Wind turbine blades continue to be the target of technological improvements by the use of better designs, materials, manufacturing, analysis and testing. As the size of turbines has grown over the past decade, designers have restrained the associated growth in blade weight to less than would have been possible through simple scaling-up of past approaches. These past improvements are briefly summarized. Manufacturing trends and design drivers are presented, as are the ways these design drivers have changed. Issues related to blade material choices are described, first for the currently dominant glass fibre technology and then for the potential use of carbon fibres. Some possible directions for future blade design options are presented, namely new planforms, aerofoils and aeroelastic tailoring. The significant improvement in sophistication of stress analysis and full-scale blade testing are also discussed.

A preliminary design study of an advanced 50 m blade for utility wind turbines is presented and discussed. The effort was part of the Department of Energy WindPACT Blade System Design Study with the goal to investigate and evaluate design and manufacturing issues for wind turbine blades in the 1–10 MW size range. Two different blade designs are considered and compared in this article. The first is a fibreglass design, while the second design selectively incorporates carbon fibre in the main structural elements. The addition of carbon results in modest cost increases and provides significant benefits, particularly with respect to blade deflection. The structural efficiency of both designs was maximized by tailoring the thickness of the blade cross‐sections to simplify the construction of the internal members. Inboard the blades incorporate thick blunt trailing edge aerofoils (flatback aerofoils), while outboard more conventional sharp trailing edge high‐lift aerofoils are used. The outboard section chord lengths were adjusted to yield the least complex and costly internal blade structure. A significant portion of blade weight is related to the root buildup and metal hardware for typical root attachment designs. The results show that increasing the number of studs has a positive effect on total weight, because it reduces the required root laminate thickness. The aerodynamic performance of the blade aerofoils was predicted using computational techniques that properly simulate blunt trailing edge flows. The performance of the rotor was predicted assuming both clean and soiled blade surface conditions. The rotor is shown to provide excellent performance at a weight significantly lower than that of current rotors of this size. Copyright © 2004 John Wiley & Sons, Ltd.

Improving wind turbine blades via bend-twist coupling confronts two difficult challenges. The first is that off-axis fiber for the major structure is difficult to fabricate. Suitable fabrics with the primary fiber-20 degrees off-axis are not commonplace and may present dimensional stability problems when handled, due to a tendency to shear when tensioned along their long dimension. These are ultimately cost issues. The second category of challenges is in the area of possible fatigue limits due to ending or curving angled fibers. Spar caps with angled fibers must either end those fibers at the edge or have them carry around a web type structure. Either approach implies additional stresses in the resin system binding the fibers and may lead to lowered fatigue allowables for design. Baseline Blade To provide results linked to other research work and current commercial turbine sizes, a 30m (98.4 ft) blade derived from a separate Sandia blade-scaling study (Ref. 4) was chosen as the baseline. This is a single shear web generic interior blade with fiberglass spar caps and skins, and balsa core for the aft panels and shear web. The basic parameters for this blade are summarized in the following table. The baseline for this work is the thinnest of the three blade variations shown.

The Low Wind Speed Technology (LWST) project seeks to develop technology that will allow wind systems to provide reduced energy costs in regions where wind speeds average around 5.8 m/s, so-called "low wind speed sites." As part of LWST, Sandia National Laboratories contracted with Knight & Carver to develop a sweep-twist adaptive blade to passively reduce operating loads, thereby allowing for a larger, more productive rotor and ultimately reducing the cost-of-energy. After design and fabrication of a 27.1 m STAR blade, static and fatigue laboratory tests were successfully carried out. Full flight testing on a Zond 750 test turbine verified the predicted performance and operating loads. The STAR blade exceeded the project goal of improving annual energy capture over the baseline by producing 10-12 % more energy.

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