An offshore wind turbine generator comprises a tower 1 and a platform 2. The tower 1 is provided with a side door 4 accessed from the platform 2 using a stairway5 leading to an upper platform 6. The upper platform 6 is formed from the upper surface of a cabinet 7 which houses a diesel backup generator. Both the backup generator and the cabinet 7 are mounted to the tower 1 by bolts, such that the cabinet and backup generator are fully supported by the tower 1. A diesel fuel tank 12 is also mounted to the tower 1 by bolts. The fuel tank supplies diesel fuel to the backup generator.