Matthew Sheahan
WIND FARMS ARE A DISQUIETING SIGHT OFF OUR COASTS, BUT A KITE-POWERED ALTERNATIVE UNDER DEVELOPMENT COULD BE SOMETHING ELSE...
Wind turbines may be impressive pieces of engineering and technology, but I find their presence offshore rather unsettling. Be it the extensive wind farm in the Thames Estuary, the forest of turbines in the North Sea, or the gathering of whirring blades off Brighton, whenever I sail close to these areas, the windmills seem to be slap bang in the way.
I know they’re well marked and usually very easy to see, but the thought of being swept into a forest of giant rotating white knives isn’t very appealing. And are they really that efficient? I’m not sure I’m convinced.
Yet the looks, efficiency and obstruction that wind farms present to offshore sailors could be about to change with a new, more radical system that could provide a more efficient means of creating green power, while also providing a staggering aerial display.
The new breed of wind generators, described generically as Airborne Wind Energy Systems (AWESS), use a device flown off a tether to generate electrical power. In essence it’s like flying a kite, but on a giant scale with an unmanned aircraft at the outer end of the line.
Among those leading the development is Ampyx Power, which is working in conjunction with rope specialist DSM.
Their system uses a tethered aircraft that has an autonomous flight control system to fly in a figure of eight configuration at a height of 200-450m. As it does so, it pulls the tether on a winch that is mounted on a platform. As the line surges out the rotation of the winch generates power.
Once the tether is reeled out to a predefined length of about 750m, the aircraft automatically returns towards a lower altitude and lower wind speed where the drum then reels the plane back in using some of the power that was generated as it was pulling the cable out. Apparently the reel-in process only uses 1% of the operational tension.
Once in, the aircraft is released and it begins its power
generating ascent once again. It’s a tricky system to envisage but you can see an animation at on Youtube in a video entitled ‘Ampyx Power Floating Airborne Wind Energy System’.
According to Ampyx Power, the windmill-style turbines that were constructed in the early 2000s were intended more for use ashore rather than at sea and will therefore reach the end of their lives between 2020 and 2025.
The company says that the benefits of its system over conventional turbine blades includes greater efficiency thanks to the height at which the plane flies. This is way above that of conventional turbine blades and therefore in a steadier stream of faster moving air.
As a result, the aircraft is smaller than the turbine blades, with a wingspan of 30m (typical wind farm blade diameters are 40-90m – the biggest are up to 164m), but will generate around the same as an onshore wind turbine at around 2-6 megawatts. In addition, the units can be installed on existing turbine bases and are easier to take away for servicing.
But while the theory sounds fine, the reality is that these are big beasts with huge wingspans. An autonomous glider-style drone with a 30m wingspan carving around the sky at 1,500ft is ‘up there’, as they say. By comparison, a cruising 40-footer’s mast is around 18m tall, while a modern Open class two-seater glider has a wingspan of around 27m.
The procedure for dealing with one of several modes of failure is also tricky to appreciate. Apparently, if the line breaks the on board control system will fly the plane back to its perch-like landing platform using the two powered props incorporated into the design.
The first example of the system, which is being developed in association with European energy company E.on, is due to be tested in County Mayo, Ireland.
If all goes well, the prospect of a wind farm that consists of an array of autonomous giant gliders weaving in the sky will move a step closer.
From a mariner’s perspective it’s tempting to hope that the new system may free up some space in our already crowded waters. But if nothing else, the spectacle of a farm of giant tethered aeroplanes will surely be worth a visit.
‘THE REALITY IS THESE ARE BIG BEASTS WITH HUGE WINGSPANS’