In recent years, the growth of capacity to generate electricity from wind energy has been extremely rapid, increasing from 1,848 megawatts (MW) in 1998 to 11,603 MW in the United States by the end of 2006 (AWEA 2006a). Some of that growth was fueled by state and federal tax incentives (Schleede 2003), as well as by state renewable portfolio standards and targets. Despite that rapid growth, wind energy amounted to less than one percent of U.S. electricity generation in 2006. To the degree that wind energy reduces the need for electricity generation using other sources of energy, it can reduce the adverse environmental impacts of those sources, such as production of atmospheric and water pollution, including greenhouse gases; production of nuclear wastes; degradation of landscapes due to mining activity; and damming of rivers. Generation of electricity by wind energy has the potential to reduce environmental impacts, because unlike generators that use fossil fuel, it does not result in the generation of atmospheric contaminants or thermal pollution, and it has been attractive to many governments, organizations, and individuals. But others have focused on adverse environmental impacts of wind-energy facilities, which include visual and other impacts on humans; and effects on ecosystems, including the killing of wildlife, especially birds and bats. Some environmental effects of wind-energy facilities, especially those concerning transportation (roads to and from the plant site) and transmission (roads and clearings for transmission lines), are common to all electricity-generating facilities; others, such as their specific aesthetic impacts, are unique to wind-energy facilities. This report provides analyses to understand and evaluate those environmental effects, both positive and negative. Like all sources of energy exploited to date, wind-energy projects have effects that may be regarded as negative. These potential or realized adverse effects have been described not only in the MidAtlantic Highlands (MAH) (Schleede 2003) but also in other parts of the country, such as California (CBD 2004) and Massachusetts (almost any issue of the Cape Cod Times, where the proposed and controversial wind-energy installation in Nantucket Sound is discussed).
GENERATING ELECTRICITY FROM WIND ENERGY
Total installed U.S. wind-energy capacity: 11,603 MW as of Dec 31, 2006. Source: American Wind Energy Association 2007. Reprinted with permission; copyright 2007, American Wind Energy Association.
Two percent of all the energy the earth receives from the sun is converted into kinetic energy in the atmosphere, 100 times more than the energy converted into biomass by plants. The main source of this kinetic energy is imbalance between net outgoing radiation at high latitudes and net incoming radiation at low latitudes. The global temperature equilibrium is maintained by a transport of heat from the equatorial to the polar regions by atmospheric movement (wind) and ocean currents. The earth’s rotation and geographic features prevent the wind from flowing uniformly and consistently. The kinetic energy of moving air that passes the rotor of a turbine is proportional to the cube of the wind speed. Hence, a doubling of the wind speed results in eight times more wind energy. Thus, the amount of air that passes through the rotor plane of a large wind turbine is sizable.
A modern 1.5 MW wind turbine with a hub height (center of rotor) and tower height of 90 meters, operating in a near optimum wind speed of 10 m/sec (36 km/h) at hub height will create more than 1.4 MW of electricity; in eight hours it will produce the amount of electricity used by the average U.S. household in one year (about 10,600 kilowatt-hour [kWh]). There is an upper theoretical limit (the Betz limit of 59%) to how much of the available energy in the wind a wind turbine can actually capture or convert to usable electricity. Modern wind turbines potentially can reach an efficiency of 50%. Almost all wind turbines operating today have a 3-bladed rotor mounted upwind of the hub containing the turbine. The blades have an aerodynamic profile like the wing of an aircraft. The force created by the lift on the blades result in a torque on the axis; the forces are transmitted through a gearbox, and a generator is used to transform the rotation into electrical energy, which is then distributed through the transmission grid (Figure 1-3). Human use of wind energy has a long history (the following summary is taken from Pasqualetti et al. 2004). Wind energy has been used for sailing vessels at least since 3,100 BC. Windmills were used to lift water and grind grain as early as the 10th century AD.
The first practical wind turbine was built by Charles Brush in 1886; it provided enough electricity for 100 incandescent light bulbs, three arc lights, and several electric motors. However, the turbine was too expensive at that time for commercial development. By the 1920s, some farms in the United States generated electricity by wind turbines, and by the 1940s wind turbines sold by Sears Roebuck and Company were providing electricity for small appliances in rural American homes; in Denmark, 40 wind turbines were generating electricity. The first wind powered turbine to provide electricity into an American electrical transmission grid was in October 1941 in Vermont. However, significant electricity generation from wind in the United States began only in the 1980s in California. Today (2006), it amounts to less than 1% of U.S. electricity generation. There has been a rapid evolution of wind-turbine design over the past 25 years. Thus, modern turbines are different in many ways from the turbines that were installed in California’s three large installations at Altamont Pass, Tehachapi, and San Gorgonio (Palm Springs) in the early 1980s.
A typical turbine structure consists of a pylon (tower or monopole) that can produce electricity at wind speeds as low as 12-14 km/h (3.3 – 3.9 m/sec). Generators typically reach peak efficiency at wind speeds of approximately 45 km/h (12.5 m/sec) and shift to a safety mode when the wind exceeds a particular speed, often on the order of 80-100 km/h (22 – 28 m/sec). Smaller generators are used for individual buildings or other uses. This report is concerned with utility-scale clusters of generators or wind-energy installations (often referred to as “wind farms”), not with small turbines used for individual agricultural farms or houses. Some of the utility-scale installations contain hundreds of turbines; for example, the wind-energy facility at Altamont Pass in California consists of more than 5,000 and those at Tehachapi and Palm Springs contain at least 3,000 turbines each, ranging from older machines as small as 100 kW installed more than 20 years ago to modern turbines of 1.5 megawatts (MW) or more (information available at www.awea.org). Adverse effects of wind turbines have been documented: a recent Final Programmatic Environmental Impact Statement (DPEIS) (BLM 2005a) lists the following: use of geologic and water resources; creation or increase of geologic hazards or soil erosion; localized generation of airborne dust; noise generation; alteration or degradation of wildlife habitat or sensitive or unique habitat; interference with resident or migratory fish or wildlife species, including protected species; alteration or degradation of plant communities, including occurrence of invasive vegetation; land-use changes; alteration of visual resources; release of hazardous materials or wastes; increased traffic; increased human-health and safety hazards; and destruction or loss of paleontological or cultural resources. These impacts can occur at the various stages of planning, site development, construction, operation, and decommissioning or abandonment (if applicable), although different phases tend to be associated with different impacts. Any or all of the impacts have the potential to accumulate over time and with the installation of additional generators.
Beneficial environmental effects result from the reduction of adverse impacts of other sources of energy generation, to the degree that wind energy allows the reduction of energy generation by other sources. This committee’s task includes an evaluation of the importance and frequency of these effects. The killing of bats and birds has been among the more obvious and objectively quantifiable effects. Birds can be electrocuted along transmission and distribution lines or killed by flying into them (Bevanger 1994; Erickson et. al. 2001, 2002; Stemer 2002). Thousands of birds die each year from collisions with wind-energy installations (BLM 2005a). The Altamont facility in California has caused the deaths of many raptors, which were members of protected species (CBD 2004; BLM 2005a). Several species of bats in North America also have been reported killed by collisions with wind-energy installations (Johnson 2005; Kunz et al. in press a). There were no fatalities of federally protected bat species known to this committee at this writing (early 2007).
Another widely cited impact of wind turbines is their visible effect on view sheds and landscapes. The scale of modern turbines makes them impossible to screen from view, often making aesthetic considerations a major basis of opposition to them (Bisbee 2004). Well-established systematic methods for evaluating aesthetic impacts are available (Smardon et al. 1986; USFS 2003), but they often are misunderstood or poorly implemented, and they will need to be adapted for assessing the unique attributes of wind-energy projects. Methods also are available for identifying the particular values and sensitivities associated with recreational and cultural resources, as discussed in Chapter 4. The regulatory system for siting and installing wind-energy projects in the United States varies widely, from a fairly thorough process in parts of California to much less rigorous processes in some other states (GAO 2005). In California, as well as in other states, the processes for evaluating and regulating wind-energy installations are evolving. In many areas of the United States, wind-energy installations have been controversial, sometimes strongly so.