4 ms·

I think you can store energy here not just in the gravitational potential energy of the water, but also in the compression of the air. I _think_ this means that

by foota 2y ago

I think you can store energy here not just in the gravitational potential energy of the water, but also in the compression of the air. I _think_ this means that you can get away with a smaller cavern than you could for just pumped hydro. You might think that you'd need a large amount of water to make the energy release work, but I think it works like this. The force of the water on the air/water interface is dependent not on the reservoir volume, but on the weight of the water in the column (which depends only on the height of the shaft). By digging a very deep shaft, you can have a very large force of water on the interface, and moving that interface an equal distance hence releases more energy than it would with a shorter shaft. This way, you can store an arbitrary (up to your ability to compress air to a sufficient pressure, dig a deep shaft, and keep everything from blowing up) amount of energy. I think if you have a 1 square meter cross section of shaft, and the shaft is 1 kilometer deep, then at the bottom the force of the water above is the weight of 1 square meter * 1 kilometer, or 1000 cubic meters of water, or 1 million kg. The force then is 9.8×10^6 newtons. Pressure is force/area, or 9.8×10^6 newtons/square meter here (since we have a unit area). There's a formula for the energy in compressed air, it's... involved. I downloaded an excel file from here: https://ehs.berkeley.edu/publications/calculating-stored-energy-pressurized-gas-vessel https://ehs.berkeley.edu/publications/calculating-stored-ene... It says under this pressure, a 1000 cubic meter tank of air at this pressure stores ~5000 KWh. The one planned in California is supposed to store 4000 MWh, so I guess they have a tank that is ~a million cubic meters. A water tank of the same size would store ~2700 MWh of energy (e.g., pumping that much water up a 1KM shaft requires that much energy), so it does seem to be more efficient. It may also be that hot air turbines are cheaper and easier to maintain than hydropower turbines, but I'm not certain.

trenchgun 2y ago
>I think you can store energy here not just in the gravitational potential energy of the water, but also in the compression of the air. I _think_ this means that you can get away with a smaller cavern than you could for just pumped hydro. + they are storing the heat extracted from compressing the air.
- lucioperca 2y ago
  isn't that used when decompressing the air, i.e. closed loop
  - jagged-chisel 2y ago
    You just pull that from the atmosphere. Compress to store [potential] energy, take the heat generated during compression and use it, decompress at time of need and let the [hot?] atmosphere supply energy to the decompressing gas. I wouldn’t call it a closed loop, but maybe a lack of deficit.
- fanf2 2y ago
  I want to know how this heat storage works. It seems kind of important?
logtempo 2y ago
also water tend to be scarse nowaday and valuable nowaday.
- 867-5309 2y ago
  they say, writing from an ocean planet
  - droopyEyelids 2y ago
    Salt water is a nightmare to include in any sort of mechanical system. It is super corrosive itself, enables galvanic corrosion, and is so “fertile” biologic fouling is a big issue.
  - logtempo 2y ago
    You don't want to put salt water in the ground. It will destroy either the soil or the aquifer.
pjc50 2y ago
> The force of the water on the air/water interface is dependent not on the reservoir volume, but on the weight of the water in the column (which depends only on the height of the shaft). Just wanted to highlight this, since it's the key insight which caused this to "click" for me. The difference between a 1km shaft and a 1km deep reservoir, when both are used for pumped hydro, is the amount of energy stored. Running a turbine at the bottom of the shaft (to where?!) would drain very quickly. But using air, which has very different properties, enables you to use the water as a "piston" to keep the air at a certain constant pressure underground. And you can store a larger volume of (more compressible) air in a space which is easier to access.
westurner 2y ago
Is there any pump efficiency advantage to multiple pressure vessels instead of one large? You could probably move the compressed air in a GPE gravitational potential energy storage system, or haul it up on a winch and set it on a shelf; but would the lateral vectors due to thrust from predictable leakage change the safety liabilities? Air with extra CO2 is less of an accelerant, but at what concentration of CO2 does the facility need air tanks for hazard procedures? FWIU, you can also get energy from a CO2 gradient: "Proof-of-concept nanogenerator turns CO₂ into sustainable power" (2024) https://news.ycombinator.com/item?id=40079784 https://news.ycombinator.com/item?id=40079784 And, CO2 + Lignin => Better than plastic; "CO2 and Lignin-Based Sustainable Polymers with Closed-Loop Chemical Recycling" (2024) https://news.ycombinator.com/item?id=40079540 https://news.ycombinator.com/item?id=40079540 From "Oxxcu, converting CO₂ into fuels, chemicals and plastics" https://news.ycombinator.com/item?id=39111825 https://news.ycombinator.com/item?id=39111825 : > "Solar energy can now be stored for up to 18 years [with the Szilard-Chalmers MOST process], say scientists" > [...] Though, you could do CAES with captured CO2 and it would be less of an accelerant than standard compressed air. How many CO2 fire extinguishers can be filled and shipped off-site per day? > Can CO2 can be made into QA'd [graphene] air filters for [onsite] [flue] capture? "Geothermal may beat batteries for energy storage" (2022) https://news.ycombinator.com/item?id=33288586 https://news.ycombinator.com/item?id=33288586 : > FWIU China has the first 100MW CAES plant; and it uses some external energy - not a trompe or geothermal (?) - to help compress air on a FWIU currently ~one-floor facility.
eastbound 2y ago
Did you mean 5000KWh (air) and 2700KWh (water), or MWh for the second? Also, 1000m3 in air is just a cube of 10m. It seems like a good illustration of the convenience of air vs water.
- foota 2y ago
  The same size here is a million cubic meters, what I figure the size of the planned California plant must be in order to store 4000MWH.

by foota 2y ago

trenchgun 2y ago

>I think you can store energy here not just in the gravitational potential energy of the water, but also in the compression of the air. I _think_ this means that you can get away with a smaller cavern than you could for just pumped hydro. + they are storing the heat extracted from compressing the air.

lucioperca 2y ago
isn't that used when decompressing the air, i.e. closed loop
- jagged-chisel 2y ago
  You just pull that from the atmosphere. Compress to store [potential] energy, take the heat generated during compression and use it, decompress at time of need and let the [hot?] atmosphere supply energy to the decompressing gas. I wouldn’t call it a closed loop, but maybe a lack of deficit.
fanf2 2y ago
I want to know how this heat storage works. It seems kind of important?

logtempo 2y ago

also water tend to be scarse nowaday and valuable nowaday.

867-5309 2y ago
they say, writing from an ocean planet
- droopyEyelids 2y ago
  Salt water is a nightmare to include in any sort of mechanical system. It is super corrosive itself, enables galvanic corrosion, and is so “fertile” biologic fouling is a big issue.
- logtempo 2y ago
  You don't want to put salt water in the ground. It will destroy either the soil or the aquifer.

pjc50 2y ago

> The force of the water on the air/water interface is dependent not on the reservoir volume, but on the weight of the water in the column (which depends only on the height of the shaft). Just wanted to highlight this, since it's the key insight which caused this to "click" for me. The difference between a 1km shaft and a 1km deep reservoir, when both are used for pumped hydro, is the amount of energy stored. Running a turbine at the bottom of the shaft (to where?!) would drain very quickly. But using air, which has very different properties, enables you to use the water as a "piston" to keep the air at a certain constant pressure underground. And you can store a larger volume of (more compressible) air in a space which is easier to access.

westurner 2y ago

Is there any pump efficiency advantage to multiple pressure vessels instead of one large? You could probably move the compressed air in a GPE gravitational potential energy storage system, or haul it up on a winch and set it on a shelf; but would the lateral vectors due to thrust from predictable leakage change the safety liabilities? Air with extra CO2 is less of an accelerant, but at what concentration of CO2 does the facility need air tanks for hazard procedures? FWIU, you can also get energy from a CO2 gradient: "Proof-of-concept nanogenerator turns CO₂ into sustainable power" (2024) https://news.ycombinator.com/item?id=40079784 https://news.ycombinator.com/item?id=40079784 And, CO2 + Lignin => Better than plastic; "CO2 and Lignin-Based Sustainable Polymers with Closed-Loop Chemical Recycling" (2024) https://news.ycombinator.com/item?id=40079540 https://news.ycombinator.com/item?id=40079540 From "Oxxcu, converting CO₂ into fuels, chemicals and plastics" https://news.ycombinator.com/item?id=39111825 https://news.ycombinator.com/item?id=39111825 : > "Solar energy can now be stored for up to 18 years [with the Szilard-Chalmers MOST process], say scientists" > [...] Though, you could do CAES with captured CO2 and it would be less of an accelerant than standard compressed air. How many CO2 fire extinguishers can be filled and shipped off-site per day? > Can CO2 can be made into QA'd [graphene] air filters for [onsite] [flue] capture? "Geothermal may beat batteries for energy storage" (2022) https://news.ycombinator.com/item?id=33288586 https://news.ycombinator.com/item?id=33288586 : > FWIU China has the first 100MW CAES plant; and it uses some external energy - not a trompe or geothermal (?) - to help compress air on a FWIU currently ~one-floor facility.

eastbound 2y ago

Did you mean 5000KWh (air) and 2700KWh (water), or MWh for the second? Also, 1000m3 in air is just a cube of 10m. It seems like a good illustration of the convenience of air vs water.

foota 2y ago
The same size here is a million cubic meters, what I figure the size of the planned California plant must be in order to store 4000MWH.