If the offshore wind industry is to be taken seriously, it will need to address its reliability and technical difficulties. Arthur D. Little has identified changes needed to make equipment more robust and reliable and to overcome the challenges offshore wind faces in securing its position in Europe’s renewable energy.

By Stephen Rogers and Matthew Jackson, Arthur D. Little

Offshore wind is in many ways an ideal form of green energy. It is clean and renewable, and can be deployed well away from public view. It is also well supported, especially in Europe, by the public and governments as a way of meeting their renewables targets.

However, despite this positive climate, the future of offshore wind is by no means assured. Supply constraints, logistical difficulties and technical concerns present significant obstacles to the expansion of the sector. The first two barriers are well known, and in some ways easier to overcome. The technical challenges are less widely recognized but present the biggest barrier to long-term growth.


The first German offshore wind farm will be Alpha Ventus which begins in July 2009. Six of the 5 MW turbines are to be supplied by REpower – their turbines are shown here at Belgium’s Thornton Bank offshore wind farm Source: Jan Oelker/REpower
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The figures are stark. Onshore, wind turbines can achieve availability levels of 97 per cent. Offshore, technical problems mean that number can be as low as 60 per cent. This problem is exacerbated by the remote nature of the installations, which makes repair times much longer.

If the offshore wind industry is to become a major player in the energy sector, it will need to address this high technical failure rate and find ways of developing equipment that is robust and reliable in an offshore environment. It will require collaboration and a willingness to share resources and knowledge. That collaboration will need to be driven by smarter customers and by governments providing research funding and direct financial incentives.

The Background

The offshore wind market is a small but growing part of the world energy market. Total capacity reached 1 GW in 2007 (around 0.01 per cent of global energy capacity) and is set to increase sevenfold over the next five years. Activity is currently confined to Europe – the lack of uptake in other major markets such as the US and China is due to the abundance of available land in these countries, meaning that governments have little incentive to subsidize offshore developments.

In Europe, planning constraints, combined with decreasing marginal load factors onshore, make offshore wind an attractive, and indeed necessary, means of meeting renewable energy targets. Wind yields offshore are at their best 50 per cent to 100 per cent greater than onshore installations.

The majority of future growth is expected to come from the UK, which currently has 404 MW of installed offshore wind power, and 464 MW planned.


In the future, as wind farm developers become bigger than the manufacturers and gain more experience, standards will need to increase Source: Arthur D. Little
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Overall growth in European wind power capacity over the next five years is expected to be 18 per cent. Offshore is set to rise to 6 per cent of total capacity, with the UK as the focus Source: BTM Consult, World Market Update 2007, Arthur D. Little

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.

There are two difficulties – one is the size of these upfront costs, and the other is the emergence of ‘hidden’ costs, resulting from technical difficulties. Offshore installation is roughly 50 per cent more expensive than for onshore, plus operations and maintenance costs are roughly twice as high.

These high costs need to be offset by strong returns. This is a function of load factors, the level of subsidy (under government control), and the technology itself. The industry has responded to the technology issue by building bigger and more powerful turbines (5 MW to 7.5 MW).


Failure rates in current wind turbine technologies are high. While this is manageable onshore, offshore it leads to greater downtimes and significantly lower availability Source: Arthur D. Little
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Successfully delivering projects of greater scale and scope means overcoming three obstacles: supply constraints, logistical difficulties and technical challenges. Supply constraints are affecting the entire wind industry, both onshore and offshore. So far as turbine and turbine-specific component manufacturers are concerned, the primary factor that is stretching capacity is the combination of consolidation following the last period of cyclical oversupply with the sharply increasing demand.

Materials such as bearings, and forged steel and cast iron components, have been in huge demand from heavy industry in general, meaning lead times of up to 40 months. However, in the medium term, as new players enter the market, these constraints will subside. In the case of gearboxes, for example, China Highspeed is already investing in its production capacity.

Clearly offshore wind facilities also present major logistical challenges in both their installation and maintenance. Civil contracting costs represent a higher proportion of upfront costs for offshore turbines (60 per cent) than for onshore turbines (25 per cent), and thus the competition with the offshore oil industry is more intense, particularly as locations move further offshore. From an infrastructure perspective, ports are often poorly adapted to manage the size of offshore turbines. Furthermore, high levels of offshore oil and gas activity and fully booked shipyards mean the supply of installation and maintenance vessels is constrained. Here again, supply and demand will adjust in time and these constraints will be overcome.

It is the third barrier, technical problems, that presents the biggest potential risk to the future of the industry. Offshore failures can be 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, as many as 20 unscheduled visits to many installations are made.


In the future, as wind farm developers become bigger than the manufacturers and gain more experience, standards will need to increase Source: Arthur D. Little
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Onshore, many serious technical failures are high-profile events, because they have the potential to cost lives as well as money – most notable was the recent disintegration of the Vestas turbine, near Arhus in Denmark, due to ‘lack of maintenance’. Several incidents in the UK and Germany, including loose blades crashing into roofs of houses, have left some commentators questioning the viability of onshore turbines in inhabited areas of the country.

This, in one sense, could strengthen the case for offshore turbines. Given, however, that ‘lack of maintenance’ is likely to be unavoidable for remote offshore turbines – as they are likely to be much larger than the onshore turbines and therefore more prone to failure and will be subjected to more extreme conditions – the prevalence of failures onshore highlights the crucial need for current offshore designs to be radically improved.

Why do turbines fail?

The heart of the problem is the technology. The machinery 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 Horns Rev wind farm disaster in 2005, following which Vestas is reported to have removed and repaired 80 of its V90 models – designed for offshore use – owing to the effects 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 changing of rotor bearings at an estimated cost of €30m ($39m).

Failures are harder to repair because they tend to happen in stormy conditions, they are often not dealt with immediately, but on an aggregated basis at intervals. That means it can be as long as three months before a turbine failure is repaired.

As sites move further offshore, these problems are likely to get worse. That could mean offshore developments in deep water areas will be seen as unviable. For example, potential sites in the German North Sea have been allocated, but it is uncertain as to whether investment will follow. A leading industry figure in the German market informed Arthur D. Little that offshore has 10 years in which to prove itself, after which it may be partially or wholly curtailed in German waters.

The bottom line of technical difficulties is that they have the potential to cripple returns. 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 offshore industry to secure its long-term future, is for its technology to become more robust and reliable. Arthur D. Little has identified three major areas that need attention. Firstly, better design of individual components (e.g.smaller, two-stage gearboxes), the drivetrain (smarter integration of key components) and foundations. Secondly, increased levels of research and development – not only in design, but also access and maintenance methods. Thirdly, more thorough certification testing so components really can withstand the offshore environment. Arthur D. Little’s analysis shows that testing is probably the crucial element that will stimulate work in the other two areas.

To date, testing has 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 a considerable amount 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 characterized by a general atmosphere of secrecy and suspicion and, as a result, there has been a fragmentation of knowledge and a 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 down the supply chain and are likely to result in not only better design, but also better type testing of components and integrated systems during the production process.

There is already evidence that, as the industry matures, customers are becoming more assertive. Shell’s exit earlier this year from the London Array is a high-profile illustration of this point. 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 proposed NaREC Centre of Offshore Excellence in Blyth, UK – could 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, exploration and production 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.