WIND ENERGY | History of Wind Energy, Wind Turbine, Wind Generators, Theory Of Wind Power, Characteristics of suitable wind power sites, Wind power scope in India
The wind turbine captures the wind’s kinetic energy in a
rotor consisting of two or more blades mechanically coupled to an electrical
generator. The turbine is mounted on a tall tower to enhance the energy
capture. Numerous wind turbines are installed at one site to build a wind farm
of the desired power generation capacity. Obviously, sites with steady high
wind produce more energy over the year.
Winds are caused because of two factors.
(1) The absorption of solar energy on the earth’s surface
and in the atmosphere.
(2) The rotation of the earth about its axis and its
motion around the sun.
Because of these factors, alternate heating and cooling
cycles occur, differences in pressure are obtained, and the air is caused to
move. The potential of Wind energy as a source of power is large. This can be
judged from the fact that energy available in the wind over the earth’s surface
is estimated to be 1.6x107 K.W Besides the energy available is free and clean.
The problems associated with Utilizing wind energy are
that:
(i) The energy is available in dilute form, because of
this conversion machines have to be necessarily large.
(ii) The availability of the energy varies considerably
over a day and with the seasons.
History of Wind Energy:
The wind has played an important role
in the history of human civilization. The first known use of wind dates back
5,000 years to Egypt, where boats used sails to travel from shore to shore. The
first true windmill, a machine with vanes attached to an axis to
produce circular motion, may have been
built as early as 2000 B.C. in ancient Babylon. By the 10th century A.D.,
windmills with wind-catching surfaces having 16 feet length and 30 feet height
were grinding grain in the areas in eastern Iran and Afghanistan.
The earliest written references to
working wind machines in western world date from the 12th century. These too
were used for milling grain. It was not until a few hundred years later that
windmills were modified to pump water and reclaim much of Holland from the sea.
The multi-vane "farm
windmill" of the American Midwest and West was invented in the United
States during the latter half of the l9th century. In 1889 there were 77
windmill factories in the United States, and by the turn of the century,
windmills had become a
major American export. Until the
diesel engine came along, many transcontinental rail routes in the U.S.
depended on large multi-vane windmills to pump water for steam locomotives.
In the 1930s and 1940s, hundreds of thousands of
electricity producing wind turbines were built in the U.S. They had two or
three thin blades which rotated at high speeds to drive electrical generators.
These wind turbines provided electricity to farms beyond the reach of power
lines and were typically used to charge storage batteries, operate radio
receivers and power a light bulb.
The development of wind power in India began in the 1986
with first wind farms being set up in coastal areas of Maharashtra, Gujarat and
Tamil Nadu with 55kW Vestas wind turbines. The capacity has significantly
increased in the last few years. India
has the fourth largest installed wind power capacity in the world following
Denmark and US. In 2009-10 India had the highest growth rate amongst all four
top countries.
Wind Turbine:
A wind turbine is a machine which utilizes the kinetic energy of wind
to produce rotational mechanical energy in its shaft. The rotational motion of
the shaft turns an electrical generator to generate electricity. There are
mainly two types of wind turbine available one is the horizontal axis type
another is vertical axis type.
Horizontal Axis Wind Turbine:
In Horizontal Axis Wind Turbine
or HAWT the turbine rotor couples the electrical generator and this turbine
generator set is placed on the top of the turbine tower. A wind sensor with
servomotor keeps the axis of the turbine along the path of the wind. The
turbines commonly have a gearbox in between the turbine shaft and the generator
shaft. A wind electric power generating station uses three blades
horizontal axis wind turbines (HAWT). Three blades design is more mechanically
stable and can have less torque ripple. The blade-length may be from 20 m to 80
m and usually of bright white colored so that any aircraft can view comfortably.
Vertical Axis Wind Turbine:
There
is another type of wind turbine which uses vertically aligned rotating shaft.
We call this turbine Vertical Axis Wind Turbines or VAWTs. As it has the
vertical axis, it does not have to align itself with the wind and hence using
these turbines are more suitable where the direction of wind significantly
varies. We can install this turbine even on the
rooftop since the height of this turbine is much lesser than that of HAWT.
Another significant advantage is that as the shaft is vertical, we can extend it
to the bottom level where we can couple a generator with the vertical shaft
with the help of ground-based gearbox which facilitates easier maintenance.
In spite of so many advantages over HAWT, we do not use VAWT
for bulk power generation as the power output is quite less in VAWT compared to
HAWT.
WIND GENERATORS:
The Wind generator is an electrical
device that converts mechanical energy received from the shaft into electrical
energy. Normally, we use induction generators in modern wind turbines. Previously,
synchronous generators were popular for this purpose. Permanent Magnet DC
generator also used in some wind turbines. The speed of the shaft can be made
high by using gearbox assembly, but we cannot make the shaft speed constant.
There may be a fluctuation in shaft speed since it depends on wind speed. So,
the speed of the rotor also varies. This variation affects the frequency,
voltage of the generated electric power.
To, overcome these issues, we normally
use an induction generator for the purpose. Because the induction generator
always produces electric power synchronized to the connected grid irrespective
of the speed of the rotor. If we use the three-phase synchronous generator,
then we first rectify the output power to DC and then convert it to AC of
desired voltage and frequency using inverter circuit. Because the alternating
power generated by the synchronous generator is not constant in voltage and
frequency, rather it varies with speed of the rotor. For the same reason, in
some cases, we use a DC generator for the purpose. In these cases, the output
DC power from generator inverted to AC of desired voltage and frequency, before
feeding it to the grid.
Power
Converter
As wind is not always constant, so
electrical potential generated from a generator is not constant, but we need a
very stable voltage to feed the grid. A power converter is an electrical device
that stabilizes the alternating output voltage transferred to the grid.
Theory Of Wind Power:
For
determining power extracted from wind by wind turbine we have to
assume an air duct as shown in the figure.
Let the
velocity of the wind at the inlet of the duct is V1 and velocity of air at the outlet of the duct is V2. Say, mass m of the air is passed through this imaginary duct per
second.
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. The 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
m= ρ.A.Va
Now, replacing m by
ρVaA in equation (1), we
get,
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.
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.
Characteristics of suitable wind power sites:
There are 5 key characteristics of a
good wind power site
1. A high average wind speed: Typically
the site would be on top of a hill or in a wide open space with no obstructions
nearby.
2.
Sufficient separation from noise-sensitive neighbours: Modern wind turbines
are remarkably quiet, but even so there are very stringent maximum noise levels
that have to be met to obtain planning consent. The minimum separation varies
depending on the turbine size.
3. Good grid connection: All of the wind turbines that we
supply require a suitable three-phase electrical supply to connect to. As a
rough guide you will need an 11 kV transformer or substation that is roughly
double the rated power output of the wind turbine you are considering, or an 11
kV three-phase power line passing close to the wind turbine site that can have
a new transformer / substation connected to it.
The larger multi-MW turbines could
grid connect to 33 kV power lines, though generally it is too expensive for
sub-1MW wind turbine projects to connect at such a high voltage.
4. Good
site access.:Wind
turbines are large and heavy, so the access roads and tracks to the site need
to be capable of taking oversize loads with no weak bridges, excessively tight
corners or steep gradients. Obviously as the proposed turbine gets larger, the
size of the constituent parts that have to be delivered get larger and the
access requirements more stringent. The smaller Endurance 55 kW turbine is
delivered on standard articulated lorries, but all of the others come on
special oversize trailers.
5. No
special environmental or landscape designations: A lot of the older
objections to wind turbines due to bird strikes have now been shown to be
unfounded, but even so it would be good practice to not install a wind
turbine(s) in an area that had special bird designations. Peat bog is also
generally a no-go area for wind turbines.
Wind power scope in India:
Wind power development in India began in the 1986
with first wind farms being set up in coastal areas of Maharasahtra
(Ratnagiri), Gujarat (Okha) and Tamil Nadu (Tuticorin) with 55 kW
Vestas wind turbines.
The capacity has significantly increased in
the last few years and as of 31 Aug 2016 the installed capacity of wind power
in India was 27,676.55 MW, mainly spread across the South, West and North
regions. Although a relative newcomer to the wind industry, compared with
countries such as Denmark or the United States, by year end 2015
India (27151 MW) had the fourth largest installed wind power capacity in
the world behind China (158000 MW), USA (74696 MW) and Germany (47420 MW),
having overtaken Spain (22987 MW) in 2015.
Wind
power accounts nearly 8.6% of India's total installed power generation capacity
and generated 28,604 million Kwh (MU) in the fiscal year 2015-16
which is nearly 2.5% of total electricity generation. The capacity
utilization factor is nearly 14% in the fiscal year 2015-16 (15% in
2014-15). 70% of wind generation is during the five months duration from May to
September coinciding with Southwest monsoon duration.
The
potential for wind farms in the country was first assessed by Dr. Jami Hossain
using a GIS platform to be more than 2,000 GW in 2011. This was subsequently
re-validated by Lawrence Berkley National Laboratory, US (LBNL) in an
independent study in 2012. As a result, the MNRE set up a committee
to reassess the potential and through the National Institute of Wind
Energy (NIWE, previously C-WET) has announced a revised estimation of the
potential wind resource in India from 49,130 MW to 302,000 MW assessed at 100m
Hub height. The wind resource at higher Hub heights that are prevailing is
possibly even more. In the year 2015, the MNRE set the target for
Wind Power generation capacity by the year 2022 at 60,000 MW.
India
has already concentrated towards the offshore wind energy for
mitigating the power deficit. The Ministry of New & Renewable Energy
(MNRE), Government of India is framing the policies and looking towards all the
possibilities to reach in the offshore energy market. A complete and accurate
analysis is being done for the Indian shoreline which reveals that
around 5–7% of wind potential may increase along eastern offshore
Barriers
Initial cost for wind turbines is greater than that of conventional fossil fuel generators and capacity expansion of existing hydro power plants with pumped storage hydro units.
Most of the wind power generation is
during the south west monsoon season when rivers usually flood with water
generating cheaper secondary hydro power. Scheduling the wind power which is
unpredictable secondary power (even on daily basis), at fair price is a problem
during monsoon season.
When large wind power plants are
located away from the load centers, laying dedicated transmission lines to
evacuate the unreliable secondary wind power is additional cost liability.
0 Comments