Indiana University Research & Creative Activity January 1998 Volume XX Number 3


ENERGYfrom the
Wind
by Mary Hrovat

As anyone who has walked along an ocean shore and faced into the breeze can attest, coastlines be windy. Residents of East Anglia in England have used their region's strong coastal winds for the past four hundred years to pump water and drain land that lies below the level of the North Sea. Today scientists are following up on this long tradition by investigating East Anglia's potential for wind-generated electricity. In the process they are gaining knowledge that can be applied to other coastal sites to develop the potential of wind power to supply clean energy from a renewable source. Bennet B. Brabson, a professor of physics at Indiana University Bloomington, spent the 1996-1997 school year on sabbatical leave participating in this research. He worked at the School of Environmental Science at the University of East Anglia in Norwich, England, where he collaborated with Jean Palutikoff, associate head of the Climatic Research Unit.

The process of generating electricity from the wind is a simple one. A slowly turning wind turbine is connected through a gear box to a fast-turning electric generator, all on top of a tall mast. The system efficiently converts the kinetic energy of the wind directly to electrical energy. Brabson and Palutikoff's research analyzes wind speeds at various locations in the United Kingdom both to understand the statistical nature of the wind and to help energy developers choose appropriate wind turbine designs and sites. UK

The researchers are also interested in the higher wind speeds and consequent greater power to be found offshore. Wind farm developers in Europe are now looking to these sites just off the coast, called "near-shore sites," where long stretches of open sea provide higher average wind speeds, where access to consumers on shore is relatively easy, and where the masts' visual impact on the landscape is minimized. However, wind speeds are particularly complex in this transition region, where large temperature differences between the land and the water set up strong convective winds. Understanding the complex patterns of air movement is important because near-shore sites can be less expensive to develop than sites further offshore. The extensive east coast along the North Sea has relatively high wind speeds and shallow water near shore, so it also has many potential wind farm sites. Brabson, Palutikoff, and Rebecca Barthelmie, an associate scientist in geography at IUB, are interested in the wind speed behavior in these complex transition regions.

Brabson explores wind speeds with a method of data analysis called Extreme Value Theory (EVT). Investigators using EVT look at extreme events--whether in wind speeds, human sports performance, or the behavior of the stock market--and quantify the events' expected frequency. In wind-speed analysis, the results can help determine whether and how a wind farm should be built. Brabson uses several statistical methods to examine the extremely high wind speed events from a data set and then to calculate expected maximum wind speeds over time. The results are typically expressed in terms of wind speeds that can be expected to be exceeded within a certain period. A wind farm designer wants turbines to withstand a 50-year quantile speed, the wind speed that is exceeded on the average once every 50 years, for the chosen site. Several methods can be used to calculate these quantiles, and Brabson and Palutikoff have completed a paper comparing the reliability of the different ways of determining the extreme speed quantiles.

East Anglia's Climatic Research Unit has gathered long time sequences of wind speed data valuable as baselines to verify extreme value analyses and increase their predictive value. Brabson has been analyzing data taken over twenty-five years on the Shetland Islands by the United Kingdom Government Meteorological Office. The Shetlands have a high average wind speed of 7.8 meters per second or 17.5 miles per hour (mph) and are a likely source of future energy, according to Brabson. Generating electricity from wind requires "high average wind speed with relatively little short-duration turbulence," according to Brabson. Long uninterrupted stretches of flat surface, such as ocean or plains, "provide the low friction necessary to maintenance of high wind speeds." Isolated mountain ridges also offer good wind sites. In the United States, the best potential wind energy sites are areas along the northwest and northeast coasts; parts of the Great Plains; mountain ridges such as the Diablo and Coast ranges in California, which already have large arrays of wind turbines; and some ridges in the Rocky Mountains. The United States also has several potential near-shore sites Brabson says.

Indiana, too, could be home to wind farms. The power output of a wind turbine is proportional to the wind speed cubed, so "a small change in average wind speed corresponds to a large change in potential power," Brabson explains. That means that while the southern Indiana average wind speed of 11 mph is only a bit lower than the 13 mph average in northern Indiana, the potential for power generation in northern Indiana is nearly twice as great.

While the United States has increased its use of wind energy since 1941, when the first wind-powered electricity generator went into operation at Grandpa's Knob, near Rutland, Vermont, wind still meets only a tiny percentage of American energy needs. But that could change. An analysis by the National Wind Technology Center indicates that conditions suitable for supplying wind energy exist over 6 percent of the contiguous United States. Wind, if fully exploited, could provide annually more than one and one half times the amount of electricity used in the United States today. In several areas of the country, electricity generated from wind energy is available at costs comparable to those of electricity generated in other ways.

Wind power generators range in size from a small one of a few kilowatts, producing sufficient power for a small farm, to a 1.5 megawatt turbine suppling the electricity for 2,000 U.S. households. Thus, a 50-turbine windfarm of large turbines provides the electric energy equivalent to the home needs of a town of 100,000 people. "Another lovely thing about these turbines is that they don't take up significant land. Collecting wind doesn't interfere with the usual farming activities of growing crops or raising livestock" Brabson says.

Storing wind energy is an important issue. The wind is not a constant source, so must be integrated into the base supplies from coal, oil, gas, and nuclear power. The owners of the wind power generators usually sell their electricity to a power company, which feeds it directly into the power grid for use by everyone connected to that grid. At present the power companies avoid the problem of storage by using wind-generated electricity as it is produced, allowing them to use less electricity generated from other sources. Brabson says that electricity generated by solar or wind energy can be stored conventionally using batteries or by using the electricity to split water into its constituent oxygen and hydrogen. In this electrolysis process, the hydrogen will be stored and later used to feed fuel cells or burned for heating. This effectively converts the generated electricity into stored hydrogen.

Elsewhere, government support has been important in developing wind energy. In Denmark, where the government strongly supports such research, 5 percent of the country's electricity comes from wind power, with some areas generating as much as 25 percent of their electricity from wind. Uneven support for research is one reason the United States has been slow to increase the use of wind energy. But Brabson notes that the United States government in 1996 established the National Wind Technology Center to coordinate research with industry and promote the use of wind energy. The center is a Colorado-based laboratory operated by the National Renewable Energy Laboratory, part of the Department of Energy. It focuses on research, development, and testing of advanced turbine systems. (See http://www.nrel.gov/wind/ for more information on the center.)

Future wind-power researchers could be in training now, thanks to a new Indiana University degree program, the Bachelor of Science in Environmental Sciences (B.S.E.S.), which Brabson helped develop. The B.S.E.S. program is an interdisciplinary program including courses from the College of Arts and Sciences and the School of Public and Environmental Affairs and developed by faculty from the geology, geography, computer science, mathematics, and chemistry departments. Brabson notes that the Department of Physics "offers a relevant course in energy studies called Environmental Physics" and adds that the department "will be building on this beginning in providing a strong curriculum for B.S.E.S. students." To this end, he has outlined a laboratory and field course in physical science measurement that may contribute to the B.S.E.S. curriculum. While at the University of East Anglia he attended lectures in meteorology, climatology, and geophysics, and he plans to bring his experience with curriculum to the design of IU physics courses for B.S.E.S. students.

Designing courses on alternative energy is not new for Brabson. His interest in wind energy came partly through teaching innovation. During the energy crises of the 1970s, he worked with several other faculty members in the physics department to develop courses that explored the physics of alternative energy sources, including solar and wind energy.

Today, in addition to planning courses to support energy research, Brabson plans to "seek out research opportunities for IU students in alternative energy sources such as wind and in analysis of meteorological and climatological variables relevant to global climate change." The geography department already has an established program in atmospheric science with expertise in wind energy research; both Scott Robeson, an assistant professor of geography at IUB, and Barthelmie work in this area. Several department members recently installed a fully instrumented 45-meter tower in the Morgan-Monroe State Forest to study fluxes of carbon dioxide, water vapor, and heat from a deciduous forest. In addition to standard meteorological instrumentation, the mast will also have acoustic anemometers at multiple levels, providing a wealth of data on wind speeds and turbulence.

The cross-disciplinary links that helped establish the B.S.E.S. program are also important in alternative energy research. One thing Brabson has noted in his work in both high energy physics and wind research is that "sharing ideas and even collaboration across discipline boundaries can be effective," as scientists in different areas use similar investigative strategies. His work developing the B.S.E.S. program led him to "view applications of physics in the broader context of several of the other physical sciences such as meteorology, climatology, oceanography, and geophysics." E



Return to the Table of Contents