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Question of the Week: Are offshore projects built to last?

As Siemens revealed it is installing a fix for faults relating to vibrations in turbine towers at the Teesside offshore wind farm, we ask whether wind projects can last under the harsh conditions at sea.

The Teesside project has had issues with vibrations at the base of the towers
The Teesside project has had issues with vibrations at the base of the towers

Question: Will offshore wind projects last their projected lifetimes?

Marc Costa-Ros - manager of innovations, the Carbon Trust:

It is becoming more apparent within the offshore wind industry that several operating offshore wind farms are experiencing a higher level of structural issues than originally anticipated. This is resulting not only in increased maintenance and repair activities — and therefore increased operational expenditure (OPEX) — but is also spreading doubt on the certainty of reaching the assumed 25-year lifetime.

Through the Offshore Wind Accelerator (OWA), the Carbon Trust has been placing an increasing focus on these issues, to assess the severity and likelihood of risks that may reduce the operating life of an offshore wind farm and evaluate the cost benefit of mitigating actions. This has included a study to identify which issues are having the greatest impact on the structural integrity of foundations to help the industry to better understand the trade off between more conservative design — increasing capital expenditure (CAPEX) — and less structural O&M — lowering OPEX — versus optimising the design — lowering CAPEX — but having more extensive O&M operations — increasing OPEX.

We are also seeing integrated approaches to improve lifetime asset integrity in both the turbine and foundation through advanced control systems and optimised array layouts to reduce fatigue from wake turbulence on the full structure.

There is still some way to go on the learning curve, but with increasing R&D efforts and more innovative solutions reaching the market, there is reason to be confident that 25-year lifetimes will be achieved.

Bernhard Lange, manager for wind farm planning and operation, Fraunhofer IWES

Let's start with two facts: the first offshore wind farm — Vindeby in Denmark — already reached its 20-year lifetime. And many projects already required serious repairs in their first years. Other issues can be expected to appear later: Is the corrosion protection good enough to withstand 20 years of service? How much wind is left in the atmosphere when there are five large wind farms upwind? What will the long-term cost of offshore O&M be?

So, will the projects last? Yes, offshore wind farms are technically feasible. But not all projects will make their owners rich and happy. As always in the development of a new industry, there is a learning curve. And offshore wind is a truly new industry — it is not just the wind industry going offshore, as only a small part of the total cost of an offshore wind farm comes from already known technology.

But as any error offshore is extremely expensive, minimising risks is the crucial point — from accurate and reliable wind measurements to prototype testing of the whole nacelle. Therefore, the success of a turbine type or wind farm might well lie in a thorough measuring, testing and validation throughout the whole lifetime of a project from planning and design to operation.

Henrik Stiesdal, CTO Siemens Wind Power

They will last longer than projected. The first offshore projects have already provided the proof — Vindeby offshore wind farm in Denmark, for example, was commissioned in 1991 with 11 turbines rated at 450kW each. All the turbines are still in operation after 23 years. In our fleet there is no single offshore project which has been closed until now. But we have five projects that have been in operation for more than ten years.

Once installed the main cost of an offshore wind project is spent. So it can be reasonable to operate the turbines as long as service costs stay controlled — and this can be more than the 20 years our turbines have been tested for.

Our direct drive SWT-6.0-154 turbine has been certified for a 25-year design lifetime, which is an additional five years compared with the previous turbine lifetime Siemens has designed towards. And these declarations can be seen as a minimum lifetime. I expect that it won't take long until the first of our customers will invite us to an anniversary celebrating 30 years of operation.

Fabio Pollicino, service area leader for project certification, DNV GL

The answer is yes, if the turbines have undergone an independent third=party assessment considering site-specific circumstances and the operational maintenance over the lifetime is done subsequently.

Offshore developments with assets like wind turbines, substations and power cables are complex projects. The industry faces challenges in implementing the highly sophisticated turbines in an offshore environment. These challenges can be addressed by using the knowledge of experienced partners who are specialised in various technical disciplines.

Collaboration between the different stakeholders and contractors must be established from the beginning if the projected lifetime is to be successfully reached. All relationships between experienced partners must be kept strong to attain successful completion of the project.

The match between the original design and final product is another key factor in the success of the turbine. State-of-the-art technology must be applied to all projects as the installation of unapproved components will significantly increase project costs and retrofits. Or replacements may be required to maintain power production for the intended lifetime.

An independent holistic concept assessment helps to increase trust, mitigate the specific risks to the project and may provide return on investment ahead of time.

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