Power Plant Engineering

NON-CONVENTIONAL ENERGY RESOURCES AND UTILISATION 65

Unlike coal or nuclear plants, public utility companies do not own most wind plants. Instead

they are owned and operated by business people who sell the electricity produced on the wind farm to

electric utilities. These private companies are known as Independent Power Producers.

Operating a wind power plant is not as simple as plunking down machines on a grassy field.

Wind plant owners must carefully plan where to locate their machines. They must consider wind avail-

ability (how much the wind blows), local weather conditions, nearness to electrical transmission lines,

and local zoning codes.

Wind plants also need a lot of land. One wind machine needs about two acres of land to call its

own. A wind power plant takes up hundreds of acres. On the plus side, farmers can grow crops around

the machines once they have been installed.

After a plant has been built, there are still maintenance costs. In some states, maintenance costs

are offset by tax breaks given to power plants that use renewable energy sources. The Public Utility

Regulatory Policies Act, or PURPA; also requires utility companies to purchase electricity from inde-

pendent power producers at rates that are fair and nondiscriminatory.

2.15.6 Recent Developments

The present windmill technology is inadequate for the low wind speed regions in the plains.
Special development projects in the following areas must be taken up so that wind energy can also be
used in the low wind speed regions.
Artificial Winds. Generation of artificial winds to drive windmills by heating large surfaces
with favorable thermodynamic properties is technically feasible. A project report has been prepared to
heat a large surface in which case the resulting current (artificial wind) can drive turbines. The efforts
needed to pursue the project in the form of money, manpower and time are huge.
Aeroelectric Plant. The low wind velocity in the plains can be augmented by the use of diffuser
at intake to wind mills. Besides the propellers, Madaras and Darrieus, there has been a plethora of
designs for wind machines. One intriguing power plant design, called the aeroelectric plant, uses the
flow up a tower that looks like a cooling tower as shown in Fig. 2.10. Its walls are heated by solar
radiation. Since the walls are circular, the sun’s rays need not be tracked as it changes position in the
sky during the day. The heated walls, in turn, heat the inside air and a flow up the tower is established.
This air flow is made to drive a number of air turbines located near the top of the tower. The driving
pressure causing air flow is given by the well-known chimney effect.

P. Carlson of Californica has proposed a slightly modified form in which, the interior air in a
very tall tower would be cooled by pumping water to the top. The water evaporates in the low pressure
air there, causing a downward flow of cooled air. The driving pressure can be calculated in a manner
similar to that for wet cooling towers. A conceptual design of such a plant called for 2.4 km high, 300
m diameter tower located in a hot desert and 10 wind turbines surrounding the tower periphery at the
bottom producing 2500 MW.

Low Wind Speed Turbines. The turbines available in India
and abroad are suitable for a rated wind speed of 3.5 m/s or more
whereas low wind speed turbines for rated values of 1.5 – 2 m/s are
needed for plain areas. Special efforts are, therefore, needed to de-
velop cheap and simple rotors, which can cut in at low wind speeds
available in the plains. The Savonious rotor and American multi-
blade type windmills have opti-mum power coefficients at a very
low tip-speed and can therefore be used as starting point to develop
windmills suitable for low wind speeds.

Sunlight Wind mil

Fig. 2.10. Aeroelectric Plant