Wind power genertaion: Most successful renewable energy

Power generation from wind has emerged as one of the most successful programs in the renewable energy sector, and has started making meaningful contributions to the overall power requirements of some States. Presently wind turbines are producing a substantial amount of electricity. Energy is a major input for overall socio-economic development. Use of fossil fuels is expected to fuel the economic development process of a majority of the world population during the next two decades. However, at some time during the period 2020-2050, fossil fuels are likely to reach their maximum potential, and their price will become higher than other renewable energy options on account of increasingly constrained production and availability. Therefore renewable is energy expected to play a key role in accelerating development and sustainable growth in the second half of the next century, accounting then to 50 to 60% of the total global energy supply.

For the operation of wind turbine to be commercially feasible, average wind speed should be in the range of 13-30 mi/hr. at 25-30 mi/hr, a turbine operates at full capacity. The two primary principles for extraction of energy from the wind:-Through the creation of either drag or lift force or combination of these two. The basic features of lift and drag are characterized as :-

• Drag is in the direction of airflow
• Lift is perpendicular to the direction of airflow
• Generation of lift always causes a certain amount of drag to be developed
• With a good aerofoil, the lift produced can be more than thirty times greater than the drag
• Lift devices are generally more efficient than drag devices

Solidity and Tip speed ratio

The tip speed ratio is defined as the ratio of the speed of the extremities of a windmill rotor to the speed of the free wind. It is a measure of the 'gearing ratio' of the rotor. Drag devices always have tip speed ratios less than one and hence turn slowly, whereas lift devices can have high tip speed ratios and hence turn quickly relative to the wind.

• Tip speed ratio = blade tip speed/wind speed

Solidity is usually defined as the percentage of the circumference of the rotor which contains material rather than air. High solidity machines carry a lot of material and have coarse blade angles. They generate much higher starting torque than low-solidity machines but are inherently less efficient than low-solidity machines. The extra materials also cost more money. However, low-solidity machines need to be made with more precision which leads to little difference in costs.

The proportion of the power in the wind that the rotor can extract is termed the coefficient of performance (or power coefficient or efficiency; symbol Cp) and its variation as a function of tip speed ratio is commonly used to characterize different types of rotor. It is physically impossible to extract all the energy from the wind, without bringing the air behind the rotor to a standstill.

Potential

Wind energy is the fastest growing renewable energy source in the world. The world wide installed capacity is growing at a rapid pace of over 30% per year.

Factors:

• Declining cost (4-6 cents k/wh)
• Technological advances
• Revenue for landowners & tax jurisdictions
• Consumer demand