In this issue

Editor's note: The Energy Services Bulletin features real answers to real questions posed to our staff at the Energy Services Power Line. We hope you find it useful.

Answering questions about wind power

Question:

I lead bus tours that travel past the huge wind farm at San Gorgonio Pass near Palm Springs, Calif. Can you give me answers to some frequently-asked questions about wind generation?

Answer:

The questions your passengers are asking are the same ones many consumers have about wind power.  We hope this helps you on your tours and increases your understanding of wind power, as well.

Q: What is the proper name for the units?

A: The machines are called wind turbines, and a cluster of wind turbines is known as a "wind farm" or a "wind powerplant." In addition to wind turbines, a utility-scale wind farm includes an underground power transmission system, control and maintenance facilities and a substation that connects the wind farm with electric utility transmission and distribution systems (the "grid").

Q: What states are using wind farms?

A: According to the American Wind Energy Association, the total installed wind energy capacity in the United States is 12,634 MW as of June 30, 2007. Texas currently leads the nation with 3,352 MW, followed closely by California. In all, 33 states have or are planning wind facilities.  The country with the highest total installed capacity is Germany with 20,621 megawatts.

Q: How do wind turbines work?

A: The kinetic energy of the wind can be changed into other forms of energy, either mechanical or electrical. For centuries in Holland, mechanical energy from windmills has been used to pump water from low-lying areas.

Wind turbines create electrical energy. The wind spins the turbine's rotor blades, which are attached to a hub mounted on a low-speed turning shaft. The low-speed shaft goes through a gearbox that increases the 19-to-30-rpm speed to approximately 1,500 rpm.

A generator then converts the mechanical energy of the high-speed shaft into electrical energy. Modern rotor blades are designed much like airplane wings. Most need wind speeds above 12-14 miles per hour to turn the rotors fast enough to generate electricity. However, if the wind gets too high, the turbine has a brake to stop the rotor blades.

Q: Why are there different sizes and types?

A: There are several reasons why a wind farm might contain different sizes and types of turbines. Part of the answer may be that different areas of the farm have different wind characteristics, and thus the tower height and rotor size were selected to optimize those winds.

Also, a farm may contain several "generations" of turbines; new designs are constantly improving the technology. For example, the "Eiffel tower" framework designs at San Gorgonia had high maintenance costs because the wind stressed nuts and bolts, so operators switched to tubular steel towers. Similarly, some early designs had two, rather than three, rotor blades, but "drag" reduced efficiency as the lower blade passed by the tower.

Q: Do computers control the turbines?

A: A computer monitors the direction of the wind, controlling electric motors that then turn the unit into the wind. The computer also continually monitors the condition of the turbine, checking for malfunctions, such as overheating gearboxes or generators.

Q: Is there any way to store the electricity wind turbines generate?

A: The electricity currently generated at the San Gorgonio farms is distributed for immediate use. Energy storage is an important technical challenge that wind farms must address in the future. For small wind farms, particularly in areas not connected to the utility transmission and distribution grid, battery storage may be cost-effective. As an example, the wind farm tour vehicle operates on batteries that are charged by wind power electricity.

For large wind farms, pumped hydro storage may be an option. This strategy uses excess wind energy to pump water from a lower reservoir to an upper reservoir. When electricity is needed, the water is released through a dam to generate hydropower. The paper entitled "Wind Energy as a Significant Source of Electricity" by R. Gerald Nix, National Renewable Energy Laboratory, contains additional information on this topic.

Q: How effective are wind turbines in generating electricity? Is it an experiment or an established power generation source?

A: Wind turbines are commercially proven and produce electricity at a competitive price today. Growing concerns about the environment and energy independence, coupled with production tax credits in the 2005 Energy Policy Act, are pushing wind development. The PTC was set to expire Dec. 31, 2007, but the 109th Congress extended it through the end of 2008.

Q: Who regulates the construction and operation of wind farms?

A: The U.S. Department of Energy and other Federal agencies regulate development and operation of power generating plants. In addition, state and local regulations and ordinances apply, such as property deed restrictions, construction engineering codes and requirements for connecting to a utility grid.

Q: How many turbines are on the San Gorgonio wind farms? How much acreage is used? Who operates the wind farm? Who owns the land?

A: Based on statistics from AWEA and the California Wind Energy Association, there are currently about 2,600 turbines on less than 1,500 acres. As older turbines are replaced, the newer ones are larger and more efficient; therefore, the farms need fewer turbines to generate the same amount of electricity. The San Gorgonio Pass area contains 30 separate farms operated by 15 different companies (corporations or individuals). Some of the operators own the land, while others lease the property from the Bureau of Land Management.