* Hollow out an area of the beach that's underwater at high tide
* Install a big tank that lifts up some number of meters.
* Lift the tank at low tide
* Let water fill the tank at high tide
* Drop your tank of heavy water like a gravity battery to generate power, at whatever rate you choose
* Release water so its easy to lift again
You open gates; let high tide naturally fill a reservoir; close the gates; let the water back out through a turbine.
They have been built but the largest are only producing ~250 MW (ETA: thats 250 PEAK, actual generation is more like 50MW) which is nothing compared to what it takes to get that, like if you're already building a seawall it only might be worth installing turbines.
It is not very likely that there are tech improvements that would make things like this more viable. Salt water is super hard on equipment and that will always be true. Any improvements in durability would likely also apply to wind components. Gravity is only powerful at large scales, so just using tidal forces means you have to harness a lot of water, which means use land use and environmental disruption. Water batteries are economical only in places with extremely specific geography.
(Sending the water through bi-directional turbines, to get power from the inflow and outflow)
And while Rance could take advantage of an estuary with a dam just 750m wide, Sihwa uses a 12.7km long seawall.
Sihwa's seawall was actually built for flood mitigation before SK realised it could work for power generations, building a 10km seawall solely for power generation sounds insane.
Hydroelectric dams essentially build a tank, but they only build one wall of the tank. Hydroelectric turbines are about 90% efficient, so you're essentially looking to extract the same amount of energy from the weight of the sea water... with the complicating factor of needing to peak smooth due to tides.
How? Don't you have to pump it out since it's below sea level?