Enersea develops reusable monopile cover for Hollandse Kust Zuid

© Enersea

Dutch engineering company Enersea has developed a reusable monopile cover for Vattenfall’s Hollandse Kust Zuid offshore wind farm. In the next 8 months the design will have to be optimised and go into serial production in order to have the first 41 covers ready for installation.

Vattenfall is building the app. 1,500 MW Hollandse Kust Zuid offshore wind farm some 22 km off the coast of Katwijk in the province of Zuid-Holland. The wind farm, consisting of 4 development zones, will comprise 140 turbines from Siemens Gamesa with 11 MW power. Construction work is planned to start in June 2021.

Vattenfall asked Sif, who is responsible for the monopile supply, to come up with a smart and environmentally friendly solution for the monopile covers which protect the airtight platform inside the monopile. Enersea, polyester manufacturer Theuws got involved and joined forces in developing a sustainable cover. They were supported by support from Stimulus Programme Kansen Voor West (Chances for West).

The new cover is to provide a more sustainable variation of the current covers. Up to now the monopile covers are made of aluminum, steel or tent cover. According to Enersea the steel and aluminum covers have never been reused for new offshore wind farms and recycling steel and aluminum specifically is an energy consuming process. With the tent covers there is the that they are blown away.

The construction consists of different fiber reinforced polyester panels looking like pieces in a pie. The top panels can be tailor made and will be able to be reused for the monopile diameters that are currently available on the market.

“It was not the first material we thought of’, Christian Larsen, project engineer for Vattenfall at HKZ, admits. ‘But we wanted a new and sustainable concept and gave our subcontractors the freedom to come up with a new concept, both in terms of construction as well as in material choice.”

Prototype
Together with engineering company Femto, who carried out the Finite Element Analysis, Enersea and Theuws developed the detailed design which led to the first prototype.

At the Theuws yard in Wieringerwerf a functional inspection and water test was carried out with positive results mid June 2020. The test was followed by further tests at Sif’s terminal at Maasvlakte 2 in Rotterdam. This time the cover was mounted on a mock up monopile so the complete construction could be tested on functionality, load resistance, water tightness and several other aspects.

The design will now have to be optimised an get ready for serial production. The first 41 covers will have to be ready in 8 months. Source: Enersea.nl