How can the offshore wind industry overcome O&M obstacles?

Matthew Jackson

Working in the offshore wind industry presents many challenges for companies, especially in dealing with operation and maintenance (O&M) challenges in harsh ocean conditions. So what approaches should be taken, asks Matthew Jackson?

The problem

Theoretically, offshore wind should be a low risk investment, in that fixed costs represent a high proportion of overall costs. This provides a level of certainty which, combined with guaranteed tariffs, makes it particularly attractive during times of volatility. But offshore installation is roughly 50% more expensive than for onshore, and O&M costs are roughly twice as much.

In this regard, technical problems present the biggest potential risk to the future of the industry. Technical failure rates in offshore wind can be high compared to onshore, and offshore failures are difficult and expensive to fix.

This is underlined by an analysis of maintenance records, which shows that while service teams for offshore wind farms are supposed to make two scheduled maintenance visits every year, unscheduled visits to many installations are made 20 times a year.

Why do turbines fail?

The heart of the problem is that the technology being used offshore is generally onshore technology that has not been modified sufficiently to meet the different demands of an offshore environment.

The classic example of this is the disaster at the Horns Rev wind farm in 2005, following which Vestas is reported to have removed and repaired 80 of its V90 models, designed for offshore use, owing to the effect of salty water and air on the generators and gearboxes, which became corrupt after only two years. A similar procedure has been reported this year, with Vestas' 30 turbines requiring a change of rotor bearings, at an estimated cost of €30m.

Failures are also harder to repair because they tend to happen in stormy conditions, and are often not dealt with when they happen, but on an aggregated basis at intervals. That means it can be as long as three months before a turbine failure is repaired. The contrast with onshore reliability is dramatic, and availability levels of 97% are regularly achieved.

As sites move further offshore, these problems are likely to get worse. That could mean offshore developments in deepwater areas will be seen as unviable. For example, all the potential sites in the German North Sea have been allocated, but it is uncertain as to whether investment will follow.

The gearbox

The main area of concern in the industry surrounds the gearbox. The reason for gearbox failure is currently not a matter of universal agreement. Data indicates that gearbox failures onshore are in line with industry averages. Offshore, it appears that gearboxes in fact perform better than other parts of the turbine. The problem with offshore turbines is that conditions are more extreme, and the downtime which results from the replacement of a gearbox has a greater effect on availability compared with, for example, the failure of a generator. The technology of offshore gearboxes therefore needs to improve, and when it does, this will have a dramatic effect on availability levels.

The direct-drive system, pioneered by Enercon, and which bypasses the need for a gearbox, could be held up as a solution to this issue. The initial higher costs would be repaid by lower maintenance costs and higher uptime levels. Siemens Wind Power is another organisation currently testing a Direct Drive model.

Realistically, the step-change required in the manufacturing facilities of the other main suppliers of turbines, all of whom use gearboxes, would be too great, and we are unlikely to see the disappearance of the gearbox in offshore installations, particularly considering the huge weight of the direct-drive system (up to 500 tonnes).

Less rigorous testing is required for onshore turbine components, as they can be replaced with relative ease, on a ‘fire-fighting’ basis, whereas with offshore this is not feasible. For gearboxes, then, better testing will be a key requirement as part of – and in addition to – the development of the technology. Offshore blades are currently tested very thoroughly, and perform relatively well considering that they receive the bulk of the torque to which the turbine is subjected. Generators are not tested as rigorously, and do not perform as well offshore.

Improved testing for gearboxes might involve breaking prototypes rather than subjecting them to limited loads as is common now. Suggestions for improving the design itself include making the gear case more flexible, and possibly reducing the size of the gearbox, to two stages rather than three.

Another solution that is not currently being considered is the possibility of complete nacelle testing. Currently the first time the components work together is when they are part of a live turbine.

The bottom line for technical difficulties is that they have the potential to cripple returns, and thus the risk profile of projects is increased and their economics more dependent on generous Government support – not a sustainable model for the future of an industry that aspires to be a key source of world renewable energy.

What is needed?

The change needed for the industry to secure its long-term future is for the technology to become more robust and reliable:

  • Better design of individual components (i.e. smaller, two-stage gearboxes); the drive train (smarter integration of key components) and foundations;
  • Increased levels of R&D – not only in design, but also access and maintenance methods;
  • More thorough certification testing so components really can withstand the offshore environment.

Analysis from Arthur D. Little shows that testing is probably the crucial element that will stimulate work in the other two areas. To date, testing has clearly been inadequate. Manufacturers have claimed it is possible to test onshore without the expense of offshore testing. However, there is clear evidence that, while it may be possible to test individual components onshore, running a turbine in real offshore conditions for at least a year would bring to light many key problems and save considerable amounts of money.

Such testing has already been shown possible, albeit with Government support. In Germany, for example, offshore testing is already taking place at Alpha Ventus (albeit on a partly commercial basis).

All this work will need to be underpinned by collaboration. To date, the industry has been characterised by a general atmosphere of secrecy and suspicion and, as a result, there has been fragmentation of knowledge and lack of research progress.

The catalyst for change will come from a shift in the balance of power away from the wind turbine manufacturers towards bigger and more experienced customers.

These customers will have the knowledge as well as the muscle to make specific demands for improvements in testing and development in a way that was impossible for small wind farm owners. These higher standards will filter all the way down the supply chain and are likely to result not only in better design, but also better type testing of components and integrated systems during the production process.

At the moment, individual company research into the causes of mechanical failures or ways of improving access and maintenance may be prohibitively expensive. Collaboration can reduce those costs significantly. In terms of testing, greater openness would facilitate the testing of integrated drive trains. Independent testing facilities – such as the New and Renewable Energy Centre (NaREC), in Blyth, UK – should continue to be used as a neutral location for such tests to be carried out without compromising secrecy. It is true that such shared schemes have been tried before and not succeeded, but in a changing climate these options will need to be considered again.

This kind of collaboration is not unusual in the energy sector. In offshore oil and gas, for example, E&P companies have collaborated for years on access and maintenance issues, and the results have benefited the entire industry. This shows that there is a clear model to follow.

Action is therefore needed from offshore wind farm owners and developers to apply pressure on turbine suppliers to ensure they invest in rigorous component testing and robust offshore-specific R&D; apply pressure on turbine and component manufacturers to take a long-term view and invest to secure a sustainable future for the offshore wind market; and finally help is needed from Governments to free up funding for public R&D centres, and projects that can act as catalysts for industry collaboration and ‘open research’.

What should particularly concentrate minds in the offshore wind industry is the clear message that without collaboration, the offshore wind industry will not mature or progress.

About the author:
Matthew Jackson is a business analyst in Arthur D. Little's Energy and Utilities practice;
Stephen Rogers is a director in Arthur D. Little's London office.


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