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284  WIND ENERGY TECHNOLOGIES


                     In the United States, our larger wind plants require advance transmission planning but
                     feed into main transmission lines and do not affect the customer distribution network.

                     GROWING USE OF WIND ENERGY FOR UTILITY SYSTEMS

                     Denmark’s situation should not cause concern in the United States. Denmark’s problem
                     is that wind has been too successful too quickly in a small country, and it must now
                     take steps to manage that success. It is unfortunate that the United States has not dealt
                     with its energy problems so decisively. At current levels of use, this issue is still some
                     distance from being a problem on most utility systems.
                       Up to the point where wind generates about 10 percent of the electricity that the
                     system is delivering in a given hour of the day, there is not an issue. There is enough
                     flexibility built into the system for reserve backup, varying loads, and so forth that
                     there is effectively little difference between a 10 percent wind system and a system
                     with 0 percent wind. Variations introduced by wind are much smaller than routine
                     variations in load (customer demand).
                       At the point where wind is generating 10–20 percent of the electricity that the system
                     is delivering in a given hour, wind variation becomes an issue that must be addressed,
                     but that probably can be resolved with wind forecasting (which is fairly accurate in the
                     time frame of interest to utility system operators), system software adjustments, and
                     other changes.
                       Once wind is generating more than about 20 percent of the electricity that the sys-
                     tem is delivering in a given hour, the system operator begins to incur significant addi-
                     tional expense because of the need to procure additional equipment that is solely
                     related to the system’s increased variability. These figures assume that the utility sys-
                     tem has an “average” amount of resources that are complementary to the wind’s vari-
                     ability (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 such as 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. Since wind is a variable energy source, doesn’t it cost utilities extra to ac-
                     commodate on a system that mostly uses fueled power plants with predictable
                     outputs?
                       However, the added cost is modest. Three major studies of utility systems with less
                     than 10 percent of their electricity supplied by wind have found the extra or “ancillary”
                     costs of integrating it to be less than 0.2 cent/kWh. Two major studies of systems with
                     wind at 20 percent or more have found the added cost to be 0.3–0.6 cent/kWh.

                     Advantage and disadvantages of wind power

                     Advantages

                     ■ Wind energy is available globally, the technology is mature, and energy production
                       is relatively inexpensive.
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