A structure for a tidal flow energy generation system is fabricated from tubular framework having tubular modules with mounts for respective tidal flow turbine nacelles. The node modules include tubular limbs extending in transverse directions and elongate tubes and provided to interconnect with the tube limbs of the node modules. The structure can be pre-fabricated and transported to a location for deployment. The structure can be deployed by means of hovering the assembled structure to the seabed, for example by means of flooding the structure.