Concern about climate change and concerted action to reduce green house gas emissions are powerful drivers for renewable energy. Wind is commercially and operationally the most viable renewable energy resource and accordingly, it is emerging as one of the largest renewable sources.
In view of growing awareness about green environment, development of renewable energy has been promoted by the government through fiscal policies issued by central and state government. These policies include tax incentives and obligation for purchase of electricity through renewable energy sources. The state government has also provided different other state-specific incentives and benefits through the individual incentive policies issued by the state government. These incentives attract the investors and come down per unit cost of energy from renewable sources.
Drives moving in the direction of reducing per mega watt (MW) capital cost of renewable sources through technological development and increase in plant utilisation, factor with overall improvement in efficiency. Drives are also moving in the direction of developing storage facilities for energy from renewable sources to make them firm and useful form of energy. Enactment of the Electricity Act 2003 has provided further support to renewable energy by stipulating purchase of a percentage of the power procurement by distribution utilities from renewable energy sources. The renewable purchase obligation for procurement of such power has been specified by various State Electricity Regulatory Commissions.
Despite all strategic policies in place, purchase of Renewable Energy Certificate has not been very encouraging. Only six out of 29 states and seven union territories are complying with the central government's Renewable Purchase Obligation (RPO) targets. SERCs must prevail upon discoms to meet them RPO obligation. While the Electricity Act, 2003, the policies framed under the Act, and also the National Action Plan for Climate Change provide for a roadmap for increasing the share of renewable in the total generation capacity in the country, there are constraints in terms of availability of wind potential evenly across different parts of the country. This inhibits the State Commissions, especially in those states where the potential of wind sources is not that significant, from specifying higher renewable purchase obligation.
The government has set a target of 175 GW power capacity from renewable sources which includes 60 GW wind power. The target set for FY 2017-18 is 14.45 GW including 4 GW for wind. On December 8, 2017, the government has issued guidelines under Section 63 of the Electricity Act, 2003, providing a framework for procurement of wind power through a transparent process of bidding including standardisation 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. These guidelines will give boost to the wind power sector as it would facilitate the windy states to go for bidding process for procurement of wind power themselves.
Status of wind energy
The wind power development in the country started in 1990s and with the conducive policy environment provided at Central and State level this segment has achieved highest growth amongst the other renewable energy technologies. The first demonstration project in India was set up in Tamil Nadu in the year 1986. At the end of 9th Five year plan the cumulative wind power installed capacity was only 1.7 GW. The present wind power installed capacity in the country is 32.4 GW which constitute around 56% of the total renewable capacity in the country.
A total wind power capacity of 32,373 MW was operational up to March 31, 2017. With an installed capacity over 7,861 MW, Tamil Nadu is at first position in wind energy. However, the growth has declined in Tamil Nadu in the last few years due to several reasons. During FY 2015-16, a capacity of 3423.05 MW was added, which is the ever highest capacity addition achieved in a single year. Out of the aforesaid capacity addition, 1261.40 MW was added in Madhya Pradesh which is the highest capacity addition achieved by a state.
Renewable energy sources is sharing 17.52 per cent of total installed capacity and headed second position after thermal energy. Out of total wind energy, 9.88 per cent is wind energy sources and balance 7.64 per cent is other sources of renewable energy. To give a fillip to renewable power in the country, the National Energy Policy proposes gradual withdrawal of the provisions of 'must-run' status and other supports such as non-levy of inter-state transmission charges for non-renewable energy. It is envisaged that as consumers become agnostic to the source of power, renewable energy will soon blend with conventional power and markets will determine dispatch rather than policy levers.
Globally, the total wind power installed capacity at the end of 2016 was around 487 GW and India ranked fourth in terms of wind power installed capacity. Top five countries of the world in respect of wind power installed capacity are China, USA, Germany, India and Spain. These five countries contribute over 80 per cent of total wind power installed capacity of the world.
The global renewable energy addition was 138.5 GW during 2016 compared to 127.5 GW added in 2015. Renewable power accounted for 55.3 per cent of the new power capacity addition during 2016. This took renewable to 16.2 per cent of global power capacity, up from 15.2 per cent in 2015. The global electricity generation from renewable reached 11.3 per cent, up from 10.3 per cent in 2015. With a capacity addition of 54.6 GW, the total global wind capacity reached 487 GW but fell back from 63 GW added in the previous year. Strongest growth took place in China 23.3 GW followed by US with 8.2 GW and Germany with 5.4 GW. In China, the cumulative capacity reached 168.7 GW. In US it reached 82.2 GW and 50 GW in Germany. India grabbed the fourth position. Spain continues to remain at fifth position with capacity of 23 GW and in UK it reached 14.5 GW.
The wind power potential in the country is assessed at 100 meter above ground level, which is estimated to be over 302 GW. Most of this potential exists in windy states namely Andhra Pradesh, Gujarat, Karnataka, Madhya Pradesh, Maharashtra, Rajasthan, Tamil Nadu and Telangana. In order to facilitate transmission of wind power from aforesaid windy states to non-windy states, provisions have been made in the tariff policy to waive the inter-state transmission charges and losses for wind power projects. The government is also developing green energy corridor to facilitate transmission of wind energy from windy state to non windy states in order to full fill their RPO obligation.
Basic Concept of Wind Energy
The differences in temperature induce circulation of air from one zone to another. This air in motion is called wind. Wind is the natural movement of air across the land or sea. It is caused by uneven heating and cooling of the earth's surface and by the earth's rotation. Land and water areas absorb and release different amount of heat received from the sun. As warm air rises, cooler air rushes in to take its place, causing local winds. The rotation of the earth changes the direction of the flow of air.
Wind electric generator converts kinetic energy from the "air in motion"(called wind) directly into electrical energy by using rotor, gearbox and generator without using conventional sources like coal, oil or natural gas for power generation. Power is available in the wind in the form of Kinetic energy. Power available in the wind is represented as follows:
P = 1/2 d AV 3
where P = Wind Power
d = Air density
A = Area intercepted
V = Wind speed
and P/A = 1/2 dV3 = WPD Where,
WPD means wind power density, which is a measure of wind Power available in the wind and can be defined as wind power per unit area. Wind Electric Generators are highly sophisticated machines based on aerodynamic principles and electronic control system.
Factors affecting wind power
Wind power generation from the wind electric generators depends on the following factors:-
Air density: The air density varies with altitude and temperature. The change in kinetic energy of wind is proportional to air density.
Rotor area or swept area: The area intercepted by rotating blades. The energy received from wind depends upon this swept area. Rotor area increases with the square of the rotor diameter. Doubled the rotor diameter will theoretically receive four times energy.
Wind speed: The power in wind varies with the cube of the wind speed. If the wind speed is twice as high it contains eight times more power. The operating efficiency of wind electric generators depends the 'tip speed ratio', which is the ratio of the rotor blade speed at its tip end to the wind speed.
In fixed speed design, the tip speed ratio varies with wind speed and this could reach optimum value at one wind speed. However, for variable speed, the change in tip speed ratio depends on both wind speed and rotor speed. For maximum rotor efficiency, the rotor speed is controlled to maintain the tip speed ratio normally at 6 to 8. Because of this flexibility, a variable speed drive option could generate more energy for the same wind speed regime
Several control techniques have been developed which are based on two distinct approaches namely stall control and Pitch control. In stall control, the rotor blades are fixed at an angle. In pitch control, the blades are gradually turned out of the wind so that the angle of attack changes. The pitch mechanism is usually activated by hydraulic power or electric motor drive.
Wind electric generator
Generally two types of generators are used in wind electric turbines Synchronous generator and Asynchronous generator.
Like the DC generator, the operation of a Synchronous Generator is also based on Faraday's law of electromagnetic induction. The difference is that the synchronous generator generates a three-phase AC voltage output from its stator windings, unlike the DC generator which produces a single DC or direct current output. The synchronous generator consists of a magnetic field on the rotor that rotates and a stationary stator containing multiple windings that supplies the generated power. The rotors magnetic field system (excitation) is created by using either permanent magnet mounted directly onto the rotor or energised electro-magnetically by an external DC current flowing in the rotor field windings.
The wound rotor synchronous generator is being used as a wind power turbine generator, but one of the major disadvantages of a synchronous generator is its complexity and cost. When the generators rotor shaft is turned by the turbines blades (the prime mover), the rotor poles will also move producing a rotating magnetic field as the North and South poles rotate at the same angular velocity as the turbine blades, (assuming direct drive). As the rotor rotates, its magnetic flux cuts the individual stator coils one by one and by Faraday's law, an emf and therefore a current is induced in each stator coil. The magnitude of the voltage induced in the stator winding is a function of the magnetic field intensity which is determined by the field current, the rotating speed of the rotor, and the number of turns in the stator winding.
Asynchronous (induction) wind power generators
Most wind turbines in the world use a so-called three phase asynchronous generator, also called an induction generator to generate alternating current. The curious thing about this type of generator is that it was originally designed as an electric motor. If the speed of the induction motor cross the synchronous speed through outside torque, beyond synchronous speed, it acts as a generator and in place to drawing power it start to generate supply. This property of the induction motor used in wind electric generators. One reason for choosing this type of generator is that it is very reliable, and tends to be comparatively inexpensive.
BE (Electrical), M Tech. Hon. (Ind. Engg.) , M. Phil (Renewable Energy), PHD Scholar, Dy. Director (Generation), M.P. Electricity Regulatory Commission Bhopal (M.P.)
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