The use of the ocean tides for energy is not new. In 620 AD in Northern Ireland at the Nendrum Monastery Mill a tidal mill was built. It used a millpond that was filled with seawater at high tide, which was released through a sluice and fed along a channel to the mill's horizontal wheel as the tide receded.
1667 England Navy Yard now at Harwich Green. http://www.harwich-society.co.uk/old/info_treadwheel.htm