A handful of companies today are working on wind turbines that, rather than being mounted on tall towers, would hover in the skies at the end of 300- to 10,000-metre tethers. They would take advantage of faster, steadier wind at higher altitudes, and likely avoid the protests over noise that conventional turbines sometimes provoke.
Don't check overhead for such devices yet, though. While prototypes have been built and tested, proponents say it will be at least a couple of years before these flying generators feed power into the electrical grid.
Ottawa-based Magenn Power Inc. has designed a balloon-like inflatable turbine based on technology that its founder, Fred Ferguson, began designing in 1978. Mr. Ferguson's Magnus Airship won a Canadian Government Award of Excellence in 1984 and was destined for, but died with, Ronald Reagan's Star Wars missile defence program.
Years later, Mr. Ferguson decided to apply the Magnus Effect, in which the backward rotation of a lighter-than-air sphere provides added lift, to an airborne wind generator. His idea became the Magenn Air Rotor System, or MARS.
The rotation of the helium-filled MARS helps keep it aloft and generates power, which is fed to the ground along the cable tethering the structure. Magenn tested a prototype at 100 metres in April 2008, says Anthony Pizarro, Magenn's director of corporate development. "That was really the first electricity generated from this type of vehicle." Magenn has since built a new, modified prototype that it hopes to fly next year, and that could enter pilot production late in 2010.
The MARS could be used in multi-unit wind farms, or singly as a power source for oil-drilling rigs and other remote installations that today rely mainly on diesel generators, Mr. Pizarro says.
Because winds are steadier at higher altitudes, and because the MARS can operate in winds from around seven to 100 kilometres an hour, Magenn believes it will convert 25 to 60 per cent of available wind energy into power, compared with 20 to 30 per cent for ground turbines - and would work on 45 per cent of the earth's surface, whereas only about 13 per cent is suitable for conventional turbines, Mr. Pizarro says.
Mr. Pizarro says the noise from the MARS will be nearly inaudible on the ground, and it should present little danger to birds because it will rotate at less than wind speed, whereas ground-based turbines can get up to seven times wind speed.
Sky WindPower Corp. is aiming for greater heights. The Oroville, Calif., company is developing a system - which Time magazine named one of the 50 best inventions of 2008 - that will have multiple rotors, rather like helicopter propellers, to keep it in the air and generate power. Len Shepard, Sky's chief executive, says the tethered craft will operate at 1,000 to 9,000 metres.
That's getting up to where airplanes fly, so Sky's devices would need reserved airspace, Mr. Shepard acknowledges. So they would be used strictly in wind farms, probably with multiple units at different altitudes in a small area.
Mr. Shepard says the rotors would be powered to take the units to operating altitude, where there would be enough wind to spin them, generating electricity and keeping the craft aloft. The angle of a unit would be controlled from the ground, so if one broke its tether it could fall, but units would be fitted with parachutes to help the rotors slow its descent, and wind farms wouldn't be located over populated areas, he says. "I wouldn't want to live under one of these things until we get comfortable with them."
So far Sky has only tested its prototypes in wind tunnels and by towing them at low altitudes, but Mr. Shepard believes they could reach commercial use in as little as three years.
He says the device can convert 50 to 75 per cent of available energy to power anywhere between 30 and 60 degrees latitude, which encompasses most of the U.S. and southern Canada.
Mr. Shepard sees Magenn's MARS not so much as a rival but as a complementary technology. "I believe all of them will work," he says.
Magenn, Sky and others working on airborne wind power designs will meet for a conference on high-altitude wind power in California in early November.