I designed a similar system (albeit a simpler, less refined one) as part of my Engineering degree a couple of years ago, I'm so pleased to see that someone else has come up with this idea and that it is being realised. Hopefully full scale systems will be rolled out and address the intermittency problems of renewable energy sources.

Rail is great for lessening friction, but that can be a problem when accelerating or breaking. Wonder if they'll end up with another track for that purpose and regular track to roll the carriages on.

Seems like a good idea, however, once the last car rolls down to the bottom, that's it! I would like to see a 'looped' or similar system where some of the power is diverted to pushing a few cars back up again - simultaneously - while using the downward-moving cars to generate power. i.e. 20 cars available for generation, move 5 cars back to the top slowly or gently while the last 15 generate. Tagging on the top end makes at least 25 cars plus possibly another 5 added to the total movement overall for extra generating.. Not 'perpetual motion' but every little helps!

You could put solar panels on the track vehicles as well or the tracked vehicles could use a hybrid battery/flywheel system as well to maximize the surface area exposed to the sun.

It looks good if not great. It needs a large number of motor/generators but it is certainly something that could be built with off the shelf components today.
It might be worthwhile to put sails on the cars.

How could anyone imagine this as cheaper than pumped hydropower storage? One way to do it does involve a railway, but the cars get used over and over, not left at the top of the hill.

I have thought about the use of trains for energy generation, but more in the line of capturing the energy that is wasted during the braking process. If there was a way to use a passing train that was decelerating to help lift these other cars or to generate energy (mechanical or electrical). This energy may also be used to help with getting the train rolling again after stopping. After all locomotives are run with electric motors that huge diesel generators power.

a simple gravity storage system. Would work well.

Maybe this works fOr emergency power purposes, but I fail to see the everyday utility, since we ARE STILL DEALING WITH REAL PHYSICAL LAW effects LIKE FRICTION, POWER CURVES, AND REDUCED CAPACITY AT EVERY TURN.

As someone doing RE, EV's, etc this looks real good except train rails won't work on such slopes needed, not enough traction. But a rack on the ground solves that as with other mountain trains with the same problem.
You could store weight cars at the top to reduce loco needs. With say 3 roads, it doesn't have to be tracks, such a unit could be very useful leveling demand, supply loads.
If you happen to have a at least small mountain handy that is. You'll need over 1,000' rise likely to be good but many places are like that on both coasts. Sadly not here in Fla.