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By Jeff Deyette
Wind power has come a long way from the windmills used throughout rural America in the early twentieth century. Ever since the energy crisis of 1973 first spurred government funding for renewable energy development, the U.S. wind industry has achieved remarkable advances in technology, cost reduction, and market growth.
The United States reached a wind energy milestone earlier this year: 10,000 megawatts (MW) of total generating capacity, or enough to power more than 2.5 million homes. Nevertheless, if we are to meet our growing energy needs and avoid the most dangerous consequences of global warming, we must substantially increase our level of investment in wind and other forms of clean energy. Fortunately, new technologies and policies are evolving to take full advantage of wind’s potential.
Standing Tall
One of the most effective advances the industry has developed for increasing the output and reducing the costs of electricity generation is building larger turbines with longer blades and placing them on taller towers. A wind turbine’s generating potential is largely determined by wind speed and rotor swept area, or the total area covered by the blades as they spin. Because the power output from a turbine increases as a function of wind speed cubed (i.e., a doubling of wind speed increases power output by a factor of eight), the higher-speed winds typically found at greater heights can generate far more electricity than low-speed winds near the ground.
In addition, a larger rotor swept area increases the amount of energy that can be captured. For example, a 50-kilowatt wind turbine with a rotor diameter of 15 meters was considered large in the 1980s, but today’s land-based wind turbines generate 30 times as much electrical output (1.5 MW) with a rotor diameter only five times larger (77 meters).
This increase in size has created some challenges. For example, larger, longer components are more costly to transport and require special cranes to assemble. In addition, the larger machines operate at higher capacity for more hours per year, increasing wear and tear on turbine components. While great strides have already been made in improving long-term durability, the industry continues to explore new techniques and materials. Some of the recent (and potential) improvements include:
Blades. Today’s turbine blades are primarily made of fiberglass, with carbon fibers included to provide additional strength. Carbon-based or carbon/glass hybrid materials would make blades lighter but stronger. In addition, advanced blade designs that allow blades to adjust to very strong winds by bending and twisting would reduce stress on the rotor.
Power converters. A turbine must produce electricity at the proper voltage and frequency to enter the electrical grid. Older turbines accomplish this by operating at a fixed speed (a braking mechanism prevents the blades from spinning faster), but this technology fails to take advantage of the energy potential of higher-speed winds. Variable-speed turbines, on the other hand, allow the blades to rotate at speeds that better match varying wind conditions, while sophisticated internal power controls compensate for fluctuations in electrical output.
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Tubular towers (right) are less expensive to
assemble than older lattice-style towers
(left) and are safer for birds. | Towers. Tubular towers are a vast improvement over older lattice-style towers because they are less costly to assemble and maintain and have reduced bird deaths by eliminating potential landing and nesting perches. But with the average tower measuring 200 feet or more in height, turbine assembly and repair is an expensive operation. One solution under investigation is a “self-erecting” tower that would allow workers to assemble the turbine close to the ground and raise it using hydraulic lifts. Another option is installing a small crane that would run on tracks up and down the length of the tower.
Growing Pains
Though the U.S. wind industry continues to expand at a rapid pace, the cost of developing a wind power project has actually increased over the past 18 months, in some cases significantly. The uncertainty of federal production incentives has deterred manufacturers from building assembly plants in the United States, requiring most turbines to be imported, and foreign-made turbines have become more expensive as the value of the U.S. dollar has fallen. At the same time, high global demand has caused most turbine manufacturers to sell out through 2008, and the cost of steel and other materials has risen sharply due mostly to higher fossil fuel prices. Other factors include the difficulties associated with using more sophisticated electronic components and increased profit margins by manufacturers.
Fortunately, none of these obstacles are insurmountable. Higher fossil fuel prices have driven up the cost of conventional power generation, enabling wind power to remain cost-competitive. Additional support for wind power in the form of a sound long-term federal energy policy would reduce uncertainty in the U.S. market and stimulate domestic manufacturing, increasing turbine supplies. Maintaining a strong national commitment to research and development will also help. For example, researchers are now exploring the possibility of incorporating concrete or composites into tower design, limiting the amount of steel needed.
The Next Generation
Two exciting new technologies hold out the promise of consistent growth for the wind industry in the coming decades: turbines that can be set in deep offshore waters, and land-based turbines that can operate cost-effectively at lower wind speeds. Tapping into the superb wind resources located far offshore will require advances in floating platform foundations, anchoring systems, and transmission technologies. For land-based turbines, generating electricity at low wind speeds will likely require even taller towers (to reach altitudes with stronger sustained winds), longer blades, and more efficient mechanical components and electronics.
It should also be noted that just as technology has not been solely responsible for wind power’s success, nor is it the only factor affecting the industry’s future. Federal and state regulations and tax incentives, for example, have helped spur the development of new wind resources since 1978. The federal production tax credit, currently extended through 2007, provides a 1.8 cents per kilowatt-hour incentive for the first 10 years of a wind turbine’s life. And 20 states require utilities to gradually increase the amount of renewable energy in their supply mix.
For generations, federal and state policies and incentives have supported fossil fuel exploration and development. Now that the urgency of addressing global warming has become clear, common sense dictates that we begin to shift a greater share of this support to a renewable resource such as wind, which has proven itself a reliable and affordable clean energy solution. Increased public and policy support can ensure this resource plays its proper role in ending our national dependence on fossil fuels and reducing the threat of global warming.
Jeff Deyette is an analyst in the Clean Energy Program.
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