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Wind as a source ofrenewable energy

M. S. Koushik, L. Balamani Sandeep

& B. Malleswara Rao*

School of Technology, GITAM University,Hyderabad 502329, A.P., India

Problem Statement

• Present WTG technology suffers from several limitations in terms of efficiency, noise generation, and danger to flying wildlife.

• The purpose of this paper is to provide an in-depth review of current WTG technology and to suggest solutions for these limitations.

Introduction• Indian Ministry of Non-

conventional Energy Sources (MNES) has set a target of achieving 10% additional grid energy from renewable sources.

• India has a potential of 49,000 MW of wind power. But only 18,192 MW of energy is being currently harnessed.

• For increased production more installations as well as new technologies needed to be adapted.

• More WTGs need to be installed nearer to the west coast of India in view of wind energy potential.

Design Considerations of WTGs (1/3)

• A Wind turbine generator is a device that converts kinetic energy of wind to electrical energy.

• The figure shows a schematic of the current WTGs with necessary gear and yawing mechanism.

• There can be a number of designs based on the number of blades, type of axis and power generation capacity, etc.

Design considerations of WTGs(2/3)

Where R→ radius of circle swept by tip of rotor blade

u →velocity of wind

2321

3221

uRTCT

uRpCP

ficienttorquecoefTC

icientpowercoeffpC

The mechanical power and torque produced from wind turbines is according to the following equations:

variation of and as a function of

Variation of CP and CT as a function of for different types of WTG (Source: Fateev, 1948)

pCTC

• When wind speed changes , rotational speed has to achieve best value of • This means that wind speed U and must be combined into a single variable.• This single variable is the ratio of turbine tip speed R to the wind speed u.

From this

pC

u

R

p

T

CC

In this way power coefficient and torque coefficient are inter related.

Design considerations of WTGs(3/3)

Studies on wind turbines

• Albert Betz was a German physicist. In 1919 he was awarded his PhD from  university of Gottingen . He published a law called Betz law in 1919.

• Betz law: According to this law, no wind turbine can capture more than 59.3% of kinetic energy in wind.

Measures to improve performance of WTGs

The factors to be considered to increase efficiency of WTGs are as follows:

• Blade length Blade number• Aerodynamic design Rotational speed• Blade shape Pitch control• Blade thickness Altitude• Blade twist Temperature

Recent trends in wind design(1/4)• Ali M Eltamaly(2009) proposed that by using

gearless WTGs the noise problem caused by high rotational speed can be reduced and overall efficiency and reliability can be enhanced .

Because of these gearless WTGs weight will be reduced and maintenance need can be eliminated . These WTGs can exploit maximum power at different wind speeds . In the variable speed operation ,reduction in mechanical stresses and increased energy capture will take place.

Recent trends in wind design(2/4)

• Richard(2009) studied the optimization of wind turbine rotor operating in uniform wind of 10m/s with respect to power coefficient and noise level via a genetic algorithm.

He has considered into account the air foil shape , chord distribution , RPM and pitch for a 74.6 m rotor while judging its performance . In his observation optimized rotor yields a 7.6% increase in annual power production.

Recent trends in wind design(3/4)

• Francois Gangnon proposed the concept of concentrating the wind by funneling through a conduit so that flux of compressed air is thereby directed to interact with the most efficient surface of a wind turbine propeller blade.

Such WTG will have advantage with both weakest and strongest winds . since the WTG is housed within the apparatus, the resulting noise caused by aerodynamic motions can be almost reduced.

In addition to this an enclosed WTG protect flying wildlife from entering into contact with WTG.

Recent trends in wind design(4/4)

• The gear box in large WTGs can be replaced by low speed permanent magnet synchronous generator(PMSG),the rotor rotates at the same speed as rotor of the turbine.

This can be directly connected to the wind turbine which results in a sample mechanical system. This results in decrease in the weight of WTG.

Conclusion • India has a potential of 49,000 MW of wind power. But only 37%

(18,192 MW) of which is currently being harnessed.• Many wind turbine configurations are possible, but the 3-bladed

HAWTGs are proved to be more efficient than the other configurations.

• Care must be taken in choosing a wind turbine generator with appropriate blade length, shape, thickness, twist, rotational speed, and pitch control for maximum efficiencies. In addition, geographical altitude and air temperature of the installation site are important parameters.

• The current wind turbine generators suffer from few limitations like lower efficiency at the low and high wind speeds, unacceptable noise level, posing danger to flying wildlife, etc. These limitations can be overcome by adopting new design strategies in WTGs. One such a strategy is to conceal turbine blades as proposed by Francois Gangnon.

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