There’s a still in the air – and it is bad news for North America’s wind turbines.
Last year saw the lowest average wind speeds in half a century across much of North America. There were long periods of motionless air across most of the Great Plains and the West, stretching through to Texas and Florida, and from Mexico to Canada.
And weather watchers say the wind drought was back again in the early weeks of 2016. “Low-wind conditions have returned to the US,” says Michael Brower of AWS Truepower, a consultancy for the country’s wind-power industry.
In much of the American West, average wind speeds were a fifth below normal in the first half of last year. As a result, the electricity output of US wind farms fell 6 per cent despite their generating capacity increasing by 9 per cent, according to government agency the Energy Information Administration.
“The possibility of a prolonged wind drought is on the minds of many in the wind industry,” says Brower.
The immediate cause, say meteorologists, is a large ridge of high pressure that formed over the north-eastern Pacific and the western half of North America in mid-2013. This diverted wind-bringing storms far north into the Arctic.
“The ridge was remarkable for its longevity, lasting from June 2013 through to mid-2015. It is the strongest in records dating back to 1960,” says Daran Rife, a meteorologist at energy consultancy DNV GL.
So what caused the high pressure? Some have blamed El Niño, the short-term shift in oceanic currents in the Pacific Ocean that is affecting weather around the world. According to analysis by Brower, Texas experienced wind droughts in 1987 and 1992, both of which were El Niño years.
But in a study published earlier this month, Rife pointed out that the still air in 2015 predated the formation of the current El Niño.
Most meteorologists believe that the persistent high pressure is at least partly a result of the Pacific Decadal Oscillation, a fluctuation that is similar to El Niño but lasts for decades. In the past two years, the oscillation has switched to its “warm” phase, meaning that the wind drought could stick around through 2016.
So far, says Rife, the wind drought has not had a significant impact on investment in wind plants, which can now deliver 5 per cent or more of US electricity when the wind blows.
But he adds that “investors naturally want to understand what happened in 2015, and what to expect in the future”. Another year of wind drought could cause some to have second thoughts.
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