Operations and maintenance (O&M) make up 25 percent of the cost of an offshore wind farm – almost as much as the wind turbines themselves, and about as much as construction and installation

Despite this, there has been relatively little attention paid to the challenges, and also the opportunities, that a massive increase in the deployment of offshore wind power will present from an access and maintenance point of view. At the recent Renewable U.K. Offshore Wind conference in the U.K.’s Liverpool, it was obvious this situation will need to change, and an increasing number of commentators and companies are recognising what an important issue it will be. Indeed, cost reductions will be necessary if O&M are not to scupper the increasing competitiveness of offshore wind in the coming decade.

Offshore maintenance and operation divide into any number of sectors, but key areas include routine access to offshore sites, improving the efficiency of the necessary maintenance, cabling and network connection, ensuring a sufficient supply chain of components and vessels, and strategies to reduce risk. Improvements in any of these fields should help to increase the energy output of an operational wind farm, and so reduce the lifetime cost of electricity.

Planned Maintenance

Among the first, and perhaps least glamourous, of the methods being deployed by offshore wind farm operators to reduce O&M costs is the use of planned maintenance. Put simply, this is about making maintenance something which is part of a routine procedure rather than reactive to faults. Reactive maintenance — for example arranging a site visit if a turbine stops working — can be expensive and sometimes impossible, in bad weather conditions for instance, or if boats and crew are unavailable. This increases the risk of an expensive wind generation asset being unable to produce electricity for weeks or even months on end.

Anders Soe-Jensen, head of offshore wind at Vestas, said,”In offshore, it is much more important that you have predictive maintenance, that you have a surveillance that lets you know exactly [what is happening at the site]. When you go out to a turbine, you don’t go out to find out what is wrong.”

Key to planned maintenance is the increased deployment of sensors in offshore wind turbines. Modern offshore wind turbines, particularly those that are custom built for offshore, will contain a huge number of sensors in key components, all feeding back information into a centralised system. The blades too are likely to soon contain sensors, such as those being developed by Risø DTU in Denmark. Blades are mainly inspected visually, but now extensive modelling and laboratory testing of turbine blade materials can provide a picture of how wind turbine blades will react under various loads, allowing built-in sensors to be calibrated to predict when a particular blade is likely to need repairing.

Given three maintenance visits a year for a single turbine, the 6400 turbines planned for the UK will collectively need some 19,200 offshore visits per year (Source: Smulders Group)

“Today we are monitoring 16,000 turbines globally, and we can see how a specific component is performing,” said Soe-Jensen, speaking in 2010.

Other companies are operating in a similar fashion. Anil Srivastava of Areva explained: ‘We have a responsibility for increasing the reliability and availability. We have three lines of intervention into a wind park. We have a scanner control system, remote management, we have more than 1000 sensors in the machine to predict the problems and solve them remotely. The second line is helicopter intervention and the third is only for heavy lift, we use a vessel,’ explains Srivastava.

Backup systems are also important in allowing the expansion of planned maintenance, with systems designed for offshore often containing several layers of safeguards to ensure that a turbine can continue running, even if only partially, in the event of a failure.

Speaking about its M5000 offshore turbine, Sebastien Hita-Perona, products director at Areva, said: ‘We have a high redundancy of components. This way we can optimise preventive and corrective maintenance, if any, and we can schedule the operation and maintenance and optimise the cost for our customer.’

Access to Offshore Wind Farms

The offshore marine environment is a harsh one, with a host of logistical and safety issues that onshore developers do not have to contend with. Taking the UK as an example, a quick look at the figures shows the need for access solutions that the massive expansion of offshore will bring.

Installing 32 GW of wind turbines by 2020 will mean transporting and maintaining around 6400 turbines with their accompanying blades, monopiles and jackets, along with the cables and related transmission systems. This will require a major scale-up of operations. For example, offshore wind turbines currently require about six site visits per year. Even assuming this can be reduced to three visits per year in future, 6,400 5-MW turbines will need some 19,200 offshore visits per year, either by boat or helicopter or some other means. That is a lot of traffic. And then the people need to get onto the turbine. Assuming two people are transfered on and off on each visit, that means four transfers per visit — or 210 per day. Systems will need to be developed to ensure the safety of those personnel in potentially rough conditions.

As well as more journeys, the waves too are likely to be higher in the upcoming offshore wind zones, with the need to work farther from the coast and in deeper waters. Some of the U.K.’s Round 3 wind farms are up to 65 km offshore, and most are in more than 30 metres of water. At the moment, most transfers are to monopile in wave heights of no more than 1.5 metres. In the future, a host of different foundation types such as gravity or floating, and larger waves, will mean that new systems of safe transfer will be necessary. Indeed, if transfers are to be restricted to wave heights of 1.5 metres, this will limit offshore work to just 200 days a year. However, increasing the safe working wave height to three metres and above could increase the number of days available for tranfers to 310 days per year, helping to reduce the cost of wind by increasing the overall availability. In order for this to happen, though, new boats with motion stabilisers will be required to improve the safety of transfers.

“We looked at technologies, but current solutions are focused on near-shore monopiles. New systems are required for Round 3 conditions. There is a technology gap in three areas — for transfer systems, for vessels and for launch and recovery systems,” explained Jan Mathiesen of the Carbon Trust.

Further out to sea, new boats with motion stabilisers will be required to mount safe personnel transfers (Source: Windcat)

Already this process is beginning to happen, with Dutch vessel operator Windcat recently launching a new boat capable of conducting personnel transfers in wave heights of up to two metres.

Furthermore, a constant shuttling to and from the coast will become increasingly impractical. Developers and offshore service providers are looking at new methods, one of which is the ‘mothership’ approach. Using this system a single large vessel would service an offshore wind farm or cluster of wind farms, staying on-site for long periods of time and deploying multiple smaller craft for day-to-day servicing.

Along with the “mothership,” centralised onshore hubs will also need to be developed, with vessels and equipment on standby. These will be needed both as bases for long-range offshore vessels and to service the offshore wind farms closer to the shore. Centres are already springing up on a small scale at several sites around the coast. In Lowestoft (near the site of the Greater Gabbard project) utility players Scottish and Southern Energy and RWE have been developing an onshore depot with fuel storage facilities, along with four 18-metre catamarans from WindCat and a helicopter on permanent charter.

At present, however, the site does not have dedicated facilities for conducting major repairs. Similarly, an onshore hub on the west coast, near Worthington, services the nearby Robin Rigg wind farm. However, while this facility is no doubt suitable to service a single relatively small offshore wind farm like Robin Rigg, it is unable to store large parts, meaning that in the event of a major problem major components will need to be taken elsewhere for repair, and no replacements will available be on-site. In the future, with much larger wind farms, it seems likely that companies will want dedicated repair facilities closer to the projects and may store or even manufacture some components nearer the sites.

It is obvious that in the coming years there will need to be huge investment in offshore access, particularly in the North Sea between the U.K., Norway, Denmark, the Netherlands and Germany. Dozens, perhaps even hundreds, of smaller access vessels will be needed, some with specialised landing equipment. Helicopters, too, will be in great demand. While some may be available from the fossil fuel industry, many will need to be tailored to the needs of offshore wind — and in any case, with oil prices set to remain high for the foreeable future, it seems unwise for the offshore wind business to try to outbid the oil industry for existing vessels. Larger boats will also be needed if the ‘mothership system’ is employed. Finally, there will be a great need for trained staff, and companies will need to invest in training to ensure that they have the necessary skills.

Collaboration on Cabling

Cable damage can also be a huge expense for an operational wind farm. Some estimates suggest that it costs between £5–£10 million (US$7.5–$15 million) to repair a cable, along with obvious losses in terms of electricity production (roughly £18,000 ($27,000) per day for a 5-MW turbine) and reputational risk. Despite this there are, as yet, no standardised practices or procedures to procure cables, share equipment and ships, secure appropriate staff, harbour access and all the other elements necessary for a safe and speedy repair.

Yet according to John Robinson, principal consultant at marine services company Intertek METOC, this is exactly what is needed. During a recent presentation he argued that the big offshore wind players should work together to set up joint centres for cable installation and maintenance at strategic locations around the coast of the UK and onwards in Europe. Developers should move away from using their own dedicated cable compounds and installation vessels, and work together to develop a more efficient system.

Windcat’s newest boats can operate in waves up to 2 metres (Source: Windcat)

“Forget individual compounds, forget project-specific vessels. Get together, share the facilities and vessels, share the knowledge, drive the industry. It will reduce the costs,” said Robinson.

Despite the advantages that increased harmonisation and cooperation could bring, so far the desire to keep cable choices and technologies confidential and a suspicion of sharing too much information with competitors has hampered efforts to set up joint O&M infrastructure for cabling and cable repair. It also remains to be seen whether developers and offshore operators will be willing to pay for a service that they may not need to use. Nonetheless it is a situation common in many other industries and remains a possible avenue for future development.

Said Robinson: “It’s not rocket science, and it’s not new. The telecoms market has been doing it; they’ve got cable maintenance agreements. It’s time we moved forward.”

Skills and Training

Ensuring that sufficient skilled O&M personnel are going to be available will be a major challenge for the offshore wind industry in the future, a concern that has been expressed by senior figures. A rough calculation that has been made suggests that one O&M job will be created for every two turbines installed. With say 6,400 turbines of 5-MW each, this will equate to requiring about 13,000 trained staff.

Even if this number of personnel can be reduced through greater efficiencies, there will still be a huge need for people. As with the cabling sector, one solution will be for operators and developers to collaborate on funding offshore skills centres and training programmes. In the UK, one example of this sort of approach is at the Furness College in Barrow, in Cumbria. Here one company is hoping to erect a wind turbine training tower 17 metres high to allow trainees to practice wind farm maintenance procedures. As the North European offshore wind boom continues it is likely that similar developments will be taking place all over the continent.

Challenges and Opportunities

The challenges facing the operation and maintenance sector of the offshore wind business are daunting, with a need for thousands of trained staff, a massive increase in vessel support, new technologies and billions in investment. At the same time, though, these sectors offer huge opportunities for businesses to tap into the surge in development. It is also worth remembering that none of these problems is overwhelming or unique. The rate of expansion of offshore wind is comparable to the expansion of North Sea oil in the 1980s or the dash for gas in the 1990s, and many of the same skills and techniques will apply.

Offshore Accelerator

Operations and maintenance have been recognised as key areas of future cost reductions, and for that reason they have been included as part of the Carbon Trust’s Offshore Wind Accelerator (OWA). The OWA has been conceived as a means of spurring innovation in a range of key areas, such as foundations, transmission, array layouts and access to offshore sites. Beginning in 2010, the Trust began a competition to find new technologies and ideas to assist access to offshore wind farms and so help to lower installation and O&M costs. More than 400 submissions were received from countries all over the world, covering a range of topics. So far, 13 have been selected to receive funding. An announcement on the winners is expected before the end of 2011.

New Sensors for Blades

Developing sensors to monitor performance and predict faults in offshore wind generators is a complex business. In 2008 Risø DTU, the Danish National Laboratory for Sustainable Energy, published a report looking at remote monitoring of offshore wind blades, where there was a gap in the sensor market. The aim was to develop systems to report faults to blades, but also to provide information on the state of the blade itself and so inform future maintenance needs. Several methods were outlined for monitoring blades, including acoustic sensing and the use of fibre-optics to determine cracks, and measure the shape of the blades to uncover deformities. Alongside this “sensor” testing, much research was conducted into the most common types of faults and distortions in wind turbine blades. In 2010 Risø announced it was working on a Smart Embedded Sensor System to help commercialise this research.