For reasons as yet not fully known, large parts of the AV 07 nacelle housing (roof, sides and floor) fell into the sea on 6 April. No persons were harmed and there was no threat to the marine environment because the nacelle only holds small amounts of operating materials. As a precautionary measure, the manufacturer's other five wind turbines have been in standby mode since then and are blocked for maintenance work.
Preparations to replace the damaged nacelle will soon begin: First, access to the AV 07 will be provided with the help of a Service Operation Vessel (SOV), which is equpped with a hydraulic gangway designed for offshore use. Specially trained industrial climbers will secure or remove the technical components located outside the machine carrier or drive train housing to prevent falling. Subsequently, the sunken parts of the nacelle housing will be recovered from the seabed and the power supply to the wind turbine restored. In the next step, the nacelle and the rotor will be rotated into a position that allows disassembly of the rotor and replacement of the nacelle.
The machine frame of the nacelle accommodates all power generation components such as rotor shaft, rotor bearing, gearbox and generator. The nacelle housing with the heli-hoist platform allows easy access to the wind turbine. The damaged nacelle of type AD 5-116 will be examined in detail after replacement at the manufacturer Adwen’s site in Bremerhaven to clarify the exact cause of the damage. It is clear thus far that the retaining bolts of the nacelle frame are broken or torn - but why it happened is currently unknown.
Evaluation of the data recorded by the Condition Monitoring System is already in progress. The visual inspections of the other five turbines started last week - when exactly they will be able to resume power production is currently still to be determined.
Update: The nacelle replacement, which was delayed due to unfavourable weather conditions, has been completed in October 2018. The complete wind farm back to power generation since early 2019.