29 February 2012

A Brief Introduction to Offshore Wind Power

This post aims to provide a broad-brush primer on the development of offshore wind projects in the U.S. and is the first of a two-part series. In the second post, I’ll explore in more detail the nascent proposal for a large wind farm off the coast of Maryland.

Among the alternative methods of power generation that this country and others are looking to develop to increasingly supplement traditional carbon-based energy sources like coal and petroleum, wind power has emerged as somewhat of a darling. Conceptually, it is perhaps the most straightforward to grasp. After all, we’ve been using wind for millennia to power boats, mills and pumps, among other tools. Just hoist some sails, wait for the breeze to pick up, and you’re off and running (or sailing, milling, pumping, etc.).

A wind farm in Texas.
(Image in public domain obtained
via Wikimedia Commons)
Wind-generated power is also, at first glance, not as fraught with some of the controversies that afflict other technologies. The fuel supply (i.e., the wind itself) is endless, free and doesn’t have to be mined or processed. Given that no exhaust or hazardous waste is produced and that, according to most studies, wind turbines don’t substantially affect local ecologies (at least relative to other man-made creations like dams, power lines and tall buildings), there appears to be little negative impact on the environment.

So why aren’t wind turbines being thrown up left and right across the country to help us along the path to energy security? Well, to some extent, they are. If you’ve driven through the right parts of California, Texas or the upper Midwest in the last few years, you’ve undoubtedly noticed. According to data (pdf) from the U.S. Energy Information Administration, wind energy consumption increased by 350 percent from 2006 to 2010, from 0.264 to 0.924 quadrillion btu (7.74 x 1010 to 2.71 x 1011 kilowatt-hours). Over the same period, wind’s contribution to our total national energy consumption, though still fairly meager, increased from about one quarter of a percent to almost 1 percent.

Existing wind power generating capacity across the U.S.
(Image from U.S. Energy Information Administration)
Of course, there are reasons why these numbers haven’t grown even higher yet. The inconsistency of wind speed with geography and time means that electricity generation varies significantly with location and with the time of day and year. Thus, some locations (e.g., parts of California, Texas and the upper Midwest, etc.) are better suited than others. And even at their best, wind turbines suffer from inherently limited efficiency (capped at 59.3 percent according to Betz’ law) and typically do not operate near full capacity (capacity factors in the ballpark of 30 percent). In order to make wind-generated electricity viable on a large scale, wind farms must have large footprints, stretching on for many tens of square kilometers (although the land beneath turbines is often still available for other uses such as agriculture or grazing). Concerns about aesthetics also sometimes accompany the large size of these farms, not to mention the size of the turbines themselves.

Nameplate generating capacity of existing offshore wind projects
by country as of 2010. (Figure extracted from National Renewable
Energy Laboratory Technical Report NREL/TP-500-40745)
Since a handful of European countries (notably Denmark and the U.K.) began deploying turbines at sea two decades ago, the prospect of harnessing offshore wind has become increasingly popular as a solution to some of the limitations of land-based wind farms. Though untested as yet, offshore wind production offers potential benefits beyond land-based production for the U.S. as well.

Foremost is the size of the resource. Offshore winds are higher velocity and more consistent on average compared to winds over land, leading to higher and more consistent power yields. With fewer concerns about noise pollution at sea, turbines could be designed to rotate at higher velocities, again leading to higher yields. Additionally, the U.S. is blessed with a prodigious coastline, meaning a large prospective area across which turbines could be deployed. The National Renewable Energy Lab has estimated that the U.S.’s gross offshore wind resource (out to 50 nautical miles from shore) is more than 4,000 gigawatts, about four times the country’s current electrical generation capacity. While development of the vast majority of the offshore area included in this estimate is unrealistic (at least in anything resembling the near term) due to a host of environmental considerations, technical constraints and conflicts with shipping and commercial interests, the upshot, as NREL concluded in its 2010 assessment of offshore wind prospects (pdf), is that the size of the resource is not a limiting factor.
U.S. offshore wind resources extending 50 nautical miles from shore at 90 meters height. A minimum wind speed of 7 meters per second is typically considered necessary for potential development. (Figure created by National Renewable Energy Laboratory and retrieved from www.windpoweringamerica.gov/windmaps)
Rather, technological, financial and regulatory issues are the most significant barriers to development of offshore wind. Existing technology for offshore wind power limits the depth at which turbines can be constructed to about 30 meters of water, thus ruling out large expanses of coastal waters (particularly off the west coast where the sea floor drops rapidly with distance from the shoreline) until deeper-water technologies are ready. Accompanying the present technological shortcomings are the myriad operational and engineering difficulties that come along with constructing and maintaining turbines in the rough and tumble (and corrosive) sea. Hence, the up-front costs of large-scale offshore wind farms — think multi-billion dollar projections — are quite high for developers and financiers. Lastly, the lack of regulatory experience for offshore wind projects in the U.S. also promises to slow permitting processes, which could stretch to 7 to 10 years in the NREL’s estimation.

Nonetheless, a handful of states, predominantly in the northeast and mid-Atlantic, already have projects in the regulatory pipeline or are considering proposed projects off their coastlines. Initiated in 2001, the Cape Wind project seeks to install 130 turbines off Massachusetts’ Cape Cod at an estimated cost of $2.5 billion and is the first project to have cleared regulatory permitting hurdles at the local, state and federal levels. With an expected capacity of more than 400 megawatts, Cape Wind could potentially meet the electricity needs of the majority of Cape Cod, Nantucket and Martha’s Vineyard. Beset by controversy from the beginning stemming from its proposed location and cost, however, its developers still face legal challenges and construction has yet to begin.
Proposed offshore wind projects (and their capacities) that have made "significant progress in the U.S. permitting process" as of 2010. (Figure extracted from National Renewable Energy Laboratory Technical Report NREL/TP-500-40745)
Beyond Massachusetts, New Jersey leads the way with progress toward developing offshore wind. The total nameplate capacity of four proposed projects off the Garden State’s coast is 1050 megawatts, according to NREL’s 2010 report, and in August 2010 Governor Chris Christie (R) signed a bill aimed at fostering offshore wind by providing financial incentives to developers.

Despite ongoing uncertainty over federal financial support, as well as mixed support in their own legislatures and electorates, several other states are also continuing their push for offshore wind. These efforts are, in part, driven by necessity owing to state laws mandating increased production and use of renewable energy in the coming years.

In Maryland, for example, the state's Renewable Energy Standard requires that renewable energy account for 20 percent of the state’s electricity by 2022, and offshore wind is viewed as a crucial step by Governor Martin O’Malley (D). However, his introduction of a bill in 2011 that sought to facilitate a large-scale offshore wind project met with significant opposition in the state legislature, chiefly because of concerns that residential and commercial consumers’ electric bills would be increased significantly to fund the project. Having evidently retooled his plan to address this and other concerns, O’Malley has reintroduced an offshore wind bill in Maryland.

In my next post, I’ll explore Maryland’s proposed plan for offshore wind, with an emphasis on the physical scope of the project and how much it could potentially contribute to the state’s energy needs.


- Schwartz, M. et al. (June 2010) Assessment of Offshore Wind Energy Resources for the United States (Technical Report NREL/TP-500-45889), National Renewable Energy Laboratory, retrieved February 29, 2012. (pdf)

- Musial, W. and Ram, B. (September 2010) Large-Scale Offshore Wind Power in the United States (Technical Report NREL/TP-500-40745), National Renewable Energy Laboratory, retrieved February 27, 2012. (pdf)

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