A WHOLE NEW KIND OF WIND TURBINE

Offshore use of vertical-axis wind turbines gets closer look

July 30, 2012 (Sandia National Laboratories)

“Sandia National Laboratories’ wind energy researchers are re-evaluating vertical axis wind turbines (VAWTs) …[They] have been around since the earliest days of wind energy...[but new research suggests] VAWT architecture could transform offshore wind technology…[because the] economics of offshore windpower are different from land-based turbines…VAWTs offer three big advantages that could reduce the cost of wind energy: a lower turbine center of gravity; reduced machine complexity; and better scalability to very large sizes.

“A lower center of gravity means improved stability afloat and lower gravitational fatigue loads…[and ] the drivetrain…at or near the surface…[makes] maintenance easier and less time-consuming. Fewer parts, lower fatigue loads and simpler maintenance all lead to reduced maintenance costs…Large offshore VAWT blades in excess of 300 meters will cost more…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…”

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“…[C]hallenges remain…Curved VAWT blades are complex, making manufacture difficult...VAWT blades must also overcome problems with cyclic loading on the drivetrain. Unlike horizontal axis wind turbines (HAWTs), which maintain a steady torque if the wind remains steady, VAWTs have two ‘pulses’ of torque and power for each blade, based on whether the blade is in the upwind or downwind position…[resulting] in unsteady loading, which can lead to drivetrain fatigue…[New] rotor designs [must] smooth out the amplitude of these torque oscillations without significantly increasing rotor cost…Another challenge is brakes…[N]ew VAWT designs will need robust aerodynamic brakes that are reliable and cost-effective, with a secondary mechanical brake…

“In the 1970s and 1980s, when wind energy research was in its infancy, VAWTs were actively developed…For a while, VAWTs held their own against HAWTs. But then wind turbines scaled up…In the 1980s, research focused more heavily on HAWT turbines, and many VAWT manufacturers left the business…But the winds of change have blown VAWTs’ way once more…”

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