The V52-850KW turbine was blown down on March at the Loughderryduff wind farm in Donegal, after high winds bent a blade to such a degree that it struck the tower. Vestas said it was caused by a failure in its pitch system.
Locals have been angered by the time it has taken for Vestas to release the information and that the full details will not be released.
The manufacturer has compiled an in-depth report into the incident, but was unable to release it citing the "technical and confidential nature of its content".
A spokesperson for Vestas said: "A thorough investigation reveals the incident is likely to have been caused by an error in the pitch system. As a result, it appears at least one blade failed to pitch out of the wind, leading to an over-speed situation in which a blade struck the tower.
"These events caused structural damage and the collapse of the turbine. The turbine has been cleared from the site and is being replaced.
The company added that it is implementing technical modifications to help ensure such errors do not recur.
Locals have raised concerns over safety after the debris from the collapse reportedly scattered over a large area. County Councillor Seamus Ó Domhnaill has called for a halt on further wind developments in Donegal until the full report is released.
The eight-turbine wind farm was closed for five days following the incident, but after an inspection by operator North West Wind the site was reopened.
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