The Borssele series: Innovation site for the ever-evolving industry

The Borssele V offshore wind farm in the Netherlands has been producing electricity since February of this year, with its two turbines being able to power as many as 25,000 households – and the project’s contribution to a sustainable, clean energy future does not stop there.

While investigating the offshore wind areas and preparing the Borssele Wind Farm Zone tenders years ago, the Dutch government earmarked the Borssele V area as a place where the industry could test and demonstrate novel, cost-effective, and sustainable solutions.

For the testing of innovations, the government had secured a subsidy of up to EUR 15 million, along with a subsidy for the electricity supplied of a maximum of EUR 35 million.

A consortium between Van Oord, Investri Offshore, and Green Giraffe won the tender for the innovation site in April 2018, with Van Oord also being the Balance of Plant contractor.

The consortium, called Two Towers, installed two Vestas 9.5 MW wind turbines on top of two monopile foundations manufactured by Sif in 2020 and later entered into a partnership with Dutch energy company Vandebron to enable the power consumers to purchase their renewable electricity directly from the project.

One of the two wind turbine foundations features Van Oord’s Slip Joint connection, making it the first time anywhere that a submerged slip joint was used on a full-sized offshore wind turbine on a fully commercial basis, according to the company.

The Slip Joint is an alternative connection between a monopile and a transition piece, consisting of two conical sections placed on top of each other. This solution makes a submerged connection possible, allowing for a more balanced weight distribution between a monopile and a transition piece.

The installation is done by sliding the wind turbine’s foundation elements over the monopile, without having to use grout or bolts.

Along with the Slip Joint foundation, the technologies being demonstrated at Borssele V include Thermally Sprayed Aluminium (TSA), Impressed Current Cathodic Protection (ICCP) optimisation, oval cable entry holes, eco-friendly scour protection, and oyster beds.

The eco-friendly scour protection and oyster beds are an integrated approach to demonstrating the performance of the scour protection and testing different outplacement methods for live European flat oysters on the two scour protections of Borssele Site V.

The project involves installing eight different reef structures with oysters underwater at the offshore wind site to determine which method works best for the long-term establishment of oyster reefs on scour protections. On the structures, oysters will be placed in various ways such as contained, loose and pre-settled.

Within the project focused on oval cable entry holes, the team at Borssele is working on the optimisation of both the entry hole dimensions for cable pull-in and the cable protection system (CPS) to minimise stress concentration in the monopile wall, which leads to reduced steel usage in the section of the foundation.

A novel coating technology, Thermally Sprayed Aluminium (TSA), which is said to be more hard-wearing, is also being demonstrated at the innovation site, together with an automated application system that could cut the coating costs in the industry.

The offshore wind farm is also featuring the Impressed Current Cathodic Protection (ICCP) system to mitigate internal corrosion of foundations by supplying a controlled direct current to the underwater surface. The ICCP system, whose current is being monitored by zinc reference electrodes, is automatically adapting to the existing conditions to provide the suitable level of corrosion protection.