Wave power plants are actually well-known. They use the energy of the waves of the sea. In principle, wave power plants are actually part of the curriculum at general education schools. See: https://en.wikipedia.org/wiki/List_of_wave_power_stations
Nevertheless, they are much less anchored in the general thinking about the use of natural energy resources (water / sea) than, for example, the competing tidal power plants, which use the energy of the water stroke from the tides. The maximum tidal range used on our planet is nowadays 12 ... 16 meters at Saint Malo in France. See: https://en.wikipedia.org/wiki/Tidal_power
The disadvantage of tidal power plants is the high investment costs, as electricity providers communicate. Those power plants, which are built in the free nature, unfortunately are correspondingly large. See: https://www.oekostromanbieter.org/oekostromanbieter-blog/145-gezeitenkraftwerk-vor-und-nachteile.html
A much more significant, but usually not communicated, disadvantage is the inefficiency of the huge plants. The duration of each operating cycle (from high tide to low tide back to high tide) is 12 hours and 25 minutes. This means that on time average (over the year) about 1 meter of water-lift per hour can be utilized, that’s all. Compared to the water-lift caused by the waves, this is extremely little. The typical swell in the ocean has a duration of a few seconds from wave crest to wave crest (depending on the wave length). See: https://en.wikipedia.org/wiki/Swell_(ocean)
For a rough calculation to estimate the magnitude of the transported energy of the waves, to be on the safe side, we estimate a wave height of half a meter and a duration of 10 seconds from wave to wave in a pessimistic calculation. See: https://de.wikipedia.org/wiki/Wasserwelle
Then we have 360 waves per hour, which makes 4470 waves in 12 hours and 25 minutes. At half a meter of wave height per each wave, that means 2235 meters of water-lift in 12 hours and 25 minutes. That is 2235/14 = 160 times as much as the tides cause. If the wind gets a little stronger and the waves get higher, which often happens, then the advantage of the wave power plant compared to the tidal power plant is even more pronounced.
Several types of wave power plants exist ( https://en.wikipedia.org/wiki/Wave_power )
- with floats (buoyancy and linear generators)
- with air flow turbines in a hollow chamber
- with water turbines, similar to the tidal power plant
- with lifting chambers
- further constructions, which work very inexpensive
It is possible to use either the transversal motion of the water in the waves or the longitudinal motion of the water in the waves, or both types of movement. There are no limits to creativity in optimizing the system.
If I consider the lifting work of one ton of water in 10 seconds over a height difference of 1 meter, I have a mechanical power of P = W pot / t = m·g·h / t = 1000 kg · 10 m/s² · 1m = 1000 Watt = 1kW
With an assumed construction price of the mechanics and hydraulics of the plant of about 300 ... 400 €, plus 150 € for a 1kW electricity-generator, we come to a (pessimistic) purchase price of the plant of maximally 500 ... 600 € per produced kilowatt.
The power corresponds to about 7 m² of the thermo-solar cells proposed by me, which would thus come to a price of 7 x 105 € = 735 € for 1 kW. (see subchapter: Thermo-solar cells) This is again about 25 % cheaper, than the already very cheap thermo-solar cells.
Disadvantage: Wave power plants need access to the ocean, so they can only be used in certain regions of the world, but there they are very advantageous. (After all, we want to avoid transporting electricity over long distances because energy-transportation over long distance is inefficient).
Advantage: Wave power plants supply electricity as long as there is swell, i.e. also at night.