7 ms·

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 scal

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
  $8000 to dig a 1m hole sounds very high - that's months of someone's salary. Surely the best drilling machines can beat the cost of paying someone with a shovel for a month? But mostly they won't be digging the holes, they will be using shafts left over from earlier mining operations.
  - adrianN 6y ago
    Those prices are probably only true once you go deep enough to require permits, ground water management and all the other complications of very deep holes.
  - LordHeini 6y ago
    That is what i found: https://minewiki.engineering.queensu.ca/mediawiki/index.php/Shaft_construction https://minewiki.engineering.queensu.ca/mediawiki/index.php/... Honestly i would have thought it to be more expensive. At higher depths the ground pressure is enormous and you need a lot of bracing. Then there is water management, air, transportation of the dug out material... When there is rock you usually need blasting or gargantuan drills which i am not sure even exists in the required diameter.
  - satisfaction 6y ago
    OH come on, I'm sure you can imagine the complexity of digging grows as the depth grows. the first meter would cost 100$ the second 150$, the 3rd 200$, the fourth 500$ the fifth 550$, the sixth 600$, etc.
- gameswithgo 6y ago
  batteries don’t last as long as a hole. some holes already exist.
  - eitland 6y ago
    Meaningfully deep holes in the ground require some maintenance as well.
    - falcolas 6y ago
      One of the biggest is groundwater removal. Behind that would be the maintenance of shoring materials in the face of earthquakes, and ensuring that it remains straight in the face of earth movement.
- syllable_studio 6y ago
  yup it's feasible. It does scale. Here are two links to research that support the feasibility and cost effectiveness of underground gravity storage. https://www.storage-lab.com/gravity-based-storage https://www.storage-lab.com/gravity-based-storage https://www.osti.gov/biblio/6517343 https://www.osti.gov/biblio/6517343
sandworm101 6y ago
>> the load of an entire large city. Maybe if you are lifting the entire city. For perspective, take electric vehicles. Each moving EV is a mass being constantly accelerated at say 0.1G. So the weight in the graviticity system to power those EVs would have to be at least 10% of the mass of all the EVs active in a city.
- syllable_studio 6y ago
  I just mean for load balancing a city running on wind and solar to optimize their costs.
- jberryman 6y ago
  > Maybe if you are lifting the entire city. This would be a really cool element in a sci-fi world
  - syllable_studio 6y ago
    A long time ago I did the napkin math to check if it'd be worth it to lift a skyscraper up and down just slightly for energy storage. You know, you'd just use adjusting ramps as the height changed ever so slowly. Not surprisingly, it's surely not worth it. The empire state building could run some tea kettles, but, yeah, no.
    - dTal 6y ago
      I calculate a rather better figure for the Empire State Building: 365000 tons × 9.81 m/s2 × 1 m = 1 MWh which ought to at least be enough to provide short term backup power to the whole building.
    - smegcicle 6y ago
      Japanese TECOREP brand demolition system generates power as it lowers material down from skyscrapers https://sipilpedia.com/tecorep-system-high-tech-demolition-systems-for-high-rises/ https://sipilpedia.com/tecorep-system-high-tech-demolition-s...
- 6y ago
gspr 6y ago
> You're thinking too small though ;). You can dig a mile deep. And you can lift enormous weights. But at that point, why wouldn't you just do a classic pumped-storage reservoir?
- syllable_studio 6y ago
  Because as noted in other comments here, all the best natural pumped-storage reservoirs are tapped. It's not feasible to build enough dams in enough places to get the job done. Furthermore, my most optimistic estimates show that underground solid mass gravity storage could compete with pumped hydro on cost anyways. One reason is that solid mass is about 2.5x heavier than water. If excavation is one of your biggest costs, this density is important.
bufferoverflow 6y ago
The deeper you dig, the heavier your cable is, and the more energy you waste on accelerating that cable. And the much bigger issue is, you have to constantly pump out water that will inevitably fill the hole. And that only costs you money.
- jungturk 6y ago
  But the water leaking in is a feature, not a bug! You run pumps during surplus periods and generate hydroelectric in demand periods as the tunnel floods.
  - bufferoverflow 6y ago
    No, it's not a feature. It's a massive problem. 1) Pumps that can pump water 150 meters or a kilometer high are very expensive and require constant expensive maintenance. 2) Where will you pump the water to? Now you have to build huge storage tanks. 3) The water never stops flowing in. Sooner or later you will run out of storage space and your expensive hole will fill up with water.
    - Ma8ee 6y ago
      Maybe pump the water to the nearest river? As long as you aren’t digging from the lowest point in the landscape it won’t be a problem to get rid of the water.
- gameswithgo 6y ago
  seems the water could be a secondary energy source, and the cable energy wouldn’t be wasted, thats just more mass to lift and drop.
  - eloff 6y ago
    Do tell how you generate energy from water at the bottom of a gravity well.
    - 6y ago
bassman9000 6y ago
FTA Each unit can be configured to produce between 1 and 20MW peak power, with output duration from 15 minutes to 8 hours. For reference, 20MW is ~4 large aerogenerators. A single nuclear PWR is 500-1000MW. It can scale up to provide 1 GW of storage - enough to balance the load of an entire large city. You'd need 50 of these installations for a single city, for 15 minutes of power, 1000 for the 8 hours.

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
$8000 to dig a 1m hole sounds very high - that's months of someone's salary. Surely the best drilling machines can beat the cost of paying someone with a shovel for a month? But mostly they won't be digging the holes, they will be using shafts left over from earlier mining operations.
- adrianN 6y ago
  Those prices are probably only true once you go deep enough to require permits, ground water management and all the other complications of very deep holes.
- LordHeini 6y ago
  That is what i found: https://minewiki.engineering.queensu.ca/mediawiki/index.php/Shaft_construction https://minewiki.engineering.queensu.ca/mediawiki/index.php/... Honestly i would have thought it to be more expensive. At higher depths the ground pressure is enormous and you need a lot of bracing. Then there is water management, air, transportation of the dug out material... When there is rock you usually need blasting or gargantuan drills which i am not sure even exists in the required diameter.
- satisfaction 6y ago
  OH come on, I'm sure you can imagine the complexity of digging grows as the depth grows. the first meter would cost 100$ the second 150$, the 3rd 200$, the fourth 500$ the fifth 550$, the sixth 600$, etc.
gameswithgo 6y ago
batteries don’t last as long as a hole. some holes already exist.
- eitland 6y ago
  Meaningfully deep holes in the ground require some maintenance as well.
  - falcolas 6y ago
    One of the biggest is groundwater removal. Behind that would be the maintenance of shoring materials in the face of earthquakes, and ensuring that it remains straight in the face of earth movement.
syllable_studio 6y ago
yup it's feasible. It does scale. Here are two links to research that support the feasibility and cost effectiveness of underground gravity storage. https://www.storage-lab.com/gravity-based-storage https://www.storage-lab.com/gravity-based-storage https://www.osti.gov/biblio/6517343 https://www.osti.gov/biblio/6517343

sandworm101 6y ago

>> the load of an entire large city. Maybe if you are lifting the entire city. For perspective, take electric vehicles. Each moving EV is a mass being constantly accelerated at say 0.1G. So the weight in the graviticity system to power those EVs would have to be at least 10% of the mass of all the EVs active in a city.

syllable_studio 6y ago
I just mean for load balancing a city running on wind and solar to optimize their costs.
jberryman 6y ago
> Maybe if you are lifting the entire city. This would be a really cool element in a sci-fi world
- syllable_studio 6y ago
  A long time ago I did the napkin math to check if it'd be worth it to lift a skyscraper up and down just slightly for energy storage. You know, you'd just use adjusting ramps as the height changed ever so slowly. Not surprisingly, it's surely not worth it. The empire state building could run some tea kettles, but, yeah, no.
  - dTal 6y ago
    I calculate a rather better figure for the Empire State Building: 365000 tons × 9.81 m/s2 × 1 m = 1 MWh which ought to at least be enough to provide short term backup power to the whole building.
  - smegcicle 6y ago
    Japanese TECOREP brand demolition system generates power as it lowers material down from skyscrapers https://sipilpedia.com/tecorep-system-high-tech-demolition-systems-for-high-rises/ https://sipilpedia.com/tecorep-system-high-tech-demolition-s...
6y ago

gspr 6y ago

> You're thinking too small though ;). You can dig a mile deep. And you can lift enormous weights. But at that point, why wouldn't you just do a classic pumped-storage reservoir?

syllable_studio 6y ago
Because as noted in other comments here, all the best natural pumped-storage reservoirs are tapped. It's not feasible to build enough dams in enough places to get the job done. Furthermore, my most optimistic estimates show that underground solid mass gravity storage could compete with pumped hydro on cost anyways. One reason is that solid mass is about 2.5x heavier than water. If excavation is one of your biggest costs, this density is important.

bufferoverflow 6y ago

The deeper you dig, the heavier your cable is, and the more energy you waste on accelerating that cable. And the much bigger issue is, you have to constantly pump out water that will inevitably fill the hole. And that only costs you money.

jungturk 6y ago
But the water leaking in is a feature, not a bug! You run pumps during surplus periods and generate hydroelectric in demand periods as the tunnel floods.
- bufferoverflow 6y ago
  No, it's not a feature. It's a massive problem. 1) Pumps that can pump water 150 meters or a kilometer high are very expensive and require constant expensive maintenance. 2) Where will you pump the water to? Now you have to build huge storage tanks. 3) The water never stops flowing in. Sooner or later you will run out of storage space and your expensive hole will fill up with water.
  - Ma8ee 6y ago
    Maybe pump the water to the nearest river? As long as you aren’t digging from the lowest point in the landscape it won’t be a problem to get rid of the water.
gameswithgo 6y ago
seems the water could be a secondary energy source, and the cable energy wouldn’t be wasted, thats just more mass to lift and drop.
- eloff 6y ago
  Do tell how you generate energy from water at the bottom of a gravity well.
  - 6y ago

bassman9000 6y ago

FTA Each unit can be configured to produce between 1 and 20MW peak power, with output duration from 15 minutes to 8 hours. For reference, 20MW is ~4 large aerogenerators. A single nuclear PWR is 500-1000MW. It can scale up to provide 1 GW of storage - enough to balance the load of an entire large city. You'd need 50 of these installations for a single city, for 15 minutes of power, 1000 for the 8 hours.