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Energy blowing in the wind

Rosalind Ezhil K DHNS

All the wind turbines being used in India are either imported or manufactured under licence, making wind energy an expensive proposition. NAL is designing a turbine for half the cost.

Wind Energy could change the face of the Indian power sector. Dr.J.J.Isaac, Head, Wind Energy Division at the National Aerospace Laboratories (NAL), Bangalore says nearly 40% of India's installed electricity capacity of over 120,000 MW could be generated from wind energy. Sadly, we get a mere 2.7% of power from wind energy today and that too, essentially using imported machines .

Wind power (3200 MW, installed capacity) has already exceeded nuclear power (2770 MW, installed capacity), in India. Cost is the major roadblock to more large scale utilisation of wind power. Typically it costs around Rs.5-6 crores per mega watt to put up a medium-scale wind turbine. This enormous expense is partly because all the wind turbines that we use in India today are either imported or manufactured under license. In fact, the know-how to manufacture wind turbines is still not really available in India. "NAL is working to provide the critical input", Dr Isaac says.

The critical element of wind turbine technology is the design of the blade and rotor. Accounting for about 35% of the total cost of the windmill, it is the blade/rotor that really decides how efficient the wind turbine is going to be. Designing the rotor, in turn, requires a thorough knowledge of aerodynamics; that is why NAL, with it's expertise in the design and development of aircraft, was ideally suited to launch this new initiative.

Project goals

NAL's goal was two-fold: first, to develop a wind turbine that is at least 50% cheaper than imported turbines but with equivalent performance levels, and, second, to ensure that the technology is suitable for Indian conditions.

Indian wind speeds, for instance, are much lower than European wind speeds, and it is known that the wind power generated is proportional to the cube of the wind speed. Lower speeds, therefore, drastically affect the wind power output. Unless a turbine is properly rated to efficiently generate electricity at these lower speeds, it is not going to work well in India.

The other factor to be considered while designing the wind turbine is that the final unit must be inexpensive and easy to maintain in a country like India. Dust accumulation degrades the performance of wind turbines and if the towers are very high, maintenance becomes an expensive and difficult affair.

Keeping all these considerations in mind, NAL is developing prototypes of wind turbines suitable for Indian conditions. To be cost-effective, it was decided to develop turbines for the medium scale (300-500 kW) range. Initially, a 300kW turbine is being developed and this will be followed by a 500kW turbine. Although wind speeds increase with height, it was decided to keep the tower at a manageable height so that, it would be easy to maintain the installed structure.

Two-bladed turbine

The tower has hinges so that the rotor can be easily brought face down. It would be very difficult to achieve this with a three bladed turbine, Dr.Isaac explained. NAL's prototypes are also two-bladed. This keeps costs down, and will be aerodynamically superior models for this power range. Two other features that make the design really attractive are that the turbines are stall-regulated and are downwind machines.

Unlike a conventional machine, the turbine faces the wind in a ‘reverse’ way. In a stall-regulated machine, power is controlled, once the wind velocity exceeds the rated value, by aerodynamically ‘spoiling’ the air flow over the blade. This avoids the costly blade pitching mechanism. Down-winding too has a tremendous advantage; the wind turbine will self- adjust and passively yaw to face the wind unlike a conventional machine which has to be driven. As Dr.Isaac points out, the essence is to arrive at a wind turbine morphology that is robust and suitable for operation in the Indian wind environment.

Industry partnership

NAL is undertaking this project in partnership with private industry. Mr E.N. Ramasamy, Chairman of the Sangeeth Group, Coimbatore willingly invested in this project,. "Like NAL, we too are committed to developing Indian technology," he says. The Sangeeth Group has in fact thrown open its wind farm at Kethanur, Coimbatore District, for NAL's trials and studies. The prototype 300kW blade is being tested this month as the speeds of the winds streaming from the Palghat gap are still good in August-September. Industry partnership has also helped NAL to streamline its costs and ensure that the goal of developing the turbine at 50% of the cost will indeed, be achieved.

Is investing in wind energy cost effective even though the windy season is so short? April to September are India's most windy months; (Southern Tamil Nadu has also a brief second season in November - mid January). "Undoubtedly" says Dr Isaac. "Any electricity generated is good and we must work at developing a mix of energy sources."

Industries get several benefits and concessions for investing in wind farms. Wind turbines, and rotors for example, are excise tax exempt. The industry, also has the facility to wheel power; a private industry that sets up a wind farm can put the generated electricity on the power grid at the point closest to the wind farm, and take it off the grid at some other point close to where the industry is located.

The NAL wind turbine development programmes are being largely funded by the New Millennium Indian Technology Leadership Initiative (NMITLI) of the Council of Scientific and Industrial Research (CSIR), the Centre for Wind Energy Technology (C-WET), Chennai and the Sangeeth Group of Companies, Coimbatore as the industrial partner. To make the rotor blades NAL is using a special composite blade fabrication technology evolved by NAL's Fibre Reinforced Plastics Division (FRPD) headed by Dr.R.M.V.G.K.Rao.

This technology was first used to fabricate aircraft wings; so the rotor/blades did not pose too much of a problem! Several Divisions in NAL are contributing to the development of this wind turbine technology. These include, in addition to the Wind Energy Division and the Fibre Reinforced Plastics Division, the Propulsion Division, the Computational and Theoretical Fluid Dynamics Division, the Structural Integrity Division and the Engineering Services Division. The blade/rotor development includes computational fluid dynamics studies, structural/materials analyses and testing, model testing and field testing of prototypes. The metal tower fabrication will be subcontracted.

The project is now entering its most exciting phase and there is expectation, both at NAL and the Sangeeth Group. "The trials in the month of September at the wind farm will be crucial", Dr.Isaac says. In the long run, however, there is little doubt that a happy wind will blow across the country bringing with it the promise of up to 45,000 MW of power.