The wind energy industry has doggedly pursued higher energy yields and lower costs of energy with each successive generation of wind turbines. As a result, the wind energy industry has lowered its costs by over 40 percent in just the past four years. Innovations in wind turbine design, materials, and the sub-component supply chain are continually yielding advances – sometimes from the smallest places.
The mature aerospace industry has provided many complementary solutions to the wind industry in terms of design, materials, manufacturing, and the operation of large rotors. Among these is the relatively recent introduction of vortex generators (VGs). These small, simple fins, usually less than 8 centimeters tall and wide, energize airflow directionally around a blade when applied in multiples and keep it from erratically scattering as it passes over the blade surface.
This image from LM Windpower, the largest global independent blade manufacturer, shows the difference in airflow over a blade during recent testing. The benefits are most pronounced close to the thickest section of the blade, near the blade root.
Lower Speed, More Energy
Lessons learned long ago in aviation show that planes with wings equipped with VGs are able to reach slower speeds before stalling out, as the VGs helped increase lift on the wings. Wind blades operate similarly to aircraft wings, in that wings capture passing wind to create loft for flight, and blades capture passing wind as loft for mechanical turning power of the rotor. The effects proven in aviation are also more pronounced at lower air speeds, when wing flap angles are more aggressively angled toward the passing wind.
Similarly, the effects of VGs appear to increase the productivity of a wind turbine more during medium and low wind speeds versus high wind speed environments. This is complementary to the fact that, in recent years, the majority of new turbines installed in the mature markets of North America and Europe are designed for lower wind speed environments.
No wind blades presently are manufactured with VGs attached out of the factory, but a robust retrofit business has evolved among some independent service providers (ISPs) to install VGs during blade maintenance and inspection.
UpWind Solutions, an ISP based in North America, says it has installed 22,000 VGs across multiple wind turbine models and found that assumptions around a General Electric (GE) 1.5 MW turbine, with a power purchase agreement of $50/MWh and operating at a 40% annual capacity factor, would see an increase in annual energy production (AEP) of around 2.2 percent and recoup the cost of VG installation in 20 months.
From the Factory, Soon
Siemens has discovered the value of VGs and other aerodynamic add-ons and has incorporated these into aftermarket power curve upgrade services, similar to UpWind’s applications. In early 2014, Siemens added VGs as a retrofit upgrade to the existing 175 wind turbines at the 630-MW London Array offshore wind project. Siemens says the aerodynamic upgrades will yield about a 1.5 percent increase in AEP.
Independent blade manufacturer LM Windpower also offers VGs as an add-on service to blades. With ISPs, turbine vendors and blade manufacturers offering VGs as add-on aftermarket services, it’s only a matter of time before vendors begin offering VGs with their standard blade offerings.
After all, they are already standard offerings on your average mallard duck.
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