Shrouded in near-silence

A new design of wind turbine could provide significantly better power output than existing mills, while overcoming some of their drawbacks, such as noise and high maintenance requirements. Victor Jovanovic, inventor of the Stormblade turbine and founder of a UK company with the same name, claimed his design incorporates all the virtues of a partially static turbine design with a more aerodynamic solution to the problem of drag. One of the biggest problems with current turbines is that once the wind gets above 60mph, they have to be shut down, because at higher speeds, a gyroscopic effect is created in the driveshaft. Gyroscopic precession tries to twist the turbine, placing stress on the blade and mechanism, causing them to break. Conversely, if the wind speed drops below about 15mph, the blades’ rotation is not fast enough to generate electricity. An alternative is to use a design where the blades are surrounded by a shroud that channels the airflow onto the turbine — a little like a scoop. Prototypes have shown that the efficiency of power generation is increased significantly — up to three times higher than a traditional three-bladed mill. However, the shroud facing into the wind, combined with the high speed of rotation of the air current, tends to create a parachute effect, and extreme forces are exerted on the tower. This means that the tower has to sit on scaffolding, rather than a single pole, and consequently would be both expensive to build and require a large amount of land. The Stormblade turbine aims to overcome these problems. ’It uses some of the principles of the shrouded system, channelling airflow into the turbine and on to the blades,’ Jovanovic said. ’It also overcomes the problem of precession, allowing the turbine to operate at much higher speeds.’ The problems experienced by existing shrouded systems have been resolved by addressing the aerodynamics. Essentially, the shroud cowling is shaped like a jet engine.

Producing less drag

’This shape provides a more slippery profile for the whole unit,’ said Jovanovic. ’The jet engine has evolved over the past half-century to produce less drag so the blades rotate more quickly.’ He believes the operational wind speed for the turbine will be from seven to 120mph, allowing much more efficient energy generation. ’For every extra 15mph over 60mph, you get eight times as much electricity,’ he said. ’So at 90mph you get 64 times as much, and at 120mph more than 4,000 times as much.’ A normal mill typically delivers between 10 and 30 per cent of the original wind power as electricity, while the new design is expected to be at least 70 per cent efficient. Because the blades are concealed and there are no gears to grind, it will be much quieter, claimed Jovanovic. ’Gearboxes are the weak point in the system, because they need regular maintenance and repairs.’ In addition, concealing the blades makes the design less dangerous to wildlife. Jovanovic, who is seeking investment and industrial partners, said: ’If all goes well, the turbines could be on the market in 18 months to two years. ’Although using the jet engine shape might reduce the power output, it would be commercially viable — which was the downfall of previous shrouded designs. While it represents something of a compromise, I’m sure that as the design evolves we will be able to get close to its efficiency figures.’