This paper evaluates the potential for co-location of offshore wind turbines at sites being developed for tidal stream arrays as a method for reducing the cost of electricity. It is shown that for a typical tidal site, MeyGen in the Pentland Firth, UK, increasing the wind turbine capacity reduces the cost of electricity compared to operating tidal stream arrays alone. This is due to increased energy yield combined with reduction of capital expenditure based on the use of common grid connection and shared support structures. Assessment is made using tidal, wave and wind resource data for a three year period. The overturning moment about the base of a monopile supporting a wind turbine with two tidal turbines is only 8% larger than for a wind turbine alone in a strong current typical of tidal farms. The increased cost of infrastructure is small relative to the increased energy yield and for all array configurations of practical interest, the levelised capital cost of energy is estimated to be 10–12% less from a co-located farm than from a tidal turbine farm alone.