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Gregory Meyer reports at CNBC that electricity generated by US wind farms fell 6 per cent in the first half of the year even as the nation expanded wind generation capacity by 9 per cent. The reason was some of the softest air currents in 40 years, cutting power sales from wind farms to utilities and the situation is likely to intensify into the first quarter of 2016 as the El Niño weather phenomenon holds back wind speeds around much of the US. "We never anticipated a drop-off in the wind resource as we have witnessed over the past six months," says David Crane.
Wind generated 4.4 per cent of US electricity last year, up from 0.4 per cent a decade earlier. But this year US wind plants' "capacity factor" has averaged just a third of their total generating capacity, down from 38 per cent in 2014. The EIA (U.S. Energy Information Administration) notes that slightly slower wind speeds can reduce output by a disproportionately large amount. "Capacity factors for wind turbines are largely determined by wind resources," according to their report "Because the output from a turbine varies nonlinearly with wind speed, small decreases in wind speeds can result in much larger changes in output and, in turn, capacity factors." In January of 2015, wind speeds remained 20 to 45 percent below normal on areas of the west coast, but it was especially bad in California, Oregon, and Washington, where those levels dropped to 50 percent below normal during the month of January.
Some also speculate the the increase in the number of wind farms may be having an effect. Since wind turbines extract kinetic energy from the air around them, and since less energy makes for weaker winds, turbines make it less windy. Technically speaking, the climate zone right behind a turbine (or behind all the turbines on a wind farm) experiences what's called a "wind speed vacuum," or a "momentum deficit." In other words, the air slows down and upwind turbines in a densely packed farm may weaken the breeze before it reaches the downwind ones. A study in 2013 also found that large wind farms could be expected to influence local and regional atmospheric circulations. "If wind farms were constructed on a truly massive scale," adds Daniel Engbar, "their cumulative momentum deficit could conceivably alter wind speeds on a global scale."
(Score: 1, Informative) by Anonymous Coward on Friday September 04 2015, @04:35AM
> That is, when you get the least solar, is when you are probably getting the most wind, and vice-versa.
Not so much. Wind tends to die off at night. Wind is driven by temperature differentials and without the sun to add heat to the ground creating a differential it all dies off. It is pretty dramatic - here is this week's data for a weather-station near me. [newsday.com] Look at the 3rd graph labeled "wind speed/wind gust" you can see how each day the wind starts at around 8:30AM and stops around 9PM - which is about 2 hours offset from sunrise and sunset (currently 6:30AM and 7:15PM at that location).
Of course that phenomenon is not universally true, but it is the norm. Some areas of geography have more consistent wind, especially near bodies of water because water holds heat much better than earth so when the sun goes away, the earth cools but the water stays warm and thus you get a breeze. Other factors include height (not necessarily altitude) the higher off the ground, the more wind.
(Score: 2) by Runaway1956 on Friday September 04 2015, @02:09PM
KCALOSAN That would be coastal California? Uh-huh - I guess I should have known better. Coastal regions have their own weather patterns, and I didn't think about that at all. I don't know where to look for a similar chart, but each day, I look at the local weather from NOAA in DeQueen, Ar. We generally get a little breeze in the evenings, and it lasts most of the night.
OH NOES! Weatherunderground says I'm full of shit, and don't know what I'm talking about!
Well, not exactly, but my local chart resembles the chart you link to. Hmmmm - now I need to look at things and figure out where I've gone wrong.
Thanks for posting, man!
(Score: 0) by Anonymous Coward on Friday September 04 2015, @04:33PM
> KCALOSAN That would be coastal California
That is right in the middle of the san fernando valley. Coastal, being near a body of water, would tend to have sustained winds even at night.