New scour-busting foundation technology heads out to sea

An innovative new technology that could save offshore wind farm operators hundreds of millions of pounds by protecting turbines against being undermined by the effect of scour will be fine-tuned under a new £1m project being run by a six-company consortium led by ScottishPower Renewables (SPR).

The Self-Installing Scour Protection for Offshore Wind Farms (SISProtect) scheme, which is expected to reduce costs for an offshore wind farm by £8.6m over its lifetime, will prototype a so-called “frond mat” system that will fitted to a suction bucket jacket (SBJ) before installation at the 714MW East Anglia 1 project, off Scotland.

“By pre-installing the scour protection system onshore and deploying at the same time as the foundation installation, this innovation will remove the need for environmentally damaging quarrying of rocks and diesel intensive installation vessels whilst providing a lower cost alternative to those currently available for the protection of offshore wind structures,” said Adam Tucker, subsea division manager at SCSS, which engineered the scour protection system.

Miriam Noonan, financial analysts at the Offshore Renewable Energy Catapult, which will run the rule over the new technology to compare it with traditional scour protection techniques – generally rock-dumping around a foundation – added: “Installation costs typically account for over 75% of the overall cost associated with scour protection systems. By being able to deploy SSCS frond mats at the same time as the wind turbine foundation installation, the associated installation costs may be significantly reduced.”

The 20-month project, backed by funding body Innovate UK, will use an SBJ supplied by SPT Offshore and installed by N-Sea at East Anglia 1. The field trial at the wind farm follows on from laboratory tests carried out by at HR Wallingford, which had previous worked with SPT and Orsted (then Dong) on earlier scour-busting solutions.

An SBJ without scour protection will also be installed at East Anglia 1, “providing a reference for the level of scour that will develop naturally at the site and ensuring that the reduced scour measured at the protected suction bucket can be properly attributed to the frond mats”, while comparisons will also be made to the foundation rock armour used at the wind farm, said the consortium.

All offshore wind farms suffer from scour impact “to some extent”, experts from project partners SCSS and SPR noted to Recharge, with turbines in the Southern North Sea “in particular” being exposed to “a very scour prone environment”.

“There are known issues with scour across the industry which in some cases are believed to have caused turbines to shut down and/or necessitated structural repairs,” they said, noting that the “sensitive” nature of information for the operators of offshore wind farms means “it is difficult to quantify this”.

The SBJ was chosen as a “most suitable” foundation type to try out the SISProtect technology due to the “smooth deployment process” of the suction-driven SBJ – as compared to monopiles which have to be hammered into the seabed.

“Worth noting that any foundation type will suffer from scour in such an environment, and therefore in order to provide the effectiveness of the system a suction bucket is completely suitable and reflective of other foundations types, including monopiles,” the SCSS / SPR experts added.

Scour, where currents and waves combine to wear-away areas around offshore turbine foundations, is relatively well understood for traditional monopiles, but remains a particularly serious issue for complex structures like steel jackets, particularly in the greater water depths being explored by the wind power industry for coming mega-developments off the UK and Germany.

Even for monopiles, scour can be a show-stopper. Research conducted at the pioneering Horns Rev 1 project off Denmark found the rock armour laid about its 80 foundations had been washed away and the seabed as much as 1.5 metres lower after three years due to the phenomenon and two turbines at the Robin Rigg wind farm off the UK in 2015 being decommission after their monopiles suffered irreparable scour.

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