The US Department of Energy (DOE) and several wind turbine developers anticipate an increase in the use of wind power given rapid advancements in turbines that can produce energy from low-speed wind. These turbines are designed for regions where the wind blows at 13 miles per hour or less, too slow for conventional equipment.

"It is a big, if not the biggest, thrust of wind design and research these days—to optimize turbines for low wind speed," says John Chinook, principal engineer of Chinook Wind, an Everson, WA, consulting firm.

Why the push to develop this new technology? The United States has vast areas that are windy, but not quite windy enough, particularly in the Great Plains from central and northern Texas to the Canadian border, many coastal areas, and the shores of the Great Lakes. In fact, the DOE estimates that wind developers will find they have 20 times more available land once the new turbines become cost-effective.

The country needs to tap into these sites if wind energy is to achieve widespread penetration and reach the ambitious goals set by the DOE. Right now, the United States produces about 6,400 megawatts of electricity from wind, less than 1% of the nation's electric supply. By 2020, the DOE wants to increase production to 100 gigawatts, about 6% of supply.

The federal agency has undertaken two programs to develop new turbines for low-speed wind sites: one focuses on large utility-scale wind farms that tie into the grid, while the other concentrates on smaller projects that can be used as distributed generation.

"We're working to improve the technologies over time so that they are cost-effective at lower- and lower-wind-speed sites," says Alan Laxson, principal project manager at the DOE's National Renewable Energy Laboratory (NREL).

The goal is to bring down the cost of generating electricity in sites designated as Class 3 and 4. (There are seven wind classes that identify the generalized distribution of the wind in an area. See table.) For large-scale wind farms, that means reducing costs from $0.05 to $0.06 per kilowatt-hour to $0.03 per kilowatt-hour by 2010 in Class 4 sites.

Economies of scale naturally make smaller distributed energy turbines more costly. By 2007, the DOE wants to see systems of 100 kilowatts or less generating power at $0.10 to $0.15 per kilowatt-hour in Class 3 wind sites, which is the current cost of using the technology in windier Class 5 sites. Wind turbines that generate 11 to 100 kilowatts are typically used by commercial and industrial energy users; smaller units are built for households. The federal agency has dispersed about $7 million in grants so far for work on reducing technology costs, and it expects to issue a solicitation for a new round of funding before the year is out.

It's not that the United States lacks high-speed wind sites. In fact, the country has enough good wind sites to produce one and a half times the electricity it consumes. However, many of the best spots—considered Class 6—are on mountains or ridgelines, or they are far away from where the power is consumed. In fact, Class 6 sites tend to be about 500 miles away from load centers on average, while Class 4 sites are only 100 miles away, according to the NREL. Placing wind generators closer to energy users is important because it can be difficult and expensive to move energy hundreds of miles over the nation's overtaxed transmission system.

The DG Advantage

Wind farms face particular transmission problems because the Federal Energy Regulatory Commission (FERC) issues penalties against power generators that cannot predict their output 24 hours ahead of time, a task that is difficult for a wind generator. Issued in 1997 as part of the FERC's Order 888, the rule was aimed at keeping an orderly flow of power across the transmission grid. It was written with fossil fuel plants in mind. Since their fuel supply—coal, oil, or gas—is consistent, fossil fuel plants can generally control their hours of operation and forecast their output. But this is not so with a wind turbine, since its fuel, the wind, cannot be transported by train, truck, or pipeline and delivered at the power plant on demand, but blows at random times and speeds. Wind turbines produce energy only when there is wind, so 24-hour predictions are nearly impossible to make. Wind farms can avoid the penalty by obtaining an exemption to the FERC rule, but the process is costly and can take as long as two years.

Distributed generation (DG) wind turbines can avoid the transmission problems that beset utility-scale wind farms, since they can be built where the power is needed and do not need to traverse miles of high-voltage transmission lines. As a result, such systems are expected to provide cost-effective renewable energy for remote businesses, commercial buildings, isolated telecommunications systems, ranches, out-of-the-way housing developments, and commercial and industrial enterprises that are grid-connected but seek independent backup supply. In third world countries, the technology may bring energy to off-grid villages that still lack electricity—nearly one-quarter of the world. Small wind turbines also are expected to replace diesel-fueled electricity in some Alaskan towns, where diesel has proven troublesome because of tank leakage, delivery problems, and air emissions.

The United States is particularly well poised to pioneer DG wind, since it is a major international manufacturer of small wind turbines, those that produce less than 100 kilowatts per year. The American Wind Energy Association (AWEA) foresees the United States' $20 million small-wind-turbine industry booming in coming years, spinning off growth in related industries, including composite products, steel, towers, power electronic equipment, and construction. The foreign market for small turbines is expected to reach 212,000 megawatts by 2020. Such growth will spur high-volume manufacturing that could reduce the cost of small wind machines by 15%–30%, according to the AWEA.

"With all of these machines, there is believed to be a substantial international market across this whole size range," says Trudy Forsythe, an NREL senior engineer for small-turbine development.

How much power might small wind turbines contribute to the US supply portfolio? The AWEA wants to see 50,000 megawatts developed by 2020, about 3% of the nation's electric supply. The number could go far higher, however, given that the United States has a 140,000-megawatt potential market for small wind. Geographically, 60% of the country has enough wind to power small turbines and 24% of the population lives in rural areas where zoning rules favor their installation.

The Bergey Windpower XL.50 Pre-Prototype in fully furled position (manually furled)

Of particular appeal are states that have incentives to bring DG wind costs lower than even the DOE envisions. For example, 35 states now require that utilities offer net metering, which spins the meter backward when the consumer's electrical output exceeds consumption, in essence banking electricity at retail rates for future use by the consumer. Several states also offer various buydowns, tax credits, and self-generation incentives. California, for example, offers a 7.5% tax credit for installing wind turbines and a $0.90-per-watt rebate.

Reaching Skyward

But it will be technology that ultimately determines the success of low-speed wind energy. Two key ways exist to capture more energy from wind: create bigger blades or erect a higher tower to reach up to where the wind blows stronger. While this may sound like a relatively easy task, it is not. Engineers must consider turbulence, wind sheer, air density, and several other factors to get the correct height and size for the proper wind speed. Too much wind can destroy the machine; too little and the turbine is not cost-effective.

"To generate energy at lower cost at these low-wind-speed sites you have to be more efficient and more innovative," says Amir S. Mikhail, president of the technology group at Clipper Windpower Inc., a Carpinteria, CA, company that is developing a low-cost, low-wind-speed system with the help of an $8.9 million grant from the DOE.

Wind developers who want to build turbines at windy elevations find construction of the machines difficult. Why? Simply because we lack cranes that reach high enough. To overcome this problem, Valmont Structures, a Valley, NE, company that specializes in steel and aluminum poles and structures, has a patent pending on a self-erecting wind tower. The modular unit operates like a giant elevator that carries the turbines upward.

Wind manufacturers are investigating a wide range of other engineering innovations to accommodate low-wind-speed sites. They include creating lighter rotors and longer blades with a wider sweep, as well as changing blade composites to provide various degrees of stiffness. Energy Unlimited Inc., a West Conshohocken, PA, wind operator, has a patent pending on a new telescopic blade called VariBlade, which can be lengthened when the wind blows slowly and contracted in high winds. The company expects the technology to increase wind energy production by 20%–33%.

Of particular interest to researchers is how taller, lighter units will fare when the wind gusts at high elevations. Durability is equally important to these machines, and to those built closer to the ground on the Great Plains, where turbulent winds, called nocturnal jets, form at night. A great deal of consideration also is being given to noise made by low-wind-speed turbines, since they are likely to be located close to homes and businesses. In addition, the drivetrain, generator, and electronic controllers must also be revamped for low-wind-speed turbines, since their weight and cost play significantly into the effectiveness of the unit. These components make up 25% of the costs of a turbine.

With DOE funding, Bergey Windpower of Norman, OK, has developed a low-noise 50-kilowatt turbine with fiberglass blades that is now undergoing testing. It is designed for either grid connection or standalone applications. Called the XL.50, the variable-speed unit is simple with only three moving parts. The unit has a direct-drive alternator and no gearbox.

Northern Power Systems, a Waitsfield, VT, subsidiary of Distributed Energy Systems Corp., was selected in March to negotiate a DOE cooperative research agreement to develop a 2-megawatt direct-drive wind turbine for low-wind-speed sites. Northern plans to advance the work it's been doing for the last three years for the NREL on a gearless drivetrain and a permanent magnet generator. Should the contract go forward, Northern expects to test the turbine by late 2006 at a low-wind-speed site in the Midwest.

Northern, Clipper Windpower, and Valmont were among 21 businesses and universities that the DOE selected in March for consideration in its four-year $60 million cost-sharing project for low-wind-speed research and development. Others include General Electric Global Research of Niskayuna, NY; Global Energy Concepts of Kirkland, WA; Massachusetts Institute of Technology of Cambridge, MA; Native American Technologies of Lakewood, CO; and the Tennessee Valley Infrastructure Group of Chattanooga, TN.

In addition to advancing turbine technology, some designers are looking at ways to create hybrid systems that combine low-speed wind with other fuels. When the wind does not blow fast enough, the alternative fuel operates the system.

For example, the DOE is investigating wind and hydropower combinations to create a stable flow of electricity. Researchers believe that hydroelectric facilities may be able to act as batteries for wind power by storing water during times of high wind. The federal agency also is looking into coupling wind turbines with hydrogen-generating electrolyzers to create DG systems that produce hydrogen and electricity.

Les Blevins, president of the Advanced Alternative Energy Corporation of Lawrence, KS, has designed a power generator that combines wind energy with biomass. When the wind does not blow, the plant burns biomass to create energy.

Blevins believes this type of system will benefit rural America and be of special appeal to developing countries, which may balk at the idea of constructing expensive wind towers that work intermittently. "Since biomass is dispatchable—you can push a button and make the biomass ignite—it's an ideal way to back up wind or solar, which are not dispatchable," he says.

His design attempts to make use of local steel and wood in third world countries for construction of the turbines and furnaces. The goal is to combine economic development with electricity generation. Blevins envisions a potential job market centered around the harvesting and transport of biomass fuel. For example, in areas of India he sees potential for rural farmers to deliver biomass to the plant and be paid in charcoal, which they can then sell.

Indeed, DG wind energy appears to dovetail well with agriculture in many parts of the world, and has already proved its worth to farmers in Germany and Denmark, according to an NREL study, "Perspectives on an NWCC/NREL Assessment of Distributed Wind." Farmers are accustomed to developing their land to produce a commodity; wind energy is another crop for them.

Technical and Political Obstacles

Still, barriers exist that sometimes make DG wind difficult. Some are technical in nature; others political.

For example, Europe is able to easily accommodate wind projects that connect into distribution lines because they use three-phase lines. In rural America, however, distribution lines are often one-phase, and need to be upgraded at great expense to accommodate DG wind turbines, according to the NREL report.

"However, given the huge rural land mass, distributed wind generation limited to areas with existing three-phase lines could still achieve substantial penetration into the U.S. grid," the report adds.

Another important consideration—perhaps the most important—is how stiff the distribution lines are at the interconnection point. Strong lines can absorb large amounts of intermittent wind power without influencing power quality; weaker or "voltage limited" lines cannot. Unfortunately, a great deal of the US rural distribution system is voltage-limited, according to the NREL.

On the political front, archaic zoning rules sometimes block installation of tall low-wind-speed turbines. Some cities and towns do not allow towers that are taller than 30 to 35 feet, yet they may need to be 65 to 120 feet. The rule dates back to the early 1900s when it was difficult to fight fires in tall structures. Many zoning boards do not know the source of the law and go by the book. "You must educate the zoning board. Sometimes that can be a time-consuming and painful process," Forsythe says. These restrictions are troublesome because, as the AWEA puts it, "putting a wind turbine on a short tower is like putting a solar array in the shade."

The AWEA has published a handbook, Permitting Small Wind Turbines, to help businesses and consumers navigate issues they are likely to face in siting their turbines. As California cases show, wind turbines sometimes come under attack from the local community because of concerns about noise, aesthetics, property values, electronic interference, safety, air traffic, and birds. The AWEA attempts to put these concerns to rest with the facts. For example, the organization notes that a sliding glass door poses more risk to birds than a wind tower. And it cites a 2003 study of 25,000 property transactions, which found wind farms had no systematic impact on property values. The study was conducted by the Washington, DC–based advocacy group, the Renewable Energy Policy Project.

The AWEA has created a model zoning rule for wind towers of up to 100 megawatts. The rule recommends tower heights of no more than 80 feet on half-acre parcels, but sets no limit for larger pieces of land. The organization advises that permitting costs do not exceed 2% of capital costs.

Can low-wind-speed DG overcome political obstacles? The AWEA recommends that proponents educate communities about the benefits of this type of technology, particularly its ability to lessen blackouts, contribute to national security, and reduce dependence on fossil fuels.

Political concerns aside, low-wind-speed technology appears to be poised on the brink of a major expansion with turbine manufacturers stepping up to the plate in assisting the DOE's mission to drive down costs.

Does that mean we may eventually see a wind turbine on every corner? Not likely, says Chinook, since a certain amount of wind speed will always be required. "It's not appropriate to put any wind turbines in a truly low-wind-speed [area]." But he adds that current efforts to develop cost-effective machines for Class 3 and 4 sites are crucial. "For the wind industry to keep growing five or 10 years from now, this is what is needed."

Elisa Wood is a Virginia-based energy writer.

DE - November/December 2004