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David - the big advantages of this system are that float-out installation means you don't need some of the huge crane-barges needed for offshore wind energy and fixed tidal devices; and easy access for maintenance means you don't have to take the unit back to base every time a minor repair is needed - which is true of other tidal devices. A further thing that determines cost is unit capacity - it costs a lot to put a foundation on to the seabed, so you need to hang as much capacity from it as you can. At 10MW, our unit is twice as big as the largest wind turbine yet installed offshore anywhere. So we predict that the capital installed cost and operating cost will be markedly less than that for offshore wind, which at present is the main plank of the UK government's renewables policy. And rate of return should be greater than for offshore wind or more conventional tidal devices. As far as wave devices are concerned, energy capture from these looks like being much less than for tidal systems, kg for kg, so there is really no competition there.