A related idea I’d love to explore is an off-grid fridge cooled via the Stirling cycle [0]. It’s essentially a Stirling engine run in reverse, using power to move heat vs. the other way around. No refrigerant is required, just an external source of power e.g. a DC electric motor. Such technology is used today for ultra-low-temperature cryonics. At least one Stirling cycle mini-fridge has been developed and brought to market; it got rave reviews from the boating community to whom it was marketed, but went out of production and was never followed up [1]. I’d love to find out why this technology hasn’t been more widely deployed.

[0] https://en.wikipedia.org/wiki/Stirling_cycle [1] http://www.cruisersforum.com/forums/f115/coleman-stirling-po...