The sun?s energy falling
on the earth produces large-scale motions of the atmosphere causing winds, which
are also influenced by small scale flows caused by local conditions such as
nature of terrain, buildings, water bodies, etc. Wind energy is extracted by turbines
to convert the energy into electricity.
A small-scale and large-scale
wind industry exists globally. The small-scale wind industry caters for urban
settings where a wind farm is not feasible and also where there is a need for
household electricity generation.
The large-scale industry is directed towards contributing to countrywide energy
Wind resource in India
The wind resource assessment in India
estimates the total wind potential
to be around 45 000 MW (mega watt). This
potential is distributed mainly in the states of Tamil Nadu,
Andhra Pradesh, Karnataka, Gujarat, Maharashtra, and Rajasthan. The technical potential that is based on the
availability of infrastructure, for example the availability of grid, is
estimated to be around 13 000 MW. In India, the wind resources fall in the low
wind regime, the wind power density being in the range of 250 -450 W/m2.
It may be noted that this potential estimation is based on certain assumptions.
With ongoing resource
assessment efforts, extension of grid, improvement in the wind turbine
technology, and sophisticated techniques for the wind farm designing, the gross
as well as the technical potential would increase in the future.
Wind power has become one
of the prominent power generation technology amongst the renewable energy technologies.
By the end of 2005, the total wind power installed
globally was about 59 084 MW, a growth of 24% over 2004. The leading countries in wind power installation
are Germany (18 428 MW), Spain (10 027 MW), the
USA (9 149 MW), India (4 430 MW) and Denmark (3 122 MW). India
has overtaken Denmark and is the fourth largest wind market in the world.
Wind energy technology
Use of wind energy
started long ago when it was used for grinding. The commercial use of wind
energy for electrical power generation started in 1970s. Horizontal axis
wind turbines are most commonly used for power generation, although some
vertical axis wind turbine designs has been developed and tested. The vertical axis turbines have
structural as well as aerodynamic
limitations and, hence, are not commercially used. The wind power generation is
simple conversion of kinetic
energy in the wind into electrical energy. However, the mechanism to
capture, transmit, and convert the energy into electrical energy involves
several stages, components, and controls. The important components/controls
of horizontal axis wind
aerodynamic power regulation,
The wind turbine technology
is being continuously improved worldwide resulting in improved performances,
optimal land use, and better grid integration. The areas in which development
work is being targeted are large size wind turbines, powerful and larger blades,
improved power electronics, and taller towers.
The rotor blade is the most
critical component of the wind turbine. It captures the wind energy and transfers
it to torque required to generate power. The aerodynamic design of the blade
is important as it determines the energy capture potential. One indicator of
effective blade design is the weight/swept area ratio. As the size of the wind turbine increases, the
size of blade length increases proportionally which results in capturing more
energy. These blades are of higher tensile
strength and lower body mass. Commonly used materials
for making the blades are composite materials like the glass fibre epoxy, carbon
epoxy, fibre-reinforced plastic, etc.
The kinetic energy
captured by the rotor blades is transferred to the generator through the
transmission shaft. Wind machines with induction generators come with
Wind machines which have
have no gear boxes since they could be designed for continuous variation according
to the wind speed. These machines have an added advantage over induction machines
because variable speed increases the energy capture. This increases the efficiency
of the system on the whole by exactly matching the wind speed to the rotor speed
of the generator. Variable speed machines grant flexibility and good power quality
but are expensive because of the power electronics involved.
Aerodynamic power regulation
Out of the two basic concepts
of aerodynamic controls, the
stall and pitch mechanisms, the pitch control is predominantly used especially
for the larger size wind turbines. Pitch regulation offers better control on
the power regulation with independent pitching of the blades. The latest concept
is active pitch or active stall.
Increasing number of larger
wind turbines (1 MW and above) are being developed with an active stall control
mechanism. At low wind speeds, the machines are usually programmed to pitch
their blades much like a pitch-controlled machine. However, when the machine
reaches its rated power and the generator is about to be overloaded, the machine
will pitch its blades in the opposite direction. This is similar to normal stall
power limitation, except that the whole blade can be rotated backwards (in the
opposite direction as is the case with pitch control).
One of the advantages
of active stall is that one can control the power output more accurately than
with stall, so as to avoid overshooting the rated power of the machine at the
beginning of a gust of wind. Another advantage is that the machine can be run
almost exactly at rated power at all high wind speeds. In active pitch control, the blade pitch angle is continuously adjusted
based on the measured parameters to generate the required power output. It has
been established that active pitch regulation reduces the wind generator output
Two most common tower
designs are lattice and tubular. Lattice tower is cheaper compared to the
tubular tower and being usually a bolted structure is easier to transport. However,
since lattice tower consists of many bolted connections, these connections need
to be tightened and checked periodically, thereby increasing the operation and
maintenance cost. By nature, tubular tower is stiffer than the lattice one. However,
the tubular tower allows full internal access to the nacelle.
Larger turbine size
improvement in the wind turbine design has lead to increased size and
performance. From machines of just 25 kW two decades ago, the commercial range
sold today is typically from 600 - 2 500 kW. As such, the largest wind turbine
capacity today is 5 MW.
With the development of higher size turbines for a required capacity, lower
number of turbines are required which has implication on the investment as well
as O&M costs.
As a result of lower
resistance, the wind resource at the offshore locations is higher in terms of
wind speed. Also, wind resources are uniform having lower variations and
turbulence. The higher capacity wind turbines, which are being developed today,
focus on the off shore applications. The related foundation technologies are
also being developed for the erection of higher capacity wind turbines. In case
of India, however, the development for offshore wind is yet to start.
Wind power in India
Wind turbines offered
in India range from 250 kW to 2 MW capacities. As of 31 March 2006, the total
installed capacity in the country was 5340 MW, which is 46% of
the total capacity of renewable resources based power generation. There are
7 manufacturers of wind turbine
generators in India.