Envision says the rotor length of its E128 can be customized to the site by adapting the blade extensions to meet site-specific requirements.

It can take years to for a wind-turbine idea to become an energy producing machine. For Denmark based Envision Energy (www.project-gc1.com) however, it took less than two year to get its two bladed, partial-pitch turbine up and generating power. Company aerodynamic engineer Kristian Godsk made the comments and more at the recent Sandia Blade Workshop. He says the design is the first of its kind and suggests that its features can cut 10% off the capital expenditure for offshore turbines.

The E128-3.6 PP 2B turbine takes most of its advantages from the two-blade design. For instance, having just one fewer blade than a convention three-blade turbine reduces production costs, and that lightens the up-tower mass which means the tower can weigh less making it easier to transport and erect. Furthermore, the two-blade design allows lifting the blade and nacelle at once, further cutting construction costs.

And there are operational advantages. For instance, the two blade rotor can be parked in a horizontal position in high wind or shear and the blade holds itself horizontal. Envision says the design is fit for sites with extreme-force winds.

Innovation in the rotor includes the fixed length, 22m center portion called the extender. The outer blade lengths pitch independently of the center section and provide the source for the partial-pitch reference. Although the extender has a fixed length, it allows customizing the rotor length by adjusting the tip or blade length as needed for a site’s prevailing wind speeds. Hence, low-wind speeds would allow longer tips for a greater swept area, and shorter tips for higher speeds.

Transformers and converters are mounted in enclosures at the base of the tower, not in the nacelle. That makes them easier to maintain when offshore. Also interesting is that the main shaft is made of carbon fiber and the flex in the shaft damps some of its loads, says Godsk.

In the most violent storm to sweep the site, wind hit 51 m/s, enough to break a cup off the turbine’s anemometer. But the controls positioned the turbine sideways to the high wind so it suffered no damage. The prototype has been running in Denmark since 2012. WPE