I've Got the Power

Backyard wind turbines turn energy consumers into suppliers

3 min read

Think wind power and you probably imagine multimegawatt-scale wind farms featuring gigantic turbines ­producing power for a few thousand homes. But a handful of companies in the United States would prefer to have each home powered by its own wind turbine.

For years, residential wind power has been a niche ­business, mainly because the turbines designed for this market cost more than many consumers were willing to spend and the units were not efficient enough to match the cost of power from the grid. But now, one company has managed to break the cost barrier with an ­affordable turbine that matches the ­efficiency of commercial wind farm turbines and ­produces power at grid prices.

In August, Southwest Wind Power, a start-up located in Flagstaff, Ariz., began selling a 1.8-kilowatt residential wind turbine dubbed SkyStream 3.7 [see photo, "In My Backyard"]. The tiny power plant sells for US $5100; total cost including installation runs between $8500 and $11 000. By comparison, the installed cost of comparable small wind devices can eclipse $30 000.

While the SkyStream turbine is not meant to wean you from the grid completely, it can trim home electricity bills by 20 to 90 percent, depending on wind velocities, electricity prices, and government incentives in your area.

SkyStream is the first device to be spun out of the U.S. Department of Energy’s Wind Energy Program. The program offers small-turbine makers technical assistance and the use of such facilities as the National Renewable Energy Laboratory Wind Technology Center, in Boulder, Colo., to help them reduce the life-cycle cost of energy generated by small wind-power systems.

”There’s not a device that’s anywhere close to matching [SkyStream’s] target cost in the $8000 range,” says Dennis Lin, a technical manager overseeing the program at the Energy Department. The device benefited greatly, he says, from the company’s having secured several million dollars in venture capital. This allowed Southwest Wind Power to do two things that are luxuries most small wind-turbine makers cannot afford: spend a lot of time optimizing the turbine’s design before creating a prototype and create the molds and tools that are staples of high-volume manufacturing. The result, says Lin, is that as the market takes off, SkyStream’s price will likely fall.

Southwest Wind Power estimates that a SkyStream unit will produce about 100 000 kWh of power during its 20â''year design life. ”Divide, say, $9000 by 100 000 kilowatt­hours, and you end up with [an average energy cost of] 9 cents per kilowatthour,” says Andrew Kruse, Southwest Wind Power’s cofounder and vice president of business development. Although, generally speaking, larger turbines are more efficient at turning the kinetic energy of wind into electrical energy, SkyStream outperforms 50- to 100-kW machines in terms of average cost of energy. Many still come in at 20 cents per kilowatthour or more—far above the DOE target of 10 to 15 cents per kilowatthour.

SkyStream’s designers focused on making the device a self-contained appliance, like a toaster or a TV set. Components usually installed at the base of a tower or indoors are squeezed into SkyStream’s nacelle (the housing behind the rotors). This saves the company a lot of extra costs in ancillary products, such as wiring and cases, and makes installation simpler. And the development of a new curved shape for the turbine’s airfoil blades has improved its efficiency, allowing it to get the most out of whatever wind is present.

”Historically, small wind rotors have been 30 to 35 percent efficient,” says Kruse. ”SkyStream comes in at around 41 percent, which is close to the efficiencies achieved by large wind turbines putting out megawatts.” The theoretical maximum rate of conversion for airfoils is 59.3 percent.

The sales potential of SkyStream is promising, says the company. ”According to the U.S. Census Bureau, there are 17 million homes in America that we believe are appropriate for a small wind system,” says Kruse. That number represents the households on a piece of property of a half acre or more in an area that has an average wind speed of 5.4 meters per second or greater.

Although it’s just a blip in the more than 10 gigawatts of wind power generated in the United States today, residential wind power has been on the rise, according to the American Wind Energy Association. The Washington, D.C., trade group estimates that U.S. sales of small wind systems jumped 62 percent to $17 ­million last year. The association predicts that sales will remain brisk as long as energy prices continue to rise and state and local governments keep small wind-power subsidies in place—incentives that can, depending on where you live, cut the total installed cost of a wind turbine by more than half.

Despite the breezy outlook, industry heavyweights—those producing megawatt-class wind turbines—are not necessarily looking to compete in the under-100-kW class. For example, a spokesman at General Electric’s renewables subsidiary says that the company will focus on the utility market for the foreseeable future.

”Tremendous demand for its 1.5-megawatt turbines and a federal production tax credit for makers of large turbines make utility-scale wind a good business to be in right now for GE,” says the DOE’s Lin. Legislation creating a similar tax credit for residential turbines has been proposed in Congress, but it is not yet law.

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