The extraction of energy from tidal currents is also a viable option. The problem is that the number of places with strong enough tidal currents are rather limited. In the US such locations are New York's East River and near the Golden Gate Bridge in San Francisco.
Fierce tidal currents, up to 12 knots, run back and forth off the most northern coast of Scotland, the Pentland Firth. There are two windows per day that ships can pass safely, otherwise stay away. Notorious are the so called Merry Men of Mey were the water comes at you from all directions. Especially during stormy weather this place is a regular hell hole.
This ship timed the passage wrongly, lost stability probably due to massive amounts of green water on deck and turtled in an instant. There were no survivors.
A number of underwater windmills could power one-third of Scotland, which is considerable.
An advantage is that there is no horizon pollution caused by the underwater windmills. In my opinion these mills are hard to service. Divers could investigate but certain repairs can probably only be done by taking it out of the water and fitting a spare watermill.