Advanced Rail Energy Storage of North America | Hacker News Reader

Advanced Rail Energy Storage of North America

aresnorthamerica.com

38 pointstomjakubowski40 comments

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...

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.

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

To be fair, dams can be immensely destructive to ecosystems, with run-off effects that harm everything around them (humans included). My ex worked for on the NGOs that campaign for better dams instead of no dams at all.

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

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.

Well I can't argue with that.

Well, it's better than the scheme for lifting and lowering cement blocks with a construction crane. And the scheme for digging deep holes in the ground and lowering big rock blocks into them. And the scheme for using electric locomotives and a heavy train in much the same way as this scheme.

The animation hand-waves important details. How are those blocks moved on the flat part of the track? There's no backup braking system. No guards around the chain. No chain lubrication system.

Performance should be roughly comparable to pumped storage with the same height difference, so why bother? Pumped storage doesn't use up much water; it's the same water going up and down, with some evaporation loss.

For fun, let's say you have a 20-ton container, and you raise it up the rail by 100m. The stored gravitational energy is about 5.5 kWh.

According to Wikipedia, Tesla Powerwall 3 has 13.5 kWh of capacity: more than two 20-ton containers raised to 100m, assuming perfect efficiency. It costs $7,300, small enough to put in your house, and also (more or less) safe enough to put in your house, unlike a 20-ton container on a rail barreling down a slope, which probably needs professional hard-hat maintenance crew.

So consider me skeptical.

You've got a free order of magnitude issues. First, a rail car typically is closer to 100 or 125 tons. 20 tons is nothing. And the sites they are selecting likely have much more than 100 meters of vertical distance. 1,000 meters would not be unreasonable in some areas, though most are probably smaller.

So a single car in this system is probably delivering 25-300 kWh of capacity depending on elevation and mass. And it scales linearly with mass, elevation, and storage space at the apex. Push 100 cars up and you've stored 2.5-30 mWh.

Their demonstration effort plans to store 12.5 mWh. It doesn't seem totally unreasonable. It's at least within the umbrella of.... maybe, but friction is going to eat a ton of energy.

Is `mWh` Mega-Watt-Hours? Reads like Milli-Watt-Hours to me, which is obviously not what you intended. I'm used to MWh?

You are correct. mWh is "milli-watt-hours" MWh is "Mega-watt-hours".

Phone typing, apologies. Too late to edit it.

Track maintenance is the single biggest cost sector of rail lines in good condition even on very low slopes. The ballast needs regular inspection and replacing even without adverse weather or underbed problems, and the track can develop cross fall or slew and/or creep in transverse and longitudinal directions over time, sometimes taking subsurface layers with it. Every other kind of gravity storage makes more sense on paper than this, even the tower crane rearranging concrete cubes proposal.

It's true that track maintenance is costly but it's mostly costly because there's a whole lot of track to maintain; many hundreds of miles of it, often in hard to reach areas. This looks like it'd be a few hundred meters at most, all parallel to each other in one place. So hopefully it's easy enough. The tower crane also requires maintenance.

These were quite popular as a startup idea once. I remember Gravitricity (now defunct) being posted here: https://news.ycombinator.com/item?id=24414497

Is this not just pumped hydro but worse?

Presumably a lot less expensive than pumped hydro to build.

Pretty much zero chance of that. The complexity (moving parts, machined parts, number of generators, number of electrical interconnects (etc.) is so much higher per kilogram basis compared to pumped hydro. Much of the country does half of pumped hydro (storing potential energy in water towers) and delivers it to your door for fractions of a penny per kg, a price that includes a complete distribution network and sourcing/purification of the water.

You have to dredge pumped hydro though. Silt accumulation is a challenging engineering problem and erases capacity over time.

My understanding is that water towers mostly exist as something to “pump against”, rather than being a vessel that gets filled and emptied repeatedly like a battery would. It does vary in level a bit, often with a circadian rhythm (but also randomly pulsatile). I just don’t think it’s a significant portion of the total water flow that its pressure supports.

I'd love to see an unbiased financial-analysis comparison: this vs. hydro vs. electrochemical.

hydro can win if all the stars align. Electrochemical is the real winner though.

This is just a grift. I doubt this thing will ever materialize. It seems like every month a new gravity storage company emerges and none of them go anywhere with their promises.

As I posted elsewhere, my power company is installing 200MWh of storage on 10 acres. It will take them about 6 months to build it out (they've not started construction yet, they project they'll be finished by june. They just finished getting all the approval they need to start work).

That sort of land efficiency and deployment speed won't be matched by any gravity storage system.

Costwise, it'll probably be in the range of $24,000,000 to install (maybe more like 30M with power electronics requirements).

> This is just a grift.

I'd like to understand why. Just too much complexity? Gravity storage is compelling to this layman.

Complexity is a big part of it along with a lot of required materials.

It takes either a lot of heavy weight or a very long decent regardless the storage system in order to store a significant amount of energy. Further, you need some very beefy generators/motors to work with that weight along with some complex equipment to ultimately convert the AC output into what the grid expects.

Look at the proposed (not built system)

https://aresnorthamerica.com/las-vegas-business-press-deal-w...

It requires 20 acres, a mining pit, 30 employees. And how much energy does it store? 12.5 MWh (15 minutes of runtime, 50MW of output). And do notice the date, 2020. From what I can find, this thing hasn't even started operating yet.

That's a VERY expensive battery which hasn't even been built yet.

All of these very special requirements for such a low storage amount is why these things are grifts.

The comparison is my electric company, which is going to install 200MWh of batteries on 10 acres of available land (it's right next to one of their big substations). It'll take them 6 months to do and the main hurdle they had was getting city approval to start work.

The reason pumped hydro is about the only appealing form of a gravity battery is because you can store just massive amounts of water conveniently which gives those systems pretty nice storage levels. Further, the equipment is near the same of any hydro dam. But even those suffer from very specific geography needs before they can get off the ground and massive amounts of hurdles with local regulations in order to even start work. There is, no joke, a proposed pumped hydro system that I know about which has been in the planning stage for the last 20 years as they've been going back and forth with the local county and community.

That's why it's a grift. The competition is chemical battery storage which has stupidly high energy density and almost instant deployment. Any gravity system that is going to be competitive needs both those things before it'd actually be a contender. I've yet to see any of these systems actually get built beyond just tiny prototypes.

Thanks for this! ...Thanks for helping me curb my naivete a bit. I think you'd appreciate this effort at even cheaper grid-scale chemical battery storage: https://www.volts.wtf/p/can-second-life-ev-batteries-work

Water storage is great, the cat's meow ... in places where water is plentiful. But there are HUGE tracts of land in the world where there isn't any water. But people still need the energy, when the winds are calm and the skies are cloudy.

Only other kinds of gravity batteries will do, so they're a necessity, especially near remote wind-farms.

"Energy Vault’s gravity-based solutions are based on the well-understood physics and mechanical engineering fundamentals of pumped hydroelectric energy storage, but replace water with custom-made composite blocks that can be made from low-cost and locally sourced materials, including local soil, mine tailings, coal combustion residuals (coal ash), and end-of-life decommissioned wind turbine blades."

"The 100 MWh gravity-based EVx system is being built adjacent to a wind farm and national grid site in Rudong, Jiangsu Province located outside of Shanghai to augment and balance China’s national energy grid...."

https://www.businesswire.com/news/home/20220505005467/en/Ene...

"China's $1bn bet on gravity to store massive amounts of green energy "

https://www.rechargenews.com/energy-transition/chinas-1bn-be...

That is utterly nonsensical. Are there HUGE tracts of land where 100 ton railcars or concrete blocks grow on trees?

If not, then how are you getting them there? On a per-mass basis what do you think is easier to transport, railcars or water?

Transporting adequate amounts of gravity storage medium is not at all a competitive advantage for non-hydro gravity storage. For that matter, it does not even constitute a meaningful factor except as a disqualifying one for the nonsensical ideas people somehow seem to get funded.

I'm not totally sold on the idea itself, but... you don't need to get a 100 ton railcar there. Ship empty railcars and fill it with rocks / sand / water or whatever you find at the destination.

Fortescue slashes electric train program but insists zero emissions 'on track'

September 04 2025 - https://www.boilingcold.com.au/fortescue-slashes-electric-tr...

  Three years after Andrew Forrest pressed go to develop an electric "Infinity Train," most of the experienced engineers who joined Fortescue's zero-emissions crusade are laid off as the miner goes back to the drawing board on how to have fossil-fuel-free locomotives by 2030.

  The engineers concluded that battery electric locomotives may be able to haul vast amounts of iron ore, eliminating 10 per cent of Fortescue's emissions, but the knock-on effects on its immense $21 billion a year integrated mine to rail to port iron ore business were unacceptable.

And: https://zero.fortescue.com/en/case-studies/infinity-train .. 404 Page not found.

Looked good for a while there: Fortescue rides the Infinity Train - https://www.electrive.com/2025/07/01/fortescue-rides-the-inf...

Two prototypes now operating (15 Dec 2025): https://electrek.co/2025/12/15/fortescue-infinity-train-elec...

Prototypes were always going to be operating, there have been prototypes of one form or another in the multi billion per annum iron ore mining business since 1970 at least.

The key from the earlier article (by a few months) was that the greater in house BEL program is being scaled back as :

   engineering studies revealed that insufficient power was generated on the downhill leg to return the train to the mine, according to numerous engineers who have not been authorised to speak to the media and have informed this story.

  The team developed two solutions to the problem, but they both had unacceptable implications for Fortescue's core business of shipping vast quantities of iron ore to Asia.

( See link for further discussion: https://www.boilingcold.com.au/fortescue-slashes-electric-tr... )

So the prototypes are delivered as ordered and will be put to use, but for now at least they won't be making any significant impact WRT the ongoing daily kilometre+ long heavy rail transport operations.

The main problem with this and many such ideas is that G (the universal gravitational constant) is just so damn small. Making this system store any serious amount of energy in a small footprint is limited by the density of materials you can raise and the height available. In a large footprint you need a lot of infra (eg: loooong rail) which has maintenance cost, and still, very small per-liter and per-m^2 efficiency.

I think this could be superior to batteries and pumped hydro in enough situations to matter.

You can build these in many more places (closer to generation/load), the capex is significantly lower, and you can probably build it a hell of a lot faster than a reservoir. This solution is also more incremental than pumped hydro and the equipment will likely last significantly longer than a lithium ion chemistry battery farm.

The biggest bottleneck for getting a big project on the grid right now is interconnection. If you can avoid having to deploy new transmission lines to a new site you can often chop 5+ years off a project's time table.

> You can build these in many more places

Batteries take up much less space for the same power footprint. Next year, my power company is installing a 200 MWh BESS on 10 acres. No way this fits into those sorts of constraints.

> capex is significantly lower

Doubtful. Steel lines and motors are cheap but not that cheap. There's also a higher ongoing maintenance cost as those things need regular monitoring/greasing/cleaning. There's also the need for more security, giant heavy blocks sliding down a hill is pretty dangerous, you'll want enough security to keep someone from hopping the fence to ride a block down/up the hill.

> you can probably build it a hell of a lot faster than a reservoir.

Faster than a reservoir, much slower than a battery farm.

> likely last significantly longer than a lithium ion chemistry battery farm.

With regular maintenance, yes. But that's also true of a battery farm. With regular maintenance, the battery farm will last forever. The expensive part of the battery farm is the initial installation. After that, it's very cheap to incrementally replace modules as they start to fail (which is around 10 to 15 years).

In terms of peak power wouldn't flywheel farms make sense ? Heavy duty, durable bearings might be a problem.

Where does the energy to lift the cars up in the first place come from? Another set of “freely available gravity” cars down the street?

this is an energy storage ("battery") system, not a generation system.

ahh that makes total sense lol

Excess solar, wind, hydro, or nuclear power.

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