Ken Visser, co-founder of Ducted Turbines International (DTI) and associate professor of mechanical and aeronautical engineering at Clarkson University, has a dream. He wants to produce the first commercially-viable ducted wind turbine for U.S. homeowners, schools, businesses and farms to generate their own electricity. If the CFRP blades on the most recent prototype perform as expected, he will be one step closer to his goal of making sustainable electricity globally accessible.
“My vision is that we could drop a box in the middle of some community that doesn’t have any power, and they could assemble the wind turbine, get it up and running and generate power,” says Visser, who started DTI with Paul Pavone. “Having the ability to make that kind of impact, that would be the greatest!”
DTI’s wind turbine has a 3-meter-diameter rotor, comprising an aluminum hub and three CFRP composite blades, with a surrounding 3.7-meter-diameter GFRP duct. The ring-shaped duct – also called a shroud – increases airflow through the turbine blades. A Clarkson University alumni’s company, Empire Fiberglass Products Inc., manufactured the duct, and Vistex Composites fabricated the CFRP blades with funding, in part, from a National Science Foundation grant.
Vistex and DTI worked together to design the blades to reduce costs and maximize performance. The blades were hand laid, using 12 to 16 layers of snap-cure epoxy woven prepreg with mostly 0/90 degree fiber orientation. The formed uncured blades were then sandwiched between a temperature-controlled rigid mold and a combination of Vistex’s Pressure Focusing Layer (PFL™) and a rigid compression mold. The PFL is a soft, compliant layer with varied thicknesses and geometries across the composite as determined by Vistex’s proprietary modeling and optimization process. Jaron Kuppers, co-founder and chief technology officer of Vistex, says the process produces parts with material properties that are comparable to or better than autoclaved parts but with a significant cost reduction.
DTI’s first turbine prototype, tested in 2016 at the University of Waterloo’s wind tunnel, utilized milled aluminum blades. Visser wasn’t necessarily looking for a composite solution for the current prototype. For him, it is all about making small wind turbines affordable – whatever the material.
Consequently, Vistex focused on short cycle times. The company can achieve a 30-minute cycle using the snap-cure prepreg from Axiom Materials and a heated tool. This will allow Vistex to fabricate more than one blade per hour and thousands of blades per year, per mold once in full production. That’s fast enough, says Kuppers, to make the CFRP blades cost competitive when using Vistex’s PFL process. “We were able to reduce the costs as compared to aluminum – and not just the kilowatt per hour, but the actual price of the blades,” he says. “We are at near-price parity with aluminum or cheaper when we’re in mass production. That’s not something you hear very often.”