The kinetic energy of waves can be converted into potential energy and then used to generate electricity by building reservoirs at sea.
When waves strike the walls of the reservoirs they will exert forces and hence pressure on them. If the walls have one way valves in them, water will enter but not exit the reservoir and continue to do so until the water pressure in the reservoir equals the pressure from the incoming wave. A head of water above sea level will thus be created in the reservoir which can be used to generate electricity with low head turbines.
The use of reservoirs which can be fixed to platforms or floating enables energy to be stored and smoother and more controlled electricity output.
If one way valves were incorporated in tidal barrages more water could be stored at high tides to enable more electricity to be generated over a longer period. of time.