Bad weather and technical problems have put foundation installation behind schedule at Vattenfall's 1500MW Hollandse Kust Zuid offshore wind farm off the Netherlands.
Only 34 monopiles out of the project's 140 have been installed during the first installation campaign, which started on 5 July.
HKZ project director Ian Bremner said the campaign had a “challenging start, due to some unexpected technical difficulties on the foundation installation vessel” Seaway Strashnov.
He said: “However, once those were resolved and we were up and running, things went really well, and the pace of installation was meeting our expectations.
“Unfortunately, further technical difficulties interrupted the momentum and we never quite recovered the earlier performance.
“The delays pushed the works further and further into adverse weather periods to the point where it was no longer viable to continue.
“This translated into us falling short of our foundation installation target for 2021.”
Bremner added that there is flexibility in the start date of the second foundation installation campaign that should allow the project to recover the installation shortfall from the first campaign.
“This means that the early challenges do not materially impact the overall schedule,” he said.
“In fact, this first campaign has provided us with lots of opportunity to learn key lessons that we can use to plan and optimize the second campaign, which is a lot more time critical,” he added.
“We are confident that foundation installation performance will improve next year.”
The second campaign should start at the beginning of March, with the installation of the remaining 106 monopiles.
Next spring, the first cables and turbines will also be installed.
The HKZ team is using the coming winter period to prepare for this new phase, Vattenfall said.
Bremner said: “We are performing a great deal of programme analysis and detailed planning to be 100% prepared for these first connections to the substations and delivery of power to the grid.
“We have to manage some very complex interfaces between cable and turbine installation and commissioning.
“There are so many activities taking place involving so many teams and contractors, and all activities are highly interconnected.
“We are turning every stone to make sure the planning is perfect and that we have all of our risks in clear view and mitigated.”