5 ms·

Why do so many of these gravity thingies show up lately? An easy calculation shows how low the storage potential is. Lets take a weight of 500 tones of steel,

Why do so many of these gravity thingies show up lately? An easy calculation shows how low the storage potential is. Lets take a weight of 500 tones of steel, which would be 63.29 cubic meters. Now sink those 500 tonnes into a hole a 100 meters deep that would make a rather lowly 0.1362 MWh of storage. https://www.wolframalpha.com/input/?i=500+*+1000+kilograms+*+StandardAcceleration+*+100+ https://www.wolframalpha.com/input/?i=500+*+1000+kilograms+*... Not sure what the cost of digging a 100 meter hole where you can sink 63 cubic meters of steel in would be, specially since water management is needed too. I am not convinced that it is worth it.

gameswithgo 6y ago
Gravitricity is claiming weights as massive as 5,000 tons and shaft depths from 150m to 1,500m
- ben_w 6y ago
  That’s equivalent to ~83 tons of lithium ion battery: http://www.wolframalpha.com/input/?i=5000%20tons%20%2A%209.8m%2Fs%2Fs%20%2A%201500m%20%2F%20%280.8MJ%2Fkg%29 http://www.wolframalpha.com/input/?i=5000%20tons%20%2A%209.8...
  - twic 6y ago
    Ah - so we can measure the specific capacity of a battery in kilometres of altitude. e = mgh, so h = e/mg. Lead-acid = 0.14 MJ/kg = 14.3 km LiFePO4 = 0.58 MJ/kg = 59.1 km LiNiMnCoO2 = 0.74 MJ/kg = 75.5 km
    - ben_w 6y ago
      Yes; how high a fully charged battery could lift itself. I guess it’s similar to counting rocket fuel in seconds (lb_force-seconds per lb_weight).
      - tgb 6y ago
        What's the analogous interpretation of the 'seconds' of a rocket fuel? How long you can burn it for?
        cstrahan 6y ago
        How long the rocket fuel could offset the force of gravity upon itself, thus suspending itself in-place. In the real world, you'd need the rocket itself (which in turn contains the rocket fuel) which adds weight, and you'd have a difficult time controlling power output so the rocket doesn't drift and lengthen/reduce the burn time -- but that's not the point. The idea is that we want a unit that relates the mass of the fuel with its total energy, and one way to approach that is to consider how long the fuel could offset the force of gravity on that fuel, which gives you a cute unit of measure in terms of time.
    - yongjik 6y ago
      And uranium = 80,620,000 MJ/kg = 8,226,530,612 km[1], or about 180% the distance to Neptune. Sometimes I wish we lived in an alternative world with fully developed nuclear power. Think about the possibilities. And no global warming! :/ [1] Not accurate, obviously.
syllable_studio 6y ago
You're thinking too small though ;). You can dig a mile deep. And you can lift enormous weights. As comments show below. Gravity is weak, but cheap. It can scale up to provide 1 GW of storage - enough to balance the load of an entire large city. Lots of these ideas are popping up right now because it's a very compelling idea which is demonstrated to work. And because climate change is driving massive growth in renewable energy (woot) we will desperately need massive amounts of energy storage in the very new future. The energy storage market is expected to grow massively year over year.
- LordHeini 6y ago
  Sure you can always get the big option but that does not mean it is feasible. What does it cost to dig and maintain a 1.5km deep shaft? I found is something around 8000-10000$ per meter. I can buy a whole lot of batteries for that. This technology just does not scale since mgh always holds true. Unlike flywheels where you get w^2. Just making the wheel out of carbon fiber and making them go fast, squares the amount of energy you can store.
  - rjmunro 6y ago
    $8000 to dig a 1m hole sounds very high - that's months of someone's salary. Surely the best drilling machines can beat the cost of paying someone with a shovel for a month? But mostly they won't be digging the holes, they will be using shafts left over from earlier mining operations.
    - adrianN 6y ago
      Those prices are probably only true once you go deep enough to require permits, ground water management and all the other complications of very deep holes.
    - LordHeini 6y ago
      That is what i found: https://minewiki.engineering.queensu.ca/mediawiki/index.php/Shaft_construction https://minewiki.engineering.queensu.ca/mediawiki/index.php/... Honestly i would have thought it to be more expensive. At higher depths the ground pressure is enormous and you need a lot of bracing. Then there is water management, air, transportation of the dug out material... When there is rock you usually need blasting or gargantuan drills which i am not sure even exists in the required diameter.
leecarraher 6y ago
this is the new solar panels on everything, 3d print everything, water from air, spectrophotometer is a tricorder... wave of kickstarter-esque ideas that already have relatively well optimized solutions that they will pick on the drawbacks of while admitting none of their own. In this case, it's the maintenance nightmare something like this would be as an underground project with a falling risk.
- eloff 6y ago
  This might not work for economic reasons, but not because of falling risk.
patall 6y ago
I do not know about Gravicity but Heindl Energy (bankrupt as of this year) planned to lift a granite block 500m in radius hydrolicly for an on paper storage capacity of 1614 GWh. source: http://www.eduard-heindl.de/energy-storage/energy-storage-system.html http://www.eduard-heindl.de/energy-storage/energy-storage-sy...
- syllable_studio 6y ago
  Wow, I didn't know they went bankrupt! Sad, thank you Heindl for paving the way forward. Innovation is truly a collaborative effort. https://heindl-energy.com/about-us/ https://heindl-energy.com/about-us/
- tzs 6y ago
  How about combining that with a landfill? Dig a very deep hole with a radius of 500 m, with a 500 m granite block that you can raise and lower in it to store and retrieve energy. When the block is raised, toss trash into the hole. Then when the block is lowered to retrieve energy it also becomes the world's largest trash compactor. Eventually, you'll get enough trash in the hole that even massively compacted you won't have enough room to make the energy storage from raising the block worthwhile. You then have to dig another hole and move the block, leaving behind a full landfill that has more trash in it than a normal landfill of that size would have.
  - patall 6y ago
    I think that neither is compacting trash that much a problem that you need a huge granite block for that (hydraulic press should be sufficient), nor do you want to move a block of granite 1km in diameter more than necessary. The idea by Heindl was to cut the granite cylinder in the place where the plant is build.
syllable_studio 6y ago
Here's the simplest quick answer I have regarding "is it worth it." This is just one example of independent research vetting that it is indeed promising. The math checks out. https://www.storage-lab.com/gravity-based-storage https://www.storage-lab.com/gravity-based-storage
- LordHeini 6y ago
  That research is not independent but made by a bancrupt startup of gravity based energy storage. And it still does not answer how the construction and running costs are calculated. Only if those are as low as claimed (which I highly doubt) something like this might be feasible. This tech just does not scale well. Digging holes is stupid expensive. Moving giant masses is not trivial and to double the storage capacity you need twice the weight or twice the height. The energy density is way too low. The only thing run by weights have been those old grandfather clocks. And even there the weights got replaced by springs and in the end batteries.
  - syllable_studio 6y ago
    My understanding is that Dr Oliver Schmidt was hired by Heindl to do this research independently. It explains everything on the link I sent, so I didn't mean to imply that he wasn't hired to do it, but he's a third party. There is other research like the 1984 U.S. PNNL that validates how underground storage is estimated to be cost effective. https://www.osti.gov/biblio/6517343 https://www.osti.gov/biblio/6517343

gameswithgo 6y ago

Gravitricity is claiming weights as massive as 5,000 tons and shaft depths from 150m to 1,500m

ben_w 6y ago
That’s equivalent to ~83 tons of lithium ion battery: http://www.wolframalpha.com/input/?i=5000%20tons%20%2A%209.8m%2Fs%2Fs%20%2A%201500m%20%2F%20%280.8MJ%2Fkg%29 http://www.wolframalpha.com/input/?i=5000%20tons%20%2A%209.8...
- twic 6y ago
  Ah - so we can measure the specific capacity of a battery in kilometres of altitude. e = mgh, so h = e/mg. Lead-acid = 0.14 MJ/kg = 14.3 km LiFePO4 = 0.58 MJ/kg = 59.1 km LiNiMnCoO2 = 0.74 MJ/kg = 75.5 km
  - ben_w 6y ago
    Yes; how high a fully charged battery could lift itself. I guess it’s similar to counting rocket fuel in seconds (lb_force-seconds per lb_weight).
    - tgb 6y ago
      What's the analogous interpretation of the 'seconds' of a rocket fuel? How long you can burn it for?
      - cstrahan 6y ago
        How long the rocket fuel could offset the force of gravity upon itself, thus suspending itself in-place. In the real world, you'd need the rocket itself (which in turn contains the rocket fuel) which adds weight, and you'd have a difficult time controlling power output so the rocket doesn't drift and lengthen/reduce the burn time -- but that's not the point. The idea is that we want a unit that relates the mass of the fuel with its total energy, and one way to approach that is to consider how long the fuel could offset the force of gravity on that fuel, which gives you a cute unit of measure in terms of time.
  - yongjik 6y ago
    And uranium = 80,620,000 MJ/kg = 8,226,530,612 km[1], or about 180% the distance to Neptune. Sometimes I wish we lived in an alternative world with fully developed nuclear power. Think about the possibilities. And no global warming! :/ [1] Not accurate, obviously.

syllable_studio 6y ago

You're thinking too small though ;). You can dig a mile deep. And you can lift enormous weights. As comments show below. Gravity is weak, but cheap. It can scale up to provide 1 GW of storage - enough to balance the load of an entire large city. Lots of these ideas are popping up right now because it's a very compelling idea which is demonstrated to work. And because climate change is driving massive growth in renewable energy (woot) we will desperately need massive amounts of energy storage in the very new future. The energy storage market is expected to grow massively year over year.

LordHeini 6y ago
Sure you can always get the big option but that does not mean it is feasible. What does it cost to dig and maintain a 1.5km deep shaft? I found is something around 8000-10000$ per meter. I can buy a whole lot of batteries for that. This technology just does not scale since mgh always holds true. Unlike flywheels where you get w^2. Just making the wheel out of carbon fiber and making them go fast, squares the amount of energy you can store.
- rjmunro 6y ago
  $8000 to dig a 1m hole sounds very high - that's months of someone's salary. Surely the best drilling machines can beat the cost of paying someone with a shovel for a month? But mostly they won't be digging the holes, they will be using shafts left over from earlier mining operations.
  - adrianN 6y ago
    Those prices are probably only true once you go deep enough to require permits, ground water management and all the other complications of very deep holes.
  - LordHeini 6y ago
    That is what i found: https://minewiki.engineering.queensu.ca/mediawiki/index.php/Shaft_construction https://minewiki.engineering.queensu.ca/mediawiki/index.php/... Honestly i would have thought it to be more expensive. At higher depths the ground pressure is enormous and you need a lot of bracing. Then there is water management, air, transportation of the dug out material... When there is rock you usually need blasting or gargantuan drills which i am not sure even exists in the required diameter.

leecarraher 6y ago

this is the new solar panels on everything, 3d print everything, water from air, spectrophotometer is a tricorder... wave of kickstarter-esque ideas that already have relatively well optimized solutions that they will pick on the drawbacks of while admitting none of their own. In this case, it's the maintenance nightmare something like this would be as an underground project with a falling risk.

eloff 6y ago
This might not work for economic reasons, but not because of falling risk.

patall 6y ago

I do not know about Gravicity but Heindl Energy (bankrupt as of this year) planned to lift a granite block 500m in radius hydrolicly for an on paper storage capacity of 1614 GWh. source: http://www.eduard-heindl.de/energy-storage/energy-storage-system.html http://www.eduard-heindl.de/energy-storage/energy-storage-sy...

syllable_studio 6y ago
Wow, I didn't know they went bankrupt! Sad, thank you Heindl for paving the way forward. Innovation is truly a collaborative effort. https://heindl-energy.com/about-us/ https://heindl-energy.com/about-us/
tzs 6y ago
How about combining that with a landfill? Dig a very deep hole with a radius of 500 m, with a 500 m granite block that you can raise and lower in it to store and retrieve energy. When the block is raised, toss trash into the hole. Then when the block is lowered to retrieve energy it also becomes the world's largest trash compactor. Eventually, you'll get enough trash in the hole that even massively compacted you won't have enough room to make the energy storage from raising the block worthwhile. You then have to dig another hole and move the block, leaving behind a full landfill that has more trash in it than a normal landfill of that size would have.
- patall 6y ago
  I think that neither is compacting trash that much a problem that you need a huge granite block for that (hydraulic press should be sufficient), nor do you want to move a block of granite 1km in diameter more than necessary. The idea by Heindl was to cut the granite cylinder in the place where the plant is build.

syllable_studio 6y ago

Here's the simplest quick answer I have regarding "is it worth it." This is just one example of independent research vetting that it is indeed promising. The math checks out. https://www.storage-lab.com/gravity-based-storage https://www.storage-lab.com/gravity-based-storage

LordHeini 6y ago
That research is not independent but made by a bancrupt startup of gravity based energy storage. And it still does not answer how the construction and running costs are calculated. Only if those are as low as claimed (which I highly doubt) something like this might be feasible. This tech just does not scale well. Digging holes is stupid expensive. Moving giant masses is not trivial and to double the storage capacity you need twice the weight or twice the height. The energy density is way too low. The only thing run by weights have been those old grandfather clocks. And even there the weights got replaced by springs and in the end batteries.
- syllable_studio 6y ago
  My understanding is that Dr Oliver Schmidt was hired by Heindl to do this research independently. It explains everything on the link I sent, so I didn't mean to imply that he wasn't hired to do it, but he's a third party. There is other research like the 1984 U.S. PNNL that validates how underground storage is estimated to be cost effective. https://www.osti.gov/biblio/6517343 https://www.osti.gov/biblio/6517343