| ▲ | pragma_x 5 days ago | |
My hunch is that they're doing this for three reasons. 1. Decompressing the gas can be used to do work, like turning a turbine or something. It's not particularly efficient, as you mention, but it can store some energy for a while. Also the tech to do this is practically off-the-shelf right now, and doesn't rely on a ton of R&D to ramp up. Well, maybe the large storage tanks do, but that should be all. So it _does_ function and nobody else is doing it this way so perhaps all that's seen as a competitive edge of sorts. 2. The storage tech has viable side-products, so the bottom-line could be diversified as to not be completely reliant on electricity generation. The compressed gas itself can be sold. Processed a little further, it can be sold as dry ice. Or maybe the facility can be dual-purposed for refrigeration of goods. 3. IMO, they're using CO2 as a working fluid is an attempt to sound carbon-sequestration-adjacent. Basically, doubling-down on environmentally-sound keywords to attract investment. Yes, I'm saying they're greenwashing what should otherwise be a sand battery or something else that moves _heat_ around more efficiently. | ||
| ▲ | s_tec 5 days ago | parent | next [-] | |
This is more of a compressed-air battery than a sand battery, except that the "air" is CO2 and it's "compressed" enough to cause a phase change. Heat-based energy storage is always going to be inefficient, since it's limited by the Carnot efficiency of turning heat back into electricity. It's always better to store energy mechanically (pumping water, lifting weights, compressing gas), since these are already low-entropy forms of energy, and aren't limited by Carnot's theorem. I don't know much about this CO2 battery, but I'm guessing the liquid-gas transition occurs under favorable conditions (reasonable temperatures and pressures). The goal is to minimize the amount of heat involved in the process, since all heat is loss (even if they can re-capture it to some extent). | ||
| ▲ | nine_k 5 days ago | parent | prev | next [-] | |
I suppose that liquid CO2 just requires much less volume to store, while keeping the pressure within reason (several dozen atm). For it to work though, the liquid should stay below 31°C (88°F), else it will turn into gas anyway. So, in a hot climate, they need to store it deep enough underground, and cool the liquid somehow below ambient temperature. | ||
| ▲ | klunger 5 days ago | parent | prev | next [-] | |
Yes, it is not clear why they have chosen CO2 beyond PR. There are other gas mixtures that would likely have better yields. | ||
| ▲ | topspin 5 days ago | parent | prev [-] | |
> they're using CO2 as a working fluid is an attempt to sound carbon-sequestration-adjacent Um no, that's unfair. CO2 is an easy engineering choice here. It's easy to compress and decompress, easy to contain, non-flamable, non-corrosive, non-toxic and cheap. It's used in many applications for these reasons. While CO2 is now a great evil among the laptop class, it has been a miracle substance in engineering for roughly 200 years now. | ||