20 ms·

The energy density for gravity is just immensely small, that's why you need dams holding back rivers to use them to generate electricity. For a 1km hole (that's

The energy density for gravity is just immensely small, that's why you need dams holding back rivers to use them to generate electricity. For a 1km hole (that's in the middle of their 500m - 1500m range) you have an energy density of 10kJ/kg of the weight that stores the energy. The energy stored in a Tesla roadster battery pack is around 50kWh which is 180MJ. This means that you need a 18,000kg weight in a 1km deep (immovable) hole to have the equivalent of a Roadster battery pack. I'd go with the battery pack.

troymc 12y ago
That's true. Unfortunately, current Tesla battery packs use lithium, which isn't super-abundant in Earth's crust. That's why companies like Ambri are looking at using other materials in the batteries they're developing for grid energy storage.
- p1mrx 12y ago
  Other materials, like lead and antimony? http://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%27s_crust http://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%... Lithium: 33 Lead: 37 Antimony: 62
  - timdiggerm 12y ago
    Well they are more common
  - mtdewcmu 12y ago
    That table uses a mass-based unit, so wouldn't that tend to create the misleading impression that lighter elements are more scarce? Energy storage capacity depends on the number of atoms, not mass (as you can intuit by comparing lithium batteries to lead or nickel-cadmium batteries -- heavier doesn't mean more powerful).
    - p1mrx 12y ago
      Well, if Pb and Sb are more scarce than Li by mass, then they're even more scarce when you're counting atoms. If Ambri's technology does pan out, it will be due to a cheaper manufacturing process, not because they're avoiding lithium.
      - mtdewcmu 12y ago
        I thought those numbers were showing that lead and antimony are more common than lithium.
- mikeyouse 12y ago
  In 2011, we mined 0.2% of known lithium reserves.. This would provide over 350 years worth of lithium at current rates. Obviously usage is dramatically increasing but so will our known reserves as the overall level of demand increases. This is also without developing a method to pull the relatively abundant lithium from sea water and without recycling any lithium we're currently disposing of. Ambri is interesting from a lifecycle and cost perspective but I don't think a lithium shortage is going to have any real impact on prices.
  - Coincoin 12y ago
    "The greatest shortcoming of the human race is our inability to understand the exponential function."
    - mikeyouse 12y ago
      That's a fine saying but even at 20% YoY increases in lithium usage, we'd still have 35 years or known reserves -- without any increase in exploration or recycling. As oil & gas have shown, if there's exponential demand for a naturally occurring element, we'll definitely find ways to pull more of it out of the ground.
    - lotsofmangos 12y ago
      Increases in known reserves can also be exponential. The known reserves are 13 million tonnes. However lithium is the 25th most abundant element and you get 20mg of it for every kg of crust, so there is a lot more to find.
    - CamperBob2 12y ago
      "Everybody who has ever claimed that something is doomed because of an exponential function was wrong."
      - tripzilch 12y ago
        "... or dead."
    - 12y ago
- tinco 12y ago
  He's not suggesting that we use lithium battery packs. He's suggesting the idea is just plain ludicrous.
- elektropionir 12y ago
  I think it's more likely we'll see an asteroid mining economy bringing lithium for batteries on Earth than millions of 1km holes with 20 ton weights storing energy for single charges of electric vehicles. Whatever local (i.e. small scale) energy storage we have in the future you can probably bet (from first principles) with 99% certainty it will be based on the electromagnetic force. Gravity is too weak to be practical for smaller scale storage and cannot give mobile storage units since you have to deal with huge weights. For large scale see the "pumped storage" system already mentioned in this thread. Just for illustration, the "Taum Sauk Hydroelectric Power Station" can produce 175MW of continuous power. If you dropped the 18T weight in the 1km shaft you'd get about 13MW averaged over the 14s fall. Then you have to lift it up again if there are still enough pieces left. Even if you found a way to store energy in nuclear interactions (i.e. "charge a nuclear battery") you don't want to have a bunch of containers full of radioactive material all over the place. If one thought it through, I wouldn't be surprised if there are in-principle issues for the charging part similar to the ones with gravity. Since we don't know of any others, this leaves only the electromagnetic force to store energy with sufficient mass (or volume) density in practical ways. Whatever it ends up being (chemical batteries, supercapacitors or something else) the future local energy storage unit will separate and hold charges apart.
awjr 12y ago
It becomes viable when you use a 500,000kg weight...about 1.2MWh This is not unachievable with some lifting systems currently exceeding this lifting weight.
- adaml_623 12y ago
  Also lifting 500 tons is a lot easier when you don't have to move it horizontally. 1.2MW isn't as much as a wind turbine though which is a pity because they conceivably could be a good pairing.
- mtdewcmu 12y ago
  In trying to ascertain how much weight is practical to lift, I came across this list of the strongest cranes, which can lift millions of kilograms (thousands of metric tons): http://enr.construction.com/products/equipment/2012/0925-the-worlds-biggest-supercranes.asp http://enr.construction.com/products/equipment/2012/0925-the...
jostmey 12y ago
Okay, so what if you built a huge artificial dam way above sea level? To store energy you would pump water uphill. Usable work could then be extracted when the water is allowed to travel back downhill.
- vinkelhake 12y ago
  This is what is currently done. http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity
- jccooper 12y ago
  Well known as "pumped storage". They're competing with it, but dry and upside down. Is it more economical? Maybe. Is it safer? See http://en.wikipedia.org/wiki/Taum_Sauk_Hydroelectric_Power_Station http://en.wikipedia.org/wiki/Taum_Sauk_Hydroelectric_Power_S... At least if this contraption breaks, there's nothing important below it.
- DanielBMarkham 12y ago
  I live near a twin-lake hydro system that does just that. Every night the lights dim for a bit when the grid starts being used to pump water back up. http://en.wikipedia.org/wiki/Smith_Mountain_Dam http://en.wikipedia.org/wiki/Smith_Mountain_Dam
- acjohnson55 12y ago
  See also: https://en.wikipedia.org/wiki/Dinorwig_Power_Station https://en.wikipedia.org/wiki/Dinorwig_Power_Station
- pbreit 12y ago
  I would think you could find an elevated lake that replenishes naturally to avoid pumping the water up. But then maybe that is just "energy".
_greim_ 12y ago
This doesn't make sense. Gravity doesn't have an energy density. The energy density of this system is going to be directly related to the density of the material being raised/lowered.
- jberryman 12y ago
  Isn't that the math that the GP posted...?
- deleted 12y ago
  [deleted]
imaginenore 12y ago
18,000 kg is just 1.58 cubic meters of lead. You can have a much much heavier weight.
mtdewcmu 12y ago
That's a devastating critique. The idea seemed a bit too good to be true, but I couldn't quite put my finger on why. Thanks for posting that. I did a little more research, and I'm not sure anymore that it's a complete deal-breaker. But it's definitely going to put limits on how far this can scale.
brute 12y ago
You just need more mass. Have a look at this concept: http://eduard-heindl.de/energy-storage/index-e.html http://eduard-heindl.de/energy-storage/index-e.html (unfortunately the english version is very sparse, the german version has some more images and videos: http://eduard-heindl.de/energy-storage/ http://eduard-heindl.de/energy-storage/ ) The idea is to cut a 1km diameter cylinder into the ground (solid rock), and then lift it up up to 500m by pumping water underneath it. The power stored can power a country for a day. I am somewhat sceptical, but this guy is totally serious about it.
- joshvm 12y ago
  But presumably you'd need more than a day's worth of power to lift the damn thing? That's probably doable, but still, I suspect that'd be the main problem.
  - elmin 12y ago
    The point is to have a way to store the excess energy we generate at off peak times like the middle of the night.
  - brute 12y ago
    The efficency is said the be 80%, just like any other pumped storage system. It just uses considerably less space than a water reservoir (actually close to none, as the top of the cylinder remains untouched) and is scalable by adjusting the radius. I guess the main problem is to keep the water confined (200bar of pressure) while keeping the mass movable. Maybe someday they build a small testing facility, so we know for sure.

troymc 12y ago

That's true. Unfortunately, current Tesla battery packs use lithium, which isn't super-abundant in Earth's crust. That's why companies like Ambri are looking at using other materials in the batteries they're developing for grid energy storage.

p1mrx 12y ago
Other materials, like lead and antimony? http://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%27s_crust http://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%... Lithium: 33 Lead: 37 Antimony: 62
- timdiggerm 12y ago
  Well they are more common
- mtdewcmu 12y ago
  That table uses a mass-based unit, so wouldn't that tend to create the misleading impression that lighter elements are more scarce? Energy storage capacity depends on the number of atoms, not mass (as you can intuit by comparing lithium batteries to lead or nickel-cadmium batteries -- heavier doesn't mean more powerful).
  - p1mrx 12y ago
    Well, if Pb and Sb are more scarce than Li by mass, then they're even more scarce when you're counting atoms. If Ambri's technology does pan out, it will be due to a cheaper manufacturing process, not because they're avoiding lithium.
    - mtdewcmu 12y ago
      I thought those numbers were showing that lead and antimony are more common than lithium.
mikeyouse 12y ago
In 2011, we mined 0.2% of known lithium reserves.. This would provide over 350 years worth of lithium at current rates. Obviously usage is dramatically increasing but so will our known reserves as the overall level of demand increases. This is also without developing a method to pull the relatively abundant lithium from sea water and without recycling any lithium we're currently disposing of. Ambri is interesting from a lifecycle and cost perspective but I don't think a lithium shortage is going to have any real impact on prices.
- Coincoin 12y ago
  "The greatest shortcoming of the human race is our inability to understand the exponential function."
  - mikeyouse 12y ago
    That's a fine saying but even at 20% YoY increases in lithium usage, we'd still have 35 years or known reserves -- without any increase in exploration or recycling. As oil & gas have shown, if there's exponential demand for a naturally occurring element, we'll definitely find ways to pull more of it out of the ground.
  - lotsofmangos 12y ago
    Increases in known reserves can also be exponential. The known reserves are 13 million tonnes. However lithium is the 25th most abundant element and you get 20mg of it for every kg of crust, so there is a lot more to find.
  - CamperBob2 12y ago
    "Everybody who has ever claimed that something is doomed because of an exponential function was wrong."
    - tripzilch 12y ago
      "... or dead."
  - 12y ago
tinco 12y ago
He's not suggesting that we use lithium battery packs. He's suggesting the idea is just plain ludicrous.
elektropionir 12y ago
I think it's more likely we'll see an asteroid mining economy bringing lithium for batteries on Earth than millions of 1km holes with 20 ton weights storing energy for single charges of electric vehicles. Whatever local (i.e. small scale) energy storage we have in the future you can probably bet (from first principles) with 99% certainty it will be based on the electromagnetic force. Gravity is too weak to be practical for smaller scale storage and cannot give mobile storage units since you have to deal with huge weights. For large scale see the "pumped storage" system already mentioned in this thread. Just for illustration, the "Taum Sauk Hydroelectric Power Station" can produce 175MW of continuous power. If you dropped the 18T weight in the 1km shaft you'd get about 13MW averaged over the 14s fall. Then you have to lift it up again if there are still enough pieces left. Even if you found a way to store energy in nuclear interactions (i.e. "charge a nuclear battery") you don't want to have a bunch of containers full of radioactive material all over the place. If one thought it through, I wouldn't be surprised if there are in-principle issues for the charging part similar to the ones with gravity. Since we don't know of any others, this leaves only the electromagnetic force to store energy with sufficient mass (or volume) density in practical ways. Whatever it ends up being (chemical batteries, supercapacitors or something else) the future local energy storage unit will separate and hold charges apart.

awjr 12y ago

It becomes viable when you use a 500,000kg weight...about 1.2MWh This is not unachievable with some lifting systems currently exceeding this lifting weight.

adaml_623 12y ago
Also lifting 500 tons is a lot easier when you don't have to move it horizontally. 1.2MW isn't as much as a wind turbine though which is a pity because they conceivably could be a good pairing.
mtdewcmu 12y ago
In trying to ascertain how much weight is practical to lift, I came across this list of the strongest cranes, which can lift millions of kilograms (thousands of metric tons): http://enr.construction.com/products/equipment/2012/0925-the-worlds-biggest-supercranes.asp http://enr.construction.com/products/equipment/2012/0925-the...

jostmey 12y ago

Okay, so what if you built a huge artificial dam way above sea level? To store energy you would pump water uphill. Usable work could then be extracted when the water is allowed to travel back downhill.

vinkelhake 12y ago
This is what is currently done. http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity
jccooper 12y ago
Well known as "pumped storage". They're competing with it, but dry and upside down. Is it more economical? Maybe. Is it safer? See http://en.wikipedia.org/wiki/Taum_Sauk_Hydroelectric_Power_Station http://en.wikipedia.org/wiki/Taum_Sauk_Hydroelectric_Power_S... At least if this contraption breaks, there's nothing important below it.
DanielBMarkham 12y ago
I live near a twin-lake hydro system that does just that. Every night the lights dim for a bit when the grid starts being used to pump water back up. http://en.wikipedia.org/wiki/Smith_Mountain_Dam http://en.wikipedia.org/wiki/Smith_Mountain_Dam
acjohnson55 12y ago
See also: https://en.wikipedia.org/wiki/Dinorwig_Power_Station https://en.wikipedia.org/wiki/Dinorwig_Power_Station
pbreit 12y ago
I would think you could find an elevated lake that replenishes naturally to avoid pumping the water up. But then maybe that is just "energy".

_greim_ 12y ago

This doesn't make sense. Gravity doesn't have an energy density. The energy density of this system is going to be directly related to the density of the material being raised/lowered.

jberryman 12y ago
Isn't that the math that the GP posted...?
deleted 12y ago
[deleted]

imaginenore 12y ago

18,000 kg is just 1.58 cubic meters of lead. You can have a much much heavier weight.

mtdewcmu 12y ago

That's a devastating critique. The idea seemed a bit too good to be true, but I couldn't quite put my finger on why. Thanks for posting that. I did a little more research, and I'm not sure anymore that it's a complete deal-breaker. But it's definitely going to put limits on how far this can scale.

brute 12y ago

You just need more mass. Have a look at this concept: http://eduard-heindl.de/energy-storage/index-e.html http://eduard-heindl.de/energy-storage/index-e.html (unfortunately the english version is very sparse, the german version has some more images and videos: http://eduard-heindl.de/energy-storage/ http://eduard-heindl.de/energy-storage/ ) The idea is to cut a 1km diameter cylinder into the ground (solid rock), and then lift it up up to 500m by pumping water underneath it. The power stored can power a country for a day. I am somewhat sceptical, but this guy is totally serious about it.

joshvm 12y ago
But presumably you'd need more than a day's worth of power to lift the damn thing? That's probably doable, but still, I suspect that'd be the main problem.
- elmin 12y ago
  The point is to have a way to store the excess energy we generate at off peak times like the middle of the night.
- brute 12y ago
  The efficency is said the be 80%, just like any other pumped storage system. It just uses considerably less space than a water reservoir (actually close to none, as the top of the cylinder remains untouched) and is scalable by adjusting the radius. I guess the main problem is to keep the water confined (200bar of pressure) while keeping the mass movable. Maybe someday they build a small testing facility, so we know for sure.