FloWind’s Extended Height to Diameter VAWT

By Paul Gipe

FloWind’s development of the Extended Height-to-Diameter (EHD) Vertical Axis Wind Turbine was the last gasp of Darrieus wind turbine development in the US.

The development of the extended height-to-diameter design followed FloWind’s attempt to commercialize a 25-meter diameter, two-bladed, Darrieus turbine in 1986. See FloWind 25 m Darrieus VAWT Installation.

The purpose of the EHD concept was multifold, but the principle reason for the design was to build taller Darrieus turbines. Darrieus, or eggbeater turbines, have an inherent limitation. They are squat and the rotor remains close to the ground. Wind speed, and, hence, power increases with height above the ground.

FloWind's EHD three-bladed turbine contrasted to its 19-meter, two-bladed commercial model.

There were other design features of the EHD version relative to FloWind’s commercial products. The EHD used three blades, harking back to Alcoa’s early commercial turbines, and the blades were made from pultruded fiberglass rather than extruded aluminum.

I did a quick scan of the old California Energy Commission Performance Reporting System’s annual reports and I couldn’t find any listing for the turbine. The prototype turbine was certainly removed by the time Florida Power and Light repowered the site in the late 1990s, removing all FloWind’s Darrieus turbines.

Final Project Report: Highenergy Rotor Development, Test and Evaluation, Sandia National Laboratory, Albuquerque, New Mexico, September, 1996, SAND 96-2205, 120 pages.