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If we think energy from wind mills is new technology, we are totally wrong. They existed in Babylonia 2,500 years ago, Persians tried them out 1,200 years ago and Europe in general has had windmills for over 700 years. Generally, the rotating blades were used to move simple mechanical parts for lifting water, pounding grains or extracting oil in mills. Wind power to move sail boats and later to explore the world by larger ships has been in vogue for thousands of years. During the 20{+t}{+h}century, it caught up in the U.S. and rest of the world for more diverse applications.

Wind turbine on the terrace of Raya's house in Chandra Layout, Bangalore

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While there are wind turbine clusters with hundreds of them dotting the landscape, we are discussing here mainly the small-scale unit practical for typical urban public buildings. They supply power for lights, TV, battery charging and such needs. With blade diameter ranging from 0.5 to 7.0 metres, and average wind speeds upwards of 2.5 metre per second, we can generate power in the range of 0.5 kW to 10 kW per hour.

For routine household needs, even smaller units with blade diameter less than 3 metres, generating up to 2 kW, can be considered. DC generators in the 12 to 24 volts range are adequate for household needs.

For such small scale, magnetic alternator-type generator serves the function. Also, horizontal axis devices deliver maximum coefficient of efficiency. These can be easily mounted atop any well-designed building. The legs of the tower cannot be directly placed on a slab, but preferably need RCC pillars or an inverted beam arrangement to transfer the load down.

Technically speaking, periodic records of wind speed across one year taken through anemometer is required to accurately assess the power generation. Altitude, air density, topography, speed, wind direction, trees, buildings and such others increase the air turbulence, reducing the power generation. Using scientific formulae based on density, velocity and wind sweep area, technical experts can advice on the installation of the turbine.

The choice of rotor depends upon the purpose of generation – slow running multiple blades are good enough for water pumps while the fast running ones with fewer blades, with wind blowing perpendicular to the blades, are required for electricity.

If the wind can create a drag and lift effect, it further boosts power generation. Of course, there will be the tail vane to rotate the blades in wind directions. Generally, the blades need to have aerodynamic design, good strength and light weight material. Accordingly, aluminium and fibre are preferred over steel.

India, on an average, has around 3 metres per second speed, making it a viable nation for tapping wind energy. Of course, this average has no meaning, for the spot speeds are important. Wind energy unit is a one-time investment, so across years of operation the cost per unit goes on reducing, making it a sustainable source of energy.