Materials Matter in Wind Turbine Blades
The basic rules of wind power apply in every discussion of design, installation, and deployment and especially to the swept area of wind turbine blades. Bigger always is better. Higher always is more powerful. More always works better than less. In fact, the rules apply geometrically. For each increase in a blades’ length, and with each corollary increase in a wind turbine blades’ sweep, energy production nearly triples; pi factors in there somewhere. For each ten-foot increase in a tower’s height, energy production multiplies by at least 2, because wind speed increases as you go higher into the atmosphere. And, by some mystical principle that defies both physics and art, two wind turbines always will pay for themselves more than twice as fast as just one. Economies of scale always apply.
Beyond “bigger is better,” however, most of the rules about wind turbine blades dictate what “thou shalt not” do. The so-called “best” blade designs double as the most old-fashioned and traditional; no one really has scored a significant breakthrough in wind turbine blade design in over a century, and the experts frankly declare blade designs have evolved to the point where they are about as good as they ever will get. In the last two decades, engineers have applied for patents on dozens of new wind turbine blade designs, but none ever has outperformed the old propeller designs for HAWT’s (Horizontal Axis Wind Turbine) and the old boat sail designs for VAWT’s (Vertical Access Wind Turbine). The triangular VAWT blade design, which dates back about 3000 years, remains arguably the finest ever; none ever has beaten it in head-to-head trials. Though most would agree today that the efficiency of a HAWT is much more desirable for modern use.
The Wind both Drives and Destroys Wind Turbine Blades
Veteran wind smiths routinely refer to “The Tehachapi Project” as a classic example of excellent design and physics gone terribly wrong. Day and night the wind blows steadily between 15 and 30 mph on California’s fabled Tehachapi Pass, better know as “The Grapevine.” In the 1970’s, visionary wind energy engineers and scientists built a sprawling—some winderati even would call it “utopian”—windfarm at the Tehachapi Summit, one of the world’s most perfect wind power sites. Using what they though were high-grade aluminum materials, the 70’s windsmiths erected hundreds of VAWT’s according to the ancient Persian design, brining them online on time and on budget.
In fulfillment of the visionaries’ wildest dreams, those handsome VAWT’s spun just as they should and generated electricity just as everyone wished. The alloyed aluminum materials showed no signs of damage from harsh winter storms or thick Tule fogs, and southern California power company executives began reformulating their long-term investment plans, diverting funds from nuclear plants to windfarms. The engineers predicted the wind turbine blades would last at least twenty years; and, as long as the blades held-up, the generators would keep right on generating. They forgot the only variable: metal fatigue. Extreme temperatures—over 100 in the Tehachapi summer and near zero in the mountain winter—expanded and contracted highly conductive aluminum, weakening it with every swell and shrink. Many of the aluminum wind turbine blades failed just five years into the experiment; some of them just disintegrated. Power company executives put their money back in nuclear plants.
Twenty-First Century Materials for Wind Turbine Blades
Not surprisingly, the most promising developments in wind turbine technology come from development of the Apache Attack Helicopter. McDonnell-Douglas and Boeing engineers shaped Apache rotors for maximum efficiency, and they fabricated them from high-tech carbon composites. The rotors deliver optimal lift with very little weight and exceptional durability. Throughout the first Gulf War, while Apaches flew sorties 24/7, none ever was grounded because of rotor blade fatigue or failure.
Those same wind power visionaries who first championed the Tehachapi Project now advocate its reprise, arguing those same ancient wind turbine blade designs fabricated from high-carbon composites finally will deliver on the promise made forty years ago.
