Railway energy storage

One of the problems with solar power and wind is that because how much electricity they produce is dictated by the weather they are not always producing power when it is needed and when it is sunny or windy they often create too much electricity and need to be disconnected.

If we want to use more wind turbines and solar panels, we need to find a good way of energy storage.
Battery technology is not yet suitable for the scale of storage we are talking about, hydrogen storage may not be viable and if it is, is a long way off.

There are ways such of storing electricity such as using excess power to spin wind turbine blades and use otherwise slow or still turbines as flywheels for storing energy, or pumping water in to a reservoir up a hill or mountain, then letting it flow down very quickly to power turbines.

That is all very well, but even that is limited in scale.

Another option is very simple, build a railway with lots and lots of gradients, with sidings, yards, or stations at all the high and low points.
Use cheap excess power to take the trains up hill and keep them there until more demand is needed then run them down hill using regenerative braking (a technology trains often already have) to feed  energy back into the grid.

This critics might say is not a very efficient way to run a railway, they may be right, but it would be a very cheap way to run a railway and it is an excuse to build a railway and an inefficient railway is better than no railway.
Of course if it is necessary to keep the service running trains could go up hill using expensive electricity and go down hill when the grid is fully supplied, it would clearly be much more suitable for goods trains than passenger transport, but cheap and erratic passenger services could still be useful.

It could be done on a large scale because the economic benefits of combined energy storage and transport infrastructure would justify it, probably...