Hi there jazz46cup, at the moment there are many types of devices, first of all there’s the largescale device, there are heaving buoys, oscillating water columns, hinge barges to name a few and within the device is the power-take-off system. There are a few types of power-take-off systems there’s hydraulic systems, air turbines, hydro turbines, direct mechanical drive systems and direct electrical drive systems. The idea behind air turbines is to drive a turbine with the oscillating air pressure in an enclosed chamber as a consequence of the oscillating water level from by the ocean waves. A direct mechanical drive power take off system consists on translating the mechanical energy of an oscillating body subjected to waves into electricity by means of an extra mechanical system driving a rotary electrical generator. Direct electrical drive power take off systems refer to systems for which the mechanical energy captured by the primary converter is directly coupled to the moving part of a linear electrical generator. Appologies if it is a little complicated if you have any further questions fire away!