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<br /> <br />Reprinted from November 1981, Vol. 103, Journal of Solar Energy Engineering <br /> <br />~i <br />i <br /> <br />One Viewpoint Concerning Unit <br />Size in the Development of Wind <br />Turbines1 <br /> <br />W. E. Howell <br /> <br />C. J. Todd2 <br /> <br />The size of wind machines best adopted for early penetration toward large-scale use <br />is affected by the size of the national interim windpower goal (/70 GW average <br />power by 2000 AD) and the experience rate coupling cost of power to number of <br />machines produced, Windpower mission studies made in 1976 are modified in the <br />light of various goal-size and experience-rate assumptions, resulting in a rather flat <br />cost minimum near 0,3-0,6 MW, suggesting that other considerations may be <br />decisive, Several of these assumptions are discussed, leading to the conclusion that, <br />although larger machines may prevail in the long run, moderate sizes are best suited <br />to the early commercialization phase, <br /> <br />Office of Atmospheric <br />Resou rces Research, <br />Bu reau of Reclamation, <br />Denver, Colo. 80225 <br /> <br />I Introduction <br /> <br />The Domestic Policy Review of Solar Energy [I] identified <br />wind as the inexhaustible energy source nearest to practical <br />application to the nation's electric utility network and <br />suggested 1,7 quads in the year 2000 (56 GW mean output)2 as <br />its contribution, Achieving this goal or any other goal of <br />comparable significance will require building machines with a <br />total generating capacity of several scores of gigawatts. It will <br />also require integration of the engineering, operation, <br />management, and marketing of windpower with utility <br />networks in an acceptable way, <br />The size of wind machines proposed for development in- <br />teracts with these requirements in several important ways, <br />Economies of scale may be achieved, up to a point, by in- <br />creasing the size of an individual machine. Other economies <br />of scale may be achieved by increasing the number of <br />machines produced, Both are invblved, along with an estimate <br />of the total generating capacity, Both affect the total cost of <br />achieving the goal and hence the size range of machines to be <br />proposed for development. <br />The purpose of the present contribution is to examine some <br />implications of machine size as this will affect the advance of <br />windpower application through the transitional stages that <br />involve engineering development of the machines, installation <br />at a variety of sites having different characteristics, operation <br />under many different conditions, and integration into many <br />different utility systems. This paper does not attempt a <br /> <br />1 The views, opinions, and conclusions contained in this material are those of <br />the authors and do not necessarily represeht those of the U. S, Government or <br />the Bureau of Reclamation. <br /> <br />2 Presently a private scientific consultant. 34 Lookout Mountain Circle, <br />Golden, Colo.. 80401, <br /> <br />3 The source publication expressed energy as heat flux before conversion to <br />other forms. Assuming 35 percent conversion efficiency, 1.7 quads per year <br />would yield 20 GW of electric power. or al?out 3 percent of expected total utility <br />generation in the year 2000. It implies installation of 50 to 60 GW of wind <br />turbine capacity. <br /> <br />Contributed by the Solar Energy Division for publication in the JOURNAL OF <br />SOLAR ENERGY ENGINEERING. Revised manuscripI received by Ihe Solar Energy <br />Division September 21, 1981. <br /> <br />306/Vol.103, NOVEMBER 1981 <br /> <br />prediction of the size of machine, or range of sizes, that may <br />ultimately dominate the scene at a mature stage of windpower <br />use several generations hence, <br />As part of the Federal Wind Energy Program, design <br />studies of windpowered electric generators were undertaken <br />early in 1974. The concerned Federal agencies, the National <br />Aeronautics and Space Administration and the Energy <br />Research and Development Administration, solicited <br />proposals from the private sector. Subsequently, the mission <br />analyses and design studies were performed by General <br />Electric Company [2], Kaman Aerospace Corporation [3], <br />and Lockheed-California Company [4]. One purpose of the <br />design studies was to achieve minimum cost per unit of energy <br />produced, Each of the companies presented its results in the <br />form of cents per kilowatt-hour (in 1976 dollars) as a function <br />of generator capacity for the thousandth (in one case, the ten- <br />thousandth) machine produced, These results have been <br />summarized in a report by the .JBF Scientific Corporation [5] <br />and further presented in graphic form as shown in Fig, I, <br />Though the results differed in many respects, they agreed that <br />the optimum machine size exceeded I MW, with two of the <br />estimates being closer to 5 MW, Subsequently, the Federal <br />Wind Energy Program proceeded with a single prototype 2- <br />MW machine and initiated development of a 2,5-MW <br />machine. Construction of 1000 machines in this category <br />would create 2.0-2,5 GW of windpower generating capacity, <br />The question of optimum machine size was addressed also <br />by Ljungstrom [6] as part of a study of windpower resources <br />in Sweden. Assuming average distributions of windspeed with <br />height above ground for the typical Swedish forested terrain <br />situations, he calculated the ground area and number of <br />machines that would be required by a lOO-MW windfarm at <br />an inland location using machines ranging from 1-IO-MW <br />capacity. He concluded that the wind farm size would decrease <br />as the machine size increased, the main reason being that the <br />larger machines would reach up to where the wind was <br />stronger. He also calculated that, for the smaller machines, <br />most of the power extracted would have to come from <br />momentum transported downward over the windfarm area by <br /> <br />Transactions of the ASM E <br />