EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: Biff383 on May 02, 2016, 01:37:37 am
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http://www.vox.com/2016/4/28/11524958/energy-storage-rail (http://www.vox.com/2016/4/28/11524958/energy-storage-rail)
A friend sent this out to me. Seems to me to not be a very efficient way to store energy. I suggested batteries.
Any thoughts?
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I don't know, the article says they're 86% efficient which is comparable to batteries, and this system should last much longer than batteries I would hope. First thoughts, I don't think this such a bad idea. The only question is how much land would this take up?
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It stinks. You aren't going to get a response time in seconds because the rail car has to accelerate up to speed under gravity alone before you can tap usable amounts of power from its motor/generator. To get the claimed 86% efficiency end to end, you need to beat 92.7% efficiency in each direction. That doesn't leave much for geartrain and rolling losses.
I would suspect its the rail lobby trying to get pork out of the green energy barrel.
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Conceptually it works - on all-electric rail lines, trains doing downhill used dynamic braking to maintain speed, and the power generated was pumped back into the power system to help power trains on the other side of the hill coming up.
Their efficiency projections though, kind of stink. Steel wheels on steel rails IS very efficient, but that very efficiency plays in both directions. It might not take a whole lot of energy to lift those blocks up the grade, but you also aren't going to get a whole lot of that back coming down.
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I thought trains already had regenerative braking systems?
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fundamentally the project is no different than the http://gravitybattery.info/ (http://gravitybattery.info/) , which is really a cable fatigue experiment.
the friction of the cable on the drum (and bending fatigue) is no different than the rail wheel on the track, except for the fact that the track and wheel can be made from a harder steel.
but with the train, you have bearing friction, bearing friction that is Multiplied according to the tangent of the slope of the track.
with the gravity battery, you have cable fatigue but low bearing losses. with a train, you have lots of bearing loss and wheel fatigue, but no cable fatigue.
in the case of a gravity battery you could make the cable drum arbitrarily large to make the cable fatigue negligible, but if you do, then the gear box friction is not longer negligible because the velocity of the cable is slow relative to the tangential velocity of the motor. so you can make the diameter of the motor larger but that increases air drag and cost.
but a train has a huge surface area and air drag. so you have to have a gear box.
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Old Old news. Its been done. Here is the one that happens to be closest to me. https://en.wikipedia.org/wiki/Helms_Pumped_Storage_Plant (https://en.wikipedia.org/wiki/Helms_Pumped_Storage_Plant) Pumped charges hydroelectric systems have been in use for nearly a century. Same idea. Much more practical.
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Dinorwig pumped storage hydro plant stores approximately 9 GWh in a similar land area with efficiency of 75%. ARES Nevada uses 106 Acres of land for 12.5 MWh with claimed 86% efficiency. Marchlyn Mawr reservoir (Dinorwig upper) is approx 50 acres area. Add another the same size as a lower reservoir, and the rest for the turbine and generator halls etc, and the area will be very similar. Over 700 times the storage capacity in a similar footprint, with a height differential of 500m - that's practical to install anywhere you've got a really deep open cast mine that's no longer economic or is abandoned. Remediate the Berkeley Pit (https://en.wikipedia.org/wiki/Berkeley_Pit) superfund site and you could put a 20GWh storage plant in it!
The efficiency could be improved with shorter larger penstocks and tail races + separating the pumps and turbines so each can be designed for maximum efficiency.
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California politicians are trying to save the world. They have set high goals for renewable energy. 50% by 2030, so that will take a lot of money out of peoples pocket and place it in the lobbyist's pockets and the rich who will get the projects.
One big problem is energy after the sun goes down. So there are billions available (some from my pocket) to be used on projects like this. Another project will be to use molten salt.
So appreciate that Californians are saving your world. :-+
I like what someone said people could do - and that is save our utility bills so we can look back at them someday and think "oh the good old days" :--
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This seems like a good alternative a hydroelectric storage plant for areas with little to no water. :-+
Efficiency is probably very comparable.
One could build this train storage near solar power plants in the desert where hydro storage is simply impossible due to the lack of water and huge evaporation losses.
Certainly more durable and less toxic materials than batteries.
A "small" capacitor bank would probably still be necessary to cover the time untill the train power kicks in.
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"Certainly more durable ... than batteries" is highly questionable. It needs sliding contacts for the power connection the whole lengthg of the track, the rail cars are mechanically complex and will need significant maintenance, and even the track will need regular maintenance due to ballast movement.
NiFe batteries are environmentally fairly benign, don't use rare minerals, are low maintenance and have life expectancies in excess of 40 years and efficiencies up to 80%. They don't have great energy density, but in a stationary application, that's not particularly important. 600 tonnes of NiFe cells could easily store the same amount of energy as the ARES Nevada project.
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It just goes to show you, there are many ways to approach energy storage. I think energy generation solutions are just as important, if not more so.
So long as people keep testing out ideas, there is hope.
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Old Old news. Its been done. Here is the one that happens to be closest to me. https://en.wikipedia.org/wiki/Helms_Pumped_Storage_Plant (https://en.wikipedia.org/wiki/Helms_Pumped_Storage_Plant) Pumped charges hydroelectric systems have been in use for nearly a century. Same idea. Much more practical.
Not to defend that rail thing but pumped storage have some serious issue. It can only be constructed where natural landscape allows (water reservoir on the mountain).
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Old Old news. Its been done. Here is the one that happens to be closest to me. https://en.wikipedia.org/wiki/Helms_Pumped_Storage_Plant (https://en.wikipedia.org/wiki/Helms_Pumped_Storage_Plant) Pumped charges hydroelectric systems have been in use for nearly a century. Same idea. Much more practical.
Not to defend that rail thing but pumped storage have some serious issue. It can only be constructed where natural landscape allows (water reservoir on the mountain).
When you have the landscape and resources for it, it's a great idea - but extremely limited in where it can be implemented. The rail thing is a lot more flexible in that regard, but it does have maintenance and efficiency issues. As for the speed it's output could be ramped up - that's going to be one of the development challenges.
I don't expect it to be a silver bullet - but I'm interested to see what they can achieve.
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I thought trains already had regenerative braking systems?
Diesel power trains do, but the energy is simply dissipated in resistor grids. Electric railways usually do what I mentioned, feed the power back into the grid. There's an incredibly large amount of switchgear involved in an electrified railway, as the loads are constantly changing AND moving. Much automated these days, but there used to be a position of Power Director who controlled the switching of substations to keep the power where the trains were.
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I thought trains already had regenerative braking systems?
Diesel power trains do, but the energy is simply dissipated in resistor grids.
Many years ago I was a manufacturing engineer involved in the testing and manufacturing of a 5500 kilo watt dynamic braking resistor being developed for the now retired EMD SD90 MAC. It truly was an experience being on the SD90 platform and testing the resistors, and it is an amazing amount of heat generated and blown out the "hatch".
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It's neat watching them come down a grade like Horseshoe Curve, clearly braking but the prime mover is in anything but idle - just to keep the fans turning fast enough. I've gotten chances twice to ride in the cab, no 90MAC though, an SD50M and a rebuilt GP30.
There's a LOT of electronics on modern locomotives, and not just for engine control. Would have probably been my dream EE job, but then with the ups and down in the industry I might have ended up like my friend the microwave engineer who hasn't been able to find work in over a year.
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With the reduction in coal production due to EPA reasons and the reduction in transport of oil and drilling / fracking supplies (fine sand etc) the railroads are really taking it on the chin lately. The days of lengthy coal trains and specific platforms like the SD90MAC are gone, sadly.
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Diesel trains tow batteries. The engines are always running when the batteries need to charge but the motive force is electric motors. To add more capacity, they just add more battery cars and more engines.
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86% efficiency end-to-end is HILARIOUS. No way. No way in hell. Not even close. This should be on KickStarter.
I hope they make me eat my words (I will gladly).
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If we can achieve 80% efficiency (end-to-end) with pumped hydroelectric storage then I think the claimed 86% of the train storage is certainly not impossible. :-/O
The train rails have less friction than the long water pipes and a geartrain has also less losses than a pump. Not by much but they can certainly make that 6% difference.
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"A body of 1000 kg is elevated 10 m. The change in potential energy can be calculated as 0.027 kWh"
"That project, called ARES Nevada, will consist in a 5.5-mile track traveling up an 8-degree slope, covering 106 acres of public land near the delightfully named town of Pahrump, Nevada. It will boast 50 MW of power capacity and be capable of producing 12.5 MWh of energy. The company expects to start construction early next year and finish by 2019."
So that is about 1 KM height. The weight must be 4600 tons. Also, trains dont like going uphill.
https://www.youtube.com/watch?v=KbUsKWbOqUU (https://www.youtube.com/watch?v=KbUsKWbOqUU)
Pardon the bad math in the video, it is still true.
Sooo, it doesnt scale. Also, compare the mass of some stone to the massive amount of water in a dam.
Also, might as well lift the weight with a cable. Take an abandoned underground oil well, make a continuous cable attach the stones, make automatic stone attachment detachment and done.
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Dinorwig pumped storage hydro plant stores approximately 9 GWh in a similar land area with efficiency of 75%. ARES Nevada uses 106 Acres of land for 12.5 MWh with claimed 86% efficiency. Marchlyn Mawr reservoir (Dinorwig upper) is approx 50 acres area. Add another the same size as a lower reservoir, and the rest for the turbine and generator halls etc, and the area will be very similar. Over 700 times the storage capacity in a similar footprint, with a height differential of 500m - that's practical to install anywhere you've got a really deep open cast mine that's no longer economic or is abandoned. Remediate the Berkeley Pit (https://en.wikipedia.org/wiki/Berkeley_Pit) superfund site and you could put a 20GWh storage plant in it!
The efficiency could be improved with shorter larger penstocks and tail races + separating the pumps and turbines so each can be designed for maximum efficiency.
All of which is true, and works as described anyplace you have ample supplies of water and appropriate elevation differences. Where you can afford the evaporative losses from yet another large reservoir. Which is not anywhere in the American Southwest. A later post raises issues with the vertical rise described finding 1 km implausible. True that it is implausible in many parts of the world, and many parts of the US. But not at all implausible in the American Southwest.
This solution might make sense in some parts of the world. Just like wind and solar whose effectiveness varies widely based on local conditions. Things like the cost of power lines to reach regions where pumped storage does make sense will factor into the decision. The answer will not lie in the first significant figure of the analysis, and will probably come down to single digits in the second significant figure. Which will probably not exceed the error limits in the analysis.
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If they have got an electric locomotive system with 93% efficiency (93% of the electrical energy fed into the overhead lines or third rail is used to move the mass of the train) then they should be contacting train operating companies and getting rich, not messing around with energy storage!
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To be fair, this project is at least founded in real physics that can be measured. The key part that I appreciate is that it can be scaled up to sizes that are practical at costs that are, well, high, but not insane. Batteries, no matter what kind you use, just aren't practical that way, and at some point will need to be wholly replaced. Rail cars, electric drive motors, and generators can all last for many decades with decent maintenance—and unlike batteries, their lifespan can be extended nearly indefinitely with good maintenance.
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Evaporation from reservoirs can be reduced by up to 90% using modular floating covers.
Also Nevada has a deep pit lake remediation problem: https://www.newsreview.com/reno/pit-lake-challenge/content?oid=7176643 (https://www.newsreview.com/reno/pit-lake-challenge/content?oid=7176643) so there's a lot of water that isn't fit for drinking already in big holes in the ground. Building banked reservoirs next to them for pumped storage hydro, to make them revenue generating could help pay for treating them to avoid ground water contamination.
NiFe cell batteries are very long lived and can be designed to be fully rebuildable. After the first couple of decades, you'd be running a maintenance program of taking the lowest performance bank out of service, and testing the batteries to see which need their plates shipped off to be reconditioned, or you might even have reconditioning facilities on-site if the installation was large enough.
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If we can achieve 80% efficiency (end-to-end) with pumped hydroelectric storage then I think the claimed 86% of the train storage is certainly not impossible. :-/O
The train rails have less friction than the long water pipes and a geartrain has also less losses than a pump. Not by much but they can certainly make that 6% difference.
So, they can take energy from the grid or whatever cyclic renewable source - transport that to the train - convert it to motor voltage or vector drive or whatever - go through the transmission system losses - and drive the unit uphill only losing 7% of the original energy? I am not an expert at all, but that is a pipe dream. What motor from input terminals to to output shaft can do that without considering any other losses - a few, but not many. I read about some 95% motors, so if you go with that the rest of the entire system can be no more than 2% loss?
No way. Not even close. Can the reverse (downhill leg) be any better? No, it is most likely worse than the uphill. Projects like this get funded by making rediculous claims. By the time the claims are proven crazy - the organizers already have a pile of cash in the name of green energy. It's a government funded Kick Starter with similar craziness.
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4600 tons raised/lowered ~ 1km. Rails typically have 20 ton limit on an axle load = 230 axles... Because of the gradient I suppose all/most driven.. Plus power rail, back and forth. Serious piece of gear.
Now, lets calculate the volume of water that weighs 4600 tons. Ok, 4600m3 = 16.5m^3
Olympic swimming pool is 2500m3 (https://en.wikipedia.org/wiki/Olympic-size_swimming_pool).
I bet pouring two roofed concrete tanks (although cheaper are not cube but have chamfered sides) on that desert, piping and pumps would peak at 0.003% of the investment cost of that railerizer.
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So, they can take energy from the grid or whatever cyclic renewable source - transport that to the train - convert it to motor voltage or vector drive or whatever - go through the transmission system losses - and drive the unit uphill only losing 7% of the original energy? I am not an expert at all, but that is a pipe dream. What motor from input terminals to to output shaft can do that without considering any other losses - a few, but not many. I read about some 95% motors, so if you go with that the rest of the entire system can be no more than 2% loss?
Baldor says their 200hp induction motors are 96.2% efficient at full load, 96.4% at 3/4th load.
just the motors make 92.5% possible.
train wheels slip as well, and you have gear box losses.
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Need to do apples to apples comparison. Pumped storage normally doesn't have transmission losses since it is done in conjunction with generation. If you are building a pumped storage facility somewhere other than a major point of generation then appropriate transmission losses will need to be included in pumped storage efficiency. Scale also needs to be considered. Piping losses and some other losses drop with scale for pumped storage, probably not for the rail system.
There are many issues with this rail storage concept, but as others have said, it at least doesn't require over unity power conversion, magic materials or technology that doesn't exist. Whether the business case exists or not depends on the specific application. Batteries and many of the other concepts laughed at in this thread have been deployed successfully where the unique circumstances justify them. One interesting possibility is that there might be locations that have appropriate time varying loads to make the physical delivery of the power an interesting part of the analysis. That is, cases where a heavy, short duration load exists at or near the top of the hill being used, while an excess of power is available nearer the bottom of the hill and appropriately time phased. Potential significant reduction in transmission losses.
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There are many issues with this rail storage concept, but as others have said, it at least doesn't require over unity power conversion, magic materials or technology that doesn't exist.
Ok, now there are seven zillion ways to store energy that could be characterized same way. What about a 100000 ton bamboo clockwork spring?
The railerizer imposes unprecedented constraints. How would you imagine finding/building a ~1.2km high "mountain" with a 5.5mile, 8 degree incline capable of ~straight track for the load of 230 driven axles?! Even if you found such place (of course close to both consumers and the producers, for that :bullshit: 93% efficiency), that 8.8km mountain track earth work (or should I write rock-blasting work) would require tunneling and bridging technology that does not exist to be economically and energetically viable (with relation to pumped-storage).
Panama Channel is a piece of cake when compared to that thingy.
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So, they can take energy from the grid or whatever cyclic renewable source - transport that to the train - convert it to motor voltage or vector drive or whatever - go through the transmission system losses - and drive the unit uphill only losing 7% of the original energy? I am not an expert at all, but that is a pipe dream. What motor from input terminals to to output shaft can do that without considering any other losses - a few, but not many. I read about some 95% motors, so if you go with that the rest of the entire system can be no more than 2% loss?
No way. Not even close. Can the reverse (downhill leg) be any better? No, it is most likely worse than the uphill. Projects like this get funded by making rediculous claims. By the time the claims are proven crazy - the organizers already have a pile of cash in the name of green energy. It's a government funded Kick Starter with similar craziness.
ABB has induction motors (not the most efficient method) with 97.9% efficiency (https://library.e.abb.com/public/1c12e00207e12437c1257b1300571036/HV_Induction_motors_technical_IEC_catalogue_EN_122007.pdf) and with a synchronous motor-generator you can achieve 99% (https://library.e.abb.com/public/52a31acd85411f82c1256f9d002a8adb/3BSM900961.pdf).
So with a 98% motor-generator the drivetrain (gears and rails) needs to be 95% to give you a total effieciency of 86%, which is actually pretty easy to achieve. Or you could choose a motor with high pole count so you wouldn't need a gearbox at all...
The efficiencies of those big machines are incredibly high. As I've said if it's possible to build a hydroelectric storage plant with 80% total efficiency (with the lossy pump and long pipes and flow losses), then it's certainly possible to achieve 86% with a big scale rail storage system.
Transmission losses are never included in the calculations since the power rarely comes and goes to the same place. Calculations start at the fence of the power plant. :D
I don't say that this system should be built everywhere but where the topography is ideal and no water is available this could be a interesting alternative.
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what would be overall efficiency of the system if the train carries batteries as cargo
and whether energy can be stored in the magnetic field big as the entire train.
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To be fair, this project is at least founded in real physics that can be measured. The key part that I appreciate is that it can be scaled up to sizes that are practical at costs that are, well, high, but not insane. Batteries, no matter what kind you use, just aren't practical that way, and at some point will need to be wholly replaced. Rail cars, electric drive motors, and generators can all last for many decades with decent maintenance—and unlike batteries, their lifespan can be extended nearly indefinitely with good maintenance.
I see your point, but especially when sotring energy, there is much more to it than just the physics behind it. If you pass water or trains up and down doesn't really matter and you need a special location for both. And how do you transport the electricity generated away from the train? Batteries? :-DD If you've got some kind of wiper, they will errode quite a lot, when you have trains going up and down all the time . And how do you hold the train up? You will always loose Energy there, the longer it has to stay there, the more (Or you need a lot of Energy to start it going downwards, which means the less energy stored, the less efficient it gets).
How about the running costs (maintenance etc.)?
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Holding the train in place on the incline is quite simple: Its this amazing technology that's been around since the Roman empire called friction brakes! Yes it takes power to either apply or release (or both) the brakes, but it takes very little if any power to keep the brakes released and none to keep them applied. Any sane design will have the brakes fail safe (ON) if power is lost.
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If you've got some kind of wiper, they will errode quite a lot, when you have trains going up and down all the time .
Every electrified rail system in the world deals with this one way or another, it's not exactly a new problem. This application is potentially less challenging in this respect than a typical rail transit system, since the rail units will spend most of their time on a single straight segment, and you won't get the massive make/break arcing that a typical transit system experiences as trains move from one electrical block to another, or have to switch pickup sides. I used to live right next to a metro rail station, the arcing you'd see at the beginning and end of third rail segments was impressive.
And how do you hold the train up? You will always loose Energy there, the longer it has to stay there, the more (Or you need a lot of Energy to start it going downwards, which means the less energy stored, the less efficient it gets).
There's an interesting glimpse of their control strategy in one of the videos--they talk about queuing a number of active units in the middle of the slope, and at any point they can add or remove units to the top or the bottom of the queue and add or remove energy in the process. That gives them a number of possible energy-positive, energy-negative, or energy-neutral maneuvers in adjusting the queue size, spacing, and position over one or more units. With a simple mechanical brake, you could hold a couple dozen units idle in the middle of the queue with basically no power consumption while adding or removing units from the top or bottom to make small adjustments. Then when you need a larger adjustment you can immediately start the entire queue moving up or down at once.
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One Cubic km battery storage center every here and there. What could go wrong with that? O0
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I think I smell something.
What you smell is my money leaving my pocket. Just another reason for California politicians to take it. :--
This is to furnish "clean" power to CA, so we can say we saved the world (while lining their pockets)
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I think the rail system has great potential!
Just think .... MacGyver could increase output by loading big rocks on the top of the rail cars to save ... * something *
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I think the rail system has great potential!
Just think .... MacGyver could increase output by loading big rocks on the top of the rail cars to save ... * something *
Why not drive the trains to the top of the hill empty, thus only using a small amount of electricity, then load the rocks on at the top before sending it down again to generate lots of electricity! The rocks could be transported up the hill by truck, resulting in free electricity!
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** Looking for a facepalm LOL ....... **
MacGuyver only needs to do this once (as he always does), so a reusable/sustainable solution isn't required.
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I find it rather disconcerting that whenever a proposal like this comes around, engineers are eager to prove it impossible. But spend money building a new substation and there's not a peep about the transformer losses up and down, or the true efficiency of the grid (the US Government claims 6% losses (https://www.eia.gov/tools/faqs/faq.cfm?id=105&t=3) which seems impossible given ~96% efficiency at each transformer), or how the chemical fuel source is finite, or how efficient the process is in terms of input-energy (e.g. chemical potential in fossil fuel) to output-energy (billable KWh near point-of-use). Weird. :popcorn:
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I find it rather disconcerting that whenever a proposal like this comes around, engineers are eager to prove it impossible. But spend money building a new substation and there's not a peep about the transformer losses up and down, or the true efficiency of the grid (the US Government claims 6% losses (https://www.eia.gov/tools/faqs/faq.cfm?id=105&t=3) which seems impossible given ~96% efficiency at each transformer), or how the chemical fuel source is finite, or how efficient the process is in terms of input-energy (e.g. chemical potential in fossil fuel) to output-energy (billable KWh near point-of-use). Weird. :popcorn:
Not quite. A new idea has to be better than or at least have the potential to be better than established technology.
This is neither. It's bollocks. This kind of shit diverts money away from projects that could make a difference, and when it fails causes more people to be cynical of all environmental projects.
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One of the most valuable books I have read is "Profiles of the Future" by Arthur Clarke. Originally written in 1960, his predictions of technology in the year 2016 have been proven both wrong and right. But the really important part of the book comes in the first two chapters where he identifies the difficulties in prediction. He identifies two sources of failure, failure of the nerve and failure of the imagination. In illustrating these issues he concludes that if an expert in a field concludes that something is possible you can take that prediction to the bank. If the expert predicts it is impossible - then not so much. Two of the illustrations of this that he provides are a deep engineering analyses provided by Cornell University and by the British Planetary Society. The analysis by Cornell was done in the 1930s, a time when Cornell was a leading institution in aeronautics. They concluded that because of drag, engine efficiency etc. transatlantic passenger aircraft transport was a silly fantasy, that such an aircraft could only carry a handful of passengers and would never be economically viable. The British Planetary Society did a learned study on the energy content of propellants, strength of materials etc. and concluded that it was physically impossible to place an object on the moon. Neither of these analyses was technically wrong. The physics and math were correct. They just analyzed the problem slightly incorrectly. The problem in the Cornell analysis was ignoring the reduced drag possible by flying at higher altitude. The British Planetary society missed the improvement in system mass fraction that is achieved in a staged rocket.
I highly recommend reading the book. Those introductory chapters are worth the entire price and more. The later chapters involving actual predictions are amusing reading, and also illustrate the other side of the problem. The things the experts who are sure something can be done and have proved to be wrong for various reasons.
Those who are sure that a system is not possible should be very sure that they understand all of the conditions on its operation.
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But no one is saying that you can't store energy by moving a train up a hill, we're just saying it's a shit way to do it, and the economics and logistics of other methods are far better.
I will buy a copy of that book though... :)
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I find it rather disconcerting that whenever a proposal like this comes around, engineers are eager to prove it impossible. But spend money building a new substation and there's not a peep about the transformer losses up and down, or the true efficiency of the grid (the US Government claims 6% losses (https://www.eia.gov/tools/faqs/faq.cfm?id=105&t=3) which seems impossible given ~96% efficiency at each transformer)
It really is that good. hard to believe, but even a 50MW transformer only weighs 50 tons. that's 1 kilowatt per kilogram power density, and the losses are about 1-2 watts per kilogram for the iron, and about the same for the copper.. assuming 50:50 cu:fe mass/weight. usually there is less copper than iron so there are more copper losses. the most efficient point is sometimes as low as 25% full load rating. so even if you figure 10 watts per kilogram losses.. that's still 99% efficient.
The lowest efficiency transformer is the pole transformer at the end of the line. i don't know what the usuall efficiencies are for them, but most of their losses are no load losses just due to the fact that the average residential load is only 2KW, and they put a 25KW transformer most everywhere feeding 1 or two or three houses.
the highest efficiency transformer is at the other end of the line, stepping up 25KVAC to something like 10-20 times that for the long distance lines. those ones are in the realm of 99.5% or better.
because the efficiency of the grid is so high.. when 5 volts dc per mile shows up on the power lines due to a magnetic disturbance from the sun, etc.. this is enough to cause 100's of amps dc to flow. which then saturates the transformers and thousands of amps of harmonic current start flowing and blow up the transformers.. takes about a minute for that to happen worst case senario. one of the problem with current transformers is the dc may saturate the current transformer so the grid won't even know there is a problem..
What is insane that we haven't spent the 50 million estimated cost.. to install a large capacitor, resistor, and spark gap in series/parallel with the neutral of the top 1000 large distribution transformers, lifting the ground return and breaking the loop for the dc voltages appearing on the line.
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But no one is saying that you can't store energy by moving a train up a hill, we're just saying it's a shit way to do it, and the economics and logistics of other methods are far better.
I will buy a copy of that book though... :)
i'm not convinced its a shit way to do it, as i described earlier the cable drum method proposed by the "gravity battery" folks is really a cable fatigue experiment.
I described elsewhere that 600 dollars in stainless steel aircraft cable (at 1/3rd the breaking load) stores about as much energy as does 10 laptop batteries.
a 1200 foot length of polypropylene rope stretched to 1/3rd its breaking strength stores about as much energy as 1 laptop battery, and costs about 44$.
But you have to have a 1200 foot deep mine shaft, and you have to keep water out of it..
Motors can run 24/7 for 25 years, so can the gear boxes provided the oil is changed. its really a cable fatigue experiment in my opinion.
but with rail cars.. motor gear box.. same problem. no cable fatigue, but now you have 100 times as much weight on the bearings. so you've traded cable fatigue for wheel bearing fatigue, and wheel bearing losses. it may turn out to be a wash.
also you have wheel creep which may cost you as much as 1% each way.
wheel creep on a train is no different than the same creep problem that differential roller screws have (used for positioning milling machines and etc), which does not provide absolute motion and must be used with glass scales.
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The point of energy storage is to be instantaneously available to fill in the gaps when demand spikes above capacity which is what we have the well proven pumped hydroelectric storage for.
I noticed that these rocks have to be pivoted to fit on the railcars before the potential energy is converted to kinetic - how long is that going to take and how much energy be expended to turn the rock 90 degrees each way?
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Not sure why they are using concrete as the mass, have you seen the price of scrap steel lately.
Yup load it up with scrap steel as it's cheaper! (thanks China)
I can think of easier methods involving hydro power.
Build a big underground reservoir (or find an existing one), and put a smaller one on the surface.
When power is in excess, pump water to the top, when it's night/high demand let whatever water is in storage back down via turbine.
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But no one is saying that you can't store energy by moving a train up a hill, we're just saying it's a shit way to do it, and the economics and logistics of other methods are far better.
I will buy a copy of that book though... :)
i'm not convinced its a shit way to do it, as i described earlier the cable drum method proposed by the "gravity battery" folks is really a cable fatigue experiment.
I described elsewhere that 600 dollars in stainless steel aircraft cable (at 1/3rd the breaking load) stores about as much energy as does 10 laptop batteries.
a 1200 foot length of polypropylene rope stretched to 1/3rd its breaking strength stores about as much energy as 1 laptop battery, and costs about 44$.
But you have to have a 1200 foot deep mine shaft, and you have to keep water out of it..
Motors can run 24/7 for 25 years, so can the gear boxes provided the oil is changed. its really a cable fatigue experiment in my opinion.
but with rail cars.. motor gear box.. same problem. no cable fatigue, but now you have 100 times as much weight on the bearings. so you've traded cable fatigue for wheel bearing fatigue, and wheel bearing losses. it may turn out to be a wash.
also you have wheel creep which may cost you as much as 1% each way.
wheel creep on a train is no different than the same creep problem that differential roller screws have (used for positioning milling machines and etc), which does not provide absolute motion and must be used with glass scales.
You seem to be under the misapprehension that someone is arguing in favour of building storage systems using drums of cable... :-//
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In my opinion the future of day range electricity storage is low efficiency but very low cost. If high efficiency comes at the expense of the need for rare geography like this it will only ever be a niche solution, it might be able to make money but it won't matter in the big scheme of things.
Where high efficiency requires high costs however (batteries and adiabatic or near isothermal pumped air storage for instance) I think the low efficiency technologies will end up eating their lunch, as another post reminded us electricity from renewable sources can have negative costs after all ... chasing efficiency so hard is silly.