USGS interactive map showing location of utility-scale wind turbines.

It gets more than its share of dramatic weather, but the U.S. South is generally not windy, at least not over land. As a result, wind power isn’t a thing there. East of Texas and south of parallel 36°30′ north – the Missouri Compromise line – the only wind farm in the entire region is a modest 18-turbine, 29-megawatt operation on a Buffalo Mountain ridgeline near Oak Ridge, Tennessee.

But the wind industry is eyeing the South, and getting encouragement from the U.S. Department of Energy. The path to making wind energy a reality in Dixie – and in other marginal wind areas of the country – is through improved technology, particularly taller towers with larger rotors, they say.

We’re talking towers as tall as 140 meters to the rotor hub, a big increase from the current 80 to 100 meters. Add in rotors with 60-meter blades and tip heights would be well over 600 feet above ground.

A 120-meter tall Suzlon tower in India. Photo from Suzlon.

The lofty towers are necessary to reach lofty goals for wind power, which has grown from almost nothing a decade ago to supply nearly 5 percent of the nation’s electricity.

“For wind to be a truly national resource and contribute 20% or more of the nation’s energy needs by 2030, future installations will need to include low wind speed sites such as the southeastern United States,” the DOE said in Enabling Wind Power Nationwide (PDF), a report released on Tuesday to coincide with the American Wind Energy Association’s big annual conference.

The industry could use fresh terrain; there’s only so many wind farms it can build in familiar venues like Iowa, Texas and Oklahoma (especially without extensive and expensive new transmission to move the power to high-demand population centers). Together, those three states accounted for more than 60 percent of the 4,850 MW of new wind power that was built in the U.S. last year.

Ultimately, offshore wind is seen as the best bet for lots of wind power in the Carolinas, Louisiana and Alabama, but still, under its 20-by-2030 scenario, the DOE projects 7,750 MW of land-based wind in seven Southern states that now total just those 29 lonely megawatts in Tennessee.

DOE’s Projected Land-Based Wind Power
Capacity in the U.S. South, 2030

The next-generation towers are key to making this possible because they give the rotor access to stronger, freer flowing wind, less impeded by terrain. But bigger rotors are an important part of the equation as well.

It sounds contradictory, but the key to making wind more widely viable is in decreasing the specific power of turbines. Here’s how that works: Specific power is the ratio of nameplate capacity to swept area of the rotor, expressed as watts per square meter. If the swept area goes up while the nameplate capacity remains the same, the specific power will drop, but the turbine can produce power in lower wind speeds, boosting capacity factor.

“This increase in capacity factor is often more than sufficient to offset the increased capital costs of a larger rotor and makes wind power economical in low wind speed sites,” the DOE said.

You can see the difference in these two images provided by the DOE. The dark blue areas are where wind power is viable, in the first map with current turbine heights, in the second one with 110-meter turbines.

Towers 110 meters tall, and taller, are commonplace in Germany in lower-wind sites. “In the southern states, the rotor diameters reach an average of more than 100 metres and the tower heights more than 130 metres,” the 2014 BWE Wind Industry in Germany report said (PDF). And Acciona is building a wind farm in Mexico using 120-meter towers made of concrete. “These wind farms represent the biggest project to date worldwide using concrete towers implemented by Acciona,” the company said in a recent release.

A chief hurdle to overcome in taller-tower deployment has been transportation logistics, but the DOE and industry say those are challenges that can be met – as they clearly are being in Germany, Mexico and elsewhere. “The height of bridges limits the diameter of towers that can be transported by truck,” the DOE report said. “Innovations to address these challenges include on-site manufacturing, modular components, and new materials and designs for larger systems.”