His comments came at the technology panel, which was discussing how Europe could deliver 33% of its power needs from wind by 2030. Developers weary from crossing grounded Europe by bus, train or car might have allowed themselves a wry smile when Kuhn cast doubt on manufacturers' performance claims. "Calculated turbine reliability figures do not automatically represent actual operational reliability," he said, adding that this chronic lack of understanding is the weakest link of the wind power industry.
Danish rotor blade supplier LM Wind Power has invested in a wind tunnel and computational fluid dynamics to help mimic field performance and help the firm design its blades. It aims to achieve within the next five years a 10% increase in turbine output while maintaining the same loads envelope with a simultaneous 20% reduction in costs. Yet Frank Nielsen, chief technology officer at LM, admitted that his modelling often coughed up rather different results to those experienced in the field.
Former chief executive of Hansen Transmissions Ivan Brems stressed the importance of being able to more accurately simulate computer-based wind turbine dynamics behaviour, including impact loads, parallel to actually determining these loads based upon actual measurement results. With this and continued turbine upscaling in mind, Hansen has further invested heavily in a 13MW gearbox test stand.
For his part, Kuhn said turbines are getting increasingly complex. Yet he added that built-in sensors that continuously monitor several functions have proven to be unreliable. Simultaneously, supervisory control and data acquisition (Scada) systems produce only synthesised, rather than real, analysis of the data that is made available.
The panel discussion soon moved to an ongoing conundrum surrounding materials. Should the industry make the most of tried and tested products or adopt innovative materials in the hope that it can improve performance? Nielsen sees a lot of potential in improving current composite materials rather than embracing the new. "We are in a constant battle in the choice for optimal resins and fibre combinations," he said. "This includes the question of whether to use polyester or epoxy-based composites. Another key question is how to remain cost-effective. And why should one consider using carbon fibres? These have the same strength properties as glass fibres, but greater stiffness and higher prices."
He has mixed feelings about the concept of producing future wind turbine components, such as rotor hubs and towers, from composite materials.
Offshore gamble
On a question of whether the industry should develop lightweight nervous fast-reacting offshore wind turbines, Henning Kruse, senior export manager at Siemens Wind Power, said that the sector above all requires reliable wind turbines. "Turbine mass will no doubt go down," he said. "But this should never be at the expense of quality."
Warming to Kruse's theme, ABB manager Claus Madsen said that nobody wants to gamble on offshore - and that proven track record is the key. He drew a parallel with the world of so-called small wind or micro-turbines, where new concepts are being constantly developed and launched with wildly varying degrees of success. "There failures have a relatively minor effect," he said. "But with mainstream wind technology, taking large risks can have big effects."
In spite of the sparring over testing systems and materials, the technology panel was not immune to that favourite debate of the wind sector: geared-drive versus direct-drive. Kuhn said that a general wind industry mood appears to favour direct-driven permanent magnet generator (PMG) solutions. For his part, Madsen argued that multiple drive concepts are being studied at the moment but added that PMG might indeed become the leading next-generation generator technology.
Geared-drive specialist Brems argued instead that for many years direct-drive systems have commanded a global market share of only 10-14%. He said that this fairly meek hold on the market indicates that prophecies of direct-drive turbines taking over in the near future are overblown. Brems also quoted study results that showed that direct-drive turbines become heavier compared to geared systems once they exceed a 2MW nameplate rating. But Brems' view is not supported by recent direct-drive product developments. For example, the new 3MW direct-drive Siemens SWT-3.0-101 nacelle weighs 73 tonnes, versus 82 tonnes for the older design 2.3MW SWT-2.3-93 geared wind turbine.
Supersize search
Over the years, turbines have become larger and larger. Will this trend ever stop? Onshore, Kruse said thinks it will. Onshore installations will not get much bigger, he said. But offshore is a different story. In the past, attempts have been made to predict maximum turbine size. Many studies indicate upscaling will not end at 10MW, but 10-15MW might be likely. Brems added that he foresaw no constraints on building gearboxes for these future behemoths.
But Kuhn urged caution over the race to grow. "An issue for me is how to reduce both risks and costs," he said. "It requires, instead, much better overall technical and overall insight. The new generation of large wind turbines will perhaps also require completely new suppliers prepared to develop something totally different."
Madsen, too, struck a more bearish tone on supersize machines. "A (better) question for me is how small can one get," he said. "Smaller size turbines are suitable for many different applications."
Kruse argued that, in order to achieve a 20% renewables goal for Europe by 2020, mature technologies are required. "Such a strategy requires reliable industrial components and systems - not fancy new technologies," he said. "In this respect we have learned a lot from automotive experiences with mass production. For the offshore market, we should take a wider view at the total process and not only focus on the actual wind turbines."
Finally, an interesting topic was raised. Is the industry right in its thrust for fully equipped offshore wind turbines - or would it be better to install simple offshore turbines with all power electronics placed onshore? Madsen argued that the sector should continue on its current path. "We are still amid a process that is focused on achieving higher reliability with today's technology," he said. "Who will be prepared to take the huge risk and provide the necessary finance to engage in an alternative that has never been tested before?"
That question could apply to many innovative ideas in the wind sector. Indeed, most of those who overcame the hellish ash from Iceland's volcano to make it to EWEC advised the industry to stick with the devil it knew.
MAJOR NEW WIND INDUSTRY TREND - BIGGER AND BETTER MACHINES
Until not long ago the number of suppliers that offered onshore turbines rated at 3MW-plus was limited to only a couple. Vestas had its V90-3.0MW while Winwind offered its WWD-3. Now an increasing number of leading wind turbine suppliers have entered the market - indicating a major new onshore wind industry trend.
Late in 2009, Siemens erected a prototype of its lightweight SWT-3.0-101 direct-drive prototype, while Vestas released a prototype of a new geared V112-3.0MW turbine.
At the April Hannover international industry fair, Enercon of Germany introduced its new generation of 3MW direct-drive wind turbines with liquid-cooled generators. And at EWEC, Repower presented new 3.2MW and 3.4MW sister products.
A parallel trend is that rotor diameters are increasing faster than turbines' rated power, an industry-wide strategy clearly aimed as a yield-boosting measure. For example, in 2002 a 90-metre rotor was considered state of the art in the 3MW class, but today's rotor diameter range covers 100-116m. Note that a 112-metre rotor has a 55% greater swept area than a 90-metre blade, so the upgrade is more significant than the numbers initially suggest. Vestas quotes that for a common location with an annual average wind speed at hub height of 6.7m/s, a V112-3.0MW, which has 112-metre blade, has a 38% greater energy production than a V90-3.0MW, which has a 90-metre blade.
Many years after MBB of Germany and Riva Galzoni of Italy ceased making single-blade wind turbines, Spanish Zaragoza-based Ades Wind Turbine is trying its fortunes again. The ambitious company has developed a highly innovative pitch-controlled downwind turbine loaded with many unusual technology features and showed a much-visited scale model in Warsaw to a critical audience. Ades project engineer Fabian Moyano said that four 250kW, 30m rotor diameter prototypes will be erected this month in Spain, following a 15-year product development period. One inherent problem with single-blade turbines has always been a high rotor blade tip speed (m/s) that often has resulted in an excessive aerodynamic noise level.
A rotor blade tip section is the fastest moving outer blade part. The maximum tip speed of the Ades 250kW is 116 m/s, whereas about 82-85 m/s is a common value for most three-blade turbines. Possible benefits of single-blade turbines are reduced nacelle and rotor mass, and potential cost savings on one or two additional blades that are otherwise required. That said, a counter-weight has to be fitted at the missing rotor blade position. A key single-blade turbine disadvantage is its aerodynamically and dynamically unbalanced rotor. With three blades or more the rotor is aerodynamically and dynamically balanced, whereas with two-blade machines the rotor is dynamically unbalanced.
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