Hexagonal windfarm meets energy and environmental requirements

Add in the fact that the site in question is a Natura 2000 area and World Heritage Site known for its bird life and the project sounds potentially very difficult to develop and build. That might be so, but the developers of Windpark Fryslân, a large near-shore windfarm in the IJsselmeer in the Netherlands, have succeeded in meeting an especially challenging brief. Following a final investment decision in October 2019, they are pressing ahead with a project that will bring much-needed clean power to the province of Friesland, known historically as ‘Frisia.’

This latest example of Dutch engineering expertise will see Windpark Fryslân supply 383 MW of electricity to the province, enough for 500,000 households and 70% of its overall wind energy target. A number of potential solutions to meet that target were discussed over the years – including a number of smaller onshore windfarms – but Windpark Fryslân eventually emerged as the solution of choice.

But for the Bouwconsortium Zuiderzeewind that is building the windfarm, in the northern part of the Ijsselmeer, just south of the Afsluitdijk, near Breezanddijk, the project isn’t completely without precedent.

In 2016, a somewhat smaller project in the IJsselmeer, the 144-MW Westermeerwind windfarm, was completed. At the time, Westermeerwind, which was built along the dikes of the Noordoostpolder, was the largest near-shore windfarm in the country. It consists of 48 turbines in two rows arranged along the Westermeer dike and one along the Noordermeer dike. A lot of experience gained during construction of Westermeerwind is being put to use with the larger Fryslân project, but as Windpark Fryslân project director Anne de Groot explained, the size of the new project made it more complex to design and build.

The turbines for Westermeerwind may be arranged in rows, but that would not have suited the larger project. “One of the most important things we needed to address during development was the visual impact of the windfarm,” Mr de Groot told OWJ. “Another was mitigating the impact on the environment of constructing and operating the windfarm.

“A lot of work went into finding the best possible location for the windfarm, in order to ensure that the environmental impact would be minimised, and identifying the best possible arrangement for the turbines,” Mr de Groot explained.

“Instead of identifying the best possible place that would maximise yield, we set out to find the best location from an environmental point of view and only then designed a windfarm that suited that area. We also had to take into account that the Netherlands Ministry of Defence has a range on the Ijsselmeer and that certain areas would be off limits as a result.

“Once we’d found the best location, we had to ensure that the visual impact would be acceptable from the shore. For this reason, we adopted a hexagonal cluster rather than rows of turbines as the basis of the design,” Mr de Groot told OWJ. “The idea behind it is that, from key viewpoints on the shore, the visual impact of the turbines is minimised.”

A windfarm would usually be designed to maximise yield and to ensure that turbines are located in a way that minimises wake effect, which is known to adversely affect production. Mr de Groot acknowledges that from the wake effect perspective a tight cluster isn’t absolutely ideal. Ideally, he said, a different arrangement with more space between the turbines would have been adopted, but the design succeeds in meeting the needs of the project and making it visually acceptable to people in the region.

The way that the windfarm is being built also departs from convention given that, by offshore windfarm standards, the water in the IJsselmeer is very shallow water, ranging from just 2.5 m to 8.0 m at the windfarm site. That precludes the use of a large jack-up vessel, as does the lack of supporting infrastructure for large vessels on the lake.

The solution adopted by Bouwconsortium Zuiderzeewind is similar to that used for the Westermeerwind project and will see pontoons used to transport foundations and towers for the turbines, and an artificial island built in the lake to act as a logistics hub and staging post for offshore activity. Pontoons will also bring assembled turbine rotors to the site, and a pontoon with a crane will install them, a process that will minimise the number of lifts required and should see turbines erected quickly and efficiently, in 24-36 hours each. Once the project has been completed and activity on the water is at an end, the island – which will be around 2 hectares in size with another 25 hectares of shallow water around it – will become a nature reserve.

The grid connection for the windfarm-in-a-lake also required a little forethought, as did the need to lay a 25-km export cable from the substation at Breezanddijk towards Bolsward. Once the export cables are installed and the substation built, Windpark Fryslân will be connected to the grid by a newly installed 40-km cable that transmission system operator TenneT is building, a project that was brought forward specifically to meet the needs of the near-shore project.

Renewable energy consultancy Pondera and service provider Ventolines, which is acting as the overall manager for the project, initiated project development back in 2008, with Pondera responsible for early development work (including feasibility studies, design, permitting, the environmental impact assessment and stakeholder collaboration), working closely with Ventolines.

The contractor for Windpark Fryslân, Van Oord, started preparatory work several months ago, having first undertaken soil investigations in late 2018. It began installing ducts through the Breezanddijk that will carry the power cables in March 2019, and construction of the transformer station at Breezanddijk is also well underway.

On 18 October 2019, Van Oord awarded a contract to EEW SPC to construct the monopile foundations for the project. Manufacturing will begin in January 2020 and each monopile will be unique and dimensioned specifically for the location at which it will be installed.

Mr de Groot said construction of the nature island for the project is due to get underway late in 2019 or early 2020. Installation of the monopile foundations for the 89 Siemens Gamesa SWT-DD-130 turbines for the project should get underway in the second half of 2020 and the first turbines are due to be installed by the end of 2020 or early 2021. The windfarm will be fully operational in 2021.

Wherever possible, the consortium is hoping to use local content in the construction of the project and the province of Fryslân is investing in it, using revenues from the sale of shares in energy company Nuon.

A total of 10 banks were responsible for successfully closing the finance for the project. Together they arranged senior debt of around €700M, the banks in question being ABN Amro, BNG, BNP Paribas, DZ Bank, Helaba, ING, KBC, KfW IPEX, NWB and Rabobank. On reaching financial close the province of Fryslân stepped in as a shareholder with a total investment of €100M, and after construction is completed citizens in the province will have the opportunity to invest in the windfarm through bonds.