50 tidal power plants anchored far out on the ocean could be used to generate electricity for hydrogen electrolysis, The tidal power plant has an electricity generator that is located on a floating platform, held in place by devices fixing it to the bottom of the sea.

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Link: http://www.renewableenergyworld.com/articles/2008/12/ocean-currents-may-bring-italy-more-tidal-energy-54240.html