in reverse). American Superconductor says it expects to build the first SeaTitan ‘in the next few years’ and enter volume produc- tion by mid-decade. Another superconductor manufacturer, Zenergy Power of Germany, has also designed a 10 MW machine, and has begun to build a 500 kW prototype with a British company, Converteam, which it expects to finish next year. Chief Executive Jens Müller is confident of securing the funding to build the full-sizedmachine and claims the technology will be fully estab- lished by the end of the decade. ‘The chal- lenge now is to industrialise the supply chain,’ he says.
Hydraulic transmission Superconducting turbines are intended to slash the weight and increase the power of large, low speed generators, but that’s only necessary if you have got rid of the gear- box. An alternative approach would be to stick with the traditional high-speed gener- ator – which is small and well proven – and try to replace the gearbox with something lighter and more reliable. One obvious contender is hydraulic trans-
mission, which is widely used where a fast, steady source of power like a diesel engine has to drive slow, heavy and irregular work – in diggers or rock crushing machinery for instance – the problem of wind turbines in reverse. But the drawback is that hydraulics are typically very inefficient: even in the best systems, scarcely 80% of the energy pumped in does useful work, and the rest is lost to the process. But now a small British company, Artemis Intelligent Power, thinks it has cracked this with a computer-con- trolled hydraulic transmission technology it calls Digital Displacement. With Digital Displacement, the wind tur-
bine blades are connected to a cam shaft that drives a series of hydraulic piston-cylin- ders arranged around it. These pump fluid through a pipe to drive the cylinders of two hydraulic motors, which in turn drive a pair of standard high speed generators. A computer controls how many of the cylin- ders are used from one millisecond to the next, using only as many as needed at any given moment, and creating an infinitely variable transmission ratio. This dramatical- ly raises the efficiency to well over 90%, and the company hopes to reach 95% eventually. It also means the system can respond instantly to changes inwind speed and keep the generators running at exact- ly the right, steady speed to deliver grid- quality power – however wild the gusts. That in turn means a Digital Displacement machine can dispense with the expensive power electronics that almost all other tur- bines need to do that job. Because the systemcontains far less steel
than a gearbox it weighs about half as much, and that should help produce more powerful turbines. ‘We see our technology getting more competitive as machines get bigger,’ says Managing Director Win Rampen.
Energy World April 2011
The Japanese engineering giant
Mitsubishi Heavy Industries seems to agree. Last December it bought Artemis as part of a £100mn deal, and plans to incorporate Digital Displacement in North Sea turbines by the middle of the decade. ‘This is a mas- sive vote of confidence in our technology,’ says Rampen.
Turn thinking on its side However much weight newer turbine designs can shed, theywould still sit atop a 100 metre tower. And some say that’s the real problem: not so much the weight per se, but where you put it. Structurally con- ventional wind turbines are ‘trying to hold up a sledgehammer in thewind’ says entre- preneur Theo Bird, the founder of Wind Power Ltd, a British company developing a turbine that turns conventional thinking if not on its head, then at least on its side. Today’s turbines make life difficult for
themselves by putting all their weight at the top of a long lever that the wind is con- stantly trying to knock down. That creates huge forces that will ultimately limit the size and power of all conventional machines, says Bird. His answer is the Aerogenerator X, a 10
MW vertical axis design featuring two diagonally outstretched arms with rigid sails at the end, which is shorter and wider than a normal turbine. There is no tower, and the arms rotate horizontally around a base that houses the generating equip- ment. Because the weight is concentrated at the bottom of the structure it is not so critical, and this means the design could work with any type of generator or gear- box. It also makes the structure more sta- ble, meaning the foundations can be smaller. The company claims its machine would be half the cost of a conventional turbine. The Aerogenerator would have a num-
ber of practical benefits. The generating equipment should be much easier to access and maintain, cutting downtime and cost, and the stability of the design makes itwell suited to floating platforms that could operate in deeper waterwhere the wind is stronger. And, critically, the design also lends itself to much larger machines. ‘Vertical axis machines are not limited by the strength of existing materials in the same way as conventional turbines,’ says Professor Feargal Brennan of Cranfield University Offshore Engineering Department. Cranfield was part of a group of British
universities and specialist engineering com- panies that helped Wind Power develop the Aerogenerator, with funding from the Energy Technology Institute (ETI), whose remit is to bring the cost of offshore wind down to the level of onshore. Wind Power is waiting to hear if the ETI will fund the next phase of detailed design work, but either way, Bird plans to build a 1 MW machine in 2012, and awind farm of 5MW machines by 2015. ‘It’s a pretty wacky con- cept at first sight, but we’ve really kicked the tyres and we’re very convinced it’s plau- sible,’ says Professor Brennan.
Not short of ideas Maybe so, but there could be stiff competi- tion for that title from superconductors and hydraulic transmission – and a rash of other developments. Clipper is developing the Britannia, a prototype 10MWmachine with an improved gearbox that reduces loads by a factor of four; EDP of Portugal will test turbines on floating platforms this year; and Gamesa is leading a Spanish industry study to research the technologies needed to build a 15 MW machine. While the challenges of offshore wind remain formidable, the industry is not short of ideas.
One solution – the 10 MW Aerogenerator X design uses a vertical axis of rotation and has weight concentrated at the base
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