Everyone has data they rely on in North America, says Andrew Garrad, head of international wind consultancy Garrad Hassan. "But I think to call it an index is to give it too much credibility." In identifying the performance gap, Garrad Hassan compared all the US wind speed data in 2007 to the best observations taken over 15 years.
The analysis revealed that winds in 2007 were about the same as the 15-year average in some areas, but poorer in others. West Texas, where thousands of megawatt of wind plant operate, saw the worst wind in 15 years. Garrad says that this is one reason for the observed shortfall of energy produced by wind turbines in the American fleet in 2007.
Robust wind indices for different regions of America that most companies can rely on would greatly help in the prediction of wind farm production. But that is a tall order to accomplish for such a large country, admits Garrad. "We have been trying to put one together but because it's such a big place, it's very difficult to do, and I would say that were quite a long way off from having such an index in a reliable form for the US," he says.