RENEWABLE ENERGY SOURCES - WIND ENERGY

INTRODUCTION
Renewable energy sources capture their energy from existing flows of energy, from on-going natural processes, such as sunshine, wind, flowing water, biological processes, and geothermal heat flows. Renewable energy resources may be used directly, or used to create other more convenient forms of energy.
Wind is commercially and operationally the most viable renewable energy resource and accordingly, emerging as one of the largest source in terms of the renewable energy sector. Wind power is the kinetic energy of wind, or the extraction of this energy by wind turbines. In 2004, wind power became the least expensive form of new power generation, dipping below the cost per kilowatt-hour of coal-fired plants. Wind power is growing faster than any other form of electrical generation, at about 37%, up from 25% growth in 2002. In the late-1990s, the cost of wind power was about five times what it is in 2005, and that downward trend is expected to continue as larger multi-megawatt turbines are mass-produced.
An estimated 1 to 3 percent of the energy from the Sun is converted into wind energy. This is about 50 to 100 times more energy than what is converted into biomass by all the plants on earth through photosynthesis.
India now ranks as a "wind superpower" with an installed wind power capacity of 1167 MW and about 5 billion units of electricity have been fed to the national grid so far.In progress are wind resource assessment programme, wind monitoring, wind mapping, covering 800 stations in 24 states with 193 wind monitoring stations in operations. Altogether 13 states of India have a net potential of about 45000 MW.
Why Wind Energy
 The project is environment friendly.
 Good wind potential to harness wind energy.
 A permanent shield against ever increasing power prices. The cost per kwh reduces over a period of time as against rising cost for conventional power projects.
 The cheapest source of electrical energy. (on a levelled cost over 20 years.)
 Least equity participation required, as well as low cost debt is easily available to wind energy projects.
 A project with the fastest payback period.
 A real fast track power project, with the lowest gestation period; and a modular concept.
 Operation and Maintenance costs are low.
 No marketing risks, as the product is electrical energy.
 A project with no investment in manpower



The wind power generation in the country is influenced to a great extent by the wind speed and wind power density prevalent at a particular potential location at any given point of time. The wind speed is affected to a large extent by the strong southwesterly monsoons, starting in May-June, and at the same time by the weaker northeastern monsoons in the winter months. It has been generally observed that 60-70% of the total wind power generation in the country takes place during June- October when the southwest monsoons are prevalent through out the country. According to a latest study, locations having an annual mean wind power density greater than 150 watts/ square meter at 30 meter hub height have been found to be suitable for development of wind power projects.
PRESENT SCENARIO OF WIND ENERGY
Exploitation of wind energy has been in place from time immemorial but the development of technology for tapping the same for generation of grid quality electricity is of a recent origin. India has been quick to make a foray in this area. It has made its mark as one of the top ranking countries in the world in wind power generation. With an installed generation capacity of 1702.30 MW as on 31.3.2005 of wind power, India now ranks 5th in the world after Germany, USA, Denmark and Spain in wind power generation. According to a recent estimate, the gross wind power generation potential in the country is estimated at 45,195 MW at 50 meter. Hub Height. Hub height is defined as the height from the Ground Level at which the hub of the propeller blades of the wind energy generator is situated.



The state wise potential and installed capacity is given in the table below:

State Gross
Potential in MW Total Installed Capacity in MW
Demonstration
Projects (MW) Private Sector
Projects (MW) Total Capacity (MW)
Andhra Pradesh 8275 5.40 87.20 92.60
Gujarat 9675 17.30 149.60 166.90
Karnataka 6620 2.60 93.60 96.20
Kerala 875 2.00 0.00 2.00
Madhya Pradesh 5500 0.60 22.00 22.60
Maharashtra 3650 6.40 392.80 399.20
Orissa 1700 6.40 18.70 25.10
Rajasthan 5400 19.40 875.60 895.00
Tamil Nadu 3050 1.10 0.00 1.10
West Bengal 450 1.60 0.00 1.60
Total 45195 62.80 1639.50 1702.30






CONTRIBUTION OF TAMIL NADU

Tamil Nadu has pioneered the effective usage of wind resources and the State Government is keen on encouraging wind energy production, Windmills in Tamil Nadu produced 55 per cent of the total wind-generated electricity in the country, the total power capacity of 1,664 MW was available from winds mills in the private sector and 9 MW of power from the windmills of tamilnadu electricity board (TNEB). The State had contributed 57 per cent of the total 2,909 MW of harnessed energy in the country. As of 2005, Tamil Nadu was one of the few states with surplus power enabling the electricity authority to sell it to neighbouring states.

PROMOTIONAL POLICIES AND SUBSIDIES

Govt. of India and state govts have developed suitable policies and guidelines for providing technical help, financial support and various other incentives for development of wind power in the country. These include R&D activities for design and development of low cost indigenous wind energy harnessing technologies, dissemination of the developed technologies through demonstration projects, setting up of the commercial wind farms through central and state government subsidy, providing financial incentives to potential entrepreneurs etc.
The various incentives that are being provided by the central and the state governments are as per the details given below:
From Central Government
 Income Tax Holiday
 Accelerated Depreciation
 Concessional Custom Duty/ Duty Free Import
 Capital/ Interest Subsidy
From State Governments
 Energy buyback, power wheeling and banking facilities
 Sales tax concession benefits
 Electricity tax exemption
 Demand cut concession offered to industrial consumers who establish power generating units from renewable energy sources
 Capital Subsidy
The table given below depicts the initiatives provided by some of the state governments towards development of commercial wind power projects.








Andhra
Pradesh Karnataka Madhya
Pradesh Maharashtra Rajasthan Tamil Nadu
Wheeling 2% of energy 2% of energy 2% of energy 2% of energy 2% of energy 2% of energy
Banking
12 months 2% p.m. for 12 months - 12 Months 12 Months 12 Months
Third Party Sale Not allowed Allowed Allowed Allowed Allowed Not Allowed
Capital Subsidy
20%
Max. Rs. 25.00 Lakh Max. Rs. 25.00
Lakh for backward areas Same as other industries 30% Max. Rs. 30.00 Lakh - -




ESSENTIAL REQUIREMENTS OF WINDMILLS
An area where a number of wind electric generators are installed is known as a wind farm. The essential requirements for establishment of a wind farm for optimal exploitation of the wind are :

1 High wind resource at particular site
2 Adequate land availability
3 Suitable terrain and good soil condition
4 Proper approach to site
5 Suitable power grid nearby
6 Techno-economic selection of WEGs
7 Scientifically prepared layout

Features of wind turbine generators

TECHNICAL DESCRIPTION

Components of wind turbine generators are as follows:

DESIGN:
During assembling, the gearbox with all the attached nacelle components is easily mounted on the top of the yaw system with no need for any additional mounting of cables,pipes etc. except for the nacelle top cover and the rotor.
The design of the gearbox housing is simple and robust, with a supporting structure which transmits all dynamic stress and forces from the rotor directly into the tower structure.
All parts and components are manufactured of certified quality steel. Every contact face is machined in CNC milling machines prior to assembly. The gearbox housing is machined in one single operation to prevent any misalignments and ensuring full compatibility between individual units. In fact, there is no need for alignment at all during the assembly, thus making maintenance easier, simpler and less costly.
This leads to the following advantages:
 A very compact, simple and robust construction
 A functional and straight forward lay-out
 Very safe and user-friendly working conditions
 Long lifetime and low operational and maintenance costs


GEARBOX HOUSING:

The very high efficiency of the transmission is reflected by the extreme-low levels of noise emission, vibration and temperature rise during operation.







The gearbox housing, is welded instead of cast since this gives a more ductile and sturdy gear construction. The integrated gearbox is designed to transmit all static and dynamic forces directly into the tower construction. Also, the gearbox acts as the structural support for the entire nacelle and incorporated parts there.
At the front of the gearbox a parking disc, brake is mounted on the high speed shaft. On the rear side, the generator is flange mounted with a flexible coupling to the high speed shaft. The electrical oil pressure pump and the hydraulic pump unit are placed on the side of the gearbox.
The gearbox has a heavy steel bottom plate, which is connected to the yaw system through 5 heavy duty silent blocks (damper supports). The system effectively eliminates the transmission of noise and vibrations from the nacelle to the tower.

SHAFT AND COG WHEELS:
The integrated gearbox has 3 stages with 4 parallel shafts or 2 stages with 3 parallel shafts depending on the generator pole number. The efficiency of the individual steps are very high. The low speed shaft is hollow and manufactured in one piece with a flange for direct mounting of the rotor. Hydraulic pressure is lead through the shaft for control of the blade tip airbrakes.

BEARINGS:
The bearings on all shafts inside the gearbox are of the spherical roller bearing type. Mounting this type of bearings on all shafts in the gearbox secures that parallelism of shafts as well as build-in axial tolerances are maintained during operation.

BRAKE SYSTEM:
The brake system is of the negative fail-safe type and consists of 3 independent blade tip airbrakes and a parking brake with primary and secondary functions controlled by a hydraulic pump unit. An active hydraulic pressure keeps the blade tips in an operational situation, but as soon as a stop command is encountered or at any loss of electrical power from the grid, the oil pressure drops which instantly releases the airbrakes.

BLADE TIP AIRBRAKES:
Each blade is equipped with a turnable blade tip which in the activated position is turned 88 degrees out of the rotor plane and thereby acting as an efficient airbrake. The blade tip is mounted on a stainless steel rod embedded in the main blade. During normal operation, the blade tip is kept in the passive (operational) position by a stainless steel wire connected to a hydraulic cylinder under pressure. There are 3 of these cylinders, one for each blade, located in each blade root at the hub.

Once the hydraulic pressure is released, all 3 blade tips will be turned independently into the braking position by the centrifugal forces arising from the rotation and a very effective decrease of the rotor speed will take place. Even with only two activated airbrakes, the rotation will be kept well below the normal operational speed.

By re-setting the hydraulic pressure, each blade tip will be turned back into the operating position and the parking brake will be released.


PARKING BRAKE:
The parking brake is a fail-safe unit with a built-in spring-activated braking force. The brake disc is mounted on the high speed shaft. An active hydraulic pressure keeps the brake caliber in the open (operational) position.




The brake pads are self-adjusting, i.e. they keep a constant clearance between brake disc and brake pads. A pad wear sensor indicates time for replacement on the wind turbine control panel.

HYDRAULIC PUMP UNIT AND HYDRAULIC OIL:
The hydraulic pressure from the pump unit controls the blade tip airbrakes and the parking brake. A filter unit secures clean hydraulic oil in the system. Only a high quality hydraulic oil is used which has an appropriate viscosity, even at extreme low temperatures.

PRIMARY BRAKE SYSTEM:
The primary brake system is controlled by the wind turbine computer and the hydraulic pump unit. The first step when encountering a stop command is to release all 3 blade tip airbrakes. Instantly the airbrakes will decrease the rotor 3peed. At 40% of the nominal rotor speed or, at the latest after15 seconds, the parking brake will be activated as the second step and bring the rotor to a complete stop.

GENERATOR:
The generator is flange mounted to a machined bracket on the rear of the gearbox. A recess on the flange secures a well defined positioning and a perfect alignment with the high speed shaft for the mounting of the elastic coupling through which the rotor torque is transmitted.


TYPE:
The generator is a highly efficient asynchronous IP54 totally enclosed machine designed and built especially to wind turbine applications. This means that the generator reaches its maximum efficiency factor already at 50% full load.




INSULATION CLASS AND MAXIMUM OUTPUT:

The name plate rating of 150 kW refers to "Class B" insulation and temperature raise. However the generator is built with "Class F" insulation which adds an extra allowable temperature rise of 20°C (36 OF). This secures against unnecessary stops due to high ambient temperatures or other operational conditions.
The maximum power output is not depending on the wind speed
only. Air pressure, air temperature and air turbulence have influence on the energy contents of the wind. This means that identical wind turbines could have widely different power out-puts at apparently equal wind speeds. It is normal to experience variations, of up to +/-15% in the maximum power output in relation to the standard power curve, i.e. at standard atmospherical conditions: Air temperature 15°C (59 OF), air pressure 1013 hPa and max. 15% turbulence intensity.

SENSOR:
To monitor the generator temperature, PT l00 temperature sensors and thermistors have been build into the windings. The PT lOO sensor is used for directly read-out of the temperature on the controller display as well as for shut-down of the turbine when exceeding a certain, user-defined temperature limit. The thermistor has a higher, build-in maximum limit, which forces the turbine to a shut-down when exceeded. Both sensors are doubled with a spare set.







COOLING EQUIPMENT:
The generator is surrounded by a ventilation duct of steel plate and is effectively cooled by a fan which forces an air flow to pass the cooling fins of the generator. The nacelle cabin is divided in a way which prevents re-circulation of the cooling air.

CABLE TWIST SENSOR:
On the underside of the yaw mounting plate a cable twist sensor is located in junction with a cogwheel in order to count the net yawing angle. At three full 360 degrees turns to one side (net), the controller automatically brings the rotor to a complete stop, un-twists the cable by counter yawing and re-starts the wind turbine.
PERFORMANCE
The figure below shows the power delivered by the windmill at the two velocity of rotation settings. The lower 80 rpm value is used to start up the windmill and for wind speeds up to 8 m/s, whereas the 120 rpm setting is used for wind speeds between 8 and 14 m/s. The design power of 90 kW is reached at a wind speed of 13 m/s. For comparison, the chart also contains the power curve of a windmill using conventional airfoil sections, which result in a undesired power output at higher wind speeds.


CONCLUSION
Inspite of the availability of various financial incentives and availability of technological know-how, the development of wind power is very tardy in the country. Urgent efforts are required for the design and development of low cost, simple to use wind turbines . Suitable extension mechanism has to be devised wherein the benefits of development of wind power can be disseminated to the rural communities, village panchayats so that collective organizational skills can be developed. By doing these, wind energy, the most valuable, pollution free energy resource can be saved and can be made available for the benefits of the future generation. benefits of the renewable energy over the non renewable energy and the availability and technical description of wind power plants in India.
REFERENCES

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