Perhaps we look too far afield for solutions. The simple is sometimes the most efficient.
Sliding Potential: Water tower, water in free fall, weight equals energy to perform work.
Return to Zero: Gas in car, gas burned to move car, fuel (gas) consumed, car stops moving, not yet to Zero. Soulution: use energy source which creates more energy than it consumes. ie electrodes thru water from batteries, hydrogen produced, unload excess occasionally?
Surface Area: More surface area such as sand or salt creates the potential for more energy force or potential whether form gravity, hydraulic, mass + air, air over hydraulic.
What say yu?