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Wind Web Tutorial WIND ENERGY POTENTIALUtilities must maintain enough power plant capacity to meet expected customer electricity demand at all times, plus an additional reserve margin. All other things being equal, utilities generally prefer plants that can generate as needed (that is, conventional plants) to plants that cannot (such as wind plants). However, despite the fact that the wind is variable and sometimes does not blow at all, wind plants do increase the overall statistical probability that a utility system will be able to meet demand requirements. A rough rule of thumb is that the capacity value of adding a wind plant to a utility system is about the same as the wind plant's capacity factor multiplied by its capacity. Thus, a 100-megawatt wind plant with a capacity factor of 35% would be similar in capacity value to a 35-MW conventional generator. For example, in 2001 the Colorado Public Utility Commission found the capacity value of a proposed 162-MW wind plant in eastern Colorado (with a 30% capacity factor) to be approximately 48 MW. For more information on the Commission's finding, see http://www.nrel.gov/docs/fy01osti/30551.pdf The exact amount of capacity value that a given wind project provides depends on a number of factors, including average wind speeds at the site and the match between wind patterns and utility load (demand) requirements. It also depends on how dispersed geographically wind plants on a utility system are, and how well-connected the utility is with neighboring systems that may also have wind generators. The broader the wind plants are scattered geographically, the greater the chance that some of them will be producing power at any given time. More reading: 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 fourth of U.S. electricity demand. The theoretical potentials of the windiest states are shown in the following table.
Experience also shows that wind power can provide at least up to a fifth of a system's electricity, and the figure could probably be higher. Wind power currently provides nearly 25% of electricity demand in the north German state of Schleswig Holstein. In western Denmark, wind supplies 100% of the electricity that is used during some hours on windy winter nights. What is needed for wind to reach its full potential in the U.S.? A number of factors are needed, including: Consistent policy support. Over the past seven years (1999-2005), the federal production tax credit has been extended four times, but three times Congress allowed the credit to expire before acting, and then only approved short durations. 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. How much energy can wind supply worldwide? As of the end of 2004, there were over 47,000 megawatts of generating capacity operating worldwide, producing some 100 billion kilowatt-hours each year—as much as 9 million average American households use, or as much as a dozen large nuclear power plants could generate. Yet this is but a tiny fraction of wind's potential. According to the U.S. Department of Energy, the world's winds could theoretically supply the equivalent of 5,800 quadrillion BTUs (quads) of energy each year--more than 15 times current world energy demand. (A quad is equal to about 172 million barrels of oil or 45 million tons of coal.) The potential of wind to improve the quality of life in the world's developing countries, where more than two billion people live with no electricity or prospect of utility service in the foreseeable future, is vast. More reading: I've heard that Denmarkis pulling back on wind development. Does that mean wind is a failure? No. In March 2004, Denmark, already the world leader in utilizing wind (which now provides 20% of national electricity needs), decided to add another 400 megawatts (MW) of onshore wind and 350 MW of offshore wind. By the year 2008, wind’s share of Danish electricity supply is expected to climb to 25%. In fact, addition, several major differences between Denmark and the U.S. suggest a basis for much greater expansion of wind in the U.S.: Denmark is small, the U.S. is not: (1) Although the U.S. has nearly twice as much installed wind equipment as Denmark, wind generates only 0.5% of our electricity, far below the 10% threshold identified by most analysts as the point at which wind's variability becomes a significant issue for utility system operators. (2) Denmark is also so small geographically (half the size of Indiana) that high winds can cause many of its wind plants to shut down almost at once--in the U.S., wind plants are much more geographically dispersed (from California to New York to Texas) and do not all experience the same wind conditions at the same time. Denmark has transformed its national power system, the U.S. has not: Rapid development of wind and new small-scale power plants within the past five years has brought Denmark to the point where power produced by so-called non-dispatchable resources in the country's West exceeds 100% of demand in the region. At many times, this excess generation leaves the country scrambling to increase electricity export capabilities to handle the surplus. This situation is essentially unimaginable in the U.S. Denmark's approach encourages community involvement, but places particular stress on low-capacity distribution networks (at the "end of the line" on transmission systems). In the U.S., our larger wind plants require advance transmission planning, but feed into main transmission lines and do not affect the customer distribution network. In Denmark, wind has been extremely successful, and utility system operators are now taking steps to manage that success; it is unfortunate that the U.S. has not dealt with its energy problems so decisively. What is the "energy payback time" for a wind turbine? The "energy payback time" is a term used to measure the net energy value of a wind turbine or other power plant--i.e., how long does the plant have to operate to generate the amount of electricity that was required for its manufacture and construction? Several studies have looked at this question over the years and have concluded that wind energy has one of the shortest energy payback times of any energy technology. A wind turbine typically takes only a few months (3-8, depending on the average wind speed at its site) to "pay back" the energy needed for its fabrication, installation, operation, and retirement. Since you can't count on the wind blowing, what does a utility gain by adding 100 megawatts (MW) of wind to its portfolio of generating plants? Does it gain anything? Or should it also add 100 MW of fueled generation capacity to allow for the times when the wind is calm? First, it needs to be understood that the bulk of the “value” of any supply resource is in the energy the resource produces, not the capacity it adds to a utility system. Having said that, utilities use fairly complicated computer models to determine the value in added capacity that each new generating plant adds to the system. According to those models, the capacity value of a new wind plant is approximately equal to its capacity factor. Thus, adding a 100-MW wind plant with an average capacity factor of 35% to the system is approximately the same as adding 35 MW of conventional fueled generating capacity. The exact answer depends on, among other factors, the correlation between the time that the wind blows and the time that the utility sees peak demand. Thus wind farms whose output is highest in the spring months or early morning hours will generally have a lower capacity value than wind farms whose output is high on hot summer evenings. At current levels of use, this issue is still some distance from being a problem on most utility systems. The rule of thumb (admittedly rough) is:
These figures assume that the utility system has an “average” amount of resources that are complementary to wind’s variability (e.g., hydroelectric dams) and an “average” amount of load that can vary quickly (e.g., electric arc furnace steel mills). Actual utility systems can vary quite widely in their ability to handle as-available output resources like wind farms. However, as wholesale electricity markets grow, fewer, larger utility systems are emerging. Therefore, over time, more and more utility systems will look like an “average” system. For detailed information on this topic, see "Grid Impacts of Wind Power: A Summary of Recent Studies in the United States," Milligan et al, National Renewable Energy Laboratory, http://www.nrel.gov/docs/fy03osti/34318.pdf More reading: Yes, but as the previous answer suggests, the added cost is modest. Three major studies of utility systems with less than 10% of their electricity supplied by wind have found the extra or "ancillary" costs of integrating it to be less than 0.2 cents per kilowatt-hour. Two major studies of systems with wind at 20% or more have found the added cost to be 0.3 to 0.6 cents per kilowatt-hour. For detailed information on this topic, see "Grid Impacts of Wind Power: A Summary of Recent Studies in the United States," Milligan et al, National Renewable Energy Laboratory, http://www.nrel.gov/docs/fy03osti/34318.pdf More reading: British Wind Energy Association
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