Chapter 2: Wind Energy Capture
By Richard Lance Christie
(Draft date 15 Oct 07)
Author's note: This is a preliminary draft and a work in progress. (Further explanation.)
Wind is a great renewable energy success story. Costs of wind-generated electricity have dropped from 40 cents per kilowatt-hour in 1981 to about 4-6 cents per kilowatt hour at the best sites today. The U.S. National Renewable Energy Laboratory (NREL) states: “The challenge for wind energy today is transmission. Most of the nation’s population doesn’t live in the windiest places.” Another challenge, addressed in more detail below, is intermittency: the wind doesn’t blow at a faster speed than the threshold of turbine power generation at any given site all the time, much less conveniently start blowing in synchrony with utility peak electricity load times.
The U.S. Department of Energy’s research and development program is focusing on two approaches which would permit using the wind resource closer to population centers:
- Develop low-speed wind turbines that will produce power at about 3.5 cents per kilowatt-hour at sites were the average wind speed in 13.5 miles per hour versus the 15 miles an hour the DOE cites as its referent for current turbines. The DOE says this would increase the land in the U.S. with cost-effective access to wind power more than twentyfold. (The specifications on the newest generation of 240-foot-sweep Danish wind turbines is that the wind speed threshold at which they start generating power is 8 mph.)
- Researchers at the National Wind Technology Center are looking at how to put wind turbines offshore in ocean water deeper than 30 meters. Much of the U.S. population lives near the coasts and average wind speeds are higher over ocean than land.
The effect of intermittency is determined by the ratio between the output of a widely-spread group of wind turbines and their peak output. For wind turbines, the ratio translates into wind being able to supply 35 percent of that block of electricity which is determined by the turbines’ collective peak output.
Section 1: The United States as a “Saudi Arabia” of Wind Energy
In 1991 the U.S. Department of Energy (DOE) published a national wind resource inventory. Based on then-current wind turbine technology, the DOE found the three most wind-rich states of North Dakota, Kansas, and Texas had enough harnessable wind energy to generate the total amount of power currently consumed by the nation. Advances in wind turbine design in Europe since 1991 allow turbines to operate at lower wind speeds, with increased efficiency at converting wind energy to electricity, and harvest the wind at greater heights. In 1991, wind turbines averaged scarcely 40 meters in height; in 2004, turbines are 100 meters tall with much longer blades, tripling their capture of available wind energy. The longer blades rotate at slower speeds, posing no risk to wildlife. A team of engineers at Stanford University re-did the DOE assessment and discovered that current generation wind turbines installed at the good wind sites in these three states alone could generate the total quads of energy needed by the United States. Currently 28 U.S. states have utility-scale wind farms feeding electricity into the local grid. The U.S. has a total of 6,300 megawatts of installed wind-generating capacity.
Although wind turbines convert wind to electricity, the electricity can be used to hydrolize water into oxygen and hydrogen. The hydrogen can then be transported to a use site in tanks or pipelines and used as a substitute for fossil fuel. Hydrogen can power both mobile and fixed energy generators, and is thus substitutable for petroleum, natural gas, and coal for running engines and firing boilers and furnaces. Hydrogen fuel is climate-benign if it is not allowed to leak into the environment in large quantities. A group of CalTech scientists recently published a simulation study which found possible adverse effects on the ozone layer, climate, and soil bacteria if a large percentage of the hydrogen generated for a “hydrogen economy” escaped into the atmosphere from leaks. The scientists favor conversion to a hydrogen economy, but caution against using leaky distribution and storage. When hydrogen is burned (oxidized) as fuel, the only combustion product is water vapor.
Wind is abundant, inexhaustible, climate-benign, and clean. It has no “fuel” cost; the only cost is the capital cost of installing the turbine to harvest it and then modest maintainance and operational costs for the turbine during its functional life. The cost of wind-generated electricity has dropped from 38 cents a kilowatt-hour (KWH) in 1980 to roughly 4 cents a KWH today on prime wind sites. Recently-signed supply contracts for wind-generated electricity in the U.S. and U.K. are providing electricity at 3 cents per KWH. The European Wind Energy Association projects the average cost per KWH will drop to 2.6 cents by 2010 and 2.1 cents by 2020. U.S. energy consultant Harry Braun calculated that, if contemporary wind turbines were mass produced like automobiles, the cost of wind-generated electricity would drop below 2 cents per KWH. By contrast, the DOE reports the cost per KWH of new natural gas or coal-fired power plant electricity is 4-6 cents.
Critics have pointed to the problem of “intermittency” in depending on wind generation for national electric energy generation. At a given site, the wind does not blow at a high enough velocity to generate power all the time, making energy production by a given wind farm intermittent. The times when wind velocity lulls are not at the discretion of the operators, and may occur at times of peak demand.
The problem of intermittency in wind generation may be minimized by two factors: First, by locating wind farms in widely distributed sites (e.g., North Dakota, Kansas, Wyoming, Texas, etc.) linked through a national energy grid, one lowers the probability that the wind will not be blowing at most generating sites at a given time. Second, high-potential wind generation sites are by definition ones where the wind is blowing at the minimum speed necessary to generate power nearly all the time. The scales used to rate site wind generation potential rate a site where the wind is strong part of the time and still part of the time much lower than a site with the same average wind speed but almost constant moderate wind velocities. Some critics of the potential of wind generation as the mainstay national energy source have incorrectly assumed that average wind velocity is used to rate site potential; the actual primary rating criterion is the percentage of time wind is blowing at the site at more than 8 miles per hour.
A. Domestic “wind farm” developments: Cape Wind is a proposed wind power facility to be located five miles off the coast of Cape Cod, Massachusetts. It has been opposed by people concerned with the impact of the wind farm on views, property values, and migrating birds. The U.S. Army Corps of Engineers was asked to do an Environmental Impact Statement to address alleged environmental impacts. The draft 3,800-page EIS was released in November, 2004, representing three years’ work by 17 federal and state agencies. The EIS concluded that Cape Wind would create significant economic, public health, and environmental benefits, and that the majorty of potential negative consequences would be minor and mitigated. As the first offshore wind power facility in the United States, Cape Wind sets an important precedent for siting similar facilities. The opposition viewpoint was expressed by Richard Barth: “Imagine a 410-foot tower (the size of a 40-story building) with three 100-foot blades rotating at almost 200 mph that sound like a loud washing machine in your front yard. Now imagine 60 of these machines within a few square miles of relatively heavily populated, pristine dairy country in the eastern migratory flyway of the United States. Wind power is not the magic bullet many hope will slay the energy dragon.”
In New York, the Maple Ridge wind farm was dedicated in 2006, making New York State home to the largest wind power operation east of the Mississippi. The farm is fruit of New York’s state utility commission adopting a requirement that 25 percent of the state’s energy come from renewable sources by 2013
In Utah, a 200 megawatt wild facility is being built in the Milford valley of Beaver County, extending north into Millard County. The wind power generated from 80 2.5 megawatt turbines would be transmitted to the Intermountain Power Project substation in Delta, which supplies power to the Southern California Public Power Authority. The project includes installation of four permanent meteorological towers and a 34.5 kilovolt underground collection system linking the turbines and the facility collector substation.
Just before passage of the 2006 Department of Defense spending bill in January, 2006, Senator John Warner (R-Va) added an amendment requiring a study of the effect of wind turbines on military radar. While it was being completed, the Federal Aviation Administration send “notices of perceived hazard” to applicants for new wind turbines, effectively shutting down the permitting process for 16 new wind power campuses. In June, 2006, the Sierra Club sued the DOD after it missed a deadline to complete the report; the report was finally released in September. It maintains that turbines can sometimes interfere with radar, and applications for projects need to be evaluated on a case-by-case basis for such interference potential. The need for the study was not clear: many military installations with radar already have wind turbines next to them, and the U.S. Navy erected four turbines at Guantanamo Bay next to their radar facility. The British military researched the issue and found that wind power “isn’t a problem for the air defense community.” The motive for Warner’s amendment appears to lie in his long-standing opposition to the Cape Wind project at Cape Cod where both his daughters own property and object to the turbines being erected in their viewshed.
Resistance to offshore wind farms in the U.S. on environmental grounds ignores the positive evaluation by the International Advisory Panel of Experts on Marine Ecology, and now the Danish energy and environmental agencies (see below), which find no adverse environmental impacts from wind farm operation after eight years’ study.
B. Wind power from residential installations: Southwest Windpower company of Arizona won a 2006 Best of What’s New Award from Popular Science for its Skystream 3.7 wind turbine. The turbine was developed in collaboration with the U.S. Department of Energy’s National Renewable Energy Laboratory. The Skystream is reportedly the first compact, user-friendly wind generator which has built-in controls and inverter that is designed to provide grid-intertie electricity at low wind speeds. The built-in controller and inverter feed 120 volt AC to the house when the turbine is running, displacing utility electricity proportional to load and the turbine’s output. If the turbine produces more electricity than the house is using at the time, it feeds the excess electricity back into the power grid for the utility to buy.
C. Wind power from tethered kite turbines: One concept for realizing near-constant wind power generation is to float an inflatable kite-like device upwards of 600 feet to capture wind at this greater height where wind is stronger and more constant.
D. Economic impact of wind turbine ownership: According to a Government Accountability Office report, locally-owned wind turbines in Minnesota generate five times more economic impact to the state economy than out-of-state-owned wind turbine units.
The U.S. Department of Energy’s “Small Wind Electric Systems” is available at <www.eere.energy.gov/regions> and Windustry of Minneapolis, NM can be contacted through <Error! Hyperlink reference not valid. The Iowa energy site has wind turbine performance comparison and cost data <Error! Hyperlink reference not valid. The Nebraska Energy Office has a Wind Resource site, <www.neo.ne.gov/renew/wind-renewables.htm>. The DOE’s Wind Powering America site is <www.eere.energy.gov/windandhydro/windpoweringamerica>.
Section 2: The International Initiative to Develop Wind Energy
In a joint assessment of global wind resources called Wind Force 12, the European Wind Energy Association and Greenpeace concluded that development of an average of 10% of the world’s windy land areas with current wind turbine technology could produce twice the projected world electricity demand as of 2020. The report noted that a number of the best wind sites are sparsely populated - the Great Plains of North America, northwest China, eastern Siberia, and the Patagonian region of Argentina - allowing far more than 10% coverage of land areas by turbines, whose base footprint takes only about 5% of wind farm land area out of crop or pasture production. The report did not assess the huge offshore wind site potential which is currently the main focus of development by European countries. It seems that wind power could satisfy total world energy needs given this potential. Renewable energy system planners propose wind power as the generating source for grid electricity and hydrogen fuel, with solar cells used to power off-grid electric applications.
Denmark leads the world in the share of its electricity from wind: 20%. It is also the world’s leading manufacturer and exporter of wind turbines. In December, 2006, the Danish energy and environmental agencies reported the results of their eight-year study of the Horns Rev and Nysted offshore wind farms’ impacts on the aquatic ecosystem including birds, fish, seals and life found on the seabed. The study found the projects “operate in harmony with the surrounding environment,” and the Danish government announced plans to double the size of both wind farms. Denmark expects to increase the share of renewable energy in the national energy portfolio to 50 percent by 2025, with the majority from wind turbines.
At 12,000 megawatts Germany had the world’s greatest wind-generation capacity as of 2003. By the end of 2003 Germany surpassed its goal of 12,500 megawatts of wind-generation capacity it had planned to reach by 2010. For Germany and other European countries, development of wind power is a national priority in order to meet national carbon emission reduction goals. Germany’s goal is to reduce its carbon emissions 40% by 2020.
The United Kingdom accepted bids for sites to develop 1,500 megawatts in April, 2001, and an additional 7,000 megawatts of wind-generating capacity in December, 2003. $15 billion will be invested in these wind farms off the east and northwest coasts of England, the north coast of Wales, and in the shallow waters of the Thames estuary. When built, one-sixth of residential electricity in the U.K. will be generated by wind. The 1,000 megawatt London Array will supply a quarter of London’s energy needs, and cost $2.7 billion to install - almost the same as the cost the nuclear energy industry claims 1,000 megawatts nuclear reactors would cost in the U.S. (actual costs always come in far higher for nuclear plants built here), without any of the nuclear waste stream costs or problems. The French are developing 4,000 megawatts of wind production capacity, following major investments by the Netherlands and Belgium.
Overall Europe’s wind-generating capacity is planned to expand from 28,400 megawatts in 2003 to 75,000 megawatts in 2010 and 180,000 megawatts in 2020. By 2020 wind energy will be satisfying the electrical needs of 195 million Europeans, half the European Economic Union’s total population. A 2004 assessment of Europe’s offshore wind-generation capacity by Garrad Hassan wind energy consulting group concluded that aggressive development of vast offshore resources could supply all of Europe’s residential electricity needs by 2020.
In fact, global wind electricity-generating capacity increased by 24 percent in 2005 to 59,100 megawatts. In 1995, world wind-generating capacity stood at less than 5,000 megawatts. Wind is the fastest-growing energy source with an average annual growth rate of 29 percent from 1995 to 2005. In the same ten years, coal use grew 2.5 percent, nuclear power by 1.8 percent, natural gas by 2.5 percent, and oil by 1.7 percent average per year.