New and Improved Wind Power
(Page 3 of 7)
June/July 2007
By Greg Pahl
Because the rotor is what actually captures the wind, its size is extremely important. In general, the larger the rotor the better, as long as it’s matched to an appropriately sized generator.
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Improved airfoil designs have boosted efficiency by as much as 35 percent at the average wind speeds typical of many residential locations. Wooden blades have been replaced by reinforced fiberglass, which reduces blade maintenance (although routine turbine and tower upkeep is still extremely important). The blades also have been redesigned to reduce the amount of noise they produce. Bergey Windpower, for example, used the new airfoil design in its 10-kilowatt BWC Excel model to improve efficiency in wind speeds as low as 9 miles per hour. In addition, new direct-drive permanent magnet alternators have been paired with sophisticated controls and inverters designed specifically for small wind turbines. Alternator efficiency on some models has been improved by about 25 percent. “We introduced the Excel back in 1983,” Bergey says. “But the one you buy today has vastly improved rotor blades and power electronics.”
Some of these advances owe at least partial credit to research and development conducted by the National Renewable Energy Laboratory’s Wind Technology Center in Golden, Colo. Bergey Windpower and several others have benefited from collaboration with the laboratory. The team-up helped Abundant Renewable Energy design two new residential, grid-connected turbines that are especially well-suited for harsh environments. In January 2006, the company shipped its first 2.5-kilowatt unit (the ARE 110), followed later that year by the 10-kilowatt model (the ARE 442). Both turbines are designed to operate quietly and produce more electricity in lower wind speed locations.
Southwest Windpower, which also collaborates with the laboratory, has been producing battery-charging wind turbines since 1987. Recently Southwest released a grid-connected turbine, the Skystream 3.7, that is paired with a monopole tower as short as 33 feet to make it easier to install in residential settings where zoning regulations often limit taller structures. Among a number of improvements, the new 1.8-kilowatt turbine has an extremely low “cogging torque” (resistance to start up), making it easier to start in low winds. The Skystream is a smaller unit with a lower price tag than industry averages (see “Residential Wind at a Glance,” below).
Plug and Play
One thing that sets the Skystream apart from the competition is its “plug and play” design. All of the sophisticated electronic components that would normally be located in separate boxes at or near the base of the tower have been incorporated into the turbine itself, making the connection to your home’s electrical system (and the grid) a relatively simple matter. Another characteristic that sets the Skystream apart is its use of the generator to control the rotor speed. Most other small wind turbines use a “furling” strategy, which turns or tilts the turbine and blades out of the wind to protect them from overspeeding in high winds, which can destroy the generator. The Skystream, on the other hand, uses what amounts to dynamic braking by the generator to limit rotor speed.
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