RMI has long advocated for an energy future based on energy efficiency and renewable resources. With 50 percent of today’s U.S. electricity serviced by carbon intensive coal, the magnitude of the transformation required to shift to a no-carbon electric system can seem, at the least daunting, and at the worst, impossible.
When constructing a vision and road map for a fossil-free U.S. electricity sector, the first questions are obvious: Technically, do we have enough renewable resources to power a growing U.S. economy now and in the future? Equally important, can we harness that energy with today’s technologies and rapidly begin this needed transition?
A closer look into recent assessments of the fastest-growing renewable energy source in the U.S., wind power, provides an excellent case study for our promising future.
Wind Power in the United States
U.S. wind power has grown at a staggering pace by any measure. Over the last decade, U.S. wind capacity grew 1,300 percent, from 2,500 MW to 35,000 MW. For perspective, that’s one third of the nuclear capacity in the U.S. In 2008 and 2009, wind accounted for 42 percent and 39 percent, respectively, of all new electric generating capacity during those years. Thus, in the U.S., wind was second only to natural gas as the fastest growing generation source by capacity.
As a source of energy, wind’s contribution provided about 71 million MWh in 2009, the estimated equivalent of about 6.5 million homes, or about 1.8 percent of the U.S. electricity consumption. While less than 2 percent of U.S. electricity generation may seem like a trivial amount, consider that only five years ago all of the non-hydro renewable generation in the U.S. accounted for approximately the same amount.
Today, non-hydro renewable electricity has increased to approximately 3.6 percent, whereas coal has decreased from 48 percent to 45 percent of U.S. electricity generation. In six states, the annual average electricity share from wind is over 5 percent. In Iowa, the state’s electricity mix is almost 15 percent wind.
Wind power’s dominance as the preferred renewable energy source to meet expanding renewable portfolio standards can be attributed to several key factors.
First, since the late 1990s, wind has been one of the most price-competitive renewable energy sources on the market (an average of $0.04/kWh with tax credits), as a result of installed cost reductions and turbine performance improvements.
Second, in 1992 the Energy Policy Act in 1992 established a federal production tax credit of $.015 (adjusted for inflation)—which has been erratically renewed by Congress since. Third, the U.S. has excellent wind resources, both in terms of capacity and energy availability across large sections of the country.
Just How Much Wind?
In 2008, a consortium of the Department of Energy, the National Renewable Energy Lab, Black & Veatch and wind industry experts, conducted research to understand the potential for a high penetration of U.S. wind energy. Published in May 2008, the report, “20% Wind Energy by 2030: Increasing Wind Energy’s Contribution to US Electricity Supply” found that the nation has more than 8,000 GW of available land-based wind resources that can be captured economically(1). For perspective, the U.S. economy’s peak annual demand is approximately 4,000 GW (4 TW) (2). This vast potential was estimated at 50-meter hub height(3), or the height of typical turbines installed in the late 1990s and early 2000s.
Size and Height Really Do Matter
Following the trends of the last decade, wind turbines have continued to increase in size, in terms of swept area and in height. Today’s modern turbines regularly approach hub heights of 80-meters to 100-meters, which has a significant impact on wind energy potential.
Typically, the higher the altitude, the faster the speed of the wind. Intuitively, it makes sense that a faster wind speed will generate more energy, all else being equal. However, the impact is not simply linear.
The amount of energy that can be extracted from wind increases with the cube of the wind speed. In other words, a 10 percent increase in wind speed equates to 33 percent increase in available energy. This phenomenon has important implications when considering the energy production of a wind turbine. At hub heights of 80 meters and 100 meters, U.S. wind capacity potentials actually increase dramatically.
In February 2010, new resource maps and estimated wind capacity and energy potentials were released through a collaborative project between NREL and AWS Truewind, LLC. These new potentials modeled wind speeds at modern turbine heights of 80 meters and 100 meters.
At gross capacity factors(4) of greater than 30 percent at 80-meter hub heights, there is almost 10,500 GW of capacity, corresponding to about 37 million GWh per year. Figure 1 shows the predicted mean annual wind speeds at 80-m height. At 100-meter hub height, that estimate jumps to 12,000 GW and nearly 45 million GWh. Again, to put this in perspective, the current annual U.S. electricity consumption is 4 million GWh. Thus, at 100-meter hub height, the developable wind potential of the U.S. is over 10 times the amount of electricity we demand annually.
Capturing the Technical Potential
The tremendous technical potential of wind provides unequivocal support that the U.S. has more than enough homegrown resources to power a no-carbon electric system.
The challenge is ensuring that we have the infrastructure, knowledge and commitment to consistently cultivate, grow and harness the potential that is available for the taking. In this way, wind serves as an excellent example of the promise and the challenges faced by many of the renewable resources that are poised to displace our conventional generation sources that contribute 40 percent of annual U.S. carbon emissions.
Although 2009 was still a good year for wind installations, totaling nearly 10,000 MW, the financial crisis took its toll on the industry. While 39 wind manufacturing plants were expanded, announced or opened, that was a decline of 33 percent over 2008, in which 58 new or expanded plants were announced. Wind turbine manufacturers experienced light turbine orders, which is providing a great deal of uncertainty for 2010 and 2011.
Additionally, the variable nature of wind (and other variable generation sources such as solar) poses challenges to the conventional protocol used in operating current electric systems. These grid integration challenges will become increasingly important to address with many of the known and emerging strategies that will make the transition more cost-effective and efficient.
A Credible Roadmap
The need for vastly increasing the penetration of wind and other non-carbon resources on the U.S. electric grid underscores the need for a roadmap that provides foundation and checkpoints for consistent growth.
RMI’s Next-Generation Utility and Reinventing Fire™ initiatives have taken on this challenge to define what is possible—technically and economically—and create a viable roadmap that could make that vision achievable.
With NGU, RMI intends to complement the efforts by NREL and others to examine the renewable resources, such as wind, and identity specific needs and outcomes in markets, policy and technology to “get there from here.”
As RMI Chief Scientist Amory Lovins has said, we need to “imagine… the world we want to create…” RMI recognizes the importance of establishing the end state vision for our clean energy future. Creating that vision is not merely an exercise in creativity but one that must be rooted in robust data, rigorously analyzed and clearly articulated.
Virginia Lacy is a senior consultant with RMI’s electricity practice.
(1) To estimate wind energy potential, NREL developed high-resolution surveys of the “available” windy land area after excluding non-developable land, such as urban areas, wilderness areas, parks, and water features. Installed capacity estimates are derived using a potential rated capacity that could be installed on the available windy land area. NREL assumed a reasonable installed nameplate capacity of 5 MW per km2.
(2) These numbers are not directly comparable and should not imply that wind could meet all of U.S. demand due to the variable nature of wind availability. To fully capture the power contribution of the wind resource to power demands requires an understanding of the time of availability of the resource.
(3) Hub height is the distance from the ground to the rotor of a wind turbine.
(4) Gross capacity factors do not include losses, which are estimated about 15% depending upon the turbine and additional factors.
--Published June 2010