Vattenfall: DanTysk – Discovering best practises

DanTysk Offshore Wind Farm is back on schedule – albeit a revised schedule – with more than half of its 80 wind turbines installed. Gunnar Groebler, Head of the Business Unit Renewables at Vattenfall’s Continental/UK regional organisation, reflects on progress and outlines the company’s view as to whether offshore wind will remain an important strategic focus.

Following Vattenfall’s recent restructuring, the division Germany, Netherlands and the UK has a portfolio of 1.9GW, which includes those on and offshore wind farms under construction. Additionally, the company is currently repowering the largest Danish onshore wind farm in in northwestern Jutland and in the UK it is building the 230MW Pen y Cymoedd wind farm in South Wales and in Scotland, a 50MW farm, north of Aberdeen, is under construction.

DanTysk was not a Vattenfall project originally but the Swedish state-owned company has no regrets in taking it over from GEO GmbH in 2007, says Mr Groebler. “Our history in onshore and offshore wind is substantial and we had a large footprint with several wind farms running and many under construction. This includes a presence in the German sector so from our side, DanTysk was a good fit in our portfolio.” 

“Size-wise and given the park layout, wake losses can be reduced. It has good wind and good soil conditions. We felt the offshore farm fitted well with our strategy going forward.”

A few years later in November 2010 Vattenfall formed a joint venture with Stadtwerke Miinchen (SWM) to develop the facility further. DanTysk is a big project, he explains. “Vattenfall had already taken the project to the final investment decision but this is still a young industry so it made sense to work with a partner on such a large project. We were looking for a strong partner that also has experience in offshore wind. We can share the knowledge and bring in know-how from both companies, share the risks and uncertainties of course.” However, Vattenfall will be the operator going forward and will run the assets from its base in Esbjerg.

For Mr Groebler, DanTysk offers a ‘pretty perfect layout’, which will help the wind farm have a particularly good wind yield and a considerable reduction in wake losses. The prevailing south-westerly winds in the area blow at an average speed of 10m per second, which, when combined with the elongated shape of the wind farm, ensures optimal operational efficiency. The shape of the site means the first rows of turbines are great at capturing the first common wind direction, he says.

First OAP in the German North Sea

As well as the particularly good wind yield, DanTysk is special in that it is believed to be the first operational offshore wind farm in the German North Sea to have an Offshore Accommodation Platform (OAP), with capacity for some 50 technicians. The OAP will be used for regular maintenance activities, as well as complete overhauls of the facilities when necessary. It will also have storage space for spare parts and a workshop.

Mr Groebler comments: “We are becoming more efficient and establishing the OAP is something we have taken onboard from the oil & gas industry. When considering that DanTysk is 70km offshore and 90km from the service hub in Esbjerg, it is simply not efficient to ship people out to the turbines each day. It takes an enormous amount of time.”

“This is more efficient but also from a health & safety point of view, it is much better for maintenance crews. Coupled with this, using the OAP will realise a huge reduction in our C02 footprint, saving on all the many crew transfer journeys.” People can easily stay for several days offshore and be comfortable, he adds.

Work on constructing DanTysk started in February 2013 and the wind farm has faced delays, which eventually meant it ended up being a year behind schedule. This was largely the result of problems regarding the converter station, which the Transmission System Operator, TenneT, is responsible for in North West Germany. “Essentially, we faced a year-long delay and had to revise our schedule to accommodate this. And clearly we have extra costs because of this delay. However, because we have fulfilled all necessary steps we are entitled to compensation from TenneT.”

A large number of offshore wind farm connections needed to be put in place in the North Sea at the same time and this has led to pressure. Delays also started to mount up in other offshore projects in the North Sea when it took many months to clear munitions remaining after the Second World War.

On track again

However, DanTysk is now well on track with the revised schedule. Out of the 80 3.6MW Siemens wind turbines, 43 had been installed by early July and all the cables were laid. The first burial campaign had started and the offshore substation was already constructed. The partners were just about to start energising the cable. The inter-array cabling was even three weeks ahead of schedule, Mr Groebler points out.

Installation, once underway, has gone relatively smoothly, he adds. “Initially, everyone was working more as individuals but now teams have been formed and we are pretty well on track. The guys from the vessel, the crane and turbine manufacturer are now working as one team. They have all been on a learning curve during the 43 installations, which has already led to some good results. We are now achieving 6 turbines in just five days! Hopefully we can keep this speed up.” DanTysk is expected to start up in November with full export beginning in 2015.

Experiences shaping current projects

There have also been lessons learnt from this particular offshore project when it comes to foundations. Vattenfall is currently developing other offshore projects and has opted for a flange connection between the monopile and Transition Piece rather than the classic grouting connection. “The traditional grouting method limits the period of installation because there has to be a certain temperature in order to grout, five degrees or more. There are both the water and air temperatures to consider and clearly, this far offshore in the North Sea temperatures can be restrictive. We wanted to enlarge the installation window.”

Although Vattenfall has used the classic hydraulic hammer piling method for DanTysk, the company is involved in research studies along with other utility companies examining vibro piling. Six monopiles have been installed onshore near Cuxhaven, three using vibro piling and three with a hydraulic hammer. Test results are expected in the autumn.

Lessons are being learnt all the time, says Mr Groebler, adding that because the sector is new it is still difficult to say what can be considered ‘conventional’ technology and practices. During the design phase of DanTysk a lot of knowledge has been gained regarding construction and about how to deal with adverse weather. “We have put a great deal of effort into planning and how to reduce the vulnerability offshore. Ultimately, we want to bring the costs down.”

Vattenfall is certainly keen to grow its offshore wind portfolio and many of these lessons will be used in the future. The company is already eyeing DanTysk neighbour Sandbank for instance, and it is working on the extension of Kentish Flats Offshore Wind Farm in the UK, which will give an additional capacity of 51MW.

Reducing costs is vital

Wind energy is very much on the company’s radar and it is looking ‘to enlarge its asset base’. “Overall we see wind as an important pillar in the new energy landscape. But it needs to mature and get the cost reductions needed. And there are absolutely clear expectations that we should bring the costs down. We are seeing the support mechanisms go ‘south’; governments are abandoning support for on and offshore wind. The industry sees and hears a clear direction from the politicians that the support level is going down.”

“But don’t get me wrong, we must bring the levelized cost of energy down, that is fair, so the industry can be sustainable in the long-term and we can be competitive in the energy production sector.” Costs can come down and this is happening, he stresses. For example, new technology developed these days is very site specific but this hasn’t always been the case. Until recently there has always been a lack of data from which to develop offshore wind farms, he comments. “But the first wind farms have been running for years and they are now out of warranty. We can gain so much experience on the generation side and this can be fed into developments to improve the operational aspects. After all, we have to live with the plant for 20 years. This is one way we can reduce cost levels. “We are also learning more about working in hostile environments. At Vattenfall we have embarked on a programme to reduce downtime due to adverse weather.”

Turbine installation speeds up

Additionally, the industry is still on a learning curve about installing turbines, he says. “As the industry matures and engineers get more experienced, the time it takes to erect the turbine is going down. For example, at DanTysk, originally it took 30 hours per turbine, but this is down to less than 20 hours even to 16 hours in some cases. “Again this is all bringing the costs down because we don’t need to charter the installation vessels so long.”

Operationally, there is the possibility of sharing servicing and maintenance contracts and maybe supply vessels etc. “At Vattenfall we tend to think in clusters. DanTysk is serviced from Esbjerg as is Horns Rev and other wind farms. If we go ahead with Sandbank it will also be served from Esbjerg, so this will also bring costs down.”

Mr Groebler says when weighing up progress of the industry overall it is on track, although he adds, that it could have been better. Considering the circumstances and given that it’s a relatively new industry, and that authorities/regulators are also learning to make decisions about offshore wind

Stability is crucial

“I am optimistic yes. We are looking forward to the introduction of the new Energy Act in Germany, which is due to be introduced in August. We are talking big money and big investments – DanTysk represents more than €lbn! Stability is needed in order to make these investment decisions. At least there will be a stable framework going forward. Developers then know when their investments will pay off. It gives the certainty. Companies feel free and able to make the necessary investment decisions.

“If framework conditions are handled properly by the politicians and the public, we can deal with the technical and financial complexity of such a project. We have more than 100 years experience in developing and constructing complex power plants as well as energy production whether it’s fossil fuels, nuclear, hydro … and wind. We have the competence and can make the necessary knowledge transfer into offshore wind. What we need though is a stable political and economical environment – for the rest we are confident that we will be able to handle it!”

Helen Hill