5 ms·

You are right, of course, but I wonder if you couldn't use "waste heat" as the energy input of this "heat battery"? This would make the economics much better: i

You are right, of course, but I wonder if you couldn't use "waste heat" as the energy input of this "heat battery"? This would make the economics much better: instead of going, say, nuclear -> steam engine -> electricity -> iron -> heat (-> electricity), you could skip the first conversion losses. Not sure how doable it would be from a chemistry point of view, though: you probably need at least one extra reagent or catalyst.

abdusco 6y ago
Source temperature of waste heat is an important factor. Heat radiating from a 2000C source is a lot more valuable & useful than that from some warm water at 60C. You can't use that heat to raise the temperature of something to 61C, for example.
- rocqua 6y ago
  But you could use a heat pump and 60C water to raise the temperature of something to 61C. And would take a lot less energy to run that heat-pump than to actually heat that something to 61C. What I've become interested in, is how easy it is to 'abuse' heat pumps like this. Could you take a heat-pump and this 60C water to heat a boiler to the point you can run a steam-turbine that produces more energy than it takes to run the heat-pump? If not at 60C water, does this work at any temperature? There remains free energy in the temperature differential between an ambient 21C and the temperature of warmer water. It seems to me this should be harvest able. There are significant limits here from the Carnot theory, but they don't say this is impossible.
  - jjk166 6y ago
    No that explicitly violates the second law of thermodynamics. A heat pump is like a water pump: it's a lot easier to move water to a tank 61 feet off the ground from another tank 60 feet off the ground than from ground level, but you can't power the pump producing 1 foot of pressure head with a turbine being driven by 1 foot of pressure head.
    - JoeAltmaier 6y ago
      Well, not without losing some water in the process. If you spill 10 gallons of water through the pump to pump 1 upward, sure that works.
      - MayeulC 6y ago
        And this is the exact idea behind ram pumps: https://en.wikipedia.org/wiki/Hydraulic_ram https://en.wikipedia.org/wiki/Hydraulic_ram
      - jjk166 6y ago
        Well in this case you need to pump 10 gallons up to get those 10 gallons to spill down. At some point in the chain, you need to consume energy from the environment to drive the system.
        MayeulC 6y ago
        > At some point in the chain, you need to consume energy from the environment to drive the system. Agreed, that's where spilling water comes into play: ┌───┐ ┃ A ┊┃ │ ┗━━━━━┛ │ │ │┃┈┈┈┈┈┈┈┈┃ └┨ B ┃ ┗━━━━━┳━━┛ ┇ ┃ C ┇ ┃ ┗━━━━━━┛ Here, B->A is driven by B->C spillage. The critical point here is that B is a low quality source, but plentiful. rocqua's point was likely similar, if you replace height with thermal energy. You can't use the energy you put in A to move it from B to A, because it costs you at least as much to move it up. However, we're not bringing it down to B. We're bringing it down to C (ambient 21°C in their example). There will be losses, but shouldn't it be doable, depending on the B-C potential? Wouldn't Peltier modules be 100% efficient in theory for rising B to A (as long as thermal losses go to the hot side, that is: tey keep a side cooler), for instance? If so, the generated energy is the one stored between A and C, minus conversion losses, minus A-B. That is, B-C minus conversions losses from A-C. Probably not very efficient at the end, though worth it if you have plenty of B (and a excellent "C" sink).
        6y ago
lambdatronics 6y ago
For short-term storage at a nuclear plant, you could use molten salt thermal storage. In terms of a 'battery,' decomposing ammonia to H2+N2 is one way to directly convert heat to chemical stored energy: https://eeme.anu.edu.au/research/research-projects/ammonia-based-energy-storage https://eeme.anu.edu.au/research/research-projects/ammonia-b... There are other more complex processes like the sulfur-iodine cycle that was investigated for producing hydrogen from nuclear heat: https://en.wikipedia.org/wiki/Sulfur%E2%80%93iodine_cycle https://en.wikipedia.org/wiki/Sulfur%E2%80%93iodine_cycle As far as I can tell, these processes are probably less economical than generating electricity & then doing electrolysis.

abdusco 6y ago

Source temperature of waste heat is an important factor. Heat radiating from a 2000C source is a lot more valuable & useful than that from some warm water at 60C. You can't use that heat to raise the temperature of something to 61C, for example.

rocqua 6y ago
But you could use a heat pump and 60C water to raise the temperature of something to 61C. And would take a lot less energy to run that heat-pump than to actually heat that something to 61C. What I've become interested in, is how easy it is to 'abuse' heat pumps like this. Could you take a heat-pump and this 60C water to heat a boiler to the point you can run a steam-turbine that produces more energy than it takes to run the heat-pump? If not at 60C water, does this work at any temperature? There remains free energy in the temperature differential between an ambient 21C and the temperature of warmer water. It seems to me this should be harvest able. There are significant limits here from the Carnot theory, but they don't say this is impossible.
- jjk166 6y ago
  No that explicitly violates the second law of thermodynamics. A heat pump is like a water pump: it's a lot easier to move water to a tank 61 feet off the ground from another tank 60 feet off the ground than from ground level, but you can't power the pump producing 1 foot of pressure head with a turbine being driven by 1 foot of pressure head.
  - JoeAltmaier 6y ago
    Well, not without losing some water in the process. If you spill 10 gallons of water through the pump to pump 1 upward, sure that works.
    - MayeulC 6y ago
      And this is the exact idea behind ram pumps: https://en.wikipedia.org/wiki/Hydraulic_ram https://en.wikipedia.org/wiki/Hydraulic_ram
    - jjk166 6y ago
      Well in this case you need to pump 10 gallons up to get those 10 gallons to spill down. At some point in the chain, you need to consume energy from the environment to drive the system.
      - MayeulC 6y ago
        > At some point in the chain, you need to consume energy from the environment to drive the system. Agreed, that's where spilling water comes into play: ┌───┐ ┃ A ┊┃ │ ┗━━━━━┛ │ │ │┃┈┈┈┈┈┈┈┈┃ └┨ B ┃ ┗━━━━━┳━━┛ ┇ ┃ C ┇ ┃ ┗━━━━━━┛ Here, B->A is driven by B->C spillage. The critical point here is that B is a low quality source, but plentiful. rocqua's point was likely similar, if you replace height with thermal energy. You can't use the energy you put in A to move it from B to A, because it costs you at least as much to move it up. However, we're not bringing it down to B. We're bringing it down to C (ambient 21°C in their example). There will be losses, but shouldn't it be doable, depending on the B-C potential? Wouldn't Peltier modules be 100% efficient in theory for rising B to A (as long as thermal losses go to the hot side, that is: tey keep a side cooler), for instance? If so, the generated energy is the one stored between A and C, minus conversion losses, minus A-B. That is, B-C minus conversions losses from A-C. Probably not very efficient at the end, though worth it if you have plenty of B (and a excellent "C" sink).
        6y ago

lambdatronics 6y ago

For short-term storage at a nuclear plant, you could use molten salt thermal storage. In terms of a 'battery,' decomposing ammonia to H2+N2 is one way to directly convert heat to chemical stored energy: https://eeme.anu.edu.au/research/research-projects/ammonia-based-energy-storage https://eeme.anu.edu.au/research/research-projects/ammonia-b... There are other more complex processes like the sulfur-iodine cycle that was investigated for producing hydrogen from nuclear heat: https://en.wikipedia.org/wiki/Sulfur%E2%80%93iodine_cycle https://en.wikipedia.org/wiki/Sulfur%E2%80%93iodine_cycle As far as I can tell, these processes are probably less economical than generating electricity & then doing electrolysis.