Vertical axis turbines missed their moment in the 1980s, but they are back, and they are getting bigger. That may come as a surprise. The technology was confined to niche applications and all but written off just a few years ago. Now they are poised for a new growth spurt in the rooftop field, and they are even heading out to sea.
The Long Road To Vertical Axis Wind Turbines
For those of you new to the topic, vertical axis wind turbines are engineered to make curved blades rotate around a central, upright pole. The US Department of Energy’s Sandia National Laboratory was experimenting with a scaled up design that resembled an egg beater back in the 1980s, as depicted in the photo at the top of this article.
The idea was eventually shelved in favor of the now-familiar wind turbine of today, which looks nothing like an egg beater. Conventional wind turbines deploy straight blades that spin in front of a horizontal axis, which is perched at the top of a narrow tower.
Vertical axis activity still persisted at the smaller end of the scale. It appeared ready to take off about ten years ago, when high profile property owners and tenants were searching for new ways to promote their green profile. Rooftop solar arrays are not particularly visible from the street, but a fringe of wind turbines is an eye catching decoration.
All kinds of small, oddly shaped configurations made an appearance, both in and out of the vertical axis field. Here in the US, sports franchises were among the early adopters. The Philadelphia Eagles snapped up a set of micro wind turbines from the firm UGE back in 2010, and the Buffalo Bills followed suit with a series of micro wind turbines around the upper reaches of Ralph Wilson Stadium in 2011.
The bloom soon fell off the rose. UGE, for example, sold its wind branch in 2016 to concentrate on the community solar field. In 2019, NBC-TV reported that the Eagles removed the wind turbines from Lincoln Financial Field for repair. Replacement plans are still up in the air as of early this year.
Never Give Up, Never Surrender
Actually, the bloom is not off the rose just yet. A glimmer of hope for the rooftop wind market appeared in 2019, when US Department of Energy’s National Renewable Energy Laboratory noted an uptick in demand for the very smallest wind turbines, defined as 1 kilowatt or less.
The Energy Department has continued to hold the vertical axis torch all along, partly due to its potential for making use of buildings and other sites where conventional wind turbines are unsuitable. The agency has also picked up the ball on the bigger end of the scale. In 2019 the agency’s ARPA-E funding office launched a grant program aimed at developing megawatt-scale vertical axis turbines for offshore wind farms.
Others have also caught on to the upscaling idea. The Norwegian company SeaTwirl, for example, is bringing a 1-megawatt vertical axis offshore wind turbine to market. The company is banking that wind developers will be attracted by cost benefits of packing more turbines into one offshore array.
At the other end of the scale is the Massachusetts firm ARC Industries, which is marketing a 3-kilowatt vertical axis turbine for rooftop use. The company just deployed its first model, dubbed the Orb, on the roof of a parking garage at Burlington International Airport.
A Rooftop Microgrid Solution
Rooftop wind also may have room to grow beyond the single-digit kilowatt scale. The big question is whether or not mid-scale, rooftop vertical axis wind turbines make bottom line sense. Maybe not on their own, but the Texas firm Hover has come up with a “Wind-Powered Microgrid™” rooftop combination system that packages solar panels and an energy storage element along with a vertical axis wind turbines.
The microgrid approach could provide more opportunities to scale up, but for now Hover is sticking with a 36-kilowatt vertical axis wind turbine.
“Installed as an array on the windward edge of a building’s roof, the ground-breaking aerodynamic design uses the building as a sail and delivers commercial scale power. A direct drive generator reduces friction and allows for low cut in speeds,” Hover explains.
“The solar photovoltaic array installed in the center of the roof acts as a complement to the turbine array, generating power during daylight hours. The energy captured by both sources is directed to Hover’s Integrated Energy Management System where the energy is combined, cleaned, and converted into 3-phase AC power, directly linked to the building management system,” the company adds.
A battery-type energy storage system enables the system to save any excess power. Hover tested the system for two years at a site in Florida. The system continued to work as designed throughout that period, despite two hurricanes. Depending on the building and the needs of its occupants, the system could enable a building to go off grid in case of emergency.
If all goes according to plan, Hover will set a new Tennessee manufacturing plant in motion early next year, to start commercial production for a dozen or so installations that are already in the planning stages.
Vertical Axis Wind Turbines Are Already Floating
Circling back around to the idea of shipping vertical axis wind turbines out to sea, let’s take a look at the goings-on over at that ARPA-E grant program. The awardees were announced in 2020, and one of them was Sandia National Laboratories. The lab was tasked to develop a new offshore version of vertical axis technology, dubbed ARCUS.
To guild the vertical axis lily, the award specified that the new wind turbines would be floated out to sea on platforms, not fixed to the seabed.
The idea of floating conventional wind turbines has already caught on in a big way, because they can be anchored in waters that are too deep for fixed-platform construction. The vertical axis twist is a new one, and it could be a game changer.
As described by ARPA-E, the vertical axis configuration can reduce costs associated with the large, bulky platforms required of conventional floating wind turbines.
“A VAWT [vertical axis wind turbine] is ideal for floating offshore sites,” ARPA-E enthused. “Its advantages over horizontal-axis wind turbines (HAWTs) include no need of yaw systems, improved aerodynamic efficiency and a lower level placement of the turbine’s drivetrain that greatly reduces floating platform mass and associated system costs.
One key difference is the replacement of a central tower with tensioned guy wires.
“The result is up to a 50% lower rotor mass than traditional VAWTs,” ARPA-E explained. “This greatly minimizes platform and system costs. Instead of designing the platform to eliminate the motion of the turbine, the project team will design the oscillating turbine-platform system to operate safely under extreme weather conditions within an allowable response.”
We’ll know more next year, when the grant period concludes.
Follow me on Twitter (for now) @TinaMCasey.
Image: Vertical axis wind turbine from the 1980s courtesy of Sandia National Laboratory.
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