By going vertical, wind farms may just get a new life.
Putting windmills upright and spacing them more tightly together can generate more electricity on less land, and kill fewer birds or bats than traditional horizontal rotating wind turbines, according to new engineering research.
The findings give new hope to an industry that often faces opposition from neighbors who complain that big wind farms take up too much space and environmentalist who worry about wildlife deaths.
There's also a big bonus: more power.
"We are finding that there are ways to arrange vertical-axis turbines wind farms by having some of the turbines rotating clockwise and others rotating counter-clockwise," said John Dabiri, professor of aeronautics and bioengineering at CalTech. "That significantly increases the amount of wind you can extract from a given footprint."
Dabiri and his colleagues have been experimenting with different ways of setting up turbines to take advantage of airflow around the turbines. His Caltech lab also works with biological systems and some of his work was inspired by the little eddies and currents generated behind schooling fish.
To figure out the optimal placement of the wind turbines, Dabiri set up a field of 24 cylindrical shaped turbines in the desert north of Los Angeles.
Dabiri says that wind turbines that rotate on a horizontal axis have a messy wake, that's why they are usually strung out in a row on a hillside for example, rather than clumped together en masse.
In fact, the most efficient way to generate power on horizontal-axis turbines is to make them taller, larger and spaced as far away as possible. That also makes them noisier, more dangerous to wildlife, and more of an eyesore to neighbors.
Big turbine blades have long been blamed for bird and bat kills. U.S. Fish and Wildlife Agency officials are investigating what happened to six golden eagles found dead last month near a three-year old wind farm near Tehachapi, Calif. The agency estimates windmills kill a half million birds a year, however the American Wind Energy Association, an industry group, disputes those figures.
Dabiri says 30-foot vertical windmills are much less dangerous since they don't use propeller-like blades to capture wind, but rotating open-framed cylinders.
"These smaller windmills are below migratory levels for birds and bats," Dabiri said. "It can be a real game changer."
In a recent paper published in the Journal of Renewable and Sustainable Energy (July 2011), Dabiri said properly spaced vertical-axis turbines increase energy production by ten-fold over their vertical counterparts.
Despite the promising results under test conditions, manufacturers of these vertical-axis wind turbines say they still face challenges in large-scale power generation. The big issues are maintenance, durability of the equipment, and converting energy to the AC power used on the electric grid, said James Horn, CEO of Windspire, a Reno-based firm that has built about 900 upright turbines in various locations around the U.S. and Europe since 2008.
Until the Caltech research project, Windspire mostly has been putting their turbines in groups of two to four. But Dabiri's experiment shows that analyzing the dynamics of the airflow around the turbines could mean a big boost in the number of generating units.
"This may be an opportunity to have turbines like ours to be placed in much more concentrated installations," Horn said. "For example, thousands of smaller turbines sitting in an area below larger ones. I do see them coexisting."