But is it possible to extract that much energy from the tides with current techniques? That starting point in their math may be invalid. But it is good to know that not very much energy is available from the tides.
If its not possible then we really shouldn't be very interested in it because it can't get us very far, 1% is a rounding error towards solving the CO2 PPM causing climate change.
The difference any individual (or even a single small to medium sized business) can make is never more than a rounding error either - I'm not convinced that means we shouldn't be interested in such changes.