Superior air power

A tethered wind turbine floating up to 300m (1,000ft) above the ground could provide cheaper electricity by picking up the stronger winds that are found at higher altitudes, according to its Canadian developers.

Each Magenn Air Rota System (MARS) device is filled with helium and functions like a spinning airship floating many times higher than a conventional wind turbine. According to

chief executive Mac Brown, the system could provide emergency power for areas hit by natural disasters.

Aerodynamic fins along each device catch the wind to power two generators that are fixed to each end of the device. Although Brown concedes that MARS will not be as intrinsically efficient as conventional fixed wind turbines he believes the system carries a number of benefits that make it a viable alternative.

'Traditional wind turbines can never run 100 per cent of the time because of the lack of wind, so they tend to operate at 26-42 per cent efficiency,' said Brown.

He believes the MARS system will be far more cost effective than conventional wind farms because of the higher electricity output it can achieve by accessing stronger, high-altitude winds.

Wide range of operation

The system can also operate at a wide range of wind speeds, from 2m/s to 28m/s. Power is passed down from the generators along the tethers to a ground station. Once there, the power can be stored in batteries or directed to a transformer that can then pass it directly to the power grid.

Each helium-filled 'airship' will be attached to three tethers to keep it stable. If only one tether were used the devices would be less stable and would have to be stationed far apart to avoid collisions.

The spin induced by the wind on the turbine also helps keep the device stable by using an aerodynamic force known as the Magnus effect — the same effect that induces swing in cricket balls. The phenomenon uses the low pressure beneath and high pressure above the balloon to give more lift, helping keep the device stabilised. It also pulls the device upwards, maximising the benefits of altitude, rather than leaving it hanging down on its tether.

The concept for the system originated from work by Magenn in the 1980s, when it designed an airship that used the Magnus effect, which it hoped would one day replace the helicopter. The Reagan administration awarded a contract to develop the technology as part of the Star Wars programme, but it was cancelled when the programme itself was pulled.

'We took the knowledge from more than 160 wind tunnel tests in that project and applied it to big airships, which could be used to move cargo at low cost,' said Brown. 'Then we turned to the possibility of floating wind turbines using the same idea.'

No fly zones

To counter the potential problem of MARS devices interfering with aircraft flight paths, Magenn plans to apply for a NOTAM (Notice to Airmen), which would create small no-fly zone around the MARS wind farms. Each tether will also carry blinking lights every 50m with additional blinking lights attached to each balloon.

Another safety feature will bring the balloons back down to earth if they come free of the tethers. A thin filament wire fitted along the length of the balloon heats up if it comes free of the tether, slicing through the balloon's fabric to let out the helium and allow the balloon to descend to safety. Each device is also made from radar-reflective material to enhance its visibility.

Magenn has made some basic prototypes and hopes to develop a 4kW commercial model by the start of next year.

Brown said MARS is suited to a number of applications besides disaster relief. It could be used in developing nations where infrastructure is limited or has been destroyed, or in areas where people live away from the main power grid.

Brown added that the US military has also shown an interest in the technology for battlefield use.