A tide motor energy source includes a tidal piston with a valved chamber. The piston drives a hydraulic ram to generate electrical power through a pressure accumulator and hydraulic motor. The ram can be locked hydraulically to enable the tidal piston to be held fixed at a desired elevation and the valves in the chamber permit it to be filled with water or air. The piston with its chamber filled with air at its low tide position and then released for controlled ascent while submerged acts as a submerged float for driving the ram upwardly while the tide runs in during one phase of its operation. The piston with its chamber filled with water while locked at its highest position as the tide begins to run out, and then released to fall under control, acts as a weight suspended in air after the water level drops below the piston for driving the ram downwardly during the second phase of its operation. The rising and falling motion of the tidal piston is used as the energy source.