I recall reading an article 20+ years ago...
...where the effects of an experimental tidal installation somewhere in Europe were able to be measured by minute changes in the Earth's rotation/wobble. It makes sense; after all, there is no free lunch. The real question is if the unintended consequences of tidal power is comparable to the known and suspected consequences of carbon-based power. As with "cold fusion", I fully expect there to be those who object to this for some real or imagined ecological impact.
One big advantage is that unlike with wind and solar, tides are completely predictable, and the energy collected from these installations is more easily integrated into the grid.
The other big question is simple economics: Does the cost of building and maintaining these installations make them competitive? How much maintenance will they require? How long will they last? As anyone who has lived near the sea or has owned a boat will tell you, the ocean is the most hostile environment to modern engineering. Mechanical components that can be expected to last for decades on shore only survive for years or months in chemically and biologically active salt water.
I will be very interested to see how effective & efficient these installations really are, when all costs are considered. The ocean represents a phenomenal amount of potential energy.
