The easiest way to squirrel away electricity in times of plenty, for use when it is scarce, is to pump water uphill with it. Such pumped storage is widely employed where local geography and hydrology permit, but it does need two basins, at different heights, to act as reservoirs, and a supply of water to fill them.
[...] Where geography does not favour pumped storage, though, the search is on for alternatives. These range from giant batteries, via caverns filled with compressed air, to huge flywheels made of carbon-fibre composites. But one firm looking into the matter eschews all these. It has stuck with the logic of pumped storage, which is to move large amounts of matter up and down hills. The difference is that in its case the matter is solid.
The firm in question calls itself ARES, which stands for Advanced Rail Energy Storage.
[...] The rocks stand in for the water in a pumped-storage system. They are carried up- and downhill by a train that is thus the equivalent of the turbines. The track the train runs on is equivalent to the tunnel. And the motors that drive the train act, like the electrical kit of a pumped-storage turbine, as generators when they run in reverse as the train rolls backwards downhill, pulled by gravity.
(Score: 1) by isj on Saturday December 03 2016, @01:53PM
Ok, energy storage by moving mass uphill on a track. The article says 8% incline over 9km. That is quite a hill.
Can someone please calculate how much energy can actually be stored by moving the equivalent of a freight train up, say, 500m?
I do see the advantage over flywheels: when the train has moved up and stops, then here is no energy loss over time because it will be stationary an no energy s required to keep it there.
(Score: 4, Interesting) by dlb on Saturday December 03 2016, @02:28PM
So if an 8% grade translates to 4.6 degrees, then sin4.5 = h/9,000m, and sin4.5 * 9,000 m gives about a 700 m change in elevation
Let's say they're moving 5,000,000 kg over that distance: PE = (5e6 kg)*(9.8 m/s^2)*(700 m) = about 34,000,000,000 J, which is around not quite 10,000 kWh.
Doesn't seem like a lot, but my slap-dash calculations are always suspect.
(Score: 0) by Anonymous Coward on Saturday December 03 2016, @06:07PM
> Doesn't seem like a lot
That's because, as TFA explains, the mass isn't in the train, its in the buckets of rocks the train hauls up and leaves suspended over the rail.
(Score: 2) by frojack on Saturday December 03 2016, @07:49PM
Or we could have just read the article...
The hill ARES has chosen has a gradient of about 8%. The track itself is just under 9km (about 5½ miles) long. 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.
The trains drop their loaded cars at the top, and run back down to pick up more.
You would need only a few generator sleds to be pulled down the hill by the cars. Or maybe they do it with cables, IDK.
Their plan is to jack up the weight cars at the top, move them off the tracks, and stack them till needed. This seems wasteful and requires lots of people and will lead to lots of down time. It would be easier just to build more cars and shunt them off to a rail yard.
What could possibly go wrong?!
No, you are mistaken. I've always had this sig.
(Score: 0, Troll) by gmrath on Sunday December 04 2016, @01:43AM
Oh, I dunno . . . perhaps a string of runaway multi-mulit-ton cars hurtling down an 8% grade with no way to stop (regenerative braking or otherwise) due to the inevitable electro-mechanical failure / human error / malicious intent. Of course, they'd probably gain enough velocity to jump the tracks half-way down, saving whatever is at the lower terminus. Bet it would be fun to watch.
(Score: 3, Insightful) by aristarchus on Sunday December 04 2016, @09:58AM
Yes, a rock spill, at speed, would not be a good thing. Far worse than a Wind-spill from those turbine thingys. But also not as bad as a petroleum spill, and certainly not as bad as uncontrolled release of radioactive material.
(Score: 1) by gmrath on Sunday December 04 2016, @08:05PM
I totally agree. Wind spill from the wind thingies may not be too much to worry about. But the bird kill should be. The rest you pointed out is spot on.
(Score: 0) by Anonymous Coward on Sunday December 04 2016, @11:34PM
> But the bird kill should be.
House cats kills many orders of magnitude more birds than windmills.
Maybe the species that typically get killed by windmills are more rare, I don't know.
(Score: 2) by Justin Case on Sunday December 04 2016, @02:41PM
So you are apparently unaware that heavy freight trains have been negotiating steep grades for over a century now? Perhaps someone has thought of these problems and come up with a solution? Like... (can you work it out before I tell you?) ... brakes!
(Score: 0) by Anonymous Coward on Sunday December 04 2016, @08:02PM
Perhaps a re-reading of the post you answered would be enlightening. I'm thinking such a thing as brake FAILURE was taken into account. Brake failures, while infrequent, do happen.
(Score: 2) by dlb on Sunday December 04 2016, @04:40AM
Or we could have just read the article...
And take all the fun out of it?
(Score: 3, Interesting) by bob_super on Saturday December 03 2016, @06:54PM
That's a pretty dumb idea, really, if you consider the footprint vs energy. In the US SouthWest, where there are lots of space and hills, it might make sense. Elsewhere, not so much.
The numbers are in TFA (sorry): This thing gets you peak 50MW for at most 15 minutes, using a 9km footprint and cable set. To get to that number, you need a pretty heavy train, so you need some seriously strong tracks.
But you ain't doing much with 50MW, unless you're looking at wind turbines very gradually slowing down. The gas plant you need to fire up before you reach the bottom of the track will output a whole lot more, so need quite a few trains to keep a constant supply.
Pumping water up (where you do have water) scales a whole lot better, and you occasionally get free energy. Pumping mercury would be fun and more energy storage per m^3.
I read somewhere about a much much better concept: Essentially a giant concrete/rock elevator (or lead, depleted U, gold, rusted iron...). Fits inside a city, even a flat one. Allows the motor/generator and power cabling to be fixed, and only requires a building-size crazy-strong foundation. Might take as much metal as the train, but is a lot more practical to maintain.
(Score: 0) by Anonymous Coward on Saturday December 03 2016, @08:15PM
> Pumping water up (where you do have water) scales a whole lot better, and you occasionally get free energy
There is no water in the desert.
> I read somewhere about a much much better concept:
Sounds conveniently undetailed.
(Score: 2) by frojack on Saturday December 03 2016, @08:20PM
You can't condemn the concept by the limitations of the demonstrator project.
They plan to elevate many more weights than would be used in a single downhill run, they warehouse these at the top, and move them to the downhill run as needed, potentially supplying a many hours of electricity generation.
As for the tracks, once the roadbed it built, you simply add more rails and wheel trucks. You are not limited to two rails.
You won't be building this on swampy ground, so the weight bearing issue as manageable. People with lesser technology have been doing this kind of moving since the Pyramids and Stonehenge.(/a> [securityscale.com]
No, you are mistaken. I've always had this sig.
(Score: 2) by bob_super on Monday December 05 2016, @06:12AM
The heavier the trains, the more power you get. The more tracks you build, the more power you get.
This requires a massive amount of land and a lot of concrete, i.e. a massive amount of water, if only once.
Ant then you gotta maintain your oversized infrastructure, including you giant mobile engine/generators and their catenary/cables. And you get no savings as this is so site-sensitive (and automatically distant from the power users) that it won't scale to more than a few systems, ever.
It's not that it doesn't work, but I wouldn't put my money on it.
(Score: 0) by Anonymous Coward on Sunday December 04 2016, @02:26AM
I did the math once a few years ago. I wanted to store two days worth of solar generated electricity for my house. It came out to a block of concrete the size of a two-car garage being hoisted 40 feet, if I recall correctly.
I also read somewhere that a single AA battery contains enough energy to lift 800 lbs. about 10 feet (assuming a perfectly efficient lifting mechanism)
Remember, gravity is the weakest of the four fundamental forces. You can fall out of an airplane and accelerate for 10,000 feet, but a few inches of concrete being held together by electromagnetic and nuclear forces will stop you cold.
Thermal storage seems more efficient. Use a heat pump to create a cold and a hot reservoir (pebbles, salt, bricks...) then use a stirling engine to extract the energy. The biggest problem with this is insulation.
(Score: 0) by Anonymous Coward on Sunday December 04 2016, @03:21AM
Actually, you can only fall out of a plane and accelerate at any appreciable rate for about 1000 feet; then you're within spitting distance of terminal velocity.
(Score: 2) by deadstick on Saturday December 03 2016, @01:57PM
Business has been slow there since the Chicken Ranch lost its airstrip.
(Score: 1) by effbee on Saturday December 03 2016, @03:34PM
That's how I first read it. Thought that won't be very popular this holiday season.
(Score: 2, Funny) by Anonymous Coward on Saturday December 03 2016, @04:05PM
Good for Thomas! Its a shifting economy and I'm glad to see someone as old as Thomas able to pick up a different career. Seems a bit mindless, but in these uncertain times you gotta accept what's available.
(Score: 0) by Anonymous Coward on Saturday December 03 2016, @08:29PM
Lol my joke about Thomas the train nodded I formative? Maybe the system is broken...
As for taking whatever job you can, that is only sometimes true. Get a job below your level and it will be that much harder to climb back up. Its a stupid system really.
(Score: 2) by Max Hyre on Sunday December 04 2016, @12:12AM