Wind has been used for a variety of purposes for grinding grain and pumping water to powering large sailing ships. The contribution of the American farm windmill in this century demonstrates what a valuable commodity wind energy can be when captured in a dispersed system of small machines. There are an estimated 30,000 operating farm windmills in the Southern Great Plains today; the average power of each windmill is about 0.25 kW and collectively they provide an average power of around 5 megawatts. The extractable wind power potential for the United States has been estimated as over 2 million megawatts with the major wind areas in the Great Plains Region, along with the coasts, off-shore and the coasts of Alaska, and Hawaii. Texas is one of the best regions in the US for utilization of wind energy. The capturable wind power in Texas was calculated to be 250,000 megawatts from 10-12 years of data taken at National Weather Service Stations in Texas. This figure is about 5 times the total installed electrical generating capacity in the State, and is the annual energy equivalent of 1.3 billion barrels of crude oil. Roughly 40% of this wind power potential is in the Panhandle and another 10% is along the Gulf Coast. Use of even a few percent of this resource would obviously have a beneficial impact on the States economy.
Types of Wind Machines
A wide variety of types and sizes of wind machines exist today. Wind turbines are classified into two general types, drag and lift. On a drag device the wind pushes the blade forcing the rotor to turn about its axis; the most common example of a drag device is the farm windmill. Drag devices characteristically produce high starting torque and are well suited to pumping water in low volumes, however they are limited in the amount of energy they can extract from the wind. Wind turbines that use lift have only a few (two, three or four) blades in contrast to the multiple blades of a drag device. One blade rotating very fast can extract as much energy as many blades rotating slower. Lift devices use slender airfoils for blades, whose shape is the same as an airplane wing. Lift devices are much more efficient than the drag devices, thus the blade area can be reduced considerably. Lift devices are further classified by axis type: horizontal (HAWT) and vertical (VAWT).
Wind Power Map
The map delineates the wind energy regions of the State. Since power and energy are closely controlled by wind-speed, the power at a particular location is dependent on local terrain and obstructions. Those regions enclosed by contour lines are suitable for the installation of wind turbines. Of course, wind turbines located at sites with higher wind-speeds will produce more energy. wind-speed also increases with height, therefore the average wind-speeds are for a height of 20 meters (66 ft), a common tower height for small wind machines.
Use of Wind Energy
Kinetic energy in the wind can be transformed by the Wind Energy Conversion Systems (WECS) into other forms of energy; electrical, mechanical, and thermal. Most of the WECS are for the generation of electricity. The stand alone systems of the 1930’s which were generally DC at 6 to 32 volts, became obsolete when inexpensive electricity became available from rural electric cooperatives. Today, manufacturers are again producing WECS which use DC generators, but the most common usage is 60 cycle AC. DC can be converted to AC by an inverter, or the WECS can be connected directly to the utility grid by use of an induction synchronous generator. If more power is produced by the WECS than is needed on site, the excess power is fed into the utility grid — under this operation the utility grid acts as a large storage. The Public Utility Regulatory Policies Act (PURPA) states that regulated utilities have to accept private generator systems on their grid and they have to pay the avoided cost for energy fed back into the grid (as a minimum the fuel adjustment cost).
In 1990, world wide there were around 20,000 wind turbines with an installed capacity of 2,000 megawatts. In 1989, they produced 2.6 billion kwh of electricity, which was the equivalent of 4 million barrels of oil. Eighty percent of the electricity generated was by wind turbines located in wind power plants in California.
Applications of WECS for producing mechanical power are being tested for pumping water; wind assist systems for irrigation water, stand alone systems, and air lift pumping. The use of WECS in producing heat is being tested by electrical resistance heating and by direct conversion in water churns.
Although the fuel is free, installing and operating a wind turbine can be expensive. Manufacturers are producing WECS with ratings from less than 1kW to 500kW. In general, installed costs for small WECS (less than 100kW) are around $3,000 per rated kW, which translated to around $0.15/kWh. As installed costs drop to $1,000 per rated kW, small WECS will generate electricity at around $0.10/kWh.
In Texas, wind and solar devices are exempt from property and sales tax. WECS of 50kW or less connected to the utility line can use Net Energy Billing.
Sources of Information
- A Siting Handbook for Small Wind Energy Conversion Systems
- Order No.: PNL-2521
- May 1978, 132 p.
- Available form NTIS, US Department of Commerce, 5383 Port Royal Road, Springfield, VA 22161
- Wind Machines
- Frank Eldridge. Van Nostrand, 1980
- Wind Power for Home and Business: Renewable Energy for the 1990s and Beyond
- Paul Gipe. Chelsea Green .Publishing Co., Box 130, Rt. 113, Post Mills, VT 05058, 1993
- Wind Power for the Homeowner
- Donald Marier. Rodale Press, 1981
- Wind Turbine Engineering Design
- David Eggleston & Forrest Stoddard. Van Nostrand Reinhold Books, 1987
Information Available From the Alternative Energy Institute
- Introduction to Wind Energy
- Wind Energy and Wind Turbines
- Wind Water Pumping
- Sources of Information for Building Your Own Wind System