These Concrete Gravity Trains May Solve the Energy Storage Problem
Energy grids fluctuate throughout the day as demand and production increase and decrease. Usually, during peak hours, demand for electricity is close to or exceeds the production capacity at that time. During off hours, usually in the night, production capacity far exceeds what is being drawn from the grid. This results in a natural unsteadiness to the energy grid and experts have been experimenting with ways to make sure that the lights always stay on.
One of the most common ways that energy is stored in large scale for the grid is through pumped hydro electric storage dams.