Wind Energy

What is wind energy?

Wind energy is a converted form of solar energy. The sun's radiation heats different parts of the earth at different rates--most notably during the day and night, but also when different surfaces (for example, water and land) absorb or reflect at different rates. This in turn causes portions of the atmosphere to warm differently. Hot air rises, reducing the atmospheric pressure at the earth's surface, and cooler air is drawn in to replace it. The result is wind. Air has mass, and when it is in motion, it contains the energy of that motion -- "kinetic energy." Some portion of that energy can converted into other forms -- mechanical force or electricity -- that we can use to perform work. How does wind energy work?

A wind energy system transforms the kinetic energy of the wind into mechanical or electrical energy that can be harnessed for practical use. Wind flows through turbines which create energy that can be used for electricity. There are two basic designs of wind electric turbines: vertical-axis, or "egg-beater" style, and horizontal-axis (propeller-style) machines. Horizontal-axis wind turbines are most common today, constituting nearly all of the "utility-scale" (100 kilowatts, kW, capacity and larger) turbines in the global market.

The Future of Wind Energy The U.S. wind energy industry turned in a solid performance in 2004, adding 389 megawatts (MW) of new generating equipment to the nationwide fleet, or enough to serve more than 100,000 average homes, according to AWEA. How many homes can one megawatt of wind energy supply? An average U.S. household uses about 10,000 kilowatt-hours (kWh) of electricity each year. One megawatt of wind energy can generate between 2.4 million and 3 million kWh annually. Therefore, a megawatt of wind generates about as much electricity as 240 to 300 households use. It is important to note that since the wind does not blow all of the time, it cannot be the only power source for that many households without some form of storage system. The "number of homes served" is just a convenient way to translate a quantity of electricity into a familiar term that people can understand. (Typically, storage is not needed, because wind generators are only part of the power plants on a utility system, and other fuel sources are used when the wind is not blowing.) How much energy can wind realistically supply to the U.S.? Wind energy could supply about 20% of the nation's electricity, according to Battelle Pacific Northwest Laboratory, a federal research lab. Wind energy resources useful for generating electricity can be found in nearly every state. U.S. wind resources are even greater, however. North Dakota alone is theoretically capable (if there were enough transmission capacity) of producing enough wind-generated power to meet more than one-third of U.S. electricity demand. What is needed for wind to reach its full potential in the U.S.? Consistent policy support Over the past five years (1999-2003), the federal production tax credit has been extended twice, but each time Congress allowed the credit to expire before acting, and then only approved short durations. The PTC expired again December 31, 2003, and as of March 2004 had still not been renewed. These expiration-and-extension cycles inflict a high cost on the industry, cause large lay-offs, and hold up investments. Long-term, consistent policy support would help unleash the industry's pent-up potential.

Nondiscriminatory access to transmission lines Transmission line operators typically charge generators large penalty fees if they fail to deliver electricity when it is scheduled to be transmitted. The purpose of these penalty fees is to punish generators and deter them from using transmission scheduling as a "gaming" technique to gain advantage against competitors, and the fees are therefore not related to whether the system operator actually loses money as a result of the generator's action. But because the wind is variable, wind plant owners cannot guarantee delivery of electricity for transmission at a scheduled time. Wind energy needs a new penalty system that recognizes the different nature of wind plants and allows them to compete on a fair basis.

New transmission lines The entire transmission system of the wind-rich High Plains, which cover the central one-third of the U.S., needs to be extensively redesigned and redeveloped. At present, this system consists mostly of small distribution lines--instead, a series of new high-voltage transmission lines is needed to transmit electricity from wind plants to population centers. Such a redevelopment will be expensive, but it will also benefit consumers and national security, by making the electrical transmission system more reliable and by reducing shortages and price volatility of natural gas. Transmission will be a key issue for the wind industry's future development over the next two decades.

by C. Ozcan