Energy Systems and Technologies for the Coming Century ...

turbines is expected to create a step change in the industry, followed by further gradualcost reductions as with previous turbine types.Lightweight bladesAs described above, geometrical similarity says that as blade length increases, bladeweight should increase with an exponent of 3 (a cubic law). In fact, several studies haveshown that over recent decades the actual exponent has averaged around 2.3, and for themost recent blade designs it is 2.2 or 2.1 (Figure 2).Figure 1: New technology and better design means that new blades are much lighterthan simple geometry would predict, based on the weight of older blade designsMany factors have aided the move to lighter blades, of which the most important hasbeen the development of blades that are much thicker than their predecessors, especiallynear the hub. Because they are stiffer at the point where the loads are highest, these newblade designs make more efficient use of materials and are lighter overall. This principlecan continue to produce even larger blades that beat the square-cube law as long as it isbacked by the necessary R&D into better design methods, new materials such as carbonfibre, and advanced manufacturing techniques.One potential drawback to using thicker airfoil shapes at the blade root is a loss ofaerodynamic efficiency. The answer may lie in high-lift designs such as multiple airfoilsfor use at the blade root (Figure 3), or the newly-developed “flat-back” airfoil, which canmaintain lift even when it is very thick.Figure 3:Multi-element airfoil to enhance lift (CFD simulation, Risø DTU)Risø International Energy Conference 2011 Proceedings Page 208