My understanding of the idea is that they plan to move the weights up the hill by train, but then unload the weight. That way, with just one car, you can move m

My understanding of the idea is that they plan to move the weights up the hill by train, but then unload the weight. That way, with just one car, you can move multiple cars' worth of weight up the hill. Now, this bottlenecks you on how quickly you can store/release energy, and you have to store a lot of cargo containers in a possibly small space, but even moving 4+ cars' worth of weight per car brings the total stored energy capacity up to that of a smaller stored-hydro plant. Not to say this is necessarily cheaper than stored hydro, but it at least costs a lot less in terms of excavation.