The wind has been harnessed to provide energy for the last 3000 years, with the first windmill being used to grind grain. Harnessing the wind for the purpose of providing electricity began around the beginning of the 20th century (Ackermann and Söder, 2000). The United States has produced electricity from wind energy since the 1970s (Johnson et al, 2003) and has provided energy for commercial projects since the early 1980s (Erickson et al, 2001).
The International Energy Agency (IEA) estimates there are 40,000 terawatt hours (TWh) per year in potential wind power worldwide (Evans et al, 2009), with the United States being able to produce 10,777 billion kWh annually (AWEA, 2009a). There are currently two types of wind turbines: horizontal axis wind turbines (HAWT) and vertical axis wind turbines (VAWT). HAWTs are the turbines and rotors that are commonly seen today with a rotor attached to a horizontal axis, while the VAWTs are turbines with the rotors attached to a vertical axis (Eriksson et al, 2008). The rotating blades of a wind turbine convert the wind into electrical energy (Herbert et al, 2007). Elevations above 2500 feet are considered to be the best elevations to site a wind turbine due to the wind speed being greater at that elevation (Berry et al, 2005), although successful projects have been installed at lower elevations.
Wind Energy Scope
Level of Activity. In 2005, only 2% of worldwide energy (17,450 TWh) was produced using wind energy technologies (Evans et al, 2009). During that same period, the growth in wind energy generating capacity for the United States averaged approximately 24% (Bird et al, 2005). The next few years continued to see an increase in installed capacity for wind energy. The year 2008 ended with an additional 8,558 megawatts (MW) of installed wind power energy, accounting for 42% of all new electricity generated for the year. This raised the amount to 25,369 MW of cumulative energy being generated by wind projects in the United States, with an additional 80 MW of energy being generated from small wind projects (<100 kilowatts); meaning that wind energy supplied approximately 1.9% of the overall energy consumed for the year (Wiser and Bolinger, 2009). According to the American Wind Energy Association’s second quarter (Q2) market report, 1,210 MW of new wind energy generating capacity was installed during the second quarter, totaling 4,070 MW of new wind power for the first half of 2009. In comparison, approximately 2,900 MW of capacity was installed during the first half of 2008. There is now an installed wind generating capacity of 29,440 MW in the United States with more than 5,000 MW of new wind energy projects currently under construction with an expected completion date in late 2009 or 2010 (AWEA, 2009b).
As of May 2009, there are approximately 304 wind energy projects in operation and development on the east coast stretching from Maine to Florida: 84 projects that are currently operational, 191 proposed projects, 19 projects that are currently under construction and 10 projects that have been suspended. Utility-scale wind power facilities can be found in 35 states, mostly concentrated in the midwestern and western states; east coast states have developed wind facilities primarily along mid-elevation mountaintops and ridges, particularly within the mid-Atlantic region and in New York State (AWEA, 2009b). Currently, there are no operating offshore wind projects in the United States; however, several projects off the east coast (e.g., Cape Wind and South Coast Wind in Massachusetts, Bluewater Wind in Delaware, and Deepwater Wind in Rhode Island and New Jersey) are in the planning stages (Snyder and Kaiser, 2009b).
Offshore wind power projects greater than three nautical miles from shore fall under the jurisdiction of the Department of Interior’s Minerals Management Service (MMS), with the exception of Florida where jurisdiction begins at nine nautical miles (MMS, 2007). The MMS is the agency responsible for leasing and regulating wind energy sites on the Outer Continental Shelf (OCS) including exploration, development, production, and decommissioning. The OCS is a submerged region of the ocean consisting of 1.7 billion acres of Federal jurisdiction lands, beginning three to nine geographical miles off the coastline and extending at least 200 miles to the edge of the U.S. coastal states’ Exclusive Economic Zone (DOI, 2009). In January, 2008 MMS officially established the OCS Alternative Energy and Alternate Use Program, which included the adoption of 52 best management practices (BMPs) to guide development and minimize potential adverse impacts of future projects. The BMPs would be a component of the review process for any renewable energy project proposed under MMS jurisdiction. As of January 2009, the MMS had received applications to develop wind energy projects at four priority lease sites off the coast of New Jersey and one priority lease site off the coast of Delaware (DOI, 2009).
At the federal level, the Department of Interior’s Fish and Wildlife Service (FWS) has the lead role in safeguarding wildlife with regard to construction and operation of wind projects. However, wind energy projects do not always trigger federal reviews and, are often permitted under state and local laws. Most state and local governments require permitting for wind projects before construction begins; these permits usually comply with the local zoning ordinances and building codes (GAO, 2005). Federal review is triggered when the project involves an action by a federal agency, such as when the project is being proposed on federal land, receives federal funds, or triggers a federal permit such as a Section 404 wetlands permit from the Army Corps of Engineers. In these cases, the acting agency must comply with the National Environmental Policy Act (NEPA) and the Endangered Species Act (ESA), among other requirements. Additionally, the Federal Aviation Administration (FAA) requires that approved lighting be placed on all structures above 200 feet, including wind turbines (Federal Aviation Administration, 2000; GAO, 2005).
Over half of the states within the United States have implemented renewable portfolio standards (RPS), which mandate that a certain percentage of generated electricity must come from renewable sources by a specific date (EERE, 2009a). Incentives to wind power include the federal production tax credit (PTC), which provides wind power owners a tax credit of 2.1 cents per kWh for projects becoming commercially operational by the end of 2012 (EERE, 2009b; Snyder and Kaiser, 2009b). The 2009 American Reinvestment and Recovery Act (ARRA) offers owners an investment tax credit (ITC) in place of the PTC which equals 30% of the eligible capital costs of the project and is not dependent upon project completion. Alternatively, project owners can select a Section 1603 cash grant instead of the PTC or the ITC. The cash grant equals 30% of the project’s eligible capital costs and is allocated 60 days after completion; construction must commence by the end of 2010 and be operational by the end of 2012 (EERE, 2009b). The states of Delaware, New Jersey, and Rhode Island have officially encouraged the development of offshore wind facilities to facilitate their RPS and energy policy objectives (DOI, 2009).
Environmental issues. Wind-based energy systems do not need water for cooling, unlike other energy systems such as geothermal, solar, and fossil fuels (Abbasi and Abbasi, 2000). Wind energy is also relatively emissions free and no combustible fuel is used to produce it (Berry et al, 2005). In a study conducted by Evans et al (2009), it was found that wind produces the lowest amount of carbon dioxide (CO2) emissions of all renewable energy sources, averaging only 25g/kWh.
The amount of land used by a wind energy project typically covers only 1-10%, with a footprint of approximately 72 km2/TWh; the remaining land is usually used for agriculture, forestry or recreational purposes (Evans et al, 2009; Fthenakis and Kim, 2009). Offshore winds tend to be stronger and more consistent than land-based winds, meaning that offshore turbines can operate at maximum capacity for a longer period of time (Snyder and Kaiser, 2009a). Significant offshore wind resources exist along the Atlantic Coast, located in close proximity to major coastal cities with extremely high energy demands (Figures 1 and 2; DOI, 2009). Conversely, terrestrial wind energy resources are often far from areas of high electricity consumption, which can necessitate a substantial investment in infrastructure to transport the power generated. However, the development of ocean-based wind energy has technical challenges in addition to higher installation and maintenance costs (DOI, 2009). Offshore turbines require design modifications and enhancements to adapt to the more demanding marine environment and climate conditions. According to the DOI (2009), these modifications include structural upgrades to weather wind-wave interactions, environmental controls to protect components from the corrosive nature of salt water, and access platforms to accommodate navigation and maintenance.
Figure 1. U.S. Night Time Electricity Use Concentrated Along Coastal Areas (DOI, 2009).
Figure 2. Population Density of the Contiguous United States (DOI, 2009).
Future of wind energy. It has been estimated that approximately 4,400 – 6,800 MW of wind energy will be installed throughout the United States in 2009 (Wiser and Bolinger, 2009). The market for small wind projects is also expected to grow 14-25% and it has been estimated that approximately 5,000 MW of energy generated by small wind projects will be installed by 2020 (Marsh, 2008). It is the goal of the Department of Energy to generate 5% of electricity from wind energy by 2020, which means that an additional capacity of approximately 72,000 - 100,000 MW will need to be installed (GAO, 2005; Kunz et al, 2007; Herbert et al, 2007). In June 2009, the U.S. House of Representatives passed the American Clean Energy and Security Act of 2009 (also known as the Waxman-Markey climate and energy bill), which is now awaiting a vote in the Senate. The bill includes a mandatory renewable electricity standard that requires electric utilities to generate 20 percent of their electricity from renewable sources by 2020.
The significant U.S. offshore wind resources could become a substantial energy source, providing a sizable amount of the country's electricity needs. According to the DOI (2009), the gross power potential from U.S. offshore wind resources is estimated at 1993 GW (6,110 TWh/y), assuming a 35% capacity factor of wind turbines. Over 20% of the electricity demands of almost all of the coastal states could be supplied by developing shallow water (< 30 meters) wind resources. Data on electricity usage indicates that coastal states utilize 78% of the nation’s electricity (DOI, 2009).
When compared to other Outer Continental Shelf regions, the Atlantic OCS has the greatest renewable energy potential, with development in the short-term (over the next 5-7 years) most likely focused on offshore wind power. The potential annual wind power resource for the aquatic region between Cape Cod, Massachusetts, and Cape Hatteras, North Carolina is estimated at 330 GW (1,012 TWh/y) under a scenario of a full build-out, which would entail the installation of more than 166,000 turbines spread over 50,000 square miles (DOI, 2009). This estimate also factors in exclusion zones—areas deemed not suitable for development, including major bird flyways, shipping lanes, military restrictions, and major tourism beaches. Currently, the region’s combined energy use is approximately 185 GW, which is derived from electricity, gasoline, fuel oil, and natural gas sources. The full build-out scenario estimate greatly exceeds the region’s combined energy use. Along the Atlantic coast, it is estimated that a significant wind resource of 253 GW (775 TWh/y) exists in shallow waters (< 30 m), which translates into an extractable shallow-water wind resource of 101 GW (310 TWh/y); this is feasible and could be developed and utilized now given the current technology (DOI, 2009). Development of deep-water wind resources is currently challenged and prohibitive due to technology constraints. Future technological advances, such as floating platforms supporting turbines, could allow access to deeper waters far from the coast where the potential wind resources are substantial.
Attempting to estimate the amount of developable ocean-based renewable energy is challenging as many factors must be considered, such as technological constraints, environmental issues, potential space-use conflicts, public opinion, and infrastructure requirements (e.g., transmission capacity, grid connection); the predominant factors regarding development potential are typically related to public sentiment and to policies enacted (or the lack thereof) by local, state, and federal governments (DOI, 2009). Many coastal states are pursing renewable energy projects in the form of offshore wind development, but there are information gaps and uncertainties regarding optimal siting locations, potential environmental impacts, and how to develop and utilize the resource in a sustainable manner. Figure 3 illustrates the possible environmental impacts of offshore wind energy during exploration, construction, and operation (DOI, 2009). Some states are taking proactive measures to determine the most appropriate areas for development by accurately identifying exclusion zones, mapping sensitive habitats, conducting environmental studies, and drafting management plans to facilitate proper site selection and minimize potential impacts (DOI, 2009). Massachusetts is the first state in the nation to develop a comprehensive ocean management plan, with final promulgation of the plan expected in December, 2009 (Massachusetts Executive Office of Energy and Environmental Affairs, 2009).
Figure 3. Possible environmental impacts of offshore wind energy during exploration, construction, and operation (DOI, 2009).