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Introducing next-generation foundation system for offshore wind turbines

  • Two wind turbines
  • 19 megawatts of renewable generating capacity
  • 25,000 households will be supplied with renewable electricity

Turning innovations into reality

Two Towers BV, consisting of Van Oord, Investri Offshore and Green Giraffe, has been awarded the project and given the opportunity to introduce advanced technologies for commercial application in future offshore wind farms with larger turbines and in deeper waters and to demonstrate the practical value. Once operational towards the end of 2020, the 19 MW offshore wind farm will provide renewable energy to 25,000 households. To contribute to the energy transition towards renewable energy in the Netherlands and to ensure a cost-efficient fulfilment of the 2030 renewable energy targets, several innovations are incorporated at the Borssele Wind Farm Site V. All of these innovations have been developed by Van Oord in cooperation with other research partners. The results of these R&D projects were taken into account by the Van Oord engineers in the design of the Borssele V foundations.


The technical innovations applied in this project are the reflection of years and years of hard work and perseverance within Van Oord, together with a wide variety of knowledge institutes and universities on research and development with a focus on reducing the Levelised Cost of Energy (LCoE) of Offshore Wind and significantly enhancing Health and Safety aspects.

Erik de Boer, Managing Partner, Investri Offshore
Erik de Boer, Managing Partner, Investri Offshore
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A world-class achievement

On 25 April 2020 the world’s first submerged Slip Joint was installed, a milestone in which Van Oord was involved from the very first draft design. The Slip Joint is an alternative connection in a wind turbine foundation. It was the first time anywhere that a submerged Slip Joint was used on a full-sized offshore wind turbine on a fully commercial basis. The design and manufacturing of the Slip Joint were certified by DNVGL in the autumn of 2019. The Slip Joint consists of two conical sections placed on top of each other. The Slip Joint is based on friction, with the weight ensuring firmness and stability. Installation takes place by sliding the wind turbine’s transition piece over the monopile, without having to use grout or bolts. Unlike standard solutions, the Slip Joint makes a submerged connection possible, allowing for a more balanced weight distribution between monopile and transition piece. It therefore opens up the possibility of manufacturing larger foundations for the next generation of wind turbines with existing manufacturing facilities and installing them at deep-sea locations using existing vessels. The Slip Joint provides a rapid, simple and safe installation solution in combination with reduced maintenance for the duration of the project.

New standard for future foundation design

At the Borssele V Site technologies such as Thermally Sprayed Aluminium (TSA), Impressed Current Cathodic Protection (ICCP) optimisation and oval cable entry holes are also incorporated.  

Thermal Sprayed Aluminium (TSA) is a novel coating technology. By heating the material using high voltage electrical current, it can be applied to a metallic surface in a similar way as paint, while the characteristics are far more durable as it creates both a barrier and cathodic protection. This allows for a design lifetime of more than 35 years. 

Internal corrosion of a foundation can significantly reduce the structural lifetime, if not properly mitigated. Impressed Current Cathodic Protection (ICCP) is an effective way of achieving such mitigation. The measurements on Borssele V will lead to optimised operation of the ICCP system.

The inter array cables that export the generated electricity are pulled in the wind turbine through entry holes in the foundation. A Cable Protection System (CPS) is used to protect the cable. Optimisation of both the entry hole dimensions and the CPS reduces structural stress concentration, resulting in less steel in the section of the foundation that is just above sea bed level.

By demonstrating these technologies, the Borssele V Site contributes to decreasing the Levelized Cost of Energy (LCoE) of offshore wind energy. It is therefore expected that the innovations will set a new standard for future foundation designs.

Eco-Scour protection

The seabed surrounding the two Borssele V wind turbines will be fitted with Eco-Scour protection. Van Oord is using this sustainable technology to explore how nature and renewable energy generation can be mutually enhancing. Oysters will be placed on the protective layer of rock on the seabed to improve biodiversity and the natural habitat for aquatic wildlife. Nature-inclusive wind farm development, environmental aspects and public consent play an important role in the large-scale roll out of shore wind. Integration of scour protection with oyster reefs will have positive effects on the marine environment. In Borssele V outplacement strategies for flat oysters will be tested.