Technological innovation in the wind sector

As wind-generated energy moves more into the mainstream, how has the understanding of wind turbine efficiency evolved?

Rod Corbett. Purely from a technical perspective, there has been little change in the understanding of joint integrity and efficiencies. There is, however, a growing awareness of the potential of adopting a cleverer approach to design and build in other industries. A parallel and directly relevant learning curve on how a technology-driven approach to joint integrity can increase efficiencies and reduce maintenance costs can be found in offshore production platform pedestal cranes, where tension control technology is now widely used on slewing bearings and has made a significant difference. The bolted joints on the crane are virtually identical to those critical joints found on the wind turbine. Exactly the same benefits of assured reliability and reduced maintenance costs transfer to wind turbines.

Christian Kjaer. Wind energy has certainly moved into the mainstream as a power generating technology. The European market is €13 billion annually out of a global market of some €50 billion. For the past two years, the EU has installed more wind energy capacity than any other power generating technology. In 2009, 39 percent (10.2 GW) of all new power capacity coming online was wind energy, followed by gas (25 percent), solar PV (17 percent) and coal (nine percent). In total, 62 percent of all new capacity was from renewables. Also the US installed more wind energy than any other technology in 2009. Wind power contributes about five percent to the EU electricity demand and increases its share by some 0.5 percentage-points per year. It is already the largest technology in terms of investments, economic activity and job creation. From 2002 to 2007, the wind energy sector created more than 33 new jobs in Europe every day of the year.

Over the past two to three decades, the cost of generating wind power has fallen by 80 percent, to a level where it is fully competitive with new coal power or gas power plants, and significantly cheaper than nuclear energy, in most European countries at the carbon and fuel prices. About half of the reduction in cost can be contributed to economies of scale in manufacturing and half of the cost reductions to improved efficiency, resulting from gradual improvements in the technology.

Mark Henderson. Banks, and more importantly, their credit committees, have become more familiar with the turbine market and the issues that arise from time to time. They have largely adhered to the traditional project finance requirement that turbines have to be 'proven' and supplied by credible - and creditworthy - companies.

Almost perversely, some sponsors have been more willing than banks to try and push the limits of what is acceptable under this 'proven' criteria, which is fine if the projects in question are to be financed by equity, but not if the projects are also to be debt financed. This was also driven a few years ago by the under-capacity of the turbine market, although by and large banks held to their principles, and now that there appears to be more equilibrium in the supply/demand of turbines, the more conservative approach of banks does not tend to be pushed as much.

One area where this may still be an issue is for offshore turbines, where new models are being developed with the resultant question marks over their potential to perform.

Marc Mühlenbach.

Wind turbine efficiency has evolved significantly, both in terms of the evolution of conventional turbine designs to capture and transform wind into electricity and in terms of evolving turbine design itself. As wind-generated energy has moved into the mainstream, it has also meant that an increasing number of the more generous sites have been tapped and greater turbine efficiency has become increasingly important as lower class sites require more efficient machines.

Several manufacturers, particularly those with a German home market, have recently rolled out 'next generation' turbine models to be able to develop projects at lower wind speed sites at attractive yields. There is a good amount of pressure on these manufacturers to develop machines that have greater hub heights and rotor diameters, yet are lighter and remain cost effective.

Simultaneously, there has been a recent push, particularly in offshore, towards more efficient direct drive technology, challenging the current balance between geared and gearless designs. Gearless designs are considered more efficient as these include fewer moving parts, and so require less maintenance. Traditionally, these machines have been costlier, however, due to size and weight issues in particular, although we could be starting to see a change in that.

How much difference do factors such as adequate lubrication, vibration isolation and potential fatigue failure from incorrectly bolted joints make to the efficient operation of turbines over a sustained period of time? 

RC. Wind turbines are subject to complex loading. The environment naturally produces extremes and the exposure to the elements adds yet another factor into the equation. Fatigue and vibration are common enemies and incorrect bolt tightening ultimately will lead to failure and costly downtime. The scale of such failures ranges from lost generation through to catastrophic structural failure. Being able to meet the correct design objectives and understanding how to achieve and maintain the correct tension across a bolted joint are essential factors if reliability and greater efficiency are to be met. Significant savings can be made in maintenance regimes where reliability is built in at the outset. The end result is minimum operation risk and lowest life cost for the power plant.

CK. European wind farms are extremely reliable and operate with availabilities above 97 percent. In the last 25 years, turbines have increased in size by a factor of 300 (from 20 kW to 6,000 kW and beyond). At the same time, the engineering base and computational tools have developed to match machine size and volume. The wind turbine manufacturers are building the world's largest rotating structures. The rotor diameter of the largest turbines is 50 percent longer than the wingspan of the world's largest aircraft - Airbus A380. This is a remarkable story, but it is far from finished: many technical challenges remain and even more spectacular achievements will follow.

Incorrectly bolted joints are not a problem in wind turbine manufacturing. Lubrication and vibration isolation are both important elements but are not the main determinants of the technical and economic efficiency of wind turbines.

What are the different factors affecting the efficiency of offshore versus onshore wind turbines?

RC. Hostile environments need and demand a different approach. Corrosion is just one factor added into the mix alongside increased and even more complex loading. However, it is rare to see these realities taken fully into consideration. When something goes wrong in an offshore environment the consequences, and the resultant costs, are far greater. Better design and build can increase reliability, particularly when it comes to applying a technology-driven approach to critical bolted joints. Operational risk is far greater offshore, so assured operational reliability is even more valuable.

CK. Offshore wind technology and practice has come a long way in a short time, but there is clearly much development still to be done. Although the fundamentals of the technology are the same onshore and offshore, it is clear that offshore wind technology is likely to diverge further from onshore technology. Methods of installation and operation are already very different from onshore wind generation, with great attention being given to reliability and access.

The dilemma for the designer is how best to trade the cost of minimising maintenance by increasing reliability - often at added cost in redundant systems or greater design margins - against the cost systems for facilitating and increasing maintenance capability. Access is critical as lost production is often the greatest cost penalty of a wind turbine fault. For that reason much attention is given to access.

MH. I cannot comment on the precise factors, but as a lender we will be keen to see that turbines have a successful operating record in the offshore environment. Given the additional degradation that the marine environment can cause on turbines, this is a factor which lenders should be particularly keen to understand from the operational track record of the turbines.

Another key area that lenders should include in their due diligence is the reliability of the turbines and their components. In the offshore environment, any down time of the turbines can be very expensive due to the additional delays that weather windows can create - certainly compared to onshore wind turbines - and the cost in terms of lost revenue and operation and maintenance expense will be that much higher.

MM. Offshore turbines have to prove durable, above all. Offshore turbines face corrosion issues and have to withstand greater wind speeds. Therefore, reduced maintenance is a key factor in cost efficiency and not an easy problem to overcome, as we have seen on the back of the experience by more than one manufacturer. Both onshore and offshore face the challenge of reducing component weight and logistical complexity for transport and installation.

In addition, the increasing scale of offshore projects will put a great deal of focus on the efficiency of the performance of offshore turbines; when considering multi-gigawatt Round 3 developments, small differences in efficiency will be considerably amplified.  

How do you see innovative engineering within the context of wind turbine manufacture developing over the next decade?

RC. It is a fact that the use of tension control technology can result in wind turbine designs that require up to 50 percent fewer bolts on critical joints for the same service rating. This significantly saves money in production build, installation and maintenance - less bolts, less drilling, less tightening, less checking. This innovation alone has the potential to significantly impact the future of wind turbine manufacture, as well as maintenance regimes. Reliable, maintenance-free bolted joints will become the 'norm' if the science is applied.

CK. Technology development in the largest unit sizes of conventional wind turbines has been particularly stimulated by the emerging offshore market, and many of the most innovative wind energy systems proposed in recent years target that market. The wind energy sector is also borrowing much experience and expertise from the offshore oil and gas sector.

Some of these systems may be the way of the future; some will undoubtedly disappear from the scene. At the very least, they illustrate the huge stimulus and demand for creative engineering that has arisen from the establishment of wind energy technology in the power industry.

MH. Whilst there appears to be another push being made towards increasing the MW capacity of wind turbines - particularly in the offshore industry - I am not convinced that this is what developers, investors and lenders really want. Instead they are generally satisfied with the current levels of capacity and would prefer that turbine manufacturers focused on making the turbines more efficient and more reliable. This not only saves them a degree of costs but generates more revenue in terms of return per €/MW of capacity.

A key area of engineering which would be a welcome development over the next decade is the potential ability to make gearboxes more reliable. Therefore, having more turbines which can be 'gearless' would be a welcome development if this cannot be achieved, or as a wider alternative.

Finally, given the greater lengths of turbine blades, will we see a growing use of lighter, stronger blades that are made out of carbon fibre? Currently this is cost-prohibitive, but will this be the case by the end of the decade?

MM. The challenge posed by direct drive turbines will move increasingly to the fore in the next decade, both onshore and offshore. Aside from turbine vendors continuing to improve their proven designs, there are also several start-up initiatives out there to increase the efficiency of existing turbine technology, be it laser-monitored blade rotation or gas/wind hybrid technology solutions to reduce intermittency, although the commercial deployment of these solutions is obviously not guaranteed. Beyond concerns of wind turbine efficiency, the issue of wind power availability will be helped considerably by affordable wind energy storage solutions.

Biographies

Rod Corbett is Managing Director, James Walker RotaBolt. Corbett's fastener experience began in automotive, aerospace and defence applications including work on Tornado, Shuttle and Formula One engines. At James Walker RotaBolt, he has been at the forefront of promoting tension control as essential in assuring bolted joint integrity across energy, petrochemicals, transport, defence and civil engineering.

Christian Kjaer was appointed Chief Executive Officer of EWEA in March 2006. He had previously held the post of Policy Director for EWEA. He drafts EWEA's direction, vision and long-term strategy in collaboration with the President and the Executive Committee. He represents the association in external forums, engages actively with the international institutions, the key stakeholders and NGOs, the members of EWEA and the media.

Mark Henderson is responsible for Investec's power and renewable energy sector investments in Europe. He has over 23 years' banking experience. Before joining Investec in 2004, Henderson was at Société Générale and Dresdner Kleinwort Benson.

Marc Mühlenbach is is an analyst in Emerging Energy Research's Europe Wind Energy Advisory Group, providing market research and analysis on the European wind energy market environments.