Australian engineer Bryan Roberts wants to build a power station in the sky — a cluster of flying windmills soaring 15,000 feet in the air — but is having trouble raising enough money to get the project off the ground.

After 25 years of research, Roberts has designed a helicopter-like rotorcraft to hoist a wind turbine high into the air, where winds are persistent and strong. The craft, which is powered by its own electricity and can stay aloft for months, feeds electricity to the ground through a cable.

Roberts, a professor of engineering at the University of Technology, Sydney, believes there is enough energy in high-altitude winds to satisfy the world’s demands. Wind-tunnel data suggests a cluster of 600 flying electric generators, or FEGs, could produce three times as much energy as the United States’ most productive nuclear power plant.

Roberts has teamed up with Sky WindPower, a San Diego startup that is trying to commercialize his invention.

The company has Federal Aviation Administration approval to conduct tests of the technology in the California desert, but needs $3 million to build full-size flying generators. The company is having trouble raising the cash because there isn’t likely to be an immediate return on investors’ money.

High-altitude winds could provide a potentially enormous renewable energy source, and scientists like Roberts believe flying windmills could put an end to dependence on fossil fuels.

At 15,000 feet, winds are strong and constant. On the ground, wind is often unreliable — the biggest problem for ground-based wind turbines. “For FEGs, the winds are much more persistent than on ground-based machines,” said Roberts. “That’s part of the benefit, more power and greater concentration.”

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