Offshore wind turbine design appears to be on a firm course, with the major manufacturers all pushing forward with advanced materials and engineering that allow for giant-sized versions of the three-bladed, horizontal windmills that are so familiar.
So let’s give Sandia National Laboratories a little credit here for throwing a thought-provoking changeup into the proceedings. The government scientists down in New Mexico are rocking the offshore boat with the suggestion that vertical-axis wind turbines “could transform offshore wind technology.”
That’s right, VAWTs, the sort of turbines we typically see offered as small-time, adjunct power producers of somewhat dubious value, are getting a whirl for offshore purposes.
Sandia says they have three distinct advantages over today’s common offshore design: a lower turbine center of gravity; reduced machine complexity; and better scalability to very large sizes.
Surprising as this is, according to Sandia, VAWTs were once more than a niche player in wind turbine development.
“In the 1970s and 1980s, when wind energy research was in its infancy, VAWTs were actively developed as windpower generators,” the lab said. “Although strange looking, they had a lot going for them: They were simpler than their horizontal-axis cousins so they tended to be more reliable. For a while, VAWTs held their own against HAWTs. But then wind turbines scaled up.”
From 1 megawatt up to 5, horizontal turbines had a big advantage, and that’s almost entirely where utility-scale wind has been in the past decade or so. Now, the turbines are getting even larger, with 6-MW turbines going in and machines up to 10 MW apparently on their way.
Ironically, while VAWTs lost out to horizontal turbines when they began to scale up, now that turbines are getting even bigger, the tide might be turning.
“Large offshore VAWT blades in excess of 300 meters will cost more to produce than blades for onshore wind turbines,” Sandia says, “but as the machines and their foundations get bigger — closer to the 10–20 megawatt (MW) scale — turbines and rotors become a much smaller percentage of the overall system cost for offshore turbines, so other benefits of the VAWT architecture could more than offset the increased rotor cost.”
The five-year Sandia VAWT program, funded with $4.1 from the U.S. Department of Eenrgy, began in January. In the first two years, the goal is to come up with several design concepts and tests them using sophisticated modeling software.
“The early favorite rotor type is the Darrieus design,” the lab said. That’s the type of design seen on the right in the image below. The turbine uses lift forces generated by the wind hitting aerofoils to create rotation, versus collecting the wind in scoops and using drag to spin the turbine, as with the Savonius VAWT.
The second, three-year phase of the program will see the researchers building and testing the selected design.
The possibility that VAWTs might be significant producers of land-based power has been tossed around a bit by wind engineers. A team of researchers at Caltech has suggested that shorter vertical-axis turbines, placed in a tight array with each turbine turning in an opposite direction to its neighbors, can be at least 10 times as efficient as horizontal-axis turbines. But a recent National Geographic piece on the future of wind turbines noted that such schemes have “yet to be proven in the field at any scale, and many wind industry experts remain skeptical about vertical-axis designs.”