An Offshore Wind Turbine Installation with a Concrete-Cast Transition Piece Between the Wind Turbine Tower and its Support

An offshore wind turbine installation, comprising:

• a wind turbine comprising a tower having a tower flange at a lower end of the tower;
• a support structure for supporting the wind turbine in offshore conditions, the support structure comprising a tower support having a support flange;
• a concrete-cast transition piece between the support flange and the tower flange, the transition piece on its lower side in mechanical contact with the support flange and supported by the support flange, and the tower flange on its lower side in mechanical contact with an upper side of the transition piece and supported by the transition piece;
• wherein the support flange is at an upper end of the tower support, and the support flange and the tower flange each comprise holes for bolts extending therethrough, the bolts directly or indirectly holding the tower flange to the tower support flange with the transition piece in between;
• wherein (A) each of the bolts extends through both the support flange and the tower flange for pulling the support flange and the tower flange towards each other by the bolts with the transition piece sandwiched in between or (B) a first number of the bolts extends through the tower flange into first threaded bushings embedded inside concrete of the transition piece and a second number of the bolts extends through the support flange into second threaded bushings embedded inside concrete of the transition piece, thereby bolting the tower flange and the support flange to opposite sides of the transition piece.