A low-cost way to generate power from small waves:
Build a large (perhaps 100 m square, 1 cm thick) transparent plastic mat designed to float on the ocean without interfering with the ecosystem.
It would have regular perforations so as not to trap water on its surface, and tiny plastic spikes
to discourage seabirds from using the mat as a place to rest. The underside would be coated in a non-toxic substance that inhibits the growth of any sea life.
Inside, place crisscrossing tubes of piezo crystals, connected by small rods. As the waves pass, these crystals are bent relative to each other, resulting in mechanical stress that generates a small voltage. As an option, each crystal unit could also have a tiny solar cell mounted to its upper surface to gather extra energy during the day. Individual units failing wouldnt significantly diminish the power output as a whole.
In suitable areas, like where there is no oceanic traffic, and the conditions are relatively calm most of the time (although storms are no problem), the mats could be interlinked to form energy collectors hundreds of square kilometers across, tethered to the ocean floor.
The point of this idea is to harness a low-grade power source as cheaply as possible, whilst doing the least amount of harm to our environment. No new technology here.
Most sources of renewable energy are low grade. A calm breeze, cloudy day, warm water bubbling from the ground for example. If we can find cheap ways to harness these power sources, perhaps we could stop depending on the centralized power grid.