[eugenekay]

Publicly available data[1] on the pilot project in Nevada suggests a total of “50MW” generation capacity is planned across 10 rail lines, but the photos on the website seem to only show 1 set being built so far - and a claimed output of 5MW. The per-car mass of 720,000 lb (321 Tonnes) being lowered 229ft=70 Meters (510ft track length x sin(26.8) degrees) in Earth’s 9.81/ms^2 gravity field represents a maximum potential energy of only 220MJ, or 61 kWh per car. Reaching 5MW peak requires a car to be dispatched every 44 seconds. 10 cars would provide about 7.5 minutes of runtime - which matches the advertised 15-minute cycle length.

This all seems reasonable - but is a far cry from the performance of existing Pumped Hydrostorage plants which routinely exceed 1GW since the 1970s, and can run for several hours per cycle. They do require lots of Water and a mountain’s worth of elevation change, which limits the site selection, whereas this system seems to work with any open-pit mine.

It will be interesting to see if this technology can be made competitive with existing grid-stabilization techniques, and what challenges will be encountered along the way.

[1] https://www.sandia.gov/files/ess/uploads/2021/LDES/Russ_Weed...

[01100011]

Pumped hydro should be expanded as part of a national water grid to cope with droughts and floods. NSF studied it and reached positive conclusions many years ago but no one is serious about implementing it.

[clickety_clack]

Environmental groups kill hydro dams, you can’t build them these days.

[bdbdbdb]

The great thing about this gravity storage system is how easy it is to scale. You just need a hill. Sure, it's not going to deliver the power of pumped hydro, but it's easier to build and much safer to operate. And it's certainly a better design than those concrete block tower designs you occasionally see which are just a windy accident waiting to happen

[Veserv]

If you have a hill then you can just put a water tank at the top and bottom and a pipe with a pump and a generator in-between. Even if your rolling mass was iron, you would only need a tank 8x larger than your rolling mass in volume (2x per dimension) to be equal in storage. Much easier to build and safer than a 300 ton railcar barreling down a hill. Also scales better, has lower operating cost, has lower capital cost, and has less energy loss.