A mine skip is loaded at the top, descends the shaft under gravity while the drive brakes regeneratively (recovering electrical energy), unloads at the bottom, then a counterweight-balanced empty return trip costs only friction losses. Adjust load, speed and drive efficiency and watch the recovered vs. consumed energy in real time.
Regenerative braking on the loaded descent recovers most of the potential energy released; the empty return trip is nearly free because a counterweight balances the skip's own mass.