'Very Long Blade' for Siemens 6MW

The maiden blade to come out of an ambitious British government-industry scheme to develop a 100-metre-long modular concept for the offshore wind market is on track to be flown by a 6MW Siemens turbine by 2016.

Designed at a down-scaled length of about 80 metres, the prototype, being developed under the aegis of the Energy Technologies Institute’s ‘Very Long Blade Project’, has been engineered by UK outfit Blade Dynamics, based on a concept that uses proprietary jointing techniques to assemble sections ranging in length from 10-25 metres into a lightweight, ultra-long unit.

Plans are to have the prototype ready for static and fatigue tests by the end of 2014, with a three-bladed rotor ready for installation on a first turbine “late in 2015”.

“This moves us full steam ahead from the design phase into prototyping of a blade,” states Blade Dynamics senior technical manager David Cripps.

“This project was started with a view to developing the blades for the next generation of ultra-large turbine, rather than those that are currently being demonstrated.

"But building a demonstration blade for the 10MW-plus class right now would be a big white elephant waiting for a turbine of this scale to be tested on.”

Blade Dynamics’ “split-blade” technology makes extensive use of carbon fibre in its modular spar structures and a novel lightweight ‘corrugated’ root configuration, while shunning the mechanical fasteners – known to create ‘hardspots’ in the blade and add considerable heft – used in other modular designs to hold the sections of the blade together.

Weighing some 40% less than conventional glass-fiber blades of like-length, the designer calculates its 100-metre model will be able to supercharge annual energy production from a turbine by up to 15%.

Manufacture and testing next year of the 80-metre prototype – which will have elements fabricated both at Blade Dynamics’ UK and US factories – will go hand-in-hand with an additional project aiming to nail down the structural and performance analysis and cost modeling of the larger 10MW-plus model.

“The technical development phase we have had during this past year has been looking at some of the issues around 10MW blades, but with a view to applying what has been learnt to the 6MW design,” says Cripps.

“More than continuing to look at the technologies involved, this second project will work up a full 10MW-plus design proper, because of course there are people now working on this size of machine, even if it is only at the concept phase.”

Siemens is understood to be developing a 10MW direct-drive model that would have a rotor diameter of some 210-metres.

“After this next phase of further prototype testing [of the Blade Dynamics blade], we will consider demonstration of a full rotor on a 6MW turbine,” notes Siemens chief technology officer Henrik Stiesdal.

“Subject to successful conclusion of the tests it is clear that the potentials of the split-blade technology of Blade Dynamics would be expected to become even more interesting as we move to even larger turbine platforms.”

Blade Dynamics’ six-tonne, 49-metre-long model for a 2MW machine, certified by GL, is the lightest blade in the world for its size.