Relative to the question regarding tidal power, there is a test scenario set up off Maui to test the viability of wave forces below the surface. Those forces are thought to more constant than wind-driven waves.
On the other hand there are huge expanses of ocean with nothing to block the wind and generally favorable wave action in consequence, like the pacific between Alaska and Hawaii...virtually nothing to block the wind. Of course there is a problem with harvesting the electricity from 3000 miles from nowhere...
Here in the Midwest some of us are being informed by American Electric Power that electric rates will jump 25%. Whether wave, wind and/or solar power are reasonable alternatives to fossil-fueled power generation, the fact that AEP owns 1 or more IDLE nuclear power generation plants, paid for by customers, is criminal. Those plants could have a significant impact on the use of fossil fuels in the Midwest, which is typically linked to acid rain on the East coast. And with the point taken relative to when it is dark and/or the wind is calm and/or misuse of arable land to produce fuels of dubious benefit versus the costs to world food supplies, it is about time America got off its duff and went back to long-term sustainable power generation with proven minor environmental impact.
Buy the ticket, take the ride. -- Hunter S. Thompson