“Dear Wind,” began a series of Internet ads launched this past spring by Idaho Power, the Gem State’s largest public utility, designed to deride the value of wind-generated energy. “You’re not here when I need you.”

For researcher and Stanford University professor Mark Jacobson, who recently co-authored a report in Proceedings of the National Academy of Sciences that confirmed enough wind capacity worldwide to power the globe more than 60 times over, the utility’s snarky ads actually ring true ... to an extent.

“Wind is intermittent,” he conceded in an interview for NPR’s Science Friday program in September, a key reason his article advocates using wind for half the world’s energy needs, or about 5.75 terawatts (TW), in a 2030 clean-energy economy.

The balance, he says, should be made up primarily of solar, with a dash of geothermal, hydroelectric, and concentrated (stored) solar energy. “[Wind and solar] are very complementary,” said Jacobson. “When winds are calm, it’s a sunny day, and vice versa. You don’t need expensive wind [energy] storage if you combine them optimally.”

To prove it, Jacobson and his research team overlaid their multisource formula for clean energy generation against two years of power demand in a representative California market. “We were able to match the hour-to-hour power demands ... with 98% reliability,” he said.

So how many 100-meter-tall wind turbines would it take to generate 5.75 TW of energy for electrical power, transportation, and other projected energy needs in 2030? About 4 million, said Jacobson, up from “several thousand” currently in operation worldwide generating about 237.5 megawatts of energy, of which North America accounts for one-fifth.

If placed on open land and shorelines only (though offshore installations are a viable option as well), that many turbines “would require about 0.6% of the world’s land,” said Jacobson, which could double as agricultural, recreational, or other purposes.

There are also ample stores of neodymium, an earth element critical to wind turbine operation and energy conversion, as well as plenty of concrete and steel. “There are no materials or resource limits” to building up the capacity, he said.

As for bird deaths caused by wind turbines, Jacobson’s study debunks the urban legend. “Turbines kill one-tenth the number of birds that coal and natural gas plants do, from land degradation to air pollution and their building footprints,” he said, adding that perhaps up to 1 billion birds are killed by building each year, another 80 million by cats, and an estimated 10 to 50 million more by communication towers, according to the American Bird Conservancy. Wind turbines, meanwhile, account for about 400,000 bird deaths annually.

The biggest threat to achieving such wind-driven energy capacity, at least in the United States, is probably politics. While polls taken by the American Wind Energy Association show 80% bipartisan support of increasing wind-energy investments, Congress is debating whether to extend wind production tax credits beyond this year.

“It’s a threat to manufacturing jobs” that ramped up when the tax credits were enacted in 2008 and have ebbed in the uncertainty of their future, said Elizabeth Salerno, director of industry and data analysis for the AWEA in Washington, D.C. “Not only is it technically possible in all aspects, but it makes economic sense.”

To listen to the full NPR Science Friday interview with Jacobson and Salerno, go to http://www.sciencefriday.com/segment/09/14/2012/wind-power-plentiful-study-says.html.

To purchase the article in PNAS, go to www.pnas.org and search in the Sept. 12, 2012, issue.