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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: 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?