MIT has some cool new energy experiments running in Portugal. Apparently they harness ocean wave energy by getting the water to push a lever that compresses air.
Changing the volume of the airspace within the OWC chamber allows for different wave frequencies and intensities to be optimized. When extended to a larger chamber, a wider range of wavelengths produce the best effect. Researchers are currently working on identifying the most efficient chamber sizes for the various wave types.
Placing these devices, called the oscillating water column (OWC), in lighthouses and breakwaters makes perfect sense.