A Californian company proposes using weighted electrically-driven rail vehicles on inclines to store energy. At times when the capacity of electricity supply exceeds demand the vehicles would be driven up inclined tracks, and when demand exceeds generation they are allowed to run down, generating electricity as they fall.
This link includes a video that shows a prototype vehicle (which appears to be built on a conventional locomotive chassis), an interview with a promoter, and an animation of a "farm" of these devices. There is a shortage of hard data, such as how much energy could be stored, for how long, and how steep the tracks are, etc., but a quick calculation shows that some thousands of these vehicles would be required for them to be useful. The control panel for this prototype has a power dial that appears to go up to only 20 kW. The promoter in the interview focuses instead on how the construction material can be recycled at end of life.
(Score: 3, Interesting) by bitstream on Tuesday July 03 2018, @11:52PM
In Australia, BHP in June 2001 had a trial with 682 ore cars and eight distributed GE AC6000CW locomotives with a total weight of 99 734 tons (99e6 kg). So just 85 train sets, but there are other complications like having to use a cog railway, wires with metal fatigue, wear, oil, sand etc. So I'll suspect the investment and maintenance will make it unfeasible.
If one could use magnetic energy storage. It may be way more efficient.