity for thousands of new jobs. 

Currently, over 120,000 Americans have wind-powered jobs - ranging from installers to

technicians and manufacturers. In fact, the role of wind turbine technician is the  second-
fastest growing job in America. 

As wind energy continues to grow in popularity, it is predicted to support more

than 600,000 new jobs by 2050. 
Disadvantages of Wind Energy 
1. Unpredictable 
Perhaps the biggest disadvantage to wind energy is that it cannot be produced
consistently. Energy will only be produced when the wind blows. 

The amount of energy produced by turbines also depends on the wind speed.
Therefore, wind energy is not well-suited to be a base load energy source - AKA our
main source of power generation. 

However, as energy storage technology continues to become more cost-effective, it

could be possible to become more reliant on wind energy. For right now though,
because of its unreliability, wind turbines have to be used in tandem with other energy
sources to meet our electricity demands. 

2. Threat to wildlife 
Wind energy does not cause environmental problems through greenhouse gas
emissions, however, turbines can have an impact on wildlife. 

Birds, bats, and other flying creatures have slim chances of surviving when taking a
direct hit from a rotating wind turbine blade. In fact, studies have estimated that
between 140,000 and 500,000 birds die from wind turbines each year. As a comparison,
collisions with buildings are estimated to kill between 365 and 988 million
birds annually.  

Carefully planning where wind farms will be built can mitigate how many bird collisions
occur. 

3. Noise 
Noise is a problem for some people that live in the proximity of wind turbines. The
generator within the turbine makes a mechanical hum, while the blades create a
“whooshing” sound as they move through the air. 
 However, the good news is, newer wind turbines generate much less noise than older
turbines, and they will likely become even quieter with more technological
advancements. 

4. Looks 
Wind turbines need to be built high in order to capture enough wind, which makes them
a prominent part of any landscape. Some people find that large wind turbines are an
eyesore, however, this is more of a personal preference. 

5. Location limitations 
In order for wind turbines to be economically viable, they need to be installed in a place
where they will produce enough electricity. Wind farms are best suited for coastal areas,
the tops of hills, and open planes - essentially anywhere with strong, reliable wind. 

Most of these suitable places tend to be in remote areas far outside of cities and towns,
in more rural areas or offshore. Because of this distance, new infrastructure, such as
power lines, have to be built in order to connect a wind farm to the power grid. 

This can be costly, and may cause some harm to the surrounding environment (i.e by
tearing down trees to make way for power lines). 

CHALLENGES OF WIND POWER

 Wind power must still compete with conventional generation sources on a

cost basis.  Even though the cost of wind power has decreased dramatically in the past
several decades, wind projects must be able to compete economically with the lowest-
cost source of electricity, and some locations may not be windy enough to be cost
competitive.
 Good land-based wind sites are often located in remote locations, far from
cities where the electricity is needed. Transmission lines must be built to bring the
 electricity from the wind farm to the city. However, building just a few already-proposed
transmission lines could significantly reduce the costs of expanding wind energy.
 Wind resource development might not be the most profitable use of the
land. Land suitable for wind-turbine installation must compete with alternative uses for
the land, which might be more highly valued than electricity generation.
 Turbines might cause noise and aesthetic pollution. Although wind power
plants have relatively little impact on the environment compared to conventional power
plants, concern exists over the noise produced by the turbine blades and visual
impacts to the landscape.
 Wind plants can impact local wildlife. Birds have been killed by flying into
spinning turbine blades. Most of these problems have been resolved or greatly reduced
through technology development or by properly siting wind plants. Bats have also been
killed by turbine blades, and research is ongoing to develop and improve solutions to
reduce the impact of wind turbines on these species. Like all energy sources, wind
projects can alter the habitat on which they are built, which may alter the suitability of
that habitat for certain species.

Application of wind energy:

1. Wind turbine occupy less space than a limited sized power station.
2. Wind mills occupies a few square meter for the base. So the land around the
turbine can to be used for agriculture.
3. With the development of advanced technologies. The efficiency of exploitation of
wind energy is increased to considerable amount.
4. Since the wind is available free of cost. Wind energy can be extracted as free source
of energy.
5. Wind turbine are a great resource to generate energy in remote areas, such as
mountain communication and deserts. where the installation of wind turbine is easy.
6. The Wind turbine can be developed in different sizes and capcity, in order to meet
out the need of various population.
7. Wind energy is environment friendly to surrounding. Since no fossil fuels (no
liberation of green house gases) are brunt to generate electricity from wind energy.
8. If wind energy developed in combination with solar energy then this energy source is
great for developed. Developing countries to provide a steady, reliable supply of
electricity
9. Generation of Electricity - Windmills harness wind energy to create electricity.
Its a clean & green form of energy.
10. Transportation - The power of the wind is used for propulsion in sailing vessels
and sail boats
11. Pumping water - Similar to windmills the energy from the wind is used to drive
a pump.
12. Milling Grain - Grain milling is certain locations are done using wind energy.
13. Sports - A number of sports use wind energy as their source like Wind Surfing,
Land Surfing, Kite boarding

Horizontal Axis Wind Turbines (HAWT)

Horizontal axis wind turbines, also shortened to HAWT, are the common style that most
of us think of when we think of a wind turbine. A HAWT has a similar design to a
windmill, it has blades that look like a propeller that spin on the horizontal axis.

Horizontal axis wind turbines have the main rotor shaft and electrical generator at the
top of a tower, and they must be pointed into the wind. Small turbines are pointed by a
simple wind vane placed square with the rotor (blades), while large turbines generally
use a wind sensor coupled with a servo motor to turn the turbine into the wind. Most
large wind turbines have a gearbox, which turns the slow rotation of the rotor into a
faster rotation that is more suitable to drive an electrical generator.

Since a tower produces turbulence behind it, the turbine is usually pointed upwind of the
tower. Wind turbine blades are made stiff to prevent the blades from being pushed into
the tower by high winds. Additionally, the blades are placed a considerable distance in
front of the tower and are sometimes tilted up a small amount.

Downwind machines have been built, despite the problem of turbulence, because they
don’t need an additional mechanism for keeping them in line with the wind. Additionally,
in high winds the blades can be allowed to bend which reduces their swept area and
thus their wind resistance. Since turbulence leads to fatigue failures, and reliability is so
important, most HAWTs are upwind machines.

HAWT Advantages
 The tall tower base allows access to stronger wind in sites with wind shear. In
some wind shear sites, every ten meters up the wind speed can increase by 20%
and the power output by 34%.

 High efficiency, since the blades always move perpendicularly to the wind,
receiving power through the whole rotation. In contrast, all vertical axis wind
turbines, and most proposed airborne wind turbine designs, involve various types
of reciprocating actions, requiring airfoil surfaces to backtrack against the wind
for part of the cycle. Backtracking against the wind leads to inherently lower
efficiency.

HAWT Disadvantages

 Massive tower construction is required to support the heavy blades, gearbox, and
generator.

 Components of a horizontal axis wind turbine (gearbox, rotor shaft and brake
assembly) being lifted into position.

 Their height makes them obtrusively visible across large areas, disrupting the
appearance of the landscape and sometimes creating local opposition.

 Downwind variants suffer from fatigue and structural failure caused by turbulence
when a blade passes through the tower’s wind shadow (for this reason, the
 majority of HAWTs use an upwind design, with the rotor facing the wind in front
of the tower).

 HAWTs require an additional yaw control mechanism to turn the blades toward
the wind.

 HAWTs generally require a braking or yawing device in high winds to stop the
turbine from spinning and destroying or damaging itself.

 Cyclic Stresses & Vibration – When the turbine turns to face the wind, the
rotating blades act like a gyroscope. As it pivots, gyroscopic precession tries to
twist the turbine into a forward or backward somersault. For each blade on a
wind generator’s turbine, force is at a minimum when the blade is horizontal and
at a maximum when the blade is vertical. This cyclic twisting can quickly fatigue
and crack the blade roots, hub and axle of the turbines.

Traditional Vertical Axis Wind Turbines (VAWT)

Vertical axis wind turbines, as shortened to VAWTs, have the main rotor shaft arranged
vertically. The main advantage of this arrangement is that the wind turbine does not
need to be pointed into the wind. This is an advantage on sites where the wind direction
is highly variable or has turbulent winds.

With a vertical axis, the generator and other primary components can be placed near
the ground, so the tower does not need to support it, also makes maintenance easier.
The main drawback of a VAWT is it generally creates drag when rotating into the wind.

It is difficult to mount vertical-axis turbines on towers, meaning they are often installed
nearer to the base on which they rest, such as the ground or a building rooftop. The
wind speed is slower at a lower altitude, so less wind energy is available for a given size
turbine. Air flow near the ground and other objects can create turbulent flow, which can
introduce issues of vibration, including noise and bearing wear which may increase the
maintenance or shorten its service life. However, when a turbine is mounted on a
rooftop, the building generally redirects wind over the roof, thus doubling the wind speed
at the turbine. If the height of the rooftop mounted turbine tower is approximately 50% of
the building height, this is near the optimum for maximum wind energy and minimum
wind turbulence.

Traditional VAWT Advantages

 They can produce electricity in any wind direction.

 Strong supporting tower in not needed because generator, gearbox and other
components are placed on the ground.

 Low production cost as compared to horizontal axis wind turbines.

 As there is no need of pointing turbine in wind direction to be efficient so yaw

drive and pitch mechanism is not needed.

 Easy installation as compared to other wind turbine.

 Easy to transport from one place to other.

 Low maintenance costs.

 They can be installed in urban areas.

 Low risk for human and birds because blades moves at relatively low speeds.

 They are particularly suitable for areas with extreme weather conditions, like in
the mountains where they can supply electricity to mountain huts.

Traditional VAWT Disadvantages

 As only one blade of the wind turbine works at a time, efficiency is very low
compared to HAWTS.

 They need an initial push to start; this initial push that to make the blades start
spinning on their own must be started by a small motor.
 When compared to horizontal axis wind turbines they are very less efficient
because of the additional drag created when their blades rotate.

 They have relative high vibration because the air flow near the ground creates
turbulent flow.

 Because of vibration, bearing wear increases which results in the increase of

maintenance costs.

 They can create noise pollution.

 VAWTs may need guy wires to hold it up (guy wires are impractical and heavy in
farm areas).
Horizontal-Axis Wind Turbine Working Principle
The horizontal-axis wind turbine (HAWT) is a wind turbine in which the main rotor shaft
is pointed in the direction of the wind to extract power. The principal components of a
basic HAWT are shown in Figure 1.
The rotor receives energy from the wind and produces a torque on a low-speed shaft.
The low-speed shaft transfers the energy to a gearbox, high-speed shaft, and
generator, which are enclosed in the nacelle for protection.
Notice how the blades are connected to the rotor and to the shaft. This shaft is called
the low-speed shaft because the wind turns the rotating assembly at a leisurely 10 to 20
revolutions per minute (rpm) typically.
The low-speed shaft connects to the gearbox, which has a set of gears that increase the
output speed of the shaft to approximately 1,800 rpm for an output frequency of 60 Hz
(or a speed of 1,500 rpm if the frequency is 50 Hz). For this reason, the shaft from the
gearbox is called the high-speed shaft.
The high-speed shaft is then connected to the generator, which converts the
rotational motion to AC voltage. This speed is critical if it is used to turn the generator
directly because the frequency of the ac from the generator is related directly to the rate
at which it is turned.
Almost all horizontal-axis wind turbines have similar components to those
discussed in this article, but there are some exceptions. For example, direct-drive
wind turbines do not have a gearbox, and they usually have a DC generator rather
than an AC generator. These may or may not include a converter to AC (which can be
located at the tower base).
In commercial turbines, a computer or programmable logic controller (PLC) is the
controller. The controller takes data from an anemometer to determine the direction the
wind turbine should be pointed, how to optimize the energy harvested, or how to
prevent over-speeding in the event of high winds.

Typical Horizontal-Axis Wind Turbine (HAWT)

Number of Blades
Horizontal-Axis Wind Turbines may be designed with one, two, three, or more blades.
The fewer blades a wind turbine has, the faster the blades must turn to harvest the
same amount of energy as a wind turbine with more blades.


 Single-Blade Turbines
Single-blade wind turbines are used in a few limited applications, but they are the least
used of all the Horizontal-Axis Wind Turbines.
To rotate smoothly, single-blade turbines must have one or two counterbalances. Figure
6 shows a single-blade wind turbine with two counterbalances.
The advantage of this type of wind turbine is the lower cost because of the use of
only one turbine blade (and the small weight savings), but single-blade turbines must
run at much higher speeds to convert the same amount of energy from the wind as two-
blade or three-blade turbines with the same size blades.
Because the single-blade turbine must run at higher speeds, more wear and fatigue are
generated on the blade and bearings in the mounting mechanism, which in turn means
higher maintenance costs over the life of the turbine.
Single-blade turbines also require extensive setup procedures to ensure that the blade
is mounted perfectly and is balanced to limit oscillation and vibration. Because of these
problems, very few single-blade turbines are in use today.
  Two-Blade Wind Turbines
Compared to three-blade turbines, two-blade wind turbines have the advantage of
saving on the cost and the weight of the third rotor blade, but they have the
disadvantage of requiring higher rotational speed to yield the same energy output. This
is a disadvantage in terms of both noise and wear of critical bearings, shafts, and
gearboxes.
 Two-blade turbines have experienced high-fatigue failures of the blade and other
mechanical parts, so they have limited application. Figure 7 shows a two-blade wind
turbine.
Another way to improve the efficiency of the two-blade turbine is to make the two
blades thicker and wider than traditional turbine blades so that the two blades can
convert more wind energy.
The thicker blades also mean that the blades are stronger and better able to resist
fatigue problems. New composite materials allow the increased size without adding
substantial weight to each blade.
These materials also allow the blade to be produced at a lower cost. Even with these
more efficient blades, however, the two-blade turbine is still slightly less efficient than
the three-blade turbine.
One advantage to a two-blade turbine is that it is faster and safer to install than the
three-blade version.
The two-blade turbine can be lifted into position after the turbine blades have been
mounted while it is still on the ground because the blades can be mounted in a
horizontal position and easily lifted as a unit.
A three-blade turbine always has one blade pointing downward if it is raised as a unit,
so it is more difficult to get the larger wind turbines off the ground as a unit for mounting.
  Three-Blade Wind Turbines
The majority of large horizontal-axis wind turbines use three blades, with the rotor
position maintained upwind by the yaw control. Figure 8 shows a three-blade wind
turbine.
The three blades provide the most energy conversion while limiting noise and vibration.
The three blades provide more blade surface for converting wind energy into electrical
energy than a two-blade or single-blade wind turbine.
The blades for the larger horizontal-axis wind turbines are so large they must be
transported individually by a truck and trailer. This also means that one or more very
large cranes are needed to set the tower and turbine in place.
The tower to hold the larger three-blade turbine must also be larger and reinforced to
support the weight and to withstand the increased wind power that is harvested to
produce its maximum output.
The blades on larger three-blade wind turbines are typically installed one at a time after
the nacelle is mounted on the tower.
 On smaller three-blade turbines, the blades can be mounted to the rotor while the rotor
is on the ground. Then the entire rotor assembly is lifted with a crane and attached to
the shaft after the nacelle is mounted on the tower.
  Five-Blade Wind Turbines
A few wind turbines have five blades to produce electrical energy efficiently from low-
speed winds. Figure 9 shows a five-blade wind turbine.
A five-blade wind generator normally has narrower and thinner blades, which creates
issues with strength. While they are excellent in low-speed winds, they become
inefficient in high-speed winds and they are noisier.
The tower and base are mounted into the roof of the building, which is a concrete-
reinforced building. This type of five-blade wind turbine needs a very strong base and
tower to hold the wind turbine in the wind.
Notice the thickness of the tower and the cowling around the blades, which helps direct
wind directly into the blades.
Comparison of Wind Turbine Blade Types
Wind turbine blades can be compared in a number of ways, such as by size, weight,
material, and the way they are manufactured.
Wind turbine blades can be made from a variety of materials, from wood for smaller
blades to aluminum and other metals for small and medium-size blades.
Turbine blades must be stiff enough to prevent the blade tips from being pushed into the
tower by high winds, yet agile enough to convert wind power into electricity efficiently.

Advantages and Disadvantages of Single-, Two-, and Three-Blade Wind Turbines

Type of
Wind Advantages Disadvantages
Turbine

1. Heavier than single- and two-

blade turbines
1. Quietest of the three types of
2. Most capital-expensive of the
turbines
three types
2. Least amount of vibration
3. Requires active yaw control to
Three- 3. Available blade pitch control
make blades face into the wind
Blade allows the blade to catch the
4. Requires the largest cranes to
Turbine maximum amount of wind
construct
4. Lowest energy cost when
5. Requires the largest and
compared to other turbines with
heaviest tower
similar size blades
6. Larger blades are more difficult
to transport to the tower site

1. Noisier than the three-blade

1. Initial cost and weight are lower
turbine
Two-Blade and they are simpler to mount
2. Produces less energy than the
Turbine 2. Produces more energy than the
three-blade turbine (when blade
single-blade turbine
size and speed are the same)

1. Least expensive 1. Noisier than the three-blade

2. Easiest to erect because of its turbine
Single- lightweight and because the blade 2. Must run at the highest speed
Blade can be mounted while it is on the to produce the same amount of
Turbine ground electrical power
3. Requires the smallest and 3. Most prone to vibration at the
lightest tower blade
Main Components Of Vertical Axis Wind Turbine
Vertical axis wind turbine are one whose axis of rotation is vertical with respect to
ground. There are many  PARTS of vertical axis wind turbine but we have discus few of
them

 Guide wire
 Hub
 Rotor 
 Blades
 Shaft 
 Brake
 Gear
 Generator
 Base

GUIDE WIRE

Vertical axis wind turbine normally needs guide wire to keep the rotor shaft in a fixed
position and maximised possible mechanical vibration

Hub

The hub is the centre of the rotor to which the rotor blades are attached. Cast iron or
cast steel is most often used. In VAWT there are two hibs upper and lower because
blades are attached at two points. 

ROTOR

The rotor is the heart of a wind turbine and consists of multiple rotor blades attached to
a hub. It is the turbine component responsible for collecting the energy present in the
wind and transforming this energy into mechanical motion. As the overall diameter of
the rotor design increases, the amount of energy that the rotor can extract from the wind
increases as well. Therefore, turbines are often designed around a certain diameter
rotor and the predicted energy that can be drawn from the wind.
ROTOR BLADES

Rotor blades are a crucial and basic part of a wind turbine.they are mainly made of
aluminium, fibber glass or carbon fibber because they provide batter strength to weight
ratio. The design of the individual blades also affects the overall design of the rotor.
Rotor blades take the energy out of the wind; they “capture” the wind and convert its
kinetic energy into the rotation of the hub. there are two types of blades use in VAWT 

 Drage force type blades ( savonius wind turbine)

 Lift force type blades (Darrieus and giromill wind turbine)

SHAFT

The shaft is the part that gets turned by the turbine blades. It in turn is connected to the
generator within the main housing

ELECTRICAL BRAKING

Braking of a small wind turbine can also be done by dumping energy from the generator
into a resistor bank, converting the kinetic energy of the turbine rotation into heat. This
method is useful if the kinetic load on the generator is suddenly reduced or is too small
to keep the turbine speed within its allowed limit.

Cyclically braking causes the blades to slow down, which increases the stalling effect,
reducing the efficiency of the blades. This way, the turbine's rotation can be kept at a
safe speed in faster winds while maintaining (nominal) power output. This method is
usually not applied on large grid-connected wind turbines.

MECHANICAL BRAKING

A mechanical brake is normally placed on the high speed shaft between the gearbox
and the generator, but there are some turbine in which the brake is mounted on the low
speed shaft between the turbine and gear box
A mechanical drum brake or disk brake is use to stop turbine in emergency situation
such as extreme gust events or over speed. This brake is also used to hold the turbine
at rest for maintenance as a secondary mean, primarily mean being the rotor lock
system. Such brakes are usually applied only after blade furling and electromagnetic
braking have reduced the turbine speed generally 1 or 2 rotor RPM, as the mechanical
brakes can create a fire inside the nacelle if used to stop the turbine from full speed.
Also the load on turbine increases if brake is applied on rated RPM. These kind of
mechanical brake are driven by hydraulic systems and connected to main control box.

GEAR BOX

The main function of the gear box is to take low rotational speed from shaft and
increase it to increase the rotational speed of the generator.Among the types of gear
stages are the plantary, helical,oarallel shaft, spure and worm types. Two or more gear
types may be combined in multiple stages. they are made up of aluminium alloys,
stainless steel and cost iron 

GENERATOR

The conversion of rotational mechanical energy to electrical energy is performed by

generator. Different types of generator have been used in wind energy system over the
years. For large, commercial size horizontal-axis wind turbines, the generator is
mounted in a nacelle at the top of a tower, behind the hub of the turbine rotor. Typically
wind turbines generate electricity through asynchronous machines that are directly
connected with the electricity grid. Usually the rotational speed of the wind turbine is
slower than the equivalent rotation speed of the electrical network - typical rotation
speeds for wind generators are 5-20 rpm while a directly connected machine will have
an electrical speed between 750-3600 rpm. Therefore, a gearbox is inserted between
the rotor hub and the generator. This also reduces the generator cost and weight

Advantages

 They can produce electricity in any wind direction

 Strong supporting tower in not needed because generator, gearbox and other
components are placed on the ground
 Low production cost as compared to horizontal axis wind turbine
 As there is no need of pointing turbine in wind direction to be efficient so yaw
drive and pitch mechanism is not needed
 Easy installation as compared to other wind turbine
 Easy to transport from one place to other
 Low maintenance cost
 They can be install in urban area
 Low risk for human and birds because blades moves at relatively low speed
 They are particularly suitable for areas with extreme weather conditions, like in
the mountains where they can supply electricity to mountain huts.

Disadvantages

 As only one blade of wind turbine work at a time so efficiency is very low
 They need a initial push to start, this action use few of its own produce electricity
 When compared to horizontal axis wind turbine they are very less efficient with
respect to  them. this is because they have an additional drag when their blades
rotates.
 They have relative high vibration because the air flow near the ground creates
turbulent flow
 Because of vibration bearing wear increase which result in the increase of
maintenance cost
 They create noise pollution

 Guy wires which hold up the machine, need some are to install 
Advantages Disadvantages

Requires power and a starting

Quieter and less vibration than horizontal-axis wind turbines motor to start the Darrieus wind
turbine

Need guy wires to ensure the

Does not need a yaw control because it can produce
pole stays vertical so blade
electricity regardless of the direction the wind is blowing
rotation is smooth

Not as efficient as horizontal-

Produces electrical energy at very low wind speeds
axis wind turbines

Slower blade speeds because the blades are closer to the

axis of rotation.

Can be installed in urban environments and residential and

commercial areas because they operate at low noise levels

More eye pleasing than some larger horizontal wind turbines;

can be coated with colors to match buildings and
surroundings because the smaller turbines are mounted low
to the ground near buildings

Vertical-axis towers are much shorter than horizontal-axis

wind turbines.

The generator is generally mounted closer to the ground, so

a crane is not needed for servicing.
Table 1 Advantages and Disadvantages of VAWTs

Difference between Horizontal and Vertical Axis Wind

Turbine
Design
Horizontal Axis Wind Turbine (HAWT) is the most commonly used design configuration
in wind turbines with rotors similar to that of aircraft rotors. In HAWTs, the rotating axis
of the blades is parallel to the direction of the wind. Vertical Axis Wind Turbine (VAWT),
on the other hand, is probably the oldest type of windmills in which the axis of the drive
shaft is perpendicular to the ground. It is a type of windmill where the main rotor shaft
runs vertically, as opposed to the horizontal axis wind turbine.
Machinery

– The horizontal axis wind turbines have the entire rotor, gearbox and generator
mounted at the top of the tower, which must be turned to face the wind direction. A
significant advantage of vertical axis wind turbine over horizontal axis type is that the
former can accept wind from any direction and thus no yaw control is needed. In
VAWTs, the wind generator, gearbox and other main turbine components can be set up
on the ground, which simplifies the wind tower design and construction and
consequently reduces the turbine cost.

Wind Conditions

– HAWTs are generally used under streamline wind conditions where a constant stream
and direction of wind is available in order to capture the maximum wind energy. HAWTs
are not effective where the wind is turbulent, so they are generally located in areas
where there is a constant directional airflow. VAWTs, on the other hand, are mainly
beneficial in areas with turbulent wind flow such as rooftops, coastlines, etc. Unlike
HAWTs, VAWTs can operate even in low wind speeds and they may be built at
locations where tall structures are prohibited.
SOURCES OF WIND:

1. Planetary or Global Winds

 Trade winds
 Westerlies
 Polar winds
2. Local Winds

CLASSIFICATION OF WIND ENERGY POTENTIAL IN INDIA:

160 sites have so far been identified in 13 states as showing promise of wind farm sites and the table
below shows the installed capacities in various cities in India
WIND ENERGY TECHNOLOGY – A Technical Overview 3.1 Background In 1891, a
Dane by the name of Poul LaCour built the first electricity-generating wind turbine. It
was improved by Danish engineers and used to supply energy during energy shortages
in World War I and World War II. The wind turbines built by the Danish company F.L
Schmidt (now a cement machinery maker) in 1941-1942 can be considered the
forerunners of modern wind turbines, and other companies, such as the American
Palmer Putnam began building turbines as well, modifying the number of blades and
tower height.

The actual technology has also improved in large spurts. By the end of 1989, a
300 kW wind turbine with a 30-m rotor diameter was state-of-the-art. Ten years later,
1500 kW turbines with a diameter of around 70m are available from many
manufacturers. Though 4-5 MW are expected within the next 2 years, the 1.5 MW
turbines remain state of-the-art. In India, a typical wind turbine is of the 200 kW type.

The Physics of Energy Extraction from Wind: The power carried by a flowing mass
of air that is called wind is the product of the cross-sectional area of the mass and the
wind, the density of the wind, ρ , and the wind speed, v.

Wind Power, P = ½ * A * v 3 (Watts)

ρ = Air density (kg/m3)

v = wind speed ( m/s)

The air density is proportional to the air temperature and the air pressure, both of which
vary with height above sea level. The power in the wind cannot be completely converted
to mechanical energy of a wind turbine.

Otherwise the air mass would be stopped completely in the intercepting rotor area and
would cause a “congestion” of the cross-sectional area for the following air masses.

The theoretical maximum of energy extraction from wind was discovered by Betz in
1926, and is written as

PBetz = ½ * ρ * A * v3 * CpBetz = ½ * ρ * A * v3 * 0.59

Though this is not a hard and fast limit such as the Carnot efficiency it happens to be a
useful rule-of-thumb estimate.

According to Betz, even if no losses occurred a wind turbine could utilize only 59% of
the wind power. In addition when unavoidable swirl losses are included, this figure
reduces to about 0.42. This happens to be observed as the current limit of well-
designed turbines today.

Factors affecting Wind Power Extraction

Elevation of Blade Hub above ground – The higher above ground one is, the higher the
wind velocity (to the 1/7th power) and since power is proportional to the cube of the
velocity, an increase in hub elevation from 30m to 50m leads to an average wind speed
7.6% higher. This becomes a significant cost-benefit trade-off since taller hubs become
more expensive.

Spacing of Wind Turbines on Wind farms – Too far a spacing will prevent the maximum
amount of wind to be intercepted. However, too close a spacing will lead to interference,
and downwind units will be less productive.

Turbines used in India D = Diameter of Turbine Area Required per Turbine =

Approximately 5 acres.

Sitting of Wind Turbine – Naturally not all locations are suitable for placement of wind
turbines. In order to be economical, most sites have to have average wind speeds of
about 10 m/s. This speed usually increases with height above ground.

Air density – The higher the density of air, the more power carried by the wind, and as
air density decreases with height above sea-level, usually sites in mountainous regions
are less preferable than those at flat, sea-level locations. (For example, in “mile’ high”
Denver, air density is only 0.84 that at sea level which reduces the available wind-borne
energy by as much as 6% in average wind velocity).

Major Components of a typical horizontal axis wind turbine From an engineering

standpoint, two types of wind turbines exist – those that use aerodynamic drag (used by
the early Persians and Chinese), and those that utilize aerodynamic lift. Modern wind-
turbines are based on those that use lift and these can be further divided into vertical
axis and horizontal axis turbines. All the turbines we will be discussing will be the
horizontal axis turbines and are by far the widest in use A wind turbine generator usually
consists of the following parts

1) Tower – Either steel lattice or tubular pole. The tubular towers are more popular
among modern turbines because of their lower airflow interference and downstream
turbulence creation. Also, they seem to be more aesthetically acceptable.

2) Rotor Blades - Current design uses either two- or three-bladed wind turbines, but
the latter are becoming more popular and have a number of technical advantages. Two-
bladed designs have the advantage that the hub is lighter and so the entire structure
can be lighter. This is traded off by the fact that threebladed designs are much better
understood aerodynamically and also have a lower noise level than the two-bladed
turbines. These blades are made of glass reinforced plastic (GRP).

3) The nacelle – This sits atop the tower and holds the rotor blades in place while
housing the gearbox and the generator. On large turbines the nacelle with rotor is
electrically yawed into or out of the wind.

3.5 Network Integration

The interaction between the turbine and the grid it is connected is very important and
both can be heavily influenced by how the other works.

Effect of Wind Turbine on Grid

The nature of wind energy extraction is such that it has fluctuating output due to variable
wind speed. These lead to voltage and power fluctuations that may be evident as flicker
effects, and voltage asymmetry, and generally affect the power quality of the network.
Fixed-speed turbines produce a power pulsation emanating from the wind share over
height. In order to avoid this, a number of measures can and are usually taken.
 Variable-wind speed turbines are able to absorb short-term power fluctuations by
using immediate storage of energy on the rotating drive train.

 Having a large number of turbines active at a wind farm also eliminates

irregularities because gusts of wind are not likely to affect all turbines at the same
time and so a smoother overall output is achieved.

 The start-up of wind turbines may lead to an inrush of high current – pitch
regulated and variable wind speed turbines are able to achieve a more fluid
transition.

Effect of Grid on Turbine

The grid also has numerous effects on the turbine performance itself. Weak grid
systems, that is those with long, low-loaded low-voltage transmission lines
experience variations in voltage depending on the load they are experiencing.
Such grids make it more difficult for wind turbines to be started up sometimes
and so can seriously lower the “online” time of turbines.

Development of the Wind Sector in India

In 1985, the MNES conducted an extensive wind data collection program
consisting of wind monitoring, wind mapping, and complex terrain projects,
covering 25 out of India’s 26 States/Union Territories. The wind resource
potential calculated as a consequence of this study was 20, 000 MW.
Consequently grid-quality wind power became the main focus of the
MNES, and it opened up the wind energy sector to private enterprise, with giant
success. Due to private sector investment, by March 1998, of the 968 MW of
installed capacity, 95% had come from industries, entrepreneurs and
businessmen (1). Lured by the incentives set up by the Ministry, wind farms had
been set up by major industrial houses, including Madras Cement Limited and
Dalmias, all over the country. A capacity of 230 MW was installed in 1994-95,
382 MW in 1995-1996 and 170 MW in 1996-1997. Between 1993 and 1997,
growth in the wind energy sector represented approximately 6 per cent of new
generating capacity installed in the country. And the government set an
ambitious target of installing 3,000 MW generating capacity by 2003. The current
1025 MW that are in operation represent about 1% of India’s total electricity
consumption.
Geographic Distribution
Tamil Nadu has the distinction of 719 MW (75% of total) wind farms at the end of
September 1998 (2). Andra Pradesh has 58 MW (6%) and Gujarat has 168.64
MW, or 16% of the total capacity installed. See the map below for more details
on wind-farm distribution

Market and Financial Aspect

Today there are over 30 companies involved in the wind energy sector in India.
One really positive thing seen in India was the emergence of numerous private
companies, which actually manufactured wind turbines and components.
 kinetic energy of wind:

 Kinetic Energy of wind is: 1/2 * mass * velocity * velocity

 momentum in the wind = mass x velocity
 Power per unit area = KE * momentum --> MV2 *MV
 So Power that can be extracted from the wind goes as velocity cubed (V 3)
 27 times more power is in a wind blowing at 60 mph than one blowing at 20 mph

For average atmospheric conditions of density and moisture contant:

Power per sq. meter = .0006 V3

 Velocity measured in meters per second

 Power then measured in Kilowatts
 1 meter per second is approximately 2 mph
 20 mph wind =10 m/s --> Power generated equals

.0006 * 103 = .0006 * 1000 = .6 KILO watts per square meter

which is 600 watts per square meter
this is identical to average solar power per square meter
Windmills cannot operate at 100% efficiency because the structure itself impedes the
flow of the wind

 Theoretical maximum efficiency is 59%

 Picaresque Dutch Windmill (4=arms) = 16%
 Rotary, multi blade = 30%
 High speed propeller (vertical) = 42%

Clearly, wind power is a highly variable source and hence energy storage is
crucial.

Rotary type windmills have high torque and are useful for pumping water

High speed propeller types have low torque and are most efficient at high rotational
velocities --> useful for generation of electricity

Betz limit
The Betz limit is the theoretical maximum efficiency for a wind turbine, conjectured by
German physicist Albert Betz in 1919. Betz concluded that this value is 59.3%, meaning
that at most only 59.3% of the kinetic energy from wind can be used to spin the turbine
and generate electricity. In reality, turbines cannot reach the Betz limit, and common
efficiencies are in the 35-45% range.

Wind turbines work by slowing down passing wind in order to extract energy. If a wind
turbine was 100% efficient, then all of the wind would have to stop completely upon
contact with the turbine—which isn't possible by looking at a wind turbine. In order to
stop the wind completely, the air wouldn't move out of the way to the back of the turbine,
which would prevent further air from coming in—causing the turbine to stop spinning.

For determining power extracted from wind by wind turbine we have to assume
an air duct as shown in the figure. It is also assumed that the velocity of the wind at the
inlet of the duct is V1 and velocity of air at the outlet of the duct is V 2. Say, mass m of the
air is passed through this imaginary duct per second.
Now due to this mass the kinetic energy of wind at the inlet of the duct is,

Similarly, due to this mass the kinetic energy of wind at the outlet of the duct is,

Hence, the kinetic energy of wind changed, during the flow of this

quantity of air from the inlet to the outlet of the imaginary duct is,
As we already said that, mass m of the air is passed through this imaginary duct in one
second. Hence the power extracted from the wind is the same as the kinetic energy
changed during the flow of mass m of the air from the inlet to the outlet of the duct.

We define power as the change of energy per second. Hence, this extracted power can
be written as,

As mass m of the air passes in one second, we refer the quantity m as the mass
flow rate of the wind. If we think of that carefully, we can easily understand that mass
flow rate will be the same at the inlet, at the outlet and as well as at every cross-section
of the air duct. Since, whatever quantity of air is entering the duct, the same is coming
out from the outlet.

If Va, A and ρ are the velocity of the air, the cross-sectional area of the duct and
density of air at the turbine blades respectively, then the mass flow rate of the wind can
be represented as
 Now, as the turbine is assumed to be placed at the middle of the duct, the wind
velocity at turbine blades can be considered as average velocity of inlet and outlet
velocities.

To obtain maximum power from wind, we have to differentiate equation (3) in

respect of V2 and equate it to zero. That is,
From, the above equation it is found that the theoretical maximum power extracted from
the wind is in the fraction of 0.5925 of its total kinetic power. This fraction is known as
the Betz Coefficient. This calculated power is according to theory of wind turbine but
actual mechanical power received by the generator is lesser than that and it is due to
losses for friction rotor bearing and inefficiencies of aerodynamic design of the turbine.
From equation (4) it is clear that the extracted power is

1. Directly proportional to air density ρ. As air density increases, the power of the
turbine increases.
2. Directly proportional to the swept area of the turbine blades. If the length of the
blade increases, the radius of the swept area increases accordingly, so turbine
power increases.
3. Turbine power also varies with velocity 3 of the wind. That indicates if the velocity
of wind doubles and the turbine power will increase to eight folds.

Tip Speed Ratio:

The Tip Speed Ratio (often known as the TSR) is of vital importance in the design

of wind turbine generators. If the rotor of the wind turbine turns too slowly, most of
the wind will pass undisturbed through the gap between the rotor blades. Alternatively if
the rotor turns too quickly, the blurring blades will appear like a solid wall to the wind.
Therefore, wind turbines are designed with optimal tip speed ratios to extract as much
power out of the wind as possible.

When a rotor blade passes through the air it leaves turbulence in its wake. If the next
blade on the spinning rotor arrives at this point while the air is still turbulent, it will not be
able to extract power efficiently from the wind. However if the rotor span a little more
slowly the air hitting each turbine blade would no longer be turbulent. Therefore the tip
speed ratio is also chosen so that the blades do not pass through too much turbulent
air.
Tip Speed Ratio Calculations

The tip speed ratio is given by dividing the speed of the tips of the turbine blades by the
speed of the wind – for example if a 20 mph wind is blowing on a wind turbine and the
tips of its blades are rotating at 80 mph, then the tip speed ration is 80/20 = 4.

Optimum Tip Speed Ratio

The optimum tip speed ratio depends on the number of blades in the wind turbine

rotor. The fewer the number of blades, the faster the wind turbine rotor needs to turn to
extract maximum power from the wind. A two-bladed rotor has an optimum tip speed
ratio of around 6, a three-bladed rotor around 5, and a four-bladed rotor around 3.

Highly efficient aerofoil rotor blade design can increase these optimum values by as

much as 25-30% increasing the speed at which the rotor turns and therefore generating
more power. A well designed typical three-bladed rotor would have a tip speed ratio of
around 6 to 7.

If the tip speed ratio is too low – for example if poorly designed rotor blades are used –
the wind turbine will tend to slow and/or stall. If the tip speed ratio is too high the turbine
will spin very fast through turbulent air, power will not be optimally extracted from the
wind, and the wind turbine will be highly stressed and at risk of structural failure.

Different types of turbine have completely different optimal TSR values – for example
a Darrieus wind turbine is a vertical axis (VAWT) design with aerofoil blades which
generate aerodynamic lift and therefore the TSR can be high, but a Savonius wind
turbine which is also a VAWT is a drag design and so the TSR will always be less than
1 – i.e. it cannot spin faster than the wind hitting it.
Pictured below is a graph showing the power coefficient for different values of tip
speed ratio for a two-bladed rotor. The theoretical maximum efficiency of a wind turbine
generator is given by the Betz Limit of around 59%. With a tip speed ratio (TSR) of just
under 6, the power coefficient for this example turbine is 0.45 (= 45%).
Wind Turbine Efficiency:
Wind turbine efficiency is a useful parameter for comparing performance of wind
turbines to other wind turbines. Comparisons of wind turbine efficiency to the
efficiency of other forms of power generation is meaningless and misleading (which is
worse than meaningless). Though that hasn't stopped people from doing it all over the
internet. In physics and engineering, efficiency is a way to compare the performance of
a device or system to some ideal or standard of perfection for that specific type of
device or system. It has no meaning outside its clearly defined mathematical formula.
For wind turbines and other power sources, the cost of energy produced is the best for
economic comparisons, but other factors such as sustainability, capacity factor, impact
on environment, and less dependence on foreign oil, are also important for setting
energy policy.
Wind Data & Energy Estimation:

Wind Survey:

SITE SELECTION CONSIDERATION FOR WECS

 The power available in the wind increases rapidly with the speed, hence wind energy
conversion machines should be located preferable in areas where the winds are strong
and persistent. Although daily winds at a given site may be highly variable, the monthly
and especially annual average are remarkably constant from year to year.

The major controbution to the wind power available at a given site is actually made by
winds with speeds above the average. Nevertheless, the most suitable sites for wind
turbines would be found in areas where the annual average wind speeds are known to
be moderately high or high.

The site choice for a single or a spatial array of WECS is an important matter when wind
electrics is looked at from the systemspoint of view of aeroturbine generators feeding
power into a convertional electric grid.

If the WECS sites are wrongly or poorly chosen the net wind electrics generated energy
per year may be sub optimal with resulting high capital cost for the WECS apparatus,
high costs for wind generated electric energy, and low Returns on Investment. Even if
the WECS is to be a small generator not tied to the electric grid, the sitting must be
carefully chosen if inordinately long break even times are to be avoided. Technical,
Economic, Evironmental, Social and Other actors are examined before a decision is
made to erect a generating plant on a specific site.
Some of the main site selection consideration are given below:

 
1.    High annual average wind speed:
2.    Availability of anemometry data:
3.    Availability of wind V(t) Curve at the proposed site:
4.    Wind structure at the proposed site:
5.    Altitude of the proposed site:
6.    Terrain and its aerodynamic:
7.    Local Ecology
8.    Distance to road or railways:
9.    Nearness of site to local centre/users:
10.  Nature of ground:
11.  Favourable land cost:
 

1.           High annual average wind speed:

The speed generated by the wind mill depends on cubic values of velocity of wind, the
small increases in velocity markedly affect the power in the wind. For example, Doubling
the velocity, increases power by a factor of 8. It is obviously desirable to select a site for
WECS with high wind velocity. Thus a high average wind velocity is the principle
fundamental parameter of concern in initially appraising WESCS site. For more detailed
estimate value, one would like to have the average of the velocity cubed.

2.           Availability of anemometry data:

It is another improvement sitting factor. The aenometry data should be available over
some time period at the precise spot where any proposed WECS is to be built and that
this should be accomplished before a sitting decision is made.
3.           Availability of wind V(t) Curve at the proposed site:

This important curve determines the maximum energy in the wind and hence is the
principal initially controlling factor in predicting the electrical output and hence revenue
return o the WECS machines.

It is desirable to have average wind speed ‘V’ such that V>=12-16 km/hr (3.5 – 4.5
m/sec) which is about the lower limit at which present large scale WECS generators ‘cut
in’ i.e., start turning. The V(t) Curve also determines the reliability of the delivered
WECS generator power, for if the V(t) curve goes to zero there be no generated power
during that time.

If there are long periods of calm the WECS reliability will be lower than if the calm
periods are short. In making such realiability estimates it is desirable to have measured
V(t) Curve over about a 5 year period for the highest confidence level in the reliability
estimate.

4.           Wind structure at the proposed site:

The ideal case for the WECS would be a site such that the V(t) Curve was flat, i.e., a
smooth steady wind that blows all the time; but a typical site is always less than ideal.
Wind specially near the ground is turbulent and gusty, and changes rapidly in direction
and in velocity. This depature from homogeneous flow is collectively referred to as “the
structure of the wind”.

5.           Altitude of the proposed site:

It affects the air density and thus the power in the wind and hence the useful WECS
electric power output. Also, as is well known, the wind tend to have higher velocities at
higher altitudes. One must be carefully to distinguish altitude from height above ground.
They are not the same except for a sea level WECS site.

6.           Terrain and its aerodynamic:

One should know about terrain of the site to be chosen. If the WECS is to be placed
near the top but not on the top of a not too blunt hill facing the prevailing wind, then it
may be possible to obtain a ‘speed-up’ of the wind velocity over what it would otherwise
be. Also the wind here may not flow horizontal making it necessary to tip the axis of the
rotor so that the aeroturbine is always perpendicular to the actual wind flow.

It may be possible to make use of hills or mountains which channel the prevailing wind
into a pass region, thereby obtaining higher wind power.

7.           Local Ecology

If the surface is base rock it may mean lower hub height hence lower structure cost. If
trees or grass or vegetation are present, all of which tend to destructure the wind, the
higher hub heights will be needed resulting in larges system costs that the bare ground
case.

8.           Distance to road or railways:

This is another factor the system engineer must consider for heavy machinery,
structure, materials, blades and other apparatus will have to be moved into any choosen
WECS site.

9.           Nearness of site to local centre/users:

This obvious criterion minimizes transmission line length and hence losses and cost.
After applying all the previous string criteria, hopefully as one narrows the proposed
WECS sites to one or two they would be relatively near to the user of the generated
electric energy.

10.       Nature of ground:

Ground condition should be such that the foundation for a WECS are secured. Ground
surface should be stable. Erosion problem should not be there, as it could possibly later
wash out the foundation of a WECS, destroying the whole system.

11.       Favourable land cost:

Land cost should be favourable as this along with other siting costs, enters into the total
WECS system cost.
12. Other conditions such as icing problem, salt spray or blowing dust should not
present at the site, as they may affect aeroturbine blades or environmental is generally
adverse to machinery and electrical apparatus.

Basic Components Of Wind Energy Conversion System:

Basic components of a Wind Electric Systems are,

 Tower
 Nacelle
 Rotor
 Gearbox
 Generator
 Braking System
 Yaw System
 Controllers
 Sensors

Aero turbines convert energy in moving air to rotary mechanical energy.  In general,
they require pitch control and yaw control (only in the case of horizontal or wind axis
machines) for proper operation.  A mechanical interface consisting of a step up gear
and a suitable coupling transmits the rotary mechanical energy to an electrical
generator.  The output of this generator is connected to the load or power grid as the
application warrants.
Yaw control.  For localities with the prevailing wind in one direction, the design of a
turbine can be greatly simplified.  The rotor can be in a fixed orientation with the swept
area perpendicular to the predominant wind direction.  Such a machine is said to be
yaw fixed.  Most wind turbines, however, are yaw active, that is to say, as the wind
direction changes, a motor rotates the turbine slowly about the vertical (or yaw) axis so
as to face the blades into the wind.  The area of the wind stream swept by the wind rotor
is then a maximum.

In the small turbines, yaw action is controlled by tail vane, similar to that in a typical
pumping windmill.  In larger machines, a servomechanism operated by a wind-direction
sensor controls the yaw motor that keeps the turbine properly oriented.

 The purpose of the controller is to sense wind speed, wind direction, shafts speeds and
torques at one or more points, output power and generator temperature as necessary
and appropriate control signals for matching the electrical output to the wind energy
input and protect the system from extreme conditions brought upon by strong winds
electrical faults, and the like.

The physical embodiment for such an agro-generator is shown in a generalized.  The

sub-components of the windmill are: 

 wind turbine or rotor

 wind mill head
  transmission and control and
 Supporting structure

 Such a machine typically is a large impressive structure.

Rotors

i.Horizontal axis rotor and

ii.Vertical axis rotor.

One advantage of vertical-axis machines is that they operate in all wind directions and
thus need no yaw adjustment.

The rotor is only one of the important components.  For an effective utilization, all the
components need to be properly designed and matched with the rest of the
components.

Windmill head

The windmill head

It supports the rotor, housing the rotor bearings.  It also houses any control mechanism
incorporated like changing the pitch of the blades for safety devices and tail vane to
orient the rotor to face the wind.  Mounting it on the top of the supporting structure on
suitable bearings facilitates the latter.

Transmission

Varying the pitch of the rotor blades, conveniently controls the rate of rotation of large
wind turbine generator operating at rated capacity or below,, but it is low, about 40 to 50
revolutions per minute (rpm).  Because optimum generator output requires much
greater rates of rotation, such as 1800 rpm, it is necessary to increase greatly the low
rotor rate of turning.  Among the transmission options are mechanical systems involving
fixed ratio gears, belts, and chains, singly or in combination or hydraulic systems
involving fluid pumps and motors.  Fixed ratio gears are recommended for top mounted
equipment because of their high efficiency, known cost, and minimum system risk.  For
bottom mounted equipment which requires a right-angle drive, transmission costs might
be reduced substantially by using large diameter bearings with ring gears mounted on
the hub to serve as a transmission to increase rotor speed to generator speed.  Such a
combination offers a high degree of design flexibility as well as large potential savings.

Generator

Either constant or variable speed generators are a possibility, but variable speed units
are expensive and/or unproved.  Among the constant speed generator candidates for
use are synchronous induction and permanent magnet types.  The generator of choice
is the synchronous unit for large aero generator systems because it is very versatile and
has an extensive database.  Other electrical components and systems are, however,
under development.

 Controls

The modern large wind turbine generator requires a versatile and reliable control
system to perform the following functions:

1. the orientation of the rotor into the wind (azimuth of yaw);

2. start up and cut-in of the equipment;
3. power control of the rotor by varying the pitch of the blades;
4. generator output monitoring - status, data computation, and storage;
5. shutdown and cut out owing to malfunction of very high winds'
6. protection for the generator, the utility accepting the power and the
prime mover;
7. auxiliary and /or emergency power; and
8. maintenance mode.

Many combinations are possible in terms of the control system and may involve the
following components:

1. Sensor - mechanical, electrical, or pneumatic:

2. Decision elements - relays, logic modules, analog circuits, a
microprocessor, a fluidics, units, or a mechanical unit; and
3. Actuators -  hydraulic, electric, or pneumatic.  A recommended
combination of electronic transducers feeding into a micro-processor
which, in turn, signals electrical actuators and provides protection through
electronic circuits, although a pneumatic slip clutch may be required.

Towers.

Four types of supporting towers deserve consideration, these are: 

 1. the reinforced concrete tower
2. the pole tower
3. the built up shell-tube tower, and
4. the truss tower

 Among these, the truss tower is favoured because it is proved and widely adaptable,
cost is low, parts are readily available, it is readily transported, cost is low, parts are
readily available, it is readily transported, and it is potentially stiff.   Shell-tube towers
also have attractive features and may prove to be competitive with truss towers.

The type of the supporting structure and its height is related to cost and the
transmission system incorporated.  It is designed to withstand the wind load during
gusts (even if they occur frequently and for very short periods).  Horizontal axis wind
turbines are mounted on towers so as to be above the level of turbulence and other
ground related effects.  The minimum tower height for a small WECS is about 10m, and
the maximum practical height is estimated to be roughly 60 m.

The turbine may be located either upwind or downwind of the tower.  In the upwind
location (i.e. the wind encounters the turbine before reaching the tower), the wake of the
passing rotor blades causes repeated changes in the wind forces on the tower.  As a
result, the tower will tend to vibrate and may eventually be damaged.  On the other
hand, if the turbine is down wind from the tower as shown in figure, the tower vibrations
are less but the blades are now subjected to severe alternating forces as they pass
through the tower wake.

 Both upwind and downwind locations have been used in WEC devices.  Downwind
rotors are generally preferred especially for the large aero generators.  Although other
forces acting on the blades of these large machines are significant, tower effects are still
important and tower design is an essential aspect of the overall system design.

Water pumping

The sun converts five million tonnes of matter into energy every second. The tiny
fraction of energy reaching earth occurs in many farms. One of these is wind energy.
Wind energy is extraction of kinetic energy from the wind for conversion into a useful
type of energy - mechanical or electrical. The use of wind energy is almost as old as
recorded history. Windmills along with watermills were among the original prime movers
that replaced animal muscle as a source of energy.

Two important aerodynamic principles are utilized in windmill operation, i.e., lift and
drag. The wind can rotate the rotor of a wind mill either by lifting (lift) the blades or by
simply pushing against it (drag). Practically a wind mill cannot extract all the power in
the wind as it depends upon many factors like the density of the air, wind speed,
atmospheric pressure, area of the rotor and design of the rotor. To extract and utilize
the maximum possible energy, two principles (lift and drag) are well adjusted while
designing a wind mill for a specific application.

There are two different types of wind machines

1. Horizontal –axis wind machine where the rotating axis is parallel to the direction of
wind flow and parallel to the ground. There are two or more aerodynamic blades
mounted on the horizontal shaft. The blade tips can travel at several times the wind
speed which results in high efficiency. The blade shape is designed by suing the same
aero-dynamic theory as for aircraft. The low-speed horizontal axis wind mills are used
mainly for mechanical purposes, like in water pumps.

2. Vertical – axis wind machines are those where the rotating axis is perpendicular to
the wind stream and to the ground. The best known vertical-axis rotor is made up of two
identical semi cylinders with their axis vertical. This was developed by the Finnish
engineer, Savonious (1931), and is being used increasingly for small wind – energy
installations. The French engineer, Davieus designed another type of vertical – axis
rotor called Davious type wind mill. Flexible metal strips in the shape of a catenary form
the rotor blades. For a given wind speed, the unit rotates more rapidly and is more
efficient that the savionious rotor. Unfortunately, the Darreieus rotor is not self-starting
even in high winds.
Lift & Drag Type Machines:

Air resistance wind turbines are propelled directly by the wind, and the (vertical) rotor
moves along with it. This means that it’s impossible for the turbine to rotate faster than
the wind. In a way, it works against the wind. This results in a very low efficiency.
Additionally, the volume of material needed to build an air resistance wind turbine is
much higher than for a lift turbine. More material has negative consequences for
performance, price and installation. Both theoretical analyses and field tests have
consistently proven air resistance wind turbines have a maximum efficiency of only
15%.

Lift propelled wind turbines have blades that resemble wings you see on airplanes.
These blades move at right angles to the wind direction, at a higher speed than the
actual wind speed. They work with the wind, like a sail, instead of against the wind. This
is why these kind of turbines are fundamentally more suitable for harvesting wind
energy. Moreover, the blades cover only a fraction of the rotor surface. This means
much less material is needed for the rotor. Aside from the these advantages, the most
important feature of the lift propelled turbine is its high efficiency. The maximum
efficiency is 59%, also called the Betz limit – this is the maximum power that can be
extracted from the wind in open flow.

To summarize, a horizontal axis wind turbine, such as The Windleaf, is the sensible
choice. Economically, practically and environmentally.
Drag-based wind turbine

In drag-based wind turbines, the force of the wind pushes against a surface, like an open sail.
In fact, the earliest wind turbines, dating back to ancient Persia, used this approach. The
Savonius rotor is a simple drag-based windmill that you can make at home (Figure 1). It works
because the drag of the open, or concave, face of the cylinder is greater than the drag on the
closed or convex section.
Lift-based Wind Turbines

More energy can be extracted from wind using lift rather than drag, but this requires specially
shaped airfoil surfaces, like those used on airplane wings (Figure 2). The airfoil shape is
designed to create a differential pressure between the upper and lower surfaces, leading to a
net force in the direction perpendicular to the wind direction. Rotors of this type must be
carefully oriented (the orientation is referred to as the rotor pitch), to maintain their ability
to harness the power of the wind as wind speed changes.
EFFECT OF SOLIDITY:

The effects of solidity σ on wind turbine performance were investigated.

Power and torque coefficients were compared by torque meter, pressure

distributions and six-component balance.

The pressure difference substantially decreased with the increase of solidity σ

The values of six-component balance were closer to the values of the torque
meter.

WIND TURBINE OPERATION POWER VERSUS WIND SPEED

CHARACTERISTICS:

1. Low speed Region

2. Maximum Power Coefficient Region
3. Constant Power Region
4. Furling Speed region (Cut out Speed & Above)
Wind Diesel Hybird System:

Combining two or more generating technologies such as wind and diesel creates a hybrid power
system. For remote locations, far from the public power grid, this is an interesting alternative for
self-sufficient power supply. If the wind conditions are good wind-hybrids can usually provide
electricity at the lowest cost for such places.

There are many different concepts for hybrid systems. Small electrical systems up to a few kW
generally use batteries and often do not have motor driven gensets. Wind and solar
photovoltaics are often combined because they complement each other on a daily and seasonal
basis. The wind often blows when the sun is not shining and vice versa.

When considering kilowatt hours, small gensets are more expensive to buy and operate than
larger machines. Therefore, batteries are cost-effective for small systems. However, the
batteries are also a troublesome part of hybrid systems because of their toxic content (when
batteries are worn out, remember that they must be properly recycled).

With larger electrical requirements engine driven gensets are normally used because of the high
expense of storing large amounts of energy in batteries. A system that consists of wind
turbine(s) and diesel genset(s) is called a wind-diesel system. In these systems, the amount of
windpower ("wind penetration") is a decisive factor for the system design.

Low wind penetration does not require complex technology. When the windpower production is
always less than the load, and other power plants are constantly on line to control grid
frequency and voltage, the windpower saves fuel by reducing the load on other power plants.
This is similar to connecting a wind turbine to a large national grid. The disadvantage is that it
does not save so much fuel, especially if an unsuitable type of diesel genset is used. Gensets
require a certain minimum load (around 25% of rated load is typical, but there are more suitable
standard gensets that can cope with long time operation at down to 0% load).

Usually a high wind penetration is most economical in small power systems provided that the
wind conditions are good because of the high cost for small-scale conventional generation.
However, traditional wind-hybrid systems for high wind penetration are rather complex. To
match the varying windpower output to the needs of the grid large batteries and/or dumploads
are usually used (sometimes in combination with custom-built diesel gensets).
A Swedish development of hybrid systems for high wind penetration recently implemented on
an isolated Estonian island has taken another approach. By selecting a wind turbine with the
most suitable characteristics for high wind penetration the overall system design is simplified.
Thus, the cost of the system can be kept down although the amount of windpower is high.

When is Wind Energy Suitable?

If you need power supply at a remote location when should you consider wind as an alternative?
The most important factors which will determine the economy of wind energy at such places
are:

 Local wind conditions - of course. If the average wind speed 10 m above ground is
less than 4 m/s, the production of a wind turbine will be so small, that it is normally not
economical. On the other hand, for windy places like many islands, wind energy is highly
suitable.

 The cost of other generating alternatives. For remote locations the transportation cost
of fuel is often very high which makes diesel generation extremely expensive.

 Seasonal variation of wind energy and load. In northern Europe, for example, the
production of a wind turbine is normally highest during the winter which is very
advantageous because usually the energy demand is also highest during the winter.
(Solar energy, on the other hand, produces very little or nothing during the winter if you
are far from the equator. But for summer cottages far north used mainly during the sunny
season, solar energy has a suitable seasonal variation.)

 The size of the power system. Extremely small loads of only a few watts are often not
economical to supply with wind energy. But for larger energy requirements, like a remote
village, wind energy is a top alternative.

EXAMPLE OF A COMMERCIAL WIND-DIESEL SYSTEM

The island Osmussaare (Swedish name Odensholm) is located at the inlet to the Gulf of
Finland, about 10 km from the Estonian coast. Today the island is a nature reserve, inhibited
permanently only by a farmer and his wife, and there is no connection to the power grid on the
mainland.

When the Estonian Border Guard ordered the construction of a radar station on the
island, they asked for a wind-diesel system to reduce the fuel consumption, compared
to using only diesel power

Transportation of fuel to the island is very costly. There is no harbour and the shallow beaches
make it impossible for deep-going boats to reach the island. During the winter, the ice situation
sometimes makes the island accessible only by helicopter.
Installation of the wind-diesel system took place at the end of 2002. The wind turbine was
installed on a lower, separate tower to not interfere with the radar (which will be installed at the
top of the tall tower).

The features of the hybrid system concept available from PitchWind can be summarized as
follows:

 Large wind capture capability

 One or more wind turbines

 One or more diesel gensets

 Diesel gensets can be shut down when the wind is sufficient

 Standard diesel gensets can be used (no clutch or flywheel needed)

 Ability to integrate solar or hydro power

 Large batteries, containing lead, acid or cadmium, are not necessary

 Open control system, based on LonWorks technology

Environmental aspects of wind power:

Wind power plant as a renewable energy source has slight influence on environment,
nevertheless people reluctantly agree to construct power plants in their neighbourhood.

One of the most common environmental aspect regard noise. The noise has two
sources: mechanical (inherent in the gearing system – excluding double feed system)
and the second one related with aerodynamics of the rotor blade. The first one is
possible to eliminate but the second one not. The aerodynamic noise arise when the
rotating blade passing the tower. That effect calls the tower thumb. The most influence
on the level of loud has wind speed. When the wind blow fast the background noise is
enough loud to drown out the tower thumb effect but when the wind is blowing lightly the
tower thumb effect is audible in long distance.
Other environmental problem is electromagnetic interference. Large structures like wind
rotor and tower can cause objectionable electromagnetic interference in the performing
of a nearby transmitters or receivers. Moreover the rotating blades can also reflect
signals what make experience interference at the blade passage frequency. The highest
influence on that effect strength has location. This problem is important for onshore
technology but in some of case large offshore power plants the problem could be
higher. The offshore power plant can interference with radar and flight paths to airfields. 

Next one environmental problem is effect on birds. The wind turbine blade is a lethal
weapon against any avian population. The birds may be killed or at least injured if the
collide with blade. The most often situation the suction draught created by wind flowing
to a turbine caught the birds and poke them into air stream headed for the blades.
Extremely dangerous are turbines with lattice towers, where the bird has possibility to
nest. Therefore often wind farms have to be sited away avian flight paths. [3]

The last one environmental problem is visual impact mainly for onshore wind farms. The
problem is related with property owners around the wind farm, who do not allow for wind
power plant installation in their neighbourhood. However that problem also regard
offshore technology for farms installed near resorts. 

One of the most valuable social advantages is new workplaces. Usually it is a job for a
local technicians and engineers. In 2007 the EU wind energy sector directly employed
about 108600 people (most of all in Denmark, Germany and Spain). About 37% of new
workplaces are in wind turbine manufacturing, 22% in components manufacturing, 16%
in wind technology development, 11% in installation, operation and maintenance, 9% in
utilities, 3% in consultants, 2% in other functions. At present generally jobs are related
with onshore technologies however offshore becoming more and more common. 
 i) Indirect Energy Use & Emission

ii) Bird life

iii) Noise

iv) Visual Impact

v) Telecommunication

vi) Safety

vii) Effects on eco system

Wind generator system capacity

Wind generators are commonly rated at 1–3kW. This will typically provide one-third to
one-half of the power needs of a residence, depending on the local wind conditions and
the house’s power consumption. In an exposed location, this size of generator can
supply all power needs and provide a surplus. Bigger wind generators are available for
farms and rural communities. The turbines’ actual energy output is typically about 25%
to 30% of its rated theoretical maximum output. The output of a wind generator will
normally be rated at a specified wind speed, and the rated wind speed may vary
between systems and manufacturers.

The electricity generation capacity of wind generator systems is directly proportional to

the amount of usable wind, which is itself a function of wind speed and cleanliness.

Wind speed and power

The wind power density is the number of watts of electrical energy produced per square
metre of air space (W/m²). This value is normally given at 10 m or 50 m above the
ground.
 In general, the available wind generation capacity is determined by the average wind
speed over the year for each location. Around New Zealand, the average wind speed is
typically greater in regions:

 along the coasts between the North and South Islands

 in the mountain ranges and immediately east of them
 towards the tops of ridges or the heads of valleys.
With large turbines, increases in wind speed lead to considerably larger increases in
energy output – when the wind speed doubles, the energy produced can increase up to
eight times. However, New Zealand studies with small domestic turbines have found the
increase is usually more linear – when wind speed doubles, the energy produced
doubles.

Wind speed fluctuates, which has an impact on wind electricity generation capacity and
operating characteristics. In general, wind speeds are as follows:

 8 kph (2 m/s) minimum is required to start rotating most small wind turbines.
 12.6 kph (3.5 m/s) is the typical cut-in speed, when a small turbine starts
generating power.
 36–54 kph (10–15 m/s) produces maximum generation power.
 At 90 kph (25 m/s) maximum, the turbine is stopped or braked (cut-out speed).
The wind power at a site can be obtained by a measurement device mounted on a pole
at the height of the future wind generator. Collecting data for a whole year is not
generally viable, so a couple of months of data can be taken and compared with data
from a local weather station and then extrapolated for the year. Devices include:

 an anemometer – giving average daily wind speed

 a wind totaliser – giving instantaneous wind speed and total wind over an
extended period.
Cut-out controls

Cut-out control options are available that:

 apply a brake to stop the turbine completely and feather the blades (reduce their
angle to the wind) to turn it to face away from the wind
 tilt back or lie down the turbine (this is known as ‘tilt-up governing’)
 steer the turbine out of the wind through aerodynamics and gravity (this is known
as ‘autofurl’)
 govern the rotational speed with an air brake to produce constant power
 feather the blades (reduce their angle to the wind) to reduce turbine speed.
Factors affecting generation capacity

A system’s generation capacity depends on its effectiveness at converting wind

pressure into turbine rotary inertia – data should be available from the system supplier.
This increases with:

 larger turbine diameter – there is more turbine blade area for the wind to impact
on and also greater risk of intrusive noise
 appropriate blade profile for the local wind speed – this varies depending on
average wind speed and also on whether the wind is constant or comes in short periods
of high velocity
 lower friction losses in the turbine shaft assembly.
Generation capacity will decrease if the turbine is located:

 lower to the ground – wind speed increases with height above the ground, with a
minimum of 10 metres recommended
 within the turbulent airspace downwind of an obstacle (for example, trees, hills,
buildings, structures) – downwind turbulence will extend to twice the obstacle height for
a distance around 20 times the obstacle height
 a distance from an upwind obstacle of more than 10 times an obstacles height.

Wind generator system installation

A wind generator system:

 will require a building consent and a resource consent
 should be installed within 100 m of the electricity supply or storage system, to
reduce line losses
 must withstand the wind and seismic loads
 usually has a concrete footing for the tower (and each guy wire)
 must have vibrations in the tower (from turbine rotating forces) dampened if it is
connected to a building
 must have protection from large animals at ground level – they like scratching
themselves on the tower and guy wires
 should have lightning arresters to protect electronic components from lightning
strikes
 needs sufficient area to lower and raise the tower for maintenance and repairs.

Meeting electricity demand

Electrical power from the wind generator system may be available at all times of the
day, but the output levels will vary according to wind speed. Excess output, generated
as AC, is converted to DC by a rectifier for storage in batteries. This will allow for peak
demand that is greater than the generator capacity.

Very small turbines are unlikely to meet total household demand for energy. Using a
solid fuel burner for space heating and solar panels for water heating will help reduce
demand for electricity, but for systems that are not grid-connected, a diesel generator
may still be required sometimes.

Wind generator pollution

Wind generators can produce noise and vibration and have a significant visual impact.
Noise can be from the turbine blades, gearbox (if used) and brush gear, as well as from
wind moving past the tower and guy wires. Noise and the visual impact may be an issue
with neighbours, and vibration may be a problem particularly if a turbine is located on a
roof.
These factors should influence decisions about the wind generator location, size and
height.