This article from my colleague Paul Gipe deserves a repost.

Quiet Revolution VAWT Total Flop, Says German Paper

I too knew years ago this well-intended Quiet Revolution technology was a flop. As a matter of fact, I knew five years ago, January 2011 to be exact. This is when a colleague who used to work for this company reached out to me regarding performance benchmarks, and to enquire about a tool/method to provide customers better information on small wind generators installed atop rooftops. Analyzing rooftop wind data from the Warwick Wind Trials, the first field trial investigating small wind turbine performance in the built environment, was the crux of my post-graduate research. Interesting, he left the company in 2013.

Here’s the rub on siting, VAWTs, HAWTs…


  • Location/Siting is PARAMOUNT.
  • VAWTs perform better if they too are mounted higher in smoothest, strongest wind, not near to the ground or close to the tops of buildings or other structures, natural canopies.
  • VAWTs blades are prone to fatigue created by centrifugal forces as the blades spin around the central axis >> they are less reliable  than HAWTs.
  • VAWTs require large bearings at the tower top to permit the shaft to rotate and thick steel cable to supper them >> more costly, especially when repairs and maintenance are needed.
  • VAWTs are less reliable and less efficient that HAWTs, and made worse if they are mounted at ground level or on top of buildings.
  • Raising a wind turbine, be it HAWT or VAWT,  into the smoothest, strongest wind ensures greater electrical production and longer machine life.

TWO | VAWT [Vertical Axis Wind Turbine]

  • Powered by wind coming from 360 degrees; does not need to be pointed into the wind; advantage where wind is highly variable.
  • Lower TSP [Tip Speed Ratio].
    Lower operating RPM (rotational speed) >> higher torque, requires a bigger, more massive generator + gear box (drive train) >> lowering efficiency.
  • Inherently lower Cp [Coefficient of Performance].
  • 360 degree rotation on aerofoil w/in wind flow each cycle >> high dynamic blade loading, pulsating torque on drive train, difficult to model wind flow accurately.
  • Drive train more accessible, since it can be placed near ground.
  • Lower audible noise.
  • If mounted on a rooftop, building redirects wind higher over the roof, doubling wind speed at turbine if mounted on roof ~50% of building height (near optimum for max wind energy and minimum turbulence) >> noise could be an issue.
  • Requires a heavier, stronger rotor assembly due to increased torque, etc. + stronger, heavier tower due to increase in turbine mass >> accounting for 60%+ in total capital installation cost.

THREE | HAWT [Horizonal Axis Wind Turbine]

  • Larger swept area >> more energy produced.
  • Performance in turbulent wind not favorable.
  • Higher RPM >> more suitable for driving a generator.
  • Gearbox turns slow blade rotation into quicker rotation (steps up) for driving an electrical generator.
  • Rotor usually positioned upwind since turbulence (mast wake) produced behind tower.
  • Downwind rotors don’t require additional controls mechanisms for keeping in line with the wind.

Quiet Revolution VAWT