4 ms·

You'd still need to capture/sequester the CO2, which to me sounds much harder (or else you're only solving the "renewable" part rather than the global warming p

You'd still need to capture/sequester the CO2, which to me sounds much harder (or else you're only solving the "renewable" part rather than the global warming part). Water is nice because it naturally precipitates out of the atmosphere and returns to oceans/lakes/etc.

api 7y ago
CO2 + 2H2O + energy -> CH4 + 2O2 Discharging the battery is this reaction in reverse. It's net zero carbon. It's basically a rechargeable fuel air battery using incredibly abundant materials so it can scale.
- stefco_ 7y ago
  Right. My point is that, as with a battery, you'd need to store the product so you can reverse the reaction. Practically none of our current infrastructure for using CH4 is set up to store the output CO2 + H20; it just dumps it into the atmosphere. If you want to reuse existing CH4 distribution pipelines, that's fine, but now you need to pipe back the CO2 to the plant that makes the CH4 in order to complete the cycle. That's much harder than pumping CH4 and would require a whole new parallel pipeline infrastructure that can transport highly pressurized CO2 back to the source plant. Alternatively, you could regenerate the CH4 on location, but then you need to pipe the energy in; in that case, you're not using CH4 to deliver energy at all. You could make the CH4 from CO2 in coal or something, but then you're no longer carbon neutral (since that CO2 will end up in the atmosphere rather than the battery). You could also try carbon capture, but honestly thermodynamics suggests that that will never be a viable solution; far easier to order your coffee black than to unmix the cream from it. My point is that, unless I'm misunderstanding something, existing distribution systems for natural gas are not useful for CH4-based battery storage.
  - pdonis 7y ago
    > My point is that, as with a battery, you'd need to store the product so you can reverse the reaction. No, you wouldn't, because CO2 is everywhere in the atmosphere. The methane making plant draws CO2 from the air around it; discharging batteries emit CO2 into the air around them. It's no different from plants taking in CO2 and animals breathing it out.
    - _Microft 7y ago
      It's not necessary, just very advisable to do it. The lower the concentration is, the harder it gets to extract something. Ideally CO_2 is captured where it is concentrated the most, i.e. right after generating it.
      - gus_massa 7y ago
        Most of the concentrated sources of CO2 are used to produce energy. The equation is like something + O2 --> CO2 + energy We want energy. The problem is that we want energy. If you try to reverse it with CO2 + more energy --> something + O2 the problem is that you need more energy to reverse the reaction. If you stick one 100% carbon capture magical device to a power plant, you will not produce any energy in the power plant. Moreover you will need to buy a lot of energy. There are some process that emit a lot of CO2, but use it mostly for the chemical reactions and not to extract energy like in cement production [1] and somewhat in blast furnaces [2]. You can capture the CO2 produced by them to get guilty free cement or steel, but is much much much more efficient to use the energy to replace the energy of a power plant that burns coal / oil / whatever. (Call it carbon emission trading.) Once we close all the power plants that burn coal / oil / whatever, it can be useful to add carbon capture. [1] https://en.wikipedia.org/wiki/Cement#CO2_emissions https://en.wikipedia.org/wiki/Cement#CO2_emissions [2] https://en.wikipedia.org/wiki/Blast_furnace#Process_engineering_and_chemistry https://en.wikipedia.org/wiki/Blast_furnace#Process_engineer...
    - zajio1am 7y ago
      What i understood that methane production needs concentrated CO2. It is possible to get that from air, but it is energy inefficient.
- gus_massa 7y ago
  For comparison, the efficiency of photosynthesis is something like 1% (probably 2% in C4) but the result is glucose instead of methane. Most organic reactions have a very low result, I'd be surprised if your reaction has more than a 10%. Most of the time the molecules have another opinion about how to combine and they don't produce what you want. And there is also a problem with the combustion, in a gas turbine you have only an efficiency up to 65%. So it's a very ineffective battery.
  - thaumasiotes 7y ago
    > Most of the time the molecules have another opinion about how to combine and they don't produce what you want. For energy storage, this is, by definition, all of the time. The fact that the molecules have a different opinion of how they should combine is what gives potential energy to the form we produce in the first place.
    - gus_massa 7y ago
      My handwave chemistry is not strong enough to be sure, but I expect that this will form also a small amount of ethane (that is not a problem) and also some soot like goo that will clog the battery and be difficult to burn cleanly anyway.
  - semi-extrinsic 7y ago
    If we want to do combustion in a gas turbine as a "battery" for the grid, then electrolysis -> hydrogen -> hydrogen burning gas turbine has a ridiculously superior efficiency and CAPEX compared to going via methane. All the big players for stationary gas turbines are bringing hydrogen as a fuel forward at a rapid rate. I believe the current plan for the first full-scale hydrogen gas turbine (400+ MW) is the Magnum powerplant in 2025-ish.

api 7y ago

CO2 + 2H2O + energy -> CH4 + 2O2 Discharging the battery is this reaction in reverse. It's net zero carbon. It's basically a rechargeable fuel air battery using incredibly abundant materials so it can scale.

stefco_ 7y ago
Right. My point is that, as with a battery, you'd need to store the product so you can reverse the reaction. Practically none of our current infrastructure for using CH4 is set up to store the output CO2 + H20; it just dumps it into the atmosphere. If you want to reuse existing CH4 distribution pipelines, that's fine, but now you need to pipe back the CO2 to the plant that makes the CH4 in order to complete the cycle. That's much harder than pumping CH4 and would require a whole new parallel pipeline infrastructure that can transport highly pressurized CO2 back to the source plant. Alternatively, you could regenerate the CH4 on location, but then you need to pipe the energy in; in that case, you're not using CH4 to deliver energy at all. You could make the CH4 from CO2 in coal or something, but then you're no longer carbon neutral (since that CO2 will end up in the atmosphere rather than the battery). You could also try carbon capture, but honestly thermodynamics suggests that that will never be a viable solution; far easier to order your coffee black than to unmix the cream from it. My point is that, unless I'm misunderstanding something, existing distribution systems for natural gas are not useful for CH4-based battery storage.
- pdonis 7y ago
  > My point is that, as with a battery, you'd need to store the product so you can reverse the reaction. No, you wouldn't, because CO2 is everywhere in the atmosphere. The methane making plant draws CO2 from the air around it; discharging batteries emit CO2 into the air around them. It's no different from plants taking in CO2 and animals breathing it out.
  - _Microft 7y ago
    It's not necessary, just very advisable to do it. The lower the concentration is, the harder it gets to extract something. Ideally CO_2 is captured where it is concentrated the most, i.e. right after generating it.
    - gus_massa 7y ago
      Most of the concentrated sources of CO2 are used to produce energy. The equation is like something + O2 --> CO2 + energy We want energy. The problem is that we want energy. If you try to reverse it with CO2 + more energy --> something + O2 the problem is that you need more energy to reverse the reaction. If you stick one 100% carbon capture magical device to a power plant, you will not produce any energy in the power plant. Moreover you will need to buy a lot of energy. There are some process that emit a lot of CO2, but use it mostly for the chemical reactions and not to extract energy like in cement production [1] and somewhat in blast furnaces [2]. You can capture the CO2 produced by them to get guilty free cement or steel, but is much much much more efficient to use the energy to replace the energy of a power plant that burns coal / oil / whatever. (Call it carbon emission trading.) Once we close all the power plants that burn coal / oil / whatever, it can be useful to add carbon capture. [1] https://en.wikipedia.org/wiki/Cement#CO2_emissions https://en.wikipedia.org/wiki/Cement#CO2_emissions [2] https://en.wikipedia.org/wiki/Blast_furnace#Process_engineering_and_chemistry https://en.wikipedia.org/wiki/Blast_furnace#Process_engineer...
  - zajio1am 7y ago
    What i understood that methane production needs concentrated CO2. It is possible to get that from air, but it is energy inefficient.
gus_massa 7y ago
For comparison, the efficiency of photosynthesis is something like 1% (probably 2% in C4) but the result is glucose instead of methane. Most organic reactions have a very low result, I'd be surprised if your reaction has more than a 10%. Most of the time the molecules have another opinion about how to combine and they don't produce what you want. And there is also a problem with the combustion, in a gas turbine you have only an efficiency up to 65%. So it's a very ineffective battery.
- thaumasiotes 7y ago
  > Most of the time the molecules have another opinion about how to combine and they don't produce what you want. For energy storage, this is, by definition, all of the time. The fact that the molecules have a different opinion of how they should combine is what gives potential energy to the form we produce in the first place.
  - gus_massa 7y ago
    My handwave chemistry is not strong enough to be sure, but I expect that this will form also a small amount of ethane (that is not a problem) and also some soot like goo that will clog the battery and be difficult to burn cleanly anyway.
- semi-extrinsic 7y ago
  If we want to do combustion in a gas turbine as a "battery" for the grid, then electrolysis -> hydrogen -> hydrogen burning gas turbine has a ridiculously superior efficiency and CAPEX compared to going via methane. All the big players for stationary gas turbines are bringing hydrogen as a fuel forward at a rapid rate. I believe the current plan for the first full-scale hydrogen gas turbine (400+ MW) is the Magnum powerplant in 2025-ish.