A company is proposing to build an advanced rail energy storage system: excess electric energy willpower engines that will transport a heavy mass up a slope. During periods of peak demand, the process will be reversed, converting the gravitational potential energy of the mass back into electric power. The company proposes to build a first commercial-scale facility that will store 12.5 MWh using a height difference of 500 m. The railroad cars have a loaded mass of 130 tonnes. How many railroad cars are required for the proposed installation? The company suggests a grid-scale storage facility might have a capacity of 16–24 GWh. For a height difference of 1000 m, how many of these railroad cars would be needed?