E.on has learned the hard way that fixing problems at sea requires far more effort than on land. It weathered many troubles with its 30 Vestas turbines installed in 2004 at Scroby Sands off the UK’s east coast. But six years on, its recently completed Robin Rigg wind farm, off the west coast, boasts one scheduled service visit a year for the wind turbines. Has E.on found what every offshore wind farm operator seeks — a reliable offshore turbine that never fails and needs little servicing?
Interestingly, the wind turbines at Robin Rigg are an update on those used at Scroby Sands, which were dogged with generator and gearbox problems, leading to their withdrawal from sale in 2007. The Vestas V90s were re-introduced to the market after a solution was found, and the manufacturer is convinced that the problems are behind them: "This machine is the most thoroughly tested machine — and the gearbox. If we were not convinced by this solution, we wouldn’t sell it," says Anders Soe Jensen, global president of Vestas Offshore.
Albert Kriener, E.on’s head of asset strategy and technical excellence, believes that one of the greatest changes in the market is that the industry now recognises the most important aspect of offshore operations and maintenance (O&M) is designing equipment that needs as little maintenance as possible. And, with nearly a decade of experience operating wind turbines offshore, Kriener knows.
E.on’s offshore portfolio comprises operating wind assets in Denmark, Germany and the UK, dating from 2001 right up to Europe’s latest offshore project, the 207MW Rødsand 2 wind farm off Denmark, completed in October. The company is also involved in more than 4GW of projects that are either in construction or at earlier stages of development.
The first generation of turbines to be built at sea were not specifically designed for offshore conditions — they provided valuable lessons for the sector. The Vestas turbines at Scroby Sands were more or less a marinised V80, which was built for onshore sites, says Kriener.
1,500 visits
In the three years up to 2009, Scroby Sands required 1,500 visits by technicians. The complications were hardly surprising, given the stronger winds offshore, where the effect of wind shear is more significant than had been originally assumed, Kriener says.
All the generators at Scroby Sands had to be replaced, and the gearboxes repaired while a long-term solution was found, which resulted in their later replacement. As well as the many access visits to fix gearboxes and generators, the technicians also had to deal with minor problems, or inspect or reset the turbines.
This level of intervention is not viable, says Kriener, from either a financial consideration or a safety viewpoint. "Nobody has money to burn on 1,500 accesses and every access carries some sort of risk," he says. Visits to wind turbines had to be reduced.
Turbine technology, fortunately, has matured significantly since then. "They are now specifically designed for offshore use, for remote operation and for higher reliability," Kriener says. "With this improvement, you are also reducing service requirements and the number of service visits to the turbines throughout the year." So much so that the Scroby Sands turbines have only two scheduled services a year now, and the 180MW Robin Rigg site has just one.
E.on’s offshore wind farms are monitored and controlled remotely from operation rooms located in its national or regional headquarters. In parallel, the turbine supplier is able to analyse the turbines’ performance remotely via the computerised data communication system known as Supervisory Control and Data Acquisition (SCADA). This data can also be accessed by local technicians at a site office near the wind farm service harbour.
Opportunistic inspections
The O&M teams plan their service programme by analysing data fed from each individual turbine, such as temperature trends and how often a turbine fails because of one particular issue, says Kriener. The operator can determine the rate of wear and whether a problem should be addressed immediately if it is severe or has safety implications, or if it can wait a few days or weeks — or even until the next scheduled service.
Potential problems can also be picked up on the spot by technicians. "When they are out there doing regular maintenance they also listen to the turbine to see whether it is making a strange noise, and carry out other checks and inspections," Kriener adds.
But technicians are always at the mercy of the weather. At just two miles from the coast, Scroby Sands should be easily accessible, but wind and waves mean it can only be reached one third of the time. At the 60MW Alpha Ventus test site off Germany that E.on co-owns with EWE and Vattenfall, the likelihood of finding three consecutive days with good weather and waves below 0.5 metres is less than 10%, even in summer.
"You may have far-shore German sites where in winter, or even in the fall or spring, you can’t get out there for two or three weeks — not even for one day," says Kriener.
At Alpha Ventus, 45 kilometres offshore, the company is experimenting with helicopter access. This can provide more opportunities for reaching the wind farm during bad weather conditions, but it does restrict the amount of tools and heavy parts that can be taken. For its near-shore wind farms, E.on prefers transfer by boat.
Improved access is one of the most important lessons learned by E.on. Since Scroby Sands, where technicians were transported in a single-hulled vessel, Kriener says there has been an evolution in vessel design. At Robin Rigg, the company commissioned a purpose-built support vessel — a 45-metre aluminium catamaran that makes the potentially hazardous transfer from boat to turbine easier to achieve.
Despite these improvements, offshore wind service technicians do need skills not required by their onshore counterparts: they have to be good sailors. "We don’t require just a turbine technician," says Kriener. "We need a technician who can withstand a half-hour or hour-long boat ride in harsh sea conditions, and who is not scared about climbing 15 or 20 metres on a ladder to a platform, with just the water beneath him."
Most maintenance of existing offshore wind farms is carried out by the turbine manufacturer, but Kriener expects offshore O&M to develop along the lines of the onshore sector, with the operator taking more control and dedicated O&M companies entering the market.
He cautions, however, that offshore wind will demand strong, large-scale players. There is little sign yet of companies emerging but Kriener predicts that, as the sector grows, competition will build. "To build that strong O&M presence will take time," he says. "The market needs to develop, but it is going to develop."
Hands on
E.on has steadily increased its involvement in maintenance over the past decade. From being almost totally dependent on the turbine manufacturer at Scroby Sands, the company is now working in mixed servicing teams with the turbine manufacturer Siemens at its Rødsand 2 wind farm, reveals Kriener.
E.on’s engineers are gathering information and, effectively, training on the job, preparing the company to take control — by itself or with a third party — once the warranty expires.
While most of the turbine maintenance will continue to be done by the supplier, possibly alongside a service contractor, E.on has a hands-on approach, insisting on being actively involved in managing and supervising the contract, Kriener stresses.
"An operator can’t afford a hands-off approach in offshore. The sites are not just wind farms any more; they are offshore power stations," he says. "There is so much value there, so much money that you can lose, and so much money you can win by knowing what’s going on and by managing sites in the proper way."
The company maintains that the high availability of its wind farms, and the resulting contribution to its bottom line, stems from this approach.
But when asked to name the key issue for offshore O&M, Kriener insists it comes back to technology. "The biggest challenge is to get a reliable turbine out there which needs a minimum of service. Reliability is a big, big topic and we are not fully where we should be."
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