In a grid-scale gravity energy storage system (a gravity battery), a massive 500-tonne cylindrical piston is suspended inside a deep vertical shaft. During times of high electricity demand, the piston is allowed to descend under gravity, turning an electric generator via a winch and cable system to feed power back into the grid.
Figure 1 shows a speed-time graph for the descending piston during a single power generation cycle.
Describe the energy transfers taking place during the descent of the piston.
You should refer to energy stores as well as transfers between energy stores for all three sections (A, B, and C) of the graph.