If the balls where captured by liquid so they can rotate without hitting each other, then the truck could drive to the top and take water from there and bring it to the bottom, because the liquid would be kept in varying areas of compression, so by the time it got to the top and was completely de-compressed, it would be better to take it to the bottom and compress it. Using compression to slow and control solid rotors going down, and creating a constant flow of them at the bottom in the liquid, would give more buffer zone for the energy power plant to never stop producing power and cause intermittent power. Note*: I think sending the truck down as a rotor is still a better idea though. Full up the truck with de-compressed water before it falls, compressing the liquid so it can be inserted into a pool of liquid with that level of compression.