As you may be aware, 134a, which is a commonly used ozone friendly automotive refrigerant, still has 1700 times the GWP of CO2. Propane is a suitable non-global warming refrigerant. I submitted the very first proposal for a NGWP refrigeration system under the EPA SNAP program almost two decades ago, and there is now an international standard based on this. Tecumseh makes DC compressors under the Masterflux brand name, and which have been widely used in military applications. I hope that the A/C system that is chosen does not add to man made global warming, which, after all, is a primary reason for the designs' existence.
The Aptera Forum
Interesting. I'm no refrigerant expert so I googled 134a and propane as GHG and learned at an EPA site that 134a since 2012 is no longer allowed in new car designs, so that's not going to happen here. (https://www.epa.gov/mvac/refrigerant-transition-environmental-impacts)
I'll let others debate the alternative refrigerants. I did find articles promoting propane (R-290) as a mobile refrigerant. This one fact sheet about R290 has a list of the pros & cons: https://refrigeranthq.com/r-290-propane-refrigerant-info-fact-sheet/
The main pro is that it is environmentally friendly as you wrote. However, the main con is that propane is obviously flammable. That 2019 fact sheet did not list mobile AC's as an approved application for this refrigerant. Has the EPA or other government organization changed that?
It has been a while since I was working in this field. There was a legal challenge years ago, where a company was suing a mobile propane refrigerant supplier, and as part of the suit fact finding, used a solenoid powered knife to release the entire refrigerant charge at once into a spark igniter.
The defendant hired the same consultant to duplicate the test with a 134a charge (134a is not in and of itself flammable) but got the same result caused by the oil circulating with the refrigerant.
My system used so little propane that there would not be a large release of energy even if the entire charge could be burned, which was very unlikely because of design safety backstops. If you were to consult https://masterflux.com/, they could make a recommendation based on state of the art. They have off the shelf DC compressors that run from 12 to 420 volts dc. They could also likely help with regulatory approvals.