NOVELTY - A combined offshore system has an offshore windmill unit (1) with a generator drawing power from wind and transferring it into electricity, an electricity export cable (2) connected to the windmill unit for supplying produced electricity to offshore or on-shore consumers, and at least one offshore wave power unit (3) for drawing power from waves. The electricity produced by the wave power unit is transferred via the same cable as the electricity produced by the windmill unit.    USE - Combined offshore system for generating electricity. Can also be used for producing electricity from wave motion, primarily ocean or sea waves as well as from wind, with extracted energy being converted to useful energy.    ADVANTAGE - The combined offshore system allows for easier and economic permission procedure, installation, and production by using pre-existing grid of electricity export cables. The offshore system is installed by installing or mooring at least one wave power unit near an already placed windmill unit and establishing energized connection between both units, simplifying maintenance at same time protecting the windmill unit from destructive waves and offering protected landing area for maintenance vessel around the windmill unit. Maintenance or change out of electricity converting equipment of wave power unit is simplified as it is performed in steady, non-moving and dry environment above water level. By removing converting equipment from wave power unit, the wave power unit itself and its mooring system can be of much lighter, simpler, more effective and less costly construction leading to simplified offshore installation.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a method for installing a combined offshore system.    DESCRIPTION OF DRAWING(S) - The drawing shows the front view of a combined offshore system with the wave power unit comprising a Bristol cylinder.    Offshore windmill unit (1)    Electricity export cable (2)    Offshore wave power unit (3)    Buoyancy module (4)    Energized connection (5)