Wieringermeer Wind Farm: Building the largest Dutch repowering project

Vattenfall is currently building one of the largest Dutch wind farms in the Wieringermeer. In this enormous stretched area, covering around 300 square kilometres, the wind has free play at all times. With 82 wind turbines, this is also the company’s largest Dutch onshore wind project developed by themselves.

We talked to Ruben Lindenburg, Project Director Construction for the wind farm to hear the experience so far.

Vattenfall will build 82 of a total of 100 wind turbines that shape Wieringermeer wind farm. Are you still working with the developers of the remaining 17 wind turbines?
Wieringermeer wind farm is a repowering project. The Dutch Government provided a permit for 100 wind turbines. The permit would be granted to one party only. Vattenfall already had some small wind farms in this area. Together with research centre ECN and Windcollectief Wieringermeer, we joined forces to apply for the permit. In September 2017, we acquired the 32 turbines from Windcollectief Wieringermeer. Up to the decision of the Council of State (Raad van State) we worked together with ECN but once the permits were in place, we each followed our own path.

Of the 82 wind turbines, 78 are located on agricultural land and 4 in the Robbenoordbos forest. Was it really necessary to build in the forest?
We often get this question. And if you look at the surroundings as an outsider, I can understand the question. The layout of the wind farm was determined by the Government’s so-called ‘Structuurvisie’ (structural concept), around 12 years ago. For one, the turbines had to be installed in single line position. That already rules out parts of the area. Also, back then, the Government invited all the stakeholders from the region. During the stakeholder process, all stakeholders, varying from farmers, communities, defence, airport, energy companies, nature conservation organisations, et cetera, could provide their input or restrictions. In the initial plan, 6 wind turbines were located in the forest but after research and consultation with our ecological experts, two wind turbines were scrapped. To construct the four wind turbines in the forest, around 3.5 has of space had to be cleared. But we are planting new trees in an adjacent area of 4 has, so we are returning more than we removed. All was done in good cooperation and in consent with nature conservation organisation Staatsbosbeheer who wish to combine forests with renewable energy production. In the design, we made sure the wind turbines would be optimally integrated in the landscape. We also provided special facilities for bats as this area is a popular place for bats.

Vattenfall/Jorrit Lousberg

What is the current status of the construction activities?
At the moment, 42 foundations and around 70% of the road and internal cable construction have been completed. Hearing me say this actually makes me realise how happy I am to see that we are half way and have made this progress. We have faced quite some challenges along the way and this has affected the original planning. Next week, the components of the first Nordex wind turbines should be arriving. I sincerely hope that the turbine installation will be a smooth process. Fingers crossed!

You mention there were some challenges. Can you mention a few?
Keep in mind that the Wieringermeer wind farm is a rather unique case for Vattenfall in the Netherlands. This is the largest onshore wind project that we are developing on our own here and I don’t think we will see many more of this size in this highly populated country. The total site covers an area of 300 square kilometres. In this enormous area we are installing 82 turbines. Imagine, it takes a 175 kilometre long round to drive from turbine to turbine. This requires quite some organisation.this enormous area we are installing 82 turbines. We already knew we had to relocate a glider airport and so we did. The new glider facility is taken over since October last year and fully operational.

Next, the soil conditions in the Wieringermeer are varying and hence challenging. We need to examine those before we create a technical design. At the start of the process, soil samples are taken at different spots across the area to determine the site specifics. Based on this, the technical design is created. For Wieringermeer, it took 5 months to create this design. Wieringermeer is built on a combination of clay and sand grounds. These require different construction approaches for the roads, staging areas and to a lesser extent, the foundations.

People tend to think that the transportation and installation of the wind turbine components (tower, hub and blades) are the most challenging aspects of building a wind farm. However, the construction of the roads, the crane hardstands, and the foundations are the most critical part. You have to imagine that ten thousands loads of sand, concrete, asphalt and steel are required during the road, cable and foundation construction work. The municipality did reinforce some existing bridges in the area to ensure that the heavy weight transport could pass. The crane hardstands have to be able to support the heavy installation cranes and their loads, and the foundations need to be able to support the turbines and towers. As an example of the variety of soil condition, in the north-western section there is an underground current running which was formed back in the ice age. Using vibro piles would be impossible as the concrete would flow away. Here we had to use pre-fab piles. The staging areas had to be piled in this area.

Also, the ground water in the Wieringermeer is relatively salty if you go a little bit deeper than usual. As a result, excess water that is pumped up during the cable burial work cannot be released in the surrounding ditches. We had to use pipes, of sometimes 7 kilometres in length and with a diameter of 60 centimetres, to transport the excess water all the way from the western part of the site to the IJsselmeer lake. All this has to be taken into consideration when creating the technical design. However carefully you design every aspect, you might learn that for some practical reasons, some of the elements are not viable in reality. This could be a road being located where there is a crossing or an underground cable running. You will have to modify the route. However, this means that you first have to take new soil samples again. If the soil is for example softer, then you will have to use concrete instead of asphalt.

It is not only the contractors that request for a change in the design. The farmers on whose lands we are building the turbines have their expectations as well. It has happened more than once that we were about to start construction activities, when we were pointed at a possible problem. For example, where a road would cross a drainage system. Then the question rises where to lay the cable, above or below the drainage system. There is no standard burial depth for drainage systems and we hit drainage canals quite some times. In addition, there are several flower farmers that will raise their ground water levels in July, August. It would be impossible to install a crane then.

These are all examples that kept on occurring, leading to additional expenses and delay. That’s why we have two-weekly meetings with the farmers involved, to take them through our plans and to provide them with the opportunity to express possible concerns or share ideas. Another change in the plan concerned the activities of our contractors. In the initial plan, Van Gelder would be responsible for the construction of the roads, the staging areas and the cable installation. BAM would follow to build the foundations and then Nordex would install the turbines. Seven months down the road, we had to change this. In some parts of the area, BAM did start before Van Gelder, building temporary roads to start the construction of the foundations, followed by Van Gelder, Nordex and in the end Van Gelder again to finish up.

Vattenfall/Jorrit Lousberg

The project was delayed for nine months due to problems with the substation. What is the current status?
In the wind farm, all our turbines are connected in groups to 15 small client stations. An electrical engineer would say we have 15 small wind farms. These client stations are connected by Liander to the substation at the Agriport A7 business park in Middenmeer. This substation is a project by regional operator Liander and national grid operator TenneT. Initially the completion of the substation was planned for July 2018 but this was delayed. It’s the chicken-and-egg story really, both TenneT and Liander wouldn’t start with the construction until we confirmed that we were going to build the wind farm and we couldn’t build the wind farm if there was no guaranteed grid connection. When we finally managed to find a short-cut, they didn’t have a contractor available. The result was a delay of 9 months. This meant we had to postpone our tender for contractors also. The substation was ready and switched on in December last year but was shut down again soon after to already extend the substation for new customers.

Do you know when you can expect to get the wind farm connected to the substation?
We had hoped to make the next available connection slot, in March, but unfortunately this didn’t happen either. Currently, we’re about to energize the first client station and we’re thrilled we came to this stage. Again, it’s a complex situation where the substation will not solely connect our wind farm. At the moment there are many developments taking place in this region. Google is going to build their facility, Microsoft is expanding and the Ministry of Waterways and Public Works is doing work at the Afsluitdijk. In the meantime we need electricity, for all the drainage systems and the work on the client stations. Last month, for example, we installed the first client station. In order to continue with our work we rented a mobile green battery to ensure electricity is available.

Sustainability is high on the agenda for Vattenfall. You already mentioned the green battery, are there more examples of sustainable initiatives?
Vattenfall aims to become fossil free within one generation. With everything we do, we try to do it in a most sustainable way. For example, the information centre/office that we have set up on site is almost energy neutral. We use wind energy, heat pumps, led lightning and re-use of rain water. This building will be removed when the wind farm is operational but the new service station, the clubhouse of the former glider airfield, will be fully energy neutral. We recently finished this service centre. At the wind farm, our employers drive electric cars or cars driven by blue diesel (Hydrotreated Vegetable Oil). In March, we won our company’s ‘Environmental Award’ award and we’re really proud we’re taking a step extra to build this wind farm as environmentally friendly as possible.

Talking about sustainability, have you considered installing solar fields near the wind turbines?
We did look at it but we decided first to concentrate on this wind farm and later in the project look at the possibilities to install solar panels. We know it is possible because we are realizing this also in other places. And if we do, they can easily be connected to the available grid system.

This article appeared in Wind Energy Magazine, No 2, 2019. Text: Sabine Lankhorst

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