Liquid CO2 energy storage

[farmerben]

I'm not convinced humans must to sequester carbon dioxide.  But if we did, what other potential benefits could we get from it?

I wonder if the economics of it could work for batteries.  The power density of liquid CO2 is greater than compressed air.  The economics of electricity-compressed electricity-gas-electricity is between 40%-50% compared to >75% for hydro and chemical storage.  

The storage capacity for liquid CO2 is much greater than I realized until recently.  At depths of >1000 ft below the ground the pressure is already there to hold CO2 in the liquid state.  If we don't get nuclear and are forced to rely on wind and solar, these reservoirs may be important for grid level batteries.  

Those CO2 cartridges found BB guns have relatively little energy compared to the same weight in batteries and thus are only good for niche applications (woodworking tools perhaps).  The economy of tank scale gets better as we get larger, but we are nowhere close to competing with methane combustion in total energy.  At some facilities that would be OK.  Forklifts, airport vehicles, etc could recharge in seconds and run for a while.  They would be much, much lighter than battery electric vehicles.  Air motors are very light compared to electric.  

At the moment it seems like spending a dollar and getting 50 cents back, but that is sorta the deal with solar energy anyway.

 

Edited November 25, 2019 by farmerben

[mikegarrison]

This makes no sense. The whole point of sequestering CO2 is to get rid of it. Using it like you propose would mean releasing it, wouldn't it?

I also don't understand the supposed reference to solar energy. Mechanically storing energy does not give us any newly accessible energy. It just stores energy we already have (and always with less than 100% efficiency). Solar power gives us new energy (since the sun is radiating it for free). Thus, no matter how efficient it is or is not, solar energy is a primary energy source, while stored energy is only ever just a storage mechanism.

[Shpaget]

There is also the energy needed to move around all the air to get access to that small fraction we're interested in. Thunderf00t did the calculation in his plastic from air video.

[kerbiloid]

8 hours ago, mikegarrison said:

Solar power gives us new energy (since the sun is radiating it for free). Thus, no matter how efficient it is or is not, solar energy is a primary energy source, while stored energy is only ever just a storage mechanism.

That's so for chemical fuels.
The nuclear fuels (uranium, thorium, deuterium, lithium) have appeared long before the Sun did, in processes of much higher energies and power. They don't represent the solar energy at all.

P.S.
Of course, carbon dioxide is just a way to redistribute the solar power.

Edited November 26, 2019 by kerbiloid

[mikegarrison]

29 minutes ago, kerbiloid said:

That's so for chemical fuels.
The nuclear fuels (uranium, thorium, deuterium, lithium) have appeared long before the Sun did, in processes of much higher energies and power. They don't represent the solar energy at all.

P.S.
Of course, carbon dioxide is just a way to redistribute the solar power.

I think you misunderstood what I was getting at. Chemical fuels we pump or dig from the ground are, in terms of human lifespans, primary energy sources. Yes, the energy ultimately came from the sun and was concentrated over time from plant and animal matter, but as far as humans are concerned these chemicals represent a source of new energy. But doing things like spinning up flywheels, pumping water to an uphill tank, compressing gasses, etc. is only storing energy that humans have to get from some other source.

[RCgothic]

Primary energy sources. Whether that's coal, oil, uranium, or hydrogen in the sun, it gives you energy you didn't have before. Whether it's inexhaustible or not (in the long term none are) is irrelevant. You find it, dig it up, whatever, and it gives you energy.

Hydrogen fuel cells, pumped hydro, batteries, compressed gas, whatever, these are secondary energy sources. You don't find them lying around and they don't give you anything for free. You have to expend an existing power source to get them and this *costs* energy.

Whenever you use a secondary energy source instead of a primary one it is because of a specific advantage that makes it more useful than a primary one - usually portability.

 

I don't think compressed/liquid/solid CO2 as a storage medium is a good idea. It's heavier than air and an asphyxiant. Small volumes become very large volumes that are easy to suffocate in. Pressurised storage is also a specific deadly hazard, highly regulated for a reason. Vehicles that are subject to accidents are a particularly bad place for a pressurised CO2 system. Plus it doesn't take CO2 out of the atmosphere to address climate change, it just recirculates it.

Edited November 26, 2019 by RCgothic

[farmerben]

12 hours ago, mikegarrison said:

Mechanically storing energy does not give us any newly accessible energy. It just stores energy we already have (and always with less than 100% efficiency). Solar power gives us new energy (since the sun is radiating it for free). 

This point is well understood.  The biggest problem with solar is the phase lag between supply and demand.  Dealing with this issue could cost as much as the generating system itself.  Pumped hydro cannot easily be scaled up to handle grid level storage in most areas.  Grid level batteries and other approaches are waiting for better technology.  Pushing liquid CO2 into underground reservoirs and tapping some of it back out is one solution.  It's not a great energy storage approach, unless you happen to be liquefying lots of CO2 anyway for other reasons.  Compressed air would be a byproduct of CO2 separation, but the storage capacity of compressed air does not scale well, and would need to operate on short cycles.

 

4 hours ago, RCgothic said:

 

I don't think compressed/liquid/solid CO2 as a storage medium is a good idea. It's heavier than air and an asphyxiant. Small volumes become very large volumes that are easy to suffocate in. Pressurised storage is also a specific deadly hazard, highly regulated for a reason. Vehicles that are subject to accidents are a particularly bad place for a pressurised CO2 system. Plus it doesn't take CO2 out of the atmosphere to address climate change, it just recirculates it.

That is all true.  It is probably safer to store CO2 underground than to store CH4 underground.  We know that CH4 which has been trapped for millions of years finds ways to burst out.  It is far more hazardous than storing spent nuclear fuel.  I'm not saying it is a good idea to store liquid CO2.  I'm asking, if we did have a system to pump liquid CO2 underground, what could we do to make the system better?

I can think of many ways to change climate and reducing CO2 to preindustrial levels is merely one of them.  And there is more than one way to do that.  The best solution by far is to make organic matter in topsoil.  And there are multiple ways to do that, the pros and cons of each method varying considerably from place to place.  I've seen conflicting data about the longevity of carbon in topsoil, and the capacity.  Land management can elevate soil carbon to 5% in most areas, 20% in prime areas, before plateauing out.  Carbon storage half-lives of between 100-1000 years are in the ballpark depending on soil type, climate, and other variables.  The capacity to capture all industrial carbon in topsoil exists.  It would entail massive social change in the way humans relate to the land, and it's not simple.  Particular methods help in particular places at particular times, and the trade off costs vary on several axis as well.