The Grand Old Train Of York (Okay, Nevada)
December 13, 2016 7:52 AM Subscribe
Sisyphus's Train Set. ARES (Advanced Rail Energy Storage) proposes to store energy in places where water turbines aren't possible. In train form.
well, maybe 1 MW output would be enough. Then build 50 of these trains.
posted by kuatto at 8:26 AM on December 13, 2016
posted by kuatto at 8:26 AM on December 13, 2016
Here's a recent piece about one of the water systems that's built in to a mountain in Massachusetts.
posted by backseatpilot at 8:29 AM on December 13, 2016
posted by backseatpilot at 8:29 AM on December 13, 2016
Would a train with an electric locomotive make more sense than some kind of cable-car/pulley arrangement?
posted by acb at 8:33 AM on December 13, 2016
posted by acb at 8:33 AM on December 13, 2016
Iron ore trains out of Kiruna, Sweden generate five times the energy they consume on the downhill run to Narvik, Norway through regenerative braking.
posted by fairmettle at 8:37 AM on December 13, 2016 [6 favorites]
posted by fairmettle at 8:37 AM on December 13, 2016 [6 favorites]
Pumped storage hydro certainly works, there's one near me.
I remember reading in Wired years ago about some guy developing flywheel storage ... wonder how he got on ...
posted by GallonOfAlan at 8:39 AM on December 13, 2016 [1 favorite]
I remember reading in Wired years ago about some guy developing flywheel storage ... wonder how he got on ...
posted by GallonOfAlan at 8:39 AM on December 13, 2016 [1 favorite]
For comparison, that Massachusetts pumped hydro plant generates 24x as much power for 32x as long. Pumped storage works because water reservoirs, on a mass basis, are pretty cheap. 20M tons of water is not that hard to store. On the other hand, 20M tons of train cars at 200 tons per = 100,000 train cars. But the ARES site has almost 3x the height difference as the Mass. plant, so maybe only 35k train cars. Still sounds impractical to scale.
posted by ryanrs at 8:55 AM on December 13, 2016
posted by ryanrs at 8:55 AM on December 13, 2016
If they made this train track into a giant loop, they could then lift the weight more than once allowing for unlimited energy storage and solving the problem where it takes up so much real estate.
posted by mattamatic at 9:01 AM on December 13, 2016 [2 favorites]
posted by mattamatic at 9:01 AM on December 13, 2016 [2 favorites]
I know precisely where that is - I drive past it twice a month to a place I contract at. There is nothing at all there, so it'd be a great use of empty land if it works. I'm assuming that they will add more parallel tracks as/if the concept is proven to create more capacity.
Interesting.
posted by Brockles at 9:02 AM on December 13, 2016
Interesting.
posted by Brockles at 9:02 AM on December 13, 2016
I visited the Cruachan Power Station in Scotland. It's a remarkably simple setup in some ways. They went hard-mode though in locating the turbines in a massive excavated cave deep underground, out of sight. It's worth a quick visit if you're in the area.
But water storage requires water and the right topography. The mass-on-a-rail approach is appealing since it only requires the right topography, and that can be simpler.
The ARES folks are claiming 80% efficiency. I have a hard time believing that given the friction of wheels on rails. But what do I know?
posted by Nelson at 9:03 AM on December 13, 2016
But water storage requires water and the right topography. The mass-on-a-rail approach is appealing since it only requires the right topography, and that can be simpler.
The ARES folks are claiming 80% efficiency. I have a hard time believing that given the friction of wheels on rails. But what do I know?
posted by Nelson at 9:03 AM on December 13, 2016
If they made this train track into a giant loop, they could then lift the weight more than once allowing for unlimited energy storage and solving the problem where it takes up so much real estate.
Er. I'm not understanding how you're getting to that conclusion. Train stores energy going up, train uses the mass of itself to come back down and regen braking (or similar) converts the mass slowly falling down the track into energy. I can't see how a circular track would work and take up less real estate. If the trains stopped at the top of a loop (and so didn't reverse down the same track) then I can see it being an alternative, but that would take MORE room.
posted by Brockles at 9:04 AM on December 13, 2016 [1 favorite]
Er. I'm not understanding how you're getting to that conclusion. Train stores energy going up, train uses the mass of itself to come back down and regen braking (or similar) converts the mass slowly falling down the track into energy. I can't see how a circular track would work and take up less real estate. If the trains stopped at the top of a loop (and so didn't reverse down the same track) then I can see it being an alternative, but that would take MORE room.
posted by Brockles at 9:04 AM on December 13, 2016 [1 favorite]
I remember reading in Wired years ago about some guy developing flywheel storage ... wonder how he got on ...--GallonOfAlan
Flywheel storage is actually pretty conventional. There are a lot of companies that offer this.
posted by eye of newt at 9:05 AM on December 13, 2016 [2 favorites]
Flywheel storage is actually pretty conventional. There are a lot of companies that offer this.
posted by eye of newt at 9:05 AM on December 13, 2016 [2 favorites]
The ARES folks are claiming 80% efficiency.
That's definitely believable. Freight trains are really, really efficient. Especially if you run them slowly, reducing rolling and wind resistance, 80% ought to be possible. Prob not 90% though.
posted by ryanrs at 9:06 AM on December 13, 2016 [2 favorites]
That's definitely believable. Freight trains are really, really efficient. Especially if you run them slowly, reducing rolling and wind resistance, 80% ought to be possible. Prob not 90% though.
posted by ryanrs at 9:06 AM on December 13, 2016 [2 favorites]
Brockles, their plan is to actually unload the train at the top, and send the empty train back down to pick up another load. The load is a concrete box filled with rocks.
posted by ryanrs at 9:07 AM on December 13, 2016
posted by ryanrs at 9:07 AM on December 13, 2016
Er. I'm not understanding how you're getting to that conclusion
I think he means turning the train into a very large conveyor belt. If the mass of an empty train is equal on both sides of the "belt" going up and down hill, then perhaps you can continuously lift more blocks up the hill instead of needing to shuttle the empty train back down? The problem would be in discharge mode: the weight of the descending load would be diminished by the mass of the other side of the loop going back up.
He could be making a perpetual energy joke too, but hey.
posted by JoeZydeco at 9:08 AM on December 13, 2016 [1 favorite]
I think he means turning the train into a very large conveyor belt. If the mass of an empty train is equal on both sides of the "belt" going up and down hill, then perhaps you can continuously lift more blocks up the hill instead of needing to shuttle the empty train back down? The problem would be in discharge mode: the weight of the descending load would be diminished by the mass of the other side of the loop going back up.
He could be making a perpetual energy joke too, but hey.
posted by JoeZydeco at 9:08 AM on December 13, 2016 [1 favorite]
their plan is to actually unload the train at the top, and send the empty train back down to pick up another load.
Not sure how I missed that bit. That seems like a lot of energy loss and messing around. Just shoving cars up and down a hill would seem to be more efficient, because there must be a lot of messing around at the loading/unloading ends that costs energy because you can't use gravity loading both times.
posted by Brockles at 9:36 AM on December 13, 2016
Not sure how I missed that bit. That seems like a lot of energy loss and messing around. Just shoving cars up and down a hill would seem to be more efficient, because there must be a lot of messing around at the loading/unloading ends that costs energy because you can't use gravity loading both times.
posted by Brockles at 9:36 AM on December 13, 2016
ARES seems to fill a weird niche -- it stores a very small amount of energy with a very high discharge rate. Even just lithium ion batteries would store about 10x as much energy per dollar. The advantage of ARES is that it can discharge incredibly fast (completely exhausting its stored power in 15 minutes), but it's not obvious to me that it's worth the high cost. Of course the cost could come down in the future.
posted by miyabo at 9:40 AM on December 13, 2016
posted by miyabo at 9:40 AM on December 13, 2016
What I love about the internet is the ability of a bunch of hot takes to better estimate energy performance than the engineers who have evaluated options, r.o.i, energy intensity of additional operations versus purchasing extra components, etc.
That, and the perpetual energy jokes that inevitably result in someone attempting to actually assess the suggestion.
It reminds me so much of my work.
With that said, if this does result in a net high cost and energy efficiency over time (counting construction impacts and costs, lifespan/repair of equipment and day to day efficiency) then it is great idea specifically because of it's relative simplicity and applicability across a variety of climates. Won't beat the areas of Maine where they can pump water into entirely different drainage basins for net energy gains, but still a piece of the overall "life can be better in the future" puzzle.
posted by meinvt at 9:44 AM on December 13, 2016 [6 favorites]
That, and the perpetual energy jokes that inevitably result in someone attempting to actually assess the suggestion.
It reminds me so much of my work.
With that said, if this does result in a net high cost and energy efficiency over time (counting construction impacts and costs, lifespan/repair of equipment and day to day efficiency) then it is great idea specifically because of it's relative simplicity and applicability across a variety of climates. Won't beat the areas of Maine where they can pump water into entirely different drainage basins for net energy gains, but still a piece of the overall "life can be better in the future" puzzle.
posted by meinvt at 9:44 AM on December 13, 2016 [6 favorites]
Iron ore trains out of Kiruna, Sweden generate five times the energy they consume ... [Not in citation given]
Actually the wording in Wikipedia about this is a little confusing, the 1/5 claim is for the descent from Riksgränsen down to Narvik, a drop of maybe 700ish meters?
Details notwithstanding, ARES looks like an interesting solution if you can reduce energy-conversion inefficiencies. Why not wed 19th and 21st century technologies?
posted by achrise at 9:52 AM on December 13, 2016
Actually the wording in Wikipedia about this is a little confusing, the 1/5 claim is for the descent from Riksgränsen down to Narvik, a drop of maybe 700ish meters?
Details notwithstanding, ARES looks like an interesting solution if you can reduce energy-conversion inefficiencies. Why not wed 19th and 21st century technologies?
posted by achrise at 9:52 AM on December 13, 2016
Just shoving cars up and down a hill would seem to be more efficient
But you'd need more cars and track which, to me anyway, is likely going to be a big part, if not the crux, of the cost portion of the cost/benefit aspect of this. The cost of building a box for rocks probably pales in comparison to the cost of building and maintaining tracks and wheeled vehicles, which leads me to,
because there must be a lot of messing around at the loading/unloading ends
I dunno, the container shipping industry pretty well has this part down to a, near literal, science. It could probably even be automated in this day and age. But, the last part,
the loading/unloading ends that costs energy because you can't use gravity loading both times.
Remember, they're using energy that the grid has to spare anyway, in theory that's free energy that would be lost otherwise. I've been to Southern Company hydro plants that didn't have pumped storage capabilities but would still pump air, literally just moving air without compressing it or storing it, whilst the generators were in motor mode because the grid needed to shed the load.
But, yea, I'm hopeful but skeptical as well. Hell, I've driven past one of the salt cavern compressed air stations that also serve to store off peak energy for peak resale, there's not much to see above ground from the road but the idea that something like that could be fiscally operable is enough to make me think that train tracks and rocks isn't totally outlandish. I wish them the best.
posted by RolandOfEld at 9:53 AM on December 13, 2016 [1 favorite]
But you'd need more cars and track which, to me anyway, is likely going to be a big part, if not the crux, of the cost portion of the cost/benefit aspect of this. The cost of building a box for rocks probably pales in comparison to the cost of building and maintaining tracks and wheeled vehicles, which leads me to,
because there must be a lot of messing around at the loading/unloading ends
I dunno, the container shipping industry pretty well has this part down to a, near literal, science. It could probably even be automated in this day and age. But, the last part,
the loading/unloading ends that costs energy because you can't use gravity loading both times.
Remember, they're using energy that the grid has to spare anyway, in theory that's free energy that would be lost otherwise. I've been to Southern Company hydro plants that didn't have pumped storage capabilities but would still pump air, literally just moving air without compressing it or storing it, whilst the generators were in motor mode because the grid needed to shed the load.
But, yea, I'm hopeful but skeptical as well. Hell, I've driven past one of the salt cavern compressed air stations that also serve to store off peak energy for peak resale, there's not much to see above ground from the road but the idea that something like that could be fiscally operable is enough to make me think that train tracks and rocks isn't totally outlandish. I wish them the best.
posted by RolandOfEld at 9:53 AM on December 13, 2016 [1 favorite]
Meinvt, the really cynical view is that ARES makes sense not on its technical merits, but because it's sitting at the intersection of a crazy-cheap BLM land lease + green energy grants + rural Nevada employment/development grants/tax breaks.
posted by ryanrs at 9:56 AM on December 13, 2016 [3 favorites]
posted by ryanrs at 9:56 AM on December 13, 2016 [3 favorites]
What I love about the internet is the ability of a bunch of hot takes to better estimate energy performance than the engineers who have evaluated options, r.o.i, energy intensity of additional operations versus purchasing extra components, etc.
But this is a discussion site, not a peer review or engineering analysis.
posted by Brockles at 9:59 AM on December 13, 2016 [2 favorites]
But this is a discussion site, not a peer review or engineering analysis.
posted by Brockles at 9:59 AM on December 13, 2016 [2 favorites]
ryanrs, totally with you on that and could very well be. I'm just expressing doubt that this is an idea which would be better 'if they only just X' where X is some semi-obvious value of more of the same, related options, etc. It also comes down to how much wasted energy is already in the grid to capture. I mean, for decades we burned methane off at dumps just to get rid of the stuff. Now it has become an obvious source for power capture. It's precisely because the infrastructure this relies upon is so basic that I'm willing to be convinced it's a net positive in the long view.
posted by meinvt at 10:00 AM on December 13, 2016
posted by meinvt at 10:00 AM on December 13, 2016
it's sitting at the intersection of a crazy-cheap BLM land lease + green energy grants + rural Nevada employment/development grants/tax breaks.
Absolutely. That particular area is pretty attractive to investment - Faraday Future were looking at land only a few miles from there for precisely that reason.
posted by Brockles at 10:01 AM on December 13, 2016
Absolutely. That particular area is pretty attractive to investment - Faraday Future were looking at land only a few miles from there for precisely that reason.
posted by Brockles at 10:01 AM on December 13, 2016
Why not wed 19th and 21st century technologies?
I'm as much in love with things from huge flywheels to flyball governors to VW Beetle simplicity to treadle lathes (seriously, I think they are amazing things that do deserve more love than we humans give them these days) but to answer the question: usually friction losses, maintenance costs, and other sundry inefficiencies. Second law of thermo blah blah blah.
posted by RolandOfEld at 10:02 AM on December 13, 2016
I'm as much in love with things from huge flywheels to flyball governors to VW Beetle simplicity to treadle lathes (seriously, I think they are amazing things that do deserve more love than we humans give them these days) but to answer the question: usually friction losses, maintenance costs, and other sundry inefficiencies. Second law of thermo blah blah blah.
posted by RolandOfEld at 10:02 AM on December 13, 2016
The thing is that there's effectively no new technology involved. Even automated loading and unloading (of bulk goods) is a problem that's been solved for 50 years, albeit not under wires. In terms of getting a prototype to market, it'd be relatively capital light.
posted by ambrosen at 10:03 AM on December 13, 2016
posted by ambrosen at 10:03 AM on December 13, 2016
This is an awesome new idea. I'm sure there are unanticipated problems that need to be solved. It sounds more solid than "maybe a kid in our underfunded schools, which I don't do anything about because I'm busy watching and discussing Game of Thrones and am 'not political', will invent free energy someday".
posted by amtho at 10:15 AM on December 13, 2016 [1 favorite]
posted by amtho at 10:15 AM on December 13, 2016 [1 favorite]
This sort of thing is great. One of the big obstacles to renewable energy is know-it-alls who say, "what about when the sun's down/wind's not blowing/etc."
Storing energy for later use is a big problem, and finding solutions is very important.
posted by explosion at 10:30 AM on December 13, 2016 [1 favorite]
Storing energy for later use is a big problem, and finding solutions is very important.
posted by explosion at 10:30 AM on December 13, 2016 [1 favorite]
I've been following this idea for a while and it is simply a creative solution for storing energy for later use. I know from Railway technology that the electric motors can be used as generators as well and this is a one of the biggest advantages of electric trains (brake energy is put back into the overhead line for other vehicles to use).
Switzerland has several large pumped storage hydroelectric facilities. I've visited one of them before (the Grimsel Pump Storage) and it is a massive and amazing feat of engineering.
As far as I understand, the primary motive is financial. The power companies are able to buy surplus (nuclear and maybe coal generated power) in the evenings when the power is cheap and then sell it during the day when the power is more expensive. I think, but I am not sure, that a certain ironic component is that the power is then sold as clean green hydroelectric energy which may be an interesting kind of Swiss energy-laundering to compliment the Swiss money laundering, but I am not sure about this part.
Anyway, there is no reason that if the financial calculations work out, this can't be implemented if the geometry is right. The concept seems clear and sound to me, but I have no idea what it costs to build and how much money can be made by storing electricity when it is cheap (evenings) and selling when it is more expensive. I think that this is another one of the investments that'll have to wait until oil and gas are expensive again (are they already?).
To me, the main environmental advantage is that we can build smaller power plants in the future if we can store energy output and use it at times that demand is high.
posted by jazh at 11:58 AM on December 13, 2016
Switzerland has several large pumped storage hydroelectric facilities. I've visited one of them before (the Grimsel Pump Storage) and it is a massive and amazing feat of engineering.
As far as I understand, the primary motive is financial. The power companies are able to buy surplus (nuclear and maybe coal generated power) in the evenings when the power is cheap and then sell it during the day when the power is more expensive. I think, but I am not sure, that a certain ironic component is that the power is then sold as clean green hydroelectric energy which may be an interesting kind of Swiss energy-laundering to compliment the Swiss money laundering, but I am not sure about this part.
Anyway, there is no reason that if the financial calculations work out, this can't be implemented if the geometry is right. The concept seems clear and sound to me, but I have no idea what it costs to build and how much money can be made by storing electricity when it is cheap (evenings) and selling when it is more expensive. I think that this is another one of the investments that'll have to wait until oil and gas are expensive again (are they already?).
To me, the main environmental advantage is that we can build smaller power plants in the future if we can store energy output and use it at times that demand is high.
posted by jazh at 11:58 AM on December 13, 2016
Clearly they need to make a helix to quiet all of those model railroaders who claim they're unprototypical.
posted by ckape at 11:59 AM on December 13, 2016 [2 favorites]
posted by ckape at 11:59 AM on December 13, 2016 [2 favorites]
Sorry... there are two things I want to add. The Ares concept emphasizes storing solar power, but I think that the biggest and best use is storing nuclear energy. That isn't as sexy and as green and is therefore, I guess, not used so much in the promotional material, but I think nuclear power plants operate at constant output (maybe I am wrong) and therefore this storage provides a great way to store the output in the evening for use in the day. The second thing is that there are losses (friction, converter efficiency etc...) and these losses will either be too great for the system to be profitable, or they won't. As another commenter wrote - it is simply better than wasting the power.
posted by jazh at 12:06 PM on December 13, 2016
posted by jazh at 12:06 PM on December 13, 2016
Well, nukes, solar, wind, coal, whatever's cheapest (right now that's wind in a lot of places, though solar is undercutting it in some deserts). This kind of thing is intended to beat natural gas peaker plants which are used right now to fill in the gaps between supply and demand. As more renewables come online, peakers are used less often since renewables can fill in many of the peaks, somewhat unpredictably, so they get comparatively expensive per kwh. That could allow odd energy storage schemes to become profitable.
posted by rhamphorhynchus at 12:26 PM on December 13, 2016 [1 favorite]
posted by rhamphorhynchus at 12:26 PM on December 13, 2016 [1 favorite]
My proposal, which involved twisting a 5-mile-long rubber band like you would on a balsa-wood airplane, was laughed at, but one day I'll be the one laughing!
posted by maxwelton at 12:52 PM on December 13, 2016
posted by maxwelton at 12:52 PM on December 13, 2016
A couple of years back there was a proposal to make a biiiiiig compressed-air reservoir for energy storage. Anyone know what came of that?
The thing I wonder about, both with compressed air and flywheels, is what happens if the containment breaks or the wheel crashes. What's the failure mode - is it an explosion, or just really noisy? We're just waking up to the fact that lithium batteries are potential fire risks; I don't think we're really conscious of the fact that energy storage can be dangerous.
posted by Joe in Australia at 1:11 PM on December 13, 2016
The thing I wonder about, both with compressed air and flywheels, is what happens if the containment breaks or the wheel crashes. What's the failure mode - is it an explosion, or just really noisy? We're just waking up to the fact that lithium batteries are potential fire risks; I don't think we're really conscious of the fact that energy storage can be dangerous.
posted by Joe in Australia at 1:11 PM on December 13, 2016
What's the failure mode - is it an explosion
Flywheels fail at energy project.
Basically, it's good they install them in underground vaults.
posted by ryanrs at 1:23 PM on December 13, 2016 [2 favorites]
Flywheels fail at energy project.
Basically, it's good they install them in underground vaults.
posted by ryanrs at 1:23 PM on December 13, 2016 [2 favorites]
Google translated article about the trains from Kiruna to Narvik.
posted by Agent X9 at 2:30 PM on December 13, 2016
posted by Agent X9 at 2:30 PM on December 13, 2016
Joe in Australia: "A couple of years back there was a proposal to make a biiiiiig compressed-air reservoir for energy storage. Anyone know what came of that? "
People have been moving forward though the first first gen plant was built in 78. There should be a couple of new plants that don't have to be coupled with natural gas generators in the next two years.
posted by Mitheral at 6:38 PM on December 13, 2016 [1 favorite]
People have been moving forward though the first first gen plant was built in 78. There should be a couple of new plants that don't have to be coupled with natural gas generators in the next two years.
posted by Mitheral at 6:38 PM on December 13, 2016 [1 favorite]
When I think of flywheels, I think of the time at Dad's lab where the heavy bronze rotor in a centrifuge failed and one of the pieces embedded itself 6 inches into a nearby concrete pillar, thankfully not passing through any humans on the way.
posted by i_am_joe's_spleen at 7:44 PM on December 13, 2016
posted by i_am_joe's_spleen at 7:44 PM on December 13, 2016
Potential-energy to kinetic-energy storage like this is useful for helping with peak demand, and much less expensive than generation. Europe has pumped water into uphill reservoirs since the 1890s (yes 1890s).
It's nearly ideal (at some loss) for storing the excess capacity of generators when demand is low. It's very helpful for quick response to short-term rapid changes in power demand. Regular plants can be quite slow to ramp upo output.
E.g. when TV shows end in the UK, millions may switch on an electric tea kettle. The Dinorwig Plant in Wales helps with that. (1700 MW output nearly equals two large nukes.)
There's a plant in Virgina nearly twice that size, capable of 3000MW. In use since 1985, it's the largest.
posted by Twang at 7:51 PM on December 13, 2016
It's nearly ideal (at some loss) for storing the excess capacity of generators when demand is low. It's very helpful for quick response to short-term rapid changes in power demand. Regular plants can be quite slow to ramp upo output.
E.g. when TV shows end in the UK, millions may switch on an electric tea kettle. The Dinorwig Plant in Wales helps with that. (1700 MW output nearly equals two large nukes.)
There's a plant in Virgina nearly twice that size, capable of 3000MW. In use since 1985, it's the largest.
posted by Twang at 7:51 PM on December 13, 2016
I think this is pretty cool if it turns out to be economical. I have wondered for a long time why more of this sort of gravity-based energy storage isn't used to help address the production/consumption balance in the electrical grid.
I was curious how much rock we're talking about for this project, so I did a little back-of-the-envelope calculation. From intro physics, the potential energy stored by a mass m at height h is E = mgh, where g is the acceleration due to gravity, 9.8 m/s2. According to the article, the track is 9 km long at 8% grade, and energy storage is 80% efficient. So the total mass of rock m = E/(.8*gh) is 12.5 MWh / (.8 * 9.8 m/s2 * 9 km * .08), or just about 8000 metric tons. According to Wolfram Alpha, "standard rock density" is 2.65 gm/cm3, and so the total volume of rock being moved around by this system at maximum capacity is just about 3000 cubic meters, which Wolfram Alpha helpfully informs me is 1.2 Olympic-sized swimming pools.
I thought that was kind of interesting, as it's somewhat less load than I had imagined before doing the calculation. From a little searching, it seems a typical rail freight car can carry around 100 metric tons, so this is something on the order of perhaps 80 loads. Depending on the logistics of loading/unloading mass from the cars, it does seem like the system could be scaled up by increasing the storage capacity at the top and bottom of the track, and we're not talking about completely ridiculous amounts of space for storage required. Storing 1000 MWh would need warehouses with the capacity of 96 Olympic-sized swimming pools, which Wolfram Alpha again helpfully notes is about the same as the capacity of a large oil tanker, or the volume of the Hindenberg zeppelin.
Seems basically reasonable to me. Of course, my back-of-the-envelope calculations are grossly simplistic, but as long as this is within an order of magnitude, scaling doesn't seem too ridiculous.
posted by biogeo at 9:11 PM on December 13, 2016 [1 favorite]
I was curious how much rock we're talking about for this project, so I did a little back-of-the-envelope calculation. From intro physics, the potential energy stored by a mass m at height h is E = mgh, where g is the acceleration due to gravity, 9.8 m/s2. According to the article, the track is 9 km long at 8% grade, and energy storage is 80% efficient. So the total mass of rock m = E/(.8*gh) is 12.5 MWh / (.8 * 9.8 m/s2 * 9 km * .08), or just about 8000 metric tons. According to Wolfram Alpha, "standard rock density" is 2.65 gm/cm3, and so the total volume of rock being moved around by this system at maximum capacity is just about 3000 cubic meters, which Wolfram Alpha helpfully informs me is 1.2 Olympic-sized swimming pools.
I thought that was kind of interesting, as it's somewhat less load than I had imagined before doing the calculation. From a little searching, it seems a typical rail freight car can carry around 100 metric tons, so this is something on the order of perhaps 80 loads. Depending on the logistics of loading/unloading mass from the cars, it does seem like the system could be scaled up by increasing the storage capacity at the top and bottom of the track, and we're not talking about completely ridiculous amounts of space for storage required. Storing 1000 MWh would need warehouses with the capacity of 96 Olympic-sized swimming pools, which Wolfram Alpha again helpfully notes is about the same as the capacity of a large oil tanker, or the volume of the Hindenberg zeppelin.
Seems basically reasonable to me. Of course, my back-of-the-envelope calculations are grossly simplistic, but as long as this is within an order of magnitude, scaling doesn't seem too ridiculous.
posted by biogeo at 9:11 PM on December 13, 2016 [1 favorite]
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The company estimates that its proposed system will be able to store 12.5 MWh of energy, and deliver it back to the grid at a rate of up to 50MW.
So 50MW for 15 minutes. And it doesn't exactly seem like the kind of system that is easy to scale.
I also like how the trains in their artist's rendering have diesel fuel tanks.
posted by ryanrs at 8:24 AM on December 13, 2016 [1 favorite]