An international agency that once brushed off the potential of wind energy has become one its biggest supporters.

The International Energy Agency (IEA) released a special report on wind power, saying that with continued improvements in technology and support from governments, offshore wind farms could generate more than 420,000 terawatt-hours per year worldwide — which is more than 18 times global electricity demand today.

Offshore Wind Outlook 2019 is a 98-page document that looks at technological advances, market forces and a geospatial analysis of where wind power can work. It's a snippet of the group's annual world energy report, which will be released on Nov. 13. IEA, which was founded in 1974 to coordinate a response to disruptions in the flow of oil, has since expanded to explore all energy issues.

"Offshore wind currently provides just 0.3% of global power generation, but its potential is vast," said Dr. Fatih Birol, the IEA’s executive director, in a press release. "More and more of that potential is coming within reach, but much work remains to be done by governments and industry for it to become a mainstay of clean energy transitions."

It's also an economic opportunity as wind is on track to become a $1 trillion business, which may explain, in part, the agency's dramatic change of heart. As David Vetter explains in Forbes:

"...the IEA was for many years unconvinced of the potential of renewable energy sources, including wind, to produce sufficient energy for the world’s needs. In 2000, renewables were little more than an 'also-ran' category in the agency’s report for that year."

Science is changing attitudes toward wind power

The first floating offshore wind turbine, floatgen, is pictured off La Turballe in western France. SEBASTIEN SALOM GOMIS / AFP / Getty Images

This backs up earlier research looking at the amount of wind energy available for harvest over our oceans. According to the study published in the Proceedings of the National Academy of Sciences, there's enough energy over the oceans to "potentially provide civilization-scale power."

To harvest that power, we would need to cover enormous stretches of the sea with turbines, a monumental engineering feat that would also have real environmental consequences. So while actually powering human civilization with wind power alone is probably impractical, the study demonstrates that floating wind farms have an immense untapped potential.

"I would look at this as kind of a green light for that industry from a geophysical point of view," said one of the study's researchers, Ken Caldeira of the Carnegie Institution for Science in Stanford, California.

The reason offshore wind power has so much more potential than land-based wind farms is that wind speeds can be as much as 70 percent higher over the sea. Part of that is because natural and human structures on land create friction that slows wind down, but researchers also found that wind over the ocean circulates from higher altitudes.

"Over land, the turbines are just sort of scraping the kinetic energy out of the lowest part of the atmosphere, whereas over the ocean, it’s depleting the kinetic energy out of most of the troposphere, or the lower part of the atmosphere," explained Caldeira.

The study found that it would take a 3 million square kilometer wind installation over the ocean to provide all of humanity’s current power needs, or 18 terawatts. That's a lot of turbines; it would need to cover an area roughly the size of Greenland. Still, it's possible.