Interesting read via Forbes
Decades ago, engineers largely dismissed vertical-axis wind turbines—which spin around a central axis like a top—because they could not match the efficiency of the propeller-like turbines common today.
But researchers have found recently that clusters of vertical-axis turbines, arranged to take advantage of each other’s turbulence, can outperform conventional wind farms. When added to conventional farms, according to a study published this month, they can even increase the older turbines’ output.
“We’re able to get significantly higher performance,” said Stanford Professor John Dabiri, “both due to the fact that you can put the turbines closer together, but also in putting the turbines together we improve the performance of the individual turbines.”
Dabiri works with vertical-axis turbines that are 10 meters tall, compared to 100 meters for a conventional horizontal-axis turbine. He arranges the small turbines the way schooling fish arrange themselves, so that the turbulence created by each fish aids, rather than hinders, the progress of the fish beside it and behind it.
Even a dead fish, placed in such a school, will move forward, propelled by the turbulence of the group.
“They’ve been able to optimize their movement in interaction with their neighbors so that the group is a more efficient system flowing through the water,” Dabiri said.
The hydrodynamics of schooling fish have been applied to wind energy before, and wind-farm operators like General Electric and Berkshire Hathaway Energy have used those insights to improve the placement of conventional turbines. But Dabiri and his team have shown that arrays of much smaller vertical-axis turbines can outperform these conventional wind farms because they respond to turbulence much better.
“I would note that they’re still doing this using conventional horizontal wind turbines. Even in these systems you can see benefits. It’s going to be something on the order of 5-20 percent, which is actually huge if you’re talking about a 300 MW wind farm project, but the thing that we are excited about is that in the vertical-axis turbine approach to this problem it can be factors of 3 and 4 and 5.”
Turbulence is bad for conventional turbines, not only reducing their efficiency, but also their lifespan. As a result, they are typically spaced far apart, and the wind that passes between them, according to Dabiri, is “wasted energy.”
Small vertical-axis turbines placed in those open spaces can capture that wind and reduce turbulence for the conventional windmills around them.