You've got a free order of magnitude issues. First, a rail car typically is closer to 100 or 125 tons. 20 tons is nothing. And the sites they are selecting like

You've got a free order of magnitude issues. First, a rail car typically is closer to 100 or 125 tons. 20 tons is nothing. And the sites they are selecting likely have much more than 100 meters of vertical distance. 1,000 meters would not be unreasonable in some areas, though most are probably smaller. So a single car in this system is probably delivering 25-300 kWh of capacity depending on elevation and mass. And it scales linearly with mass, elevation, and storage space at the apex. Push 100 cars up and you've stored 2.5-30 mWh. Their demonstration effort plans to store 12.5 mWh. It doesn't seem totally unreasonable. It's at least within the umbrella of.... maybe, but friction is going to eat a ton of energy.