The utility is now using its experience to develop maintenance processes that are setting the standard for the current round of projects.
The offshore wind industry is a paradox. Like the bumblebee flying, it should not work, but it does, says Lars Thanning Pedersen, head of asset management and markets in wind power at Danish utility Dong Energy. "If you saw a list of everything that could go wrong, you wouldn't have started. But you solve problems as you go along, and we are now at the point where we can say that we can achieve a reliability of production that is close to onshore, albeit at a higher cost," he says.
The sector can trace its roots back to the Danish government's decision to include offshore wind in the energy mix in the late 1990s. "Companies did it because they were forced to by politicians - not because they wanted to - and saw a strategic opportunity," Pedersen says. Against this backdrop, the industry owes its very existence to enthusiastic engineers who thought that it was an interesting technical challenge, he adds. Their mindset was that problems were there to be overcome.
"The first offshore turbines were designed in a more innocent age, when we believed that almost anything could be done. There was confidence in the technology and a can-do attitude. If that attitude hadn't been there, offshore would never have got off the ground," he says.
That optimism spilled into the expectations for operations, and a belief that servicing an offshore wind farm would be the same as for onshore but with a boat, Pedersen says. More than ten years down the road we know that much of these optimistic assumptions did not play out. Offshore is definitely not the same as onshore, and there are few areas in which this is more apparent than in operations and maintenance (O&M).
Sited in a highly corrosive environment, and subject to loads that are not often experienced onshore, they suffer greater maintenance issues, particularly with the foundations and the cabling installation. "When we started ten years ago, we thought that we would just put the technology in, and then it would maintain itself for 20 years, and then we would take it out and decommission it," he says.
However, grouting proved to be a significant problem, with some causing turbines to tilt within their monopile foundations. Unlike oil and gas platforms that are more stable due to their sheer weight, wind turbines are relatively light and experience a lot of bending during their lifecycle.
But access immediately became the biggest issue, particularly in winter when reaching the turbines can be extremely difficult. It was soon realised that planning and logistics become much more significant than when maintaining onshore projects. This led to a much greater emphasis on reliability and preventative maintenance.
Borrowing from oil and gas
The offshore wind industry looked for solutions in the oil and gas industry, where there are shared characteristics. But many of these solutions have had to be reinvented and refined over the last ten years. The early access vessels were the same as those used for oil and gas platforms, and it is only now that specialised jack-up vessels dedicated to operations and maintenance are coming on to the market. Purpose-built tools for offshore wind farm O&M lag about four years behind construction. Pedersen points out that Dong is trying to bring this forward, as they will provide increased reliability and lower costs.
"Because offshore turbines are so big, and the revenues are higher than onshore, you stand to lose a lot more money when things go wrong. Therefore, reliability needs to be a higher priority," Pedersen says.
"But things do go wrong, so the ability to predict problems and react quickly is even more important in order to safeguard the business case." This led to Dong investing in the technical capabilities in the office, much more than was anticipated ten years ago, and technical knowledge has been built up in-house.
With its portfolio of operating capacity growing from 200MW to 2.2GW in ten years, Dong's operational data has accumulated in equal proportions. The company has been able to analyse it to identify major failure types and develop solutions to predict future failures occurring. As a result, preventative measures have been introduced, and corrective maintenance has been included within the planned maintenance, which the company believes will lead to increased yield and reduced maintenance costs.
Ten years ago Dong's offshore wind farms were relatively near shore, such as the 40MW Middelgrunden project, 3.5 kilometres from the Danish coast. Now the wind farms include the 367MW Walney project in the UK, which is 15 kilometres offshore, in much harsher conditions and therefore much harder to access. Remote diagnostics and monitoring has become an essential area of technical expertise both for short-term benefits as well as to protect the assets in the long term, says Pedersen. It is also one area in which offshore can learn the most from onshore in disseminating the data. "In terms of interpreting it and extracting the really important information, we need to view it as a key area for development," says Pedersen.
Being able to fix - or at least identify and manage — problems remotely is key, says Pedersen. "Solutions such as putting the turbine into curtailed mode — in fact, everything that can be done to prevent a turbine from shutting down so that you are able to assess whether it is a critical or a temporary failure, or something that can be overridden, is a worthwhile investment for all large players in the industry."
In the past three or four years Dong has looked at the lessons from early wind farms to improve subsequent projects. A significant development was to move from project servicing to a more portfolio-based approach. "Because the equipment we need is very specialised and expensive — such as jack-ups — we need a portfolio to fully utilise that and achieve economies of scale," Pedersen says. "We have projects in the UK and Denmark, and we try to see how we can capture the synergies between them instead of trying to optimise each project on its own."
Dong is also working on procurement synergies across northern European projects, from obtaining spare parts, through sharing vessels to deploying human resources, such as technicians, efficiently across several projects. "If you have three to four projects close together, then you can share the contingency and standby vessels, which will increase reliability and help share overhead costs. Sourcing components on a larger scale will also bring value. Sharing technical competencies and technicians will be a focus," he says.
Dong now believes that it can repeat the cost-reduction path that onshore has experienced over the past 20 years, bringing the offshore sector a step closer to cost parity. According to Pedersen, the higher costs and the vulnerability of the infrastructure are due to the immaturity of the sector, so improvements are possible. "There is also potential in managing that risk to an acceptable level, so that it will be a profitable industry. But we still benefit from the fact that there is a lot more wind offshore."
Dong has set a target to reduce its cost of energy by 40% by 2020, with a EUR 100/MWh target for all investment decisions. This will be a steep trajectory, and Dong is looking to O&M for a contribution to these savings. This may be a daunting challenge, but Dong believes it is one that has to be met, as the current subsidy levels for offshore cannot be sustained.