Offshore wind rules ‒ Det Norske Veritas

OW10_totaal_2.jpg 6 0

Being known as one of the world’s biggest classification societies within the offshore and maritime sectors, DNV has also been a major player in the wind industry for over 25 years. After the recent acquisition of KEMA, the new company, DNV KEMA Energy & Sustainability, is today undoubtedly one of the world’s largest wind energy consultancies and the leading society when it comes to offshore wind certification in particular.

As a consultant and certification body, more than 240 DNV KEMA staff provide services in the wind energy sector, with more than 80 working within offshore wind. It has wind teams located in Denmark, the UK, Germany, The Netherlands, Norway, the US, China, South Korea, Singapore, Brazil and India.

Although much of their work concerns the type certification of onshore and offshore turbines and project certification of offshore wind farms, including the turbine, foundations and substations, DNV KEMA also carries out advisory services for initial site selection, wind resource assessment and energy analysis to power performance testing, technical due diligence for investors, grid interconnection and operational risk management. “We answer questions such as – is there sufficient wind resource, what is the uncertainty in energy production and are the estimated future O&M costs sufficient, etc.” Claus Christensen, DNV KEMA’s Head of Department Wind Energy Certification Centre says.

DNV KEMA is dedicated to developing standards for the industry and making new rules (where industry need exists) and this is almost like painting the Forth Bridge – i.e. a never-ending task. Mr Christensen comments: “Because the industry continues to mature, new designs and techniques can be used that occasionally approach the boundaries of science, materials and engineering understanding. Turbine sizes, substations and offshore sites are increasing in size and they are in more challenging environments. Therefore, the industry requires vigilance in maintaining standards to keep pace with technology developments, enabling safe deployment and long term operation.” 

Additionally, DNV’s Maritime Group has supported the development of all types of installation and service vessels, which has included the development of the world’s first class notations for these vessels to improve safety and promote uniform standards. “This draws uniquely upon our maritime classification leadership,” says Mr Christensen.

Standardising the industry

In a bid to get the overall cost of wind energy down, DNV has worked in close cooperation with the wind industry since 2001 to develop unified approaches to building wind energy technology and methodologies. The knowledge that has been built up over the years is published in its standards, rules, guidelines and recommended practices. The company is also leading international efforts to standardise design practices through active participation in the International Electrotechnical Commission (IEC) and other standards bodies.

DNV KEMA is dedicated to developing standards for the industry and making new rules (where industry need exists) and this is almost like painting the Forth Bridge – i.e. a never-ending task. Mr Christensen comments: “Because the industry continues to mature, new designs and techniques can be used that occasionally approach the boundaries of science, materials and engineering understanding. Turbine sizes, substations and offshore sites are increasing in size and they are in more challenging environments. Therefore, the industry requires vigilance in maintaining standards to keep pace with technology developments, enabling safe deployment and long term operation.”

DNV-OS-JIOI July update

For instance DNV’s well-known standard for the design of offshore wind turbine foundation structures, DNV-OS-JIOI, was originally created in 2004 and this was revised in 2007. But a Joint Industry Project, led by DNV KEMA, looked to improve the basis for calculating the axial load capacity of large diameter grouted connections without shear keys and to review the designs following concerns over certain grouting issues. This meant that DNV-0S-J101 was updated again in 2011.

A further update will be released in July, following analysis of material and cyclical loading tests results by DNV KEMA and industry experts to establish rules around the use of shear keys in grouted connections. Use of shear keys in grouted connections offers an opportunity to reduce substructure costs, thus reducing the overall cost of energy.

OW10_totaal_2.jpg 6 1

DNV’s standard for substations was issued in 2009 and it hopes to update this in 2012 as well. “A lot has happened in just a few years, when considering that the first wind farms had a direct link to onshore substations. Now everything is being pushed further away from shore on AC substations and developing into these very large HVDC platforms. The industry has been talking about manned platforms but with this increase in size there is naturally much more equipment and if they are to be manned then safety becomes an even more important factor.”

Knowledge sharing

Providing the industry with the most up-to-date guidelines and standards is quite a challenge, he admits. “New knowledge development is usually being carried out in Joint Industry Projects, with major players throughout the value chain participating. Most find knowledge sharing very useful, even between competitors. Unfortunately, in certain areas it is sometimes difficult to get sufficient feedback. The industry rightly expects state-of-the-art standards but in general the offshore wind industry is more closed and knowledge sharing and feedback from the projects can be difficult.

“I can understand that the players hold their hard earned knowledge and experience as a competitive advantage. Of course, some developers have built up 10 years of knowledge concerning offshore wind farm operation and there are still newcomers who may want to gain the benefits of this past effort. But yes, it is at times difficult to get sufficient information that may be shared. However, all of our rules are developed together with industry so there is a common consensus.”

Subsea cable challenges

One area where he believes that there is still a lack of rules and guidance is related to subsea cables. However, DNV KEMA has launched a new JIP to address this topic. Although there is plenty of knowledge and experience installing long, subsea power transfer cables in the offshore industry, he says, the number of cables and connection points within an offshore wind farm collection system is significantly higher.

Cable sizes can vary, voltage levels can vary, routing options can be limited and jack-up vessels can be inadvertently positioned over cables resulting in damage, so there are many more unique challenges within offshore wind. When considering floating offshore wind turbines, cables with large free-span will also be a challenge.

In the oil and gas and trans-ocean communication sectors, very large vessels carry out the installation – usually in one continuous motion. But given the need for multiple, relatively short cable installation runs, the use of smaller vessels to navigate within an offshore wind farm, the entry of some new installation contractors and construction schedule demands, the opportunities for technical difficulties is greater than single subsea crossing projects, he stresses.

OW10_totaal_2.jpg 6 2

“It has been publicly documented that there have been more failures, especially related to cable installations.” But having said this, DNV KEMA is currently working on producing guidelines for subsea cables within wind farms and aims to issue its Recommended Practices in October this year.

DNV KEMA also has a long list of ongoing work looking at electrical systems, turbines in hurricanes, assessing remaining useful life and wind farm service vessels, where new standards or guidance will be coming out in 2012 and 2013. There is also work ongoing related to safe worker transfer and access systems.

Aiming for a harmonised set of international rules

Clearly there is the issue of international standards. Everyone wants to get the cost of wind energy down and to make it more efficient and yet at the same time, there are no complete global firm set of rules and regulations to apply to the whole industry.

Mr Christensen believes this is changing however. “DNV KEMA, and the industry overall, is pushing for international standards. It is important for the sector to have its own rules in order to have a more competitive industry and one that consistently performs in a safe and reliable manner.”

When it comes to the wind turbine, definitely the industry is adapting to IEC rules, he says. But of course, it takes time – sometimes up to five years – to develop new standards in the international standardisations committees. “That is why we develop our own rules in the areas where the international rules are lacking, because ours can be completed in one to two years. Our own rules can then be used or referenced in the international standardisations committees in the longer term.” He points out that a few years ago there were different Danish, German, and Dutch schemes but already The Netherlands has adopted the IEC scheme and the Danish one is currently being revised.

“In most cases the industry is moving towards IEC and other classification societies are also moving closer to the IEC. There does seem to be a consensus, naturally being pushed along by the industry. There is pressure to be more aligned. Maritime and offshore classification societies, such as DNV, also participate in different committees and new class societies want to get involved in wind and be part of it, so I think closer harmonisation is already there to some extent.”

Mr Christensen believes that in a few years we could see standards in place for an entire wind farm. Those for turbines, foundations, substations are already almost complete, he adds.

So does he believe that essentially the industry will become self-regulating? Rather than seeing overall EU legislation, Mr Christensen thinks it will be a mixture of country regulators and then indirect governance from the insurance and finance industry. For instance, Germany has its own special certification and regulatory authority, BSH, which is driving legislation for German wind farms, while other countries will be driven by the finance and insurance sectors, he says. A question on France remains, as it is not yet exactly clear. With the UK, there have been a lot of talk about establishing rules but there is currently no requirement for certification, he adds. And in the US, there is the Certified Verification Agent system, which is also used in the in oil and gas industry.

Slowdown creates upturn dnv

Regarding Europe’s 2020 ambitions, Mr Christensen has a somewhat unusual view some may say. “I think we all faced an exponential growth curve with the targets but now it doesn’t look quite like that. There are some delays, which may help the industry as a whole. We need to be realistic and capture learning to get the costs down. Ironically, I think the financial slowdown has helped the engineering of projects and we expect that they will be better as a result.” It gives the industry an opportunity to process the experience it has gained and make the next step forward.

“For example there is a lack of skilled people in the industry, but now we have the time to find these engineers and technicians. If the rate of growth was going on as an exponential curve, I think there would be more newcomers and more opportunities for mistakes due to inexperience. Whereas long-term participants with experience and knowledge will remain, invest in the industry and continue to train people so the industry has skilled people to face the challenge ahead. I am very positive, now there is steadier growth; there is more chance for capture and learning. The industry can get the right people in and train people and deliver good projects.” 

Helen Hill

Related news

List of related news articles