• Wind is considered an indirect form of solar energy. This is because wind is driven by temperature differences on the surface of the Earth caused by sunshine. For centuries, wind has been used to sail ships, grind grain, and pump water. Now, people use it to generate electricity. The windmills built long ago had many blades, but modern wind turbines have two or three blades. Wind turbine blades can be up to 82 feet (25 metres) long.
• The blades drive a generator that produces electricity, much like steam turbines. The longer the blades and the faster the wind speed are, the more is the electricity generated by the turbine. Wind turbines are placed on towers because the wind blows harder and more steadily at these heights. A typical 600 kW turbine has a blade diameter of 35 metres and is mounted on a 50-metre concrete or steel tower.
• To produce the maximum amount of electricity, wind turbines need to be located in areas where the wind blows at a constant speed. Wind speed is described by seven “classes.” Class 7 winds are extremely strong, while Class 2 winds are mild breezes. Generally, Class 4 winds and above are considered adequate for a wind turbine to produce electricity. New turbine designs now take advantage of less windy areas by using better blades, more electronic controls, and other improvements. Some new turbines can also operate efficiently over a wide range of wind speeds.
• Large groups of wind turbines, called wind farms or wind plants, are connected to electric utility power lines and provide electricity to many people. Wind energy can be used for stand-alone systems or fed into the grid. The immediate demand for rural energy supply in developing countries is for smaller machines in the 5-100 kW range. These can be connected to small, localised microgrid systems and used in conjunction with diesel generating sets and/or solar photovoltaic systems. These types of hybrid systems are ideally suited both for energy resource optimisation as well as cost reduction measures. Battery power backup system may be needed in view of the intermittent nature of both solar and wind, energy.

Criteria for Site Selection

• The ideal and best possible site for locating a wind energy system is at the top of a smooth well rounded hill having a gentle slope and open areas like the shorelines of sea or lake. Ideally, the average wind speed should vary from 6.5 to 8 m/s for useful power production. Prime wind sites have average wind speeds greater than 7.5 m/s (27 kmhour). Offshore sites provide excellent opportunities for wind turbines. Sites with wind speed varying between 3-4 m/s may also be feasible. The mountain coastal terrain offers some of the best wind power generation sites.
• The power that can be generated from a modern wind turbine is usually related to the square of the wind speed. This means that a site with twice the wind speed of another will generate four times as much energy.
• Good wind speed data is critical to determining the economic feasibility of a wind project.

Application of Wind Energy 

• Domestic use: to provide power for homes in remote areas for lighting, and other appliances such as radios and televisions;
• Water pumping: to provide clean water for drinking and washing, water for fish farming, animal fanning and irrigation systems; 
• Large-scale power generation: by connecting wind farms to the national grid.

Working of Wind Energy Systems

• The wind turbine is the main component of a wind energy system. As it rotates, it drives a generator to produce electricity. A modem wind turbine usually consists of the following components: Blades, Rotor, Transmission, Generator, and Controls. 
• Shaped like the wings of a plane, blades capture the wind. They are made of Fibre Reinforced Plastic (FRP). Most turbines have two or three blades. As the blades are moved by the wind, they turn a central hub. All the blades of a turbine and the central hub to which the blades are attached make up the rotor.
• The rotor is connected through a series of gears (transmission) to an electrical generator, Gears connect the low-speed shaft to the high-speed shaft and increase the rotational speeds from about 30 to 60 rotations per minute (rpm) to about 1200 to 1500 rpm, which is the rotational speed required by most generators to produce electricity.

• The generator in wind energy systems is similar in construction to the generators used in thermal power plants. The controls start up the systems at wind speeds of about 8 to 16 miles per hour (mph) and shut them off at about 65 mph. Turbines cannot operate at wind speeds above about 65 mph because their generators could overheat. Wind turbines are rated by their maximum power output in kilowatts (kW) or in megawatts. For commercial utility-sized projects, the most common turbines sold are in the range of 600 kW- 1000 kW (one megawatt) - large enough to supply electricity to 600-1 000 homes. The newest commercial turbines are rated at 2 Megawatts.

India’s Wind Energy Status 

• India’s wind energy sector is led by indigenous wind power industry and has shown consistent progress. The expansion of the wind industry has resulted in a strong ecosystem, project operation capabilities and manufacturing base of about 10,000 MW per annum. The country currently has the fourth highest wind installed capacity in the world with total installed capacity of 39.25 GW (as on 31st March 2021) and has generated around 60.149 Billion Units during 2020-21.
• The Government is promoting wind power projects in entire country through private sector investment by providing various fiscal and financial incentives such as Accelerated Depreciation benefit; concessional custom duty exemption on certain components of wind electric generators. Besides, Generation Based Incentive (GBI) Scheme was available for the wind projects commissioned before 31 March 2017. 
• In addition to fiscal and other incentives as stated above, following steps also have been taken to promote installation of wind capacity in the country:
  • Technical support including wind resource assessment and identification of potential sites through the National Institute of Wind Energy, Chennai.
  • In order to facilitate inter-state sale of wind power, the inter-state transmission charges and losses have been waived off for wind and solar projects to be commissioned by March, 2022.
  • Issued Guidelines for Tariff Based Competitive Bidding Process for Procurement of Power from Grid Connected Wind Power Projects with an objective to provide a framework for procurement of wind power through a transparent process of bidding including standardization of the process and defining of roles and responsibilities of various stakeholders. These Guidelines aim to enable the Distribution Licensees to procure wind power at competitive rates in a cost effective manner.

Potential of Wind Energy in India

• Wind is an intermittent and site-specific resource of energy and therefore, an extensive Wind Resource Assessment is essential for the selection of potential sites. The Government, through National Institute of Wind Energy (NIWE), has installed over 800 wind-monitoring stations all over country and issued wind potential maps at 50m, 80m, 100m and 120m above ground level.The recent assessment indicates a gross wind power potential of 302 GW in the country at 100 meter and 695.50 GW at 120 meter above ground level. Most of this potential exists in seven windy States as given below:-