Reaping the wind
(appeared in August 2014)

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The windmill arm is an airplane wing which is fixed upright, says S.Ananthanarayanan.

This is the principle behind the industry of harnessing wind power, which now forms just 1.6% of generation in India, but is fast progressing. Denmark is the world leader in wind power and the share of wind power in Denmark is over 30 %, with the target for 100% by 2050.

Coming back to the airplane wing, it is the shape or profile of the wing that reacts with the stream of air, to create an upward force, on each wing, which lifts the load in between. This same force which arises when air moves over a curved surface similarly acts on the wanes of the windmill when the wind blows, and it acts in the same sense on each wane, to turn them round in a vertical circle. The traditional windmills of Holland thus predate the invention of the airplane in making use of aerodynamics. And in the current concern to reduce the use of fossil fuels and pollution, wind power has become a compelling alternative. Denmark moved rapidly after the oil crisis of 1973 and developed expertise in building and installing wind driven electric generators, both in the country and as an exporter.

The modern application of wind energy is no longer a machine to drive a grain mil, but it is to drive the rotor of an electric dynamo, and the arrangement is called a wind turbine. The wanes are no longer made of wood and canvas, but are giant structures of fiberglass reinforced plastic, with struts and supports of sophisticated composite materials. And the arrangement has to bear a huge load, with the transmission and generator that work for weeks and months without a break. Denmark, in fact, had a head-start in wind turbine research as it had got into the field as early as 1897, with facilities which included a wind tunnel.

Special design

In the same way as the airplane wing has been specialized for different loads and wind speeds, the wind turbine wanes are also specially designed, based on dimensions and the wind conditions. As outer ends of the wanes move faster than the inner part, the profile of wanes, which can be as long as 82 metres, needs to optimized along the length to present the best surface to the wind at each point and to get the best conversion of energy. And the material and construction of the wanes needs to be good enough at all places and the connection to the central hub needs to be designed to stand huge load. Poul (Poho) Hummelshoj of the Danish Technical University, at Roskilde, just outside Copenhagen, during a presentation to journalists at the Euroscience Conference at Copenhagen said that the force at the central hub was like that of a motor car pressing down through a lever that was seven km long!

The research facility, which is housed near a now unused nuclear facility that had been set up under the legendary Niels Bhors, has separate departments which study the whole spectrum of the science of wind turbines, from material, structural design, both of the wanes as well as the support, mechanical transmission to the electric generator. They use sophisticated micro and macro material science to arrive at the most suitable materials, and laser beams and the way they are scattered, to analyse air dynamics and best design the placement of turbines in a farm of turbines.

What wind turbines need to function is just the engineering and a reasonably continuous stream of air, at least 4-5 metre per second and not more than 25-30 metres per second. Most coastal areas and hilltops have ample wind and are good places to set up several wind turbines, to act together, as a wind farm. The usual wind turbines have been smaller and rated at 225 kilowatts, of which one would need four for a megawatt. But the present wind turbines have span of 164 metres and capacity of 8 Mw. A farm of these giants, each one larger than three football fields standing on end, can generate power in thousands of megawatts, larger than a nuclear plant. A farm known as the East Anglia Array is planned for 7,200 MW, using 1,028 of the 164 meter turbines. And wind turbines do it all without mining and transporting coal or any of the CO and CO2 pollution, and without the need to dispose of ash, or nuclear waste.

India now has wind turbines in many states and the capacity installed is over 20,000 MW, which is 8.5% of the total capacity, although this accounts for only 1.6% of the total power generated. This is far below the capacity installed in other countries, but India still ranks as the 5th, worldwide. And the Ministry of New and Renewable Energy has assessed the potential of wind resources at more than 1,00,000 MW, otherwise assess.

The negatives associated with wind power are usually the cost, which is greater, per MW installed, than conventional plants, the noise from the generators and the fast moving arms, and dangers to birds. There are technical solutions to noise from generators and locating the turbines far from cities could save people from the ‘whoosh’ of the arms. There is also the trend now to locate the farms out at the sea, as off-shore facilities, either on steel and concrete stilts or even on floating platforms. These, of course, have higher costs for installation, maintenance and transmission of electricity. There is also the avenue of uninhabited islands near shorelines.

As for the cost, the investment is generally being made by the State electricity authorities, with a growing market of private investment, mostly by pension funds, etc. Despite high initial cost, the low running costs can lead to interesting economics. Moreover, “inviting people in an area to invest in the Wind Farms that serve them would also help reduce resistance, as this would give the use users the comfort of ownership,” said Poho.

As for the danger to birds, Poho said that there had been a number of studies and the risk from wind turbines was found to be not more than the usual dangers that birds faced. Danger to some birds and migratory birds does seem to be well founded, in many places, and would benefit from more study and effort to find a solution. But the overpowering benefits of clean power and saving the environment from pollution is a competing reason, and the number of wind turbines the world over is continuously rising.

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