Submitted to: Windpower
Publication Type: Proceedings
Publication Acceptance Date: 7/1/2007
Publication Date: 8/1/2007
Citation: Vick, B.D., Clark, R.N., Carr, D. 2007. Analysis of wind farm energy produced in the United States. In: Proceedings of the AWEA Windpower 2007 Conference, June 3-6, 2007, Los Angeles, California. 2007 CD-ROM.
Interpretive Summary: The land owner royalty payments for wind farms (currently ranging from $3500 to $5000 per installed megawatt per year) are desired by many farmers and ranchers across the United States, and the property and school taxes paid by the wind farm owner also help the economically depressed rural communities. In addition, only 5 to 10% of the land occupied by wind turbines is used for the generation of electricity (i.e. land is needed only for tower foundation, buried electrical wire, and road system for servicing wind turbines), and the other 90 to 95% of the land can still be used for farming and ranching operations. Over the period 2002 to 2006 we estimated the electricity produced by wind farms in almost every state with over 10 megawatts (10 thousand kilowatts) of installed wind turbine capacity (wind generated electricity for Hawaii which had 49 megawatts of installed wind turbine capacity in 2006 was not estimated). For 2006 we estimated the average annual wind farm efficiency for each state with over 10 megawatts of installed wind turbine capacity (except Hawaii). In addition, we determined how the efficiency of wind farms in Texas could be improved and how the percentage of renewable energy generation in Texas and California could be increased. The states with the most efficient wind farms were determined to be in the middle part of the country (the Great Plains) and the wind farm efficiency on the East and West coast was significantly lower. However, wind farm electricity in the east and west is needed more because of the much higher electrical load (i.e. more people live in those regions). The states with the highest wind farm efficiency were Oklahoma and Nebraska (annual average of 41% of rated wind farm capacity). The two states with largest amount of wind generated electricity in U.S. were Texas and California (6.5 and 4.9 terawatt-hours, respectively). One terawatt-hour is equal to one billion kilowatt-hours. Texas and California could increase their total percentage of renewable energy significantly by combining solar produced electricity with wind farms. This is because the highest wind energy (at 164 ft height and higher) occurs in late evening and early morning hours (in both Texas and California) while highest solar energy occurs in late morning and afternoon. In Texas, we determined that increasing a wind turbine rotor diameter by 8% would result in a 17% improvement in efficiency while increasing the tower height 25% would result in only a 9% improvement in efficiency. In 2006, we estimated that 0.64% of the total electricity generated in the United States was from wind farms (26.3 out of a total of 4138 terawatt-hours generated). If we are to generate 20% of electricity in the United States with wind energy by 2020 (President Bush’s goal) then large transmission lines will need to be built between the eastern and western United States to the Great Plains because wind farms in the Great Plains have the most abundant wind resource, and there is a large land area available for wind farms. A possible alternative to adding transmission lines costing hundreds of billions of dollars is to convert excess wind-generated electricity in the Great Plains to hydrogen or some other fuel that could be trucked or piped to both coasts, but the efficiency of conversion of wind energy to fuel, storage cost of fuel, transmission cost, and the efficiency of conversion from fuel back to energy needs to be improved significantly.
Technical Abstract: The electricity generated by wind farms in almost every state in the United States with over 10 MW of wind turbine capacity was analyzed over a five-year period (2002 to 2006). The total amount of wind generated electricity in the United States for 2006 was estimated at 26.3 terawatt-hours which was 0.64% of the total electricity generated in the United States. The average wind farm capacity factor for several states was estimated during 2006 and the highest wind farm capacity factor achieved was 41% (Nebraska and Oklahoma tied). Besides capacity factor, another way of estimating wind farm efficiency was developed by normalizing the wind farm output by wind farm rotor swept area instead of megawatt rating of wind farm. How well wind generation in different states matched utility load was also discussed. Capacity factors for the same wind turbine were determined for 15 different states which indicated which states had the best wind resource. Increasing the wind turbine rotor diameter by 8% was shown to be better at increasing wind farm output than increasing the hub height an additional 25 meters from 75 to 100 meters, at least in the state of Texas.