Oooh, okay, I see waht you mean. Well, there's an inherent issue with this I'm afraid... easiest way to demonstrate it would be as such: Take an empty cup and stuff a crumpled paper towel into the bottom of it, then invert it. Place it in your sink on a few coins so there is a gap between the rim of the cup and the sink itself. Keep a hand on the cup to hold it down. Now, fill the sink with water, keeping the cup held down so it doesn't float to the surface, and making sure to keep it open-end down. Once the water has risen over the top of the cup, feel free to drain it. Take the paper towel out, and notice that it's dry. The reason for this is the water cannot overcome the air pressure in the cup. The same thing would happen with your idea - the tidal force wouldn't have enough pressure to build up more than a few PSI in that accumulator, not enough to do any significant workload.