It still has a rotor, drivetrain, generator and so on, but it is shaped like a tornado — and early field tests suggest it can churn out up to 600% of the production of a like-rated horizontal-axis turbine.

The Invelox system, being developed by US start-up SheerWind, works by capturing wind as slow as 3.2km/h, feeding it into an array of intake vents at the top of its funnel-topped tower and channelling it down to power a turbine at ground level.

Trials