Grumble Grumble Grumble
Tidal Power actually has even less viable locations then Geothermal power. What is the average difference in height between high tide and low tide? (6 feet?, 12 feet? How many Hydropower dams do you know of that are only 12 feet tall???) And capturing and diverting the high tide in significant amounts is bound to have environmental consequences for fish migration and habitat.
What might be a more viable solution would be to harness the power of Waves. The major issue with both is that locations with either strong wave or tidal power potential are usually far away from where the power demands are....
FAQ: Energy on the high seas - CNET News.com