70% of our planet is covered with water. The density is 1000 times higher than air. Pressure levels of just 10 meter of water column equal 100 km of atmosphere. So the fluctuation of these levels represent a dense form of renewable energy. One form of this renewable energy is the wave motion, which is
caused by the top layer of the ocean being forced to move through wind and surface-friction. This motion continuous to far under the water surface (up to approx. 100m) and represents a vast renewable energy resource.
The levels of power given are averages of one meter of wave crest with. Wave devices can convert several meters of wave crest width in one device. A “point absorber” like the symphony can even capture the energy equivalent to ca. 30 meters crest width with a relatively small diameter. This creates a theoretical potential of more than 1MW of average average power for one device.
In practice this however is much lower and more in the area of 200 – 500 kW in average, with rated powers up to 1 to 2MW for an operation in high waves. In severe storms, the peak levels of wave power are largely exceeding the average (useful) power levels. Wave energy converters (WECs) usually have a survival mode when incident power levels exceed a certain level (similar to the concept of cut-off speed in wind turbines). The struggle of survivability is demanding, especially for non-submerged devices that have to handle the peak loads caused by waves of up to 25m. Such environmental conditions for example are avoided by ships, and offshore platforms are designed to have deck heights far above the sea surface.
A lot of information about this topic is given on Wikipedia and other sites.