With demand for wind turbine components surging, developers piling on pressure to deliver ever-larger turbines, and insurance companies demanding tougher reliability clauses, manufacturers are facing an engineering minefield. Eize de Vries reports.The huge worldwide demand for wind turbines is accompanied by varying shortages of key components such as bearings, generators, gearboxes and rotor blades. For instance, reported delivery periods for larger bearings now range up to 18 months. This continuing shortage situation has serious implications, both for meeting production planning for new build, and the necessary replacement components for maintenance of existing installations.
Component shortages in the face of high demand have made it necessary for suppliers to explore alternative sourcing channels. However, some unorthodox channels can prove to carry significant risk. According to a senior manager at the world’s largest bearing supplier, SKF, the worldwide bearing shortage is creating fresh opportunities for sellers of counterfeit components. He adds that such inferior bearing forgeries are often difficult to differentiate from original precision-made equivalents, with even the stamped make and type number and packaging looking identical. Representatives of the German Schaeffler Group, manufacturers of FAG and INA bearings, confirm similar experiences. Both suppliers observe that at least a number of premature mechanical failures in machinery, including wind turbine drive trains, can be traced back to the use of inferior quality imitation bearings.
These and other supply chain imperfections result, according to industry sources, in a substantial proportion of poor quality components becoming integrated into today’s wind turbine supply chain. Potential future costs to correct failures as a result of these technical imperfections can be substantial. As an example, a faulty gearbox bearing in a 2 MW turbine costing €100 can, in a worst-case scenario, result in a €200,000–€250,000 bill for a replacement unit, including additional equipment like a crane and manpower costs.Reliability and lifetime issues
For years now there has been great dissatisfaction among wind turbine operators and insurance companies about the poor performance of several series production wind turbine makes and types. As far back as 2002, a number of German insurance companies – faced with excessive insurance payments for turbine failures – introduced measures to counter perceived reliability issues. Known as the ‘Inspection Clause,’ this compulsory part of the wind turbine insurance contracts involved regular drive train and rotor blade inspections, including compulsory recondition/replacement measures. A regular ongoing claim is that new wind turbine models with unsolved teething problems are still being prematurely taken into series production. For instance, a recent article in the German weekly Der Spiegel contains opinions and quotes from several technical (insurance company) experts in support of this viewpoint. The article reports on rotor blade defects and multiple total-loss failures observed within the 19,000 wind turbine fleet operating in Germany. Additional problems reported in the Der Spiegel article point at expensive and difficult to repair cracks in multiple concrete foundations, and total loss of installation cases due to nacelle fires.
Wind turbines are getting bigger all the time and require high quality components clipper windpower
Experiences in the Netherlands confirm the seriousness and frequency of such failures. According to well-informed Dutch sources in the Flevopolder province, which has the country’s highest wind turbine intensity, up to 50% and perhaps more of all geared installations suffer from premature and recurring gearbox and/or generator failures.
The frequency and wide nature of reported problems has prompted wind industry parties to call for a renewed focus on product reliability as well as substantially increased service life, seen as a badly needed priority shift.Design is everything
A key insight into the issue comes from Carsten Søresen. As owner/director of Denmark’s Green-ener-tech, which removes used wind turbines from repowering sites, then refurbishes and reinstalls them in emerging markets such as Eastern Europe, he gets to see first-hand which components and systems age badly. Søresen says he is generally satisfied with the quality of the used turbines he buys, even when they are rather old, saying: ‘[Up to] 450 kW–500 kW size, turbines are usually well designed and substantially over dimensioned – 100 kW turbines were, for instance, typically fitted with a 200 kW – 250 kW rated gearbox. I have dismantled Vestas turbines twenty years old with the gearbox still in excellent condition. The mechanical design of today’s turbines is generally more compact and design safety margins are, in my view, much smaller. Another key difference I’ve noticed is that the gearbox of a modern 750 kW turbine contains almost the same amount of oil as an old 100 kW turbine.’
While the over-engineered turbines of decades past may indeed display admirable reliability qualities, modern makes perhaps try walking a fine balancing act between maximizing output for minimized costs and with minimal overall built-in system reserves. Perhaps sometimes, in their eagerness to achieve the ultimate, they overbalance.
Eize De Vries is Wind Technology Correspondent with Renewable Energy World