When Wind Power Needs a 'Haircut'
In a remarkably honest recent article -- nestled away in a rather obscure (for laymen) trade journal -- we learn that in the wind energy industry 'haircut' has come to mean downward revision of wind energy capacity statistics that had been too high. Thus the phrase "giving the statistics a haircut."
As AWS Trupower puts it, "About a decade ago the wind industry became aware that wind farms in general were producing less energy than predicted. At that time, projects were falling short in production by roughly 10 percent on average relative to preconstruction P50 estimates made several years earlier. This phenomenon led to the well-known 'haircut' that investors and lenders began applying to correct energy projections for what was being experienced in the field."
The article then explores the many ways installed capacity can have little to do with actual...er...capacity capacity. "Contributing factors include blade pitch or yaw misalignments, anemometer calibration drift, and other control setting errors. The turbine’s actual power curve is another loss source because it often does not match up with the official or advertised density-adjusted power curve. High-wind events that trigger a wind turbine to shut down and undergo a restart cycle when winds lighten (known as the wind hysteresis effect) are another source of lost energy."
For an example AWS provides the above chart of a properly aligned turbine versus the output of a badly aligned turbine.
So are wind energy statistics reliable? Intelligent haircutting has helped the industry a lot, says AWS.