Our Chief Engineer, Damon Vander Lind, explains what a power curve is and why ours is interesting:
A power curve shows how much power a wind generation device can make at any given wind speed. A large part of the Makani system design effort, and a large focus of traditional turbine design, is improving power generation in low winds.
Power curves are generally given as a linear graph plotting power output to wind speed. For comparison, an example power curve for a wind turbine and an AWT are shown.
To tell the precise benefit of an AWT from these curves is hard, because the performance in average conditions is important and the performance at improbable wind speeds is not. To improve the comparison, the plot below considers each bin over the range of wind speeds, and contracts or expands it according to the probability of that wind speed at a class 2 or ‘medium’ wind site. Because wind of 7-8 m/s is the most probable, that bin is the widest.
Most wind turbines reach full rated capacity at 13-15 m/s, meaning that they don’t perform as well at these lower wind speeds. AWTs, however, reach full capacity at lower winds, and thus work significantly better in average conditions. To add to this benefit, AWTs also fly at higher altitude, where winds are stronger. The orange region shows the power output under a typical profile of wind speed with altitude, but plotted against the wind measured at the wind turbine’s height. The benefit of AWTs comes in roughly equal parts from increased operating altitude and better light wind performance.
Having flown in enough wind conditions to generate this power curve is one of the most important results of Makani’s test program. It gives us increased confidence in our ability to design and build a grid-scale system that flies as we expect it to.
—Damon Vander Lind
