We've studied tidal energy harvesting for decades,
--but are no closer to economical systems than we were in the mid-20th century. The answer to J. McGrew's doubts are "It's tougher than you can imagine." Both initial cost and maintenance are far in excess of energy returns. But the biggest roadblock is scarcity of locations that have enough potential tidal energy to be worth it if we COULD economically boost output. San Francisco Bay is a possible source of strong, sustainable tidal flow and is close to users and the distribution network; but I think that's all there is in the USA. The best in this Hemisphere probably is the Bay of Fundy; but nature has provided little else. Efforts to capture energy in these "best" spots have so far defeated development efforts. But the point is, such locations with reachable locations and adequate energy potential, even with some great tech breakthrough, are too rare worldwide to ever add significant shares of world power.
