I’m playing with the up and down part of tidal energy since the Google boys are proposing to use it, at least in part, to power their floating barges.
British windmills produces 260kW on average. By my math, 1 kW of electricity can be produced by 31,400 cubic feet of displaced water pulling on a string (30 ft cube = 10 light bulbs when the tide is coming in, or 5 full-time with a battery).
One windmill is thus equal to a 250’ submerged cube of air, pulling on a machine to convert the force to electricity.
That is a really big cube. There is some potential for generating power with ships at anchor and we’re working on that for local applications. But stick with nuclear power to generate national electricity. Japan’s Oi nuclear complex alone has 4.5 GW of capacity. That is equal to 17,000 average windmills.
In total Japan has around 47 GW of nuclear capacity. This is like 180,000 ugly windmills. Japan reportedly plans to use 20% of its nuclear electricity to produce Hydrogen. This is smart of the Japanese as Hydrogen can run fuel-cells and Japan does not have oil shale deposits.