New and Improved Wind Power
(Page 4 of 7)
June/July 2007
By Greg Pahl
Jim Green, senior project leader at the Wind Technology Center, explains the advantages and disadvantages of these two strategies: “The furling method is passive and relatively fail-safe because when the wind forces become sufficiently high the turbine will furl,” he says. “The alternative approach used by Skystream hopefully will be a reliable strategy, but it does require some active control in the machine. They address that by having redundant systems and fairly fail-safe power designs.” If the power goes off in a grid failure, for example, there is a switch that stops the turbine.
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“One of the reasons I think the Skystream approach is going to be attractive is that the rotor speed is truly limited,” Green says. “Furling wind turbines, on the other hand, tend to let the rotor accelerate to generate the high thrust that causes the furling to take place. So, there are some higher speeds and higher forces involved that the whole machine has to deal with in that approach — but with proper design that’s OK.”
However, when it comes to tower height, residential wind expert Mick Sagrillo and others in the industry stress that the 33-foot tower that’s often part of the Skystream package is simply not tall enough to avoid wind turbulence; most in the industry recommend an 80-foot tower minimum.
“The site always determines the height of the tower,” Sagrillo says. The three most common mistakes that people make with small wind installations, according to Sagrillo, are: 1. Too short a tower; 2. Too short a tower; and 3. Too short a tower. Bergey also emphasizes this point by comparing a turbine on a short tower to a solar power collector in the shade.
Kruse argues that a general rule of thumb is to ensure the rotor extends at least 20 to 30 feet above any surrounding object within 500 feet of the tower. He agrees that a site should be thoroughly assessed; while the 33-foot monopole tower may perform well in the Texas panhandle, a taller tower might be required in areas such as upstate New York or Vermont.
At least one new Skystream feature impresses virtually all observers — the turbine’s wireless communication system. It enables the homeowner to track the turbine’s output and other operational statistics on their home computer and also allows for real-time troubleshooting if a problem should develop. Software patches and other system upgrades can be uploaded to the turbine via the same system, eliminating the need to lower the turbine to the ground for these procedures.
Real-world Performance
So, how do residential wind turbines actually perform? If they are properly installed and maintained, the record is good. Bergey Windpower, with installations in all 50 states and more than 90 countries, has a long track record of success. Abundant Renewable Energy has only a small number of its new ARE 110 turbines installed so far, but early feedback has been positive.
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