This is my idea of a cheap and sustainable power plant to be anchored somewhere in the open ocean and exposed to the waves there.

Principle

The three satellites form a tripod system which oscillates against the center body as waves travel through the arrangement. The center body is guided passively by the linkage to roll into a position where the piston can freely oscillate within the hydraulic cylinder. This forces are comparatively small.
A pelton or francis turbine placed within the center body (where there is lots of space for all sorts of equipment) will convert the hydraulic pressure into electric energy.

In practice each of the bodies will be fabricated to have a density of 0.5, so that it is half submerged. The mass of the main body should be equivalent to the sum of the masses of the satellite bodies.

Energy harvest

To give you some idea about the amount of energy the system can produce with a main body radius of, say, 10 meters:

1. A radius of 10 meters gives the center ball a volume of 4200 m³ while the satellites will have a radius of 7 m. So the total mass of all four bodies will be 4200 tons.
2. If waves oscillate the satellite masses against the center mass at an amplitude of only 2 meters with a half period of 2.5 s (= wave period of 5s) the piston will produce a hydraulic power of 33 MW.
3. Say, we can harvest half of it as electric power, isn't that a lot?
4. The system will be able to withstand monster waves up to 20 m. For bigger waves (like Tsunamis), it will have to flood its air chambers with water to increase its density > 1 and dive to the sea ground.

Better think big

Unfortunately, it is almost hopeless to produce energy with a printed 3D model of say R = 5cm, at an amplitude of 5cm. My calculation routine (which is part of the code) shows that at a period 1/s the hydraulic energy will be 0.5 Watt, which might not even be enough to press out a little fountain on top of the piston linkage, unless piston, seal and cylinder are fabbed with high precision.

Code

Better scale the thing as a whole. Didn't take much care on parametrizing everything. But I put many comments to guide you through the easy and straight forward code. For faster coding I used my library shortcuts.scad. Sorry for that, but it is so handy ...