Can small wind turbines outperform conventional wind farms?
Stanford professor John Dabiri has recently described the benefits of small wind turbines against conventional wind farms. He highlights how in previous years large vertical-axis turbines were dismissed in preference to the efficiency of the more common propellor-like turbines of today.
Dabiri highlighted that recently researchers have found that clusters of vertical-axis turbines, arranged to take advantage of each other's turbulence can actually outperform conventional wind farms.
“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.”
Professor Dabiri works with smaller vertical-axis turbines that are 10 meters in height. He arranges the smaller turbines the way schooling fish arrange themselves, so the turbulence created by each fish rather than hindering, supports the progress of each fish beside and behind it creating a propulsion movement generated 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. (Source: Forbes).
This concept has been applied to wind energy before and operators such as GE have used similar concepts to improve the placement of conventional wind farms. Professor Dabiri and his supporting team have however shown that arrays of much smaller vertical-axis turbines can outperform these conventional wind farms because they respond to turbulence much better.
In a study published this month in the journal Wind Energy, researchers from Stanford, Johns Hopkins, and the University of Delaware simulated the addition of small vertical-axis turbines to a conventional wind farm, and found the mix not only improves the performance of the farm, but also of the older turbines.
With the small turbines added, the mixed-turbine wind farm “produces up to 32 percent more power than the traditional one and the power extracted by the large turbines alone is increased by 10 percent, caused by faster wake recovery from enhanced turbulence due to the presence of the small turbines,” according to the study.
Vertical-axis turbines also present less threat to wildlife.
“Of all the companies that are out there operating these, there have been no reported bird or bat strikes,” Dabiri said. “This is for two reasons: one, of course, they’re closer to the ground so they’re not going to be necessarily in the flight corridor. But they also have this rotation around a vertical axis which has a very different visual signature than the very fast moving blades of a conventional wind turbine.”
Windmills kill between 140,000 and 328,000 birds in the U.S. each year, according to a study published in 2013 in the journal Biological Conservation.
Vertical-axis wind turbines have 12-20 components, Dabiri said, compared to about 8,000 components in a conventional turbine, so they should have longer lifetimes and lower costs for operations and maintenance.
The smaller turbines haven’t caught on yet, Dabiri said, because the startup companies now producing them have not yet produced a design resilient enough to withstand the environment.
“There’s certainly interest in installing these wind turbines, but the challenge has been delivering a product that’s bug free. Most of the companies that sell these are startups that are still trying to work through the kinks of building something that will last 20 years,” he said.
“There are a couple of companies that are close to having something that I would recommend to my parents to buy—that’s the metric that I use—but they’re not quite there yet. So there is still work to be done in terms of the reliability required, especially when you’re making so many of them.”