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A Californian company proposes using weighted electrically-driven rail vehicles on inclines to store energy. At times when the capacity of electricity supply exceeds demand the vehicles would be driven up inclined tracks, and when demand exceeds generation they are allowed to run down, generating electricity as they fall.
This link includes a video that shows a prototype vehicle (which appears to be built on a conventional locomotive chassis), an interview with a promoter, and an animation of a "farm" of these devices. There is a shortage of hard data, such as how much energy could be stored, for how long, and how steep the tracks are, etc., but a quick calculation shows that some thousands of these vehicles would be required for them to be useful. The control panel for this prototype has a power dial that appears to go up to only 20 kW. The promoter in the interview focuses instead on how the construction material can be recycled at end of life.
(Score: 4, Informative) by bitstream on Tuesday July 03 2018, @05:08PM (3 children)
Let's take a example like the Coo-Trois-Ponts Hydroelectric Power Station [wikipedia.org] in Belgium. The data for this station is:
Effective water volume: 8 450 000 m³
Effective hydraulic head: 275 m
Thus it can hold 2.28e13 J (22.8 terrajoules)
Decently heavy train [wikipedia.org]: 3000 ton (3e6 kg)
So it would take 2815 big trains barked up along a 275 meter steep to get the same energy capacity. Not to mention all complexity and manufacturing pollutants.
Another eye opener, a normal laptop battery ~173 kJ (48 Wh) equals 2 cubic meters of water falling down 9 meters (69 cubic feet falling 30 feet).
Conclusion: They are barking up the wrong gravity rails ;-) ..or someone is looking to get some cash.
(who pays? who benefits?)
Gravity storage seems attractive superficially until you do the physics. Better to get started on liquid nuclear reactors, flow batteries etc. Get some He3 from the moon for research etc.
Pumped-storage hydroelectricity [wikipedia.org]
List of pumped-storage hydroelectric power stations [wikipedia.org]
(Score: 2) by VLM on Tuesday July 03 2018, @07:29PM
There's an easier hand wavy engineering argument that its difficult to get a straight answer because I'm sure it varies a lot, but very hand wavy Hoover Dam squirts ten million pounds of water per second, so a mechanical contrivance that continuously flung a million pounds of "not water" thru similar "engineering sane and reasonable" distances, would generate about a tenth of a hoover dam.
So if you're impressed with Hoover Dam as a mechanical engineering achievement, and impressed with things that move about that weigh a million pounds (like very large train engines) to handle similar amounts of power using pulleys and baling wire and duct tape takes either something ten times bigger or ten times heavier than "already fairly impressive existing upper limit". In other words without substantial evidence to the contrary it aint happening.
(Score: 2, Interesting) by dmanny on Tuesday July 03 2018, @09:00PM (1 child)
Of course rolling stock costs more than water, pound for pound.
The Wikipedia list misses some facilities by having a threshold of 1000MW.
I remember when this operation failed. The story today made me look into the current status, it appears to be online. It operates at a head of approximately 850 foot.
https://en.wikipedia.org/wiki/Taum_Sauk_Hydroelectric_Power_Station [wikipedia.org]
I also found the WP list of hydroelectric failures interesting.
https://en.wikipedia.org/wiki/List_of_hydroelectric_power_station_failures [wikipedia.org]
But your point is clear. That is a lot of trains, 2815. Making them each have 3e6 kg mass would be nearly impossible. Water in a reservoir stacks much nicer than trains. The energy efficiency is one thing, the maintenance costs for that much rolling stock would be prohibitive.
(Score: 3, Interesting) by bitstream on Tuesday July 03 2018, @11:52PM
In Australia, BHP in June 2001 had a trial with 682 ore cars and eight distributed GE AC6000CW locomotives with a total weight of 99 734 tons (99e6 kg). So just 85 train sets, but there are other complications like having to use a cog railway, wires with metal fatigue, wear, oil, sand etc. So I'll suspect the investment and maintenance will make it unfeasible.
If one could use magnetic energy storage. It may be way more efficient.