The developer said it will open a new tender in case Senvion is unable to rectify the problem and deliver the 54 6MW turbines on time.
Senvion (formerly Repower) said that anomalies have been registered in the rotor bearings of offshore turbines in its 6MW class turbines. Wear was identified after examination, with inadequate lubrication of the bearings found to be the root cause.
"Remedial action can be taken by directly injecting additional lubricant," added a spokesperson. Further examinations are being conducted with external specialists.
Senvion declined to name the projects at which the faults were discovered, but said that the turbines "remain fully functional" despite the anomaly.
A spokesperson for RWE said that the developer still remains "optimistic that Senvion is able to deliver reliable wind turbines" on time, but that in order "not to jeopardise the project" a back-up supplier will be found.
The construction permit for the 332MW project requires work to start on the project no later than July.
Senvion's 6MW turbines have been installed at the 295MW Thornton Bank projects in the UK and are due to be installed on the 295MW Nordsee Ost wind farm in German waters.