Density helps. But environmental issues help more. There are only so many viable locations for large-scale hydro storage, and it always means drowning some valley. Just building a set of rails up a hill is much less environmentally invasive.
One of the biggest wins of this model, really, is the low environmental impact, relative to hydro or batteries. Fewer regulatory hurdles, more potential locations. But in the end, cost effectiveness is what will win, and to some degree, that will be location-dependent. Is there geography we can exploit? Will it be in a populated area? What's the proximity to wind or solar farms?
Solving the storage problem in a cost-effective way is the key to transitioning from poison fuels to clean power. Once it's cheaper than coal/LNG/nuclear, the world will switch over quickly.
Rocks have about 4 times the density of water, thus you'll need 1/4 of the volume of a reservoir to hold as much energy. Since pilling trains is much more expensive than holding water, I can assure you this project will use much more land area than an equivalent lake.
Also, this thing requires a straight line high inclination slope and plain areas both up and down. I don't know how that compares with high walled valleys, but it is not a very common formation in nature. All said, it may be useful because it uses a different kind of landscape from water storage, so it can increase the total capacity.
Anyway, I agree, costs alone will say how much of it is created.
One of the biggest wins of this model, really, is the low environmental impact, relative to hydro or batteries. Fewer regulatory hurdles, more potential locations. But in the end, cost effectiveness is what will win, and to some degree, that will be location-dependent. Is there geography we can exploit? Will it be in a populated area? What's the proximity to wind or solar farms?
Solving the storage problem in a cost-effective way is the key to transitioning from poison fuels to clean power. Once it's cheaper than coal/LNG/nuclear, the world will switch over quickly.