Ontario, Canada has carved out a niche for itself as a hub of green technology. One of the latest clean tech innovations to come out of that province is DARWIND5, a vertical axis wind turbine (VAWT). Designed by Harvistor, it comes with a promise of more oomph than existing models for small-scale wind power generation. According to the company, recent tests showed that its technology can achieve 35 percent more kilowatt hours per year than current VAWTs for the same sweep area, besides operating at 25 percent lower heights than similarly priced market leaders.
Harvistor says it approached the DARWIND5 design like F1 racing, with performance boosted by a new type of rotor blade telemetry and geometry. This translates into new airfoil shapes, which allow the rotor system to completely avoid power-robbing dynamic stall, a reaction that occurs when airfoils rapidly change the angle of attack.
Individually, each rotor has a longer power stroke than previously thought possible because the new airfoil shape flies upside down and right side up during key parts of rotation, like a stunt airplane doing a full loop. During rotation, the lift forces change twice from moving away from the shaft to moving toward the shaft, making for the longer stroke. All of these forces occur on the windward side of the turbine – any turbulence exits on the leeward side, where it doesn't affect the turbine. This avoids individual torque peaks, which are a major cause of wind turbine breakdowns
With nameplate power (capacity under ideal conditions) ranging between 500 watts and 1.5 kilowatts in a 1.2-meter (3.9-ft) working diameter, DARWIND5 operates at a speed that ranges between 4 m (13.2 ft) and 24 m (78.7 ft) per second. It doesn’t need a brake because it self-regulates the top RPM – until now, unregulated top speeds have been a problem with VAWT design. A cantilevered tilt mount design reportedly makes cleaning and repairing an easy task, allowing it to be done anytime without power production loss or delays.
DARWIND5 is mounted 25 to 35 percent lower than the nacelle of horizontal axis wind turbines. Being lower to the ground is better, claims Harvistor, because it does not affect property values and makes the turbine more aesthetically pleasing, which should assuage the fears of people who find wind turbines an eyesore.
The turbine was based on the Darrieus design, also known as the “eggbeater." It expanded on previous efforts carried out by the National Research Council Canada and Ministry of Natural Resources as well as Sandia National Labs. Sandia's pioneering work in 1974 (which carries on to this date) resulted in the first commercial Darrieus systems. These were produced by Flowind and used in California by PG&E and Southern California Edison between 1984 and 1996. DARWIND5 improves Flowind’s design by making it more reliable. The design features lower and more evenly placed rotor blade loads, thanks to less vibration.
The project was developed and tuned on supercomputer 3D CFD software and used a performance simulation tool called Beater. The tests carried out in June of this year validated DARWIND5’s performance, meaning the Beater tool can now be used to upgrade DARWIND5 turbines into the MW class. The field test height was 3.5 meters (11.48 ft) and was performed in stationary and moving set-ups.
Harvistor says its ownership of the rotor blade and engineer design gives it a competitive edge. The company has submitted a project to KickStarter that was pending approval at the time of writing this article.
Video of the June, 2012 field test can be viewed below (although disregard the voice over saying the date is 2011).
By Le My
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