Variability and energy payback of wind
The following was posted yesterday in response to a letter in the Casper (Wyo.) Star-Tribune talking about wind's "intermittency" and wondering how much net energy a wind turbine produces:
Wind is actually more variable than "intermittent"--a typical wind farm will generate some electricity 65% to 90% of the time, depending on the wind speed patterns. Much of the time, it will be generating at less than full capacity, which is why its "capacity factor" (its average generation divided by its full capacity) is more like 40% at the best sites.
Second, wind has a rapid "energy payback"--something that has been documented by numerous studies in the U.S. and elsewhere dating back to the 1980s. A wind turbine typically takes only a few months (3-8, depending on the average wind speed at its site) to "pay back" the energy needed for its fabrication, installation, operation, and retirement.