I found some information online about absorption air conditioners, and in the examples given, often solar thermal was the heat source for the absorption process.
The downside is that it appears companies are targeting large commercial applications rather than small home or mobile applications. There may be a point where making it smaller makes it stop working, or it may be that this is still in its infancy.
I think refrigeration of all types is going to require a lot of energy, whether it be thermal, mechanical, or electrical.
The most common example of absorption refrigeration seen today is the RV refrigerator. The same principle should work for refrigeration, freezing, and air conditioning. In an RV fridge, they use 12vdc, 120vac, and propane to input the heat. I don't know what temperatures they need. I read somewhere that they get less efficient when it is hotter outside.
Evacuated solar tubes are relatively inexpensive (see http://www.beyondoilsolar.com/solar_water.htm
), and ought to be able to be mounted on the roof of a bus. There are also propane and diesel and kerosene fired small boilers out there that can also be used to heat water. Hot water ought to be able to be used to heat the hot side of an absorption process. As a side effect, you would also get winter time heat, and hot water out of the process.
I'm continually looking for lower energy alternatives to air conditioning (and other forms of refrigeration). So far I haven't found much useful though.
I'm planning to make hot water an important part of my energy plan in my bus. I plan to use radiant heat, and supplement that with heater cores with fans. I'm planning to have multiple sources of heat to input to the system, including the engine, solar, a diesel boiler, and a propane boiler. I plan to have multiple zones of output. If I can figure out a way to integrate that hot water system with an absorption refrigeration system, I will do so. My boilers will be located outside of the living space, preferably all together and in a nice fire-safe space. Actually, the core of the system will be a closed loop glycol mixture system. I'll use a liquid to liquid heat exchanger to connect that to the engine and also to provide hot potable water. I know I'll also need an expansion tank.
I suspect that in the short term, I'll have to stick with a conventional compressor based refrigeration setup. Long term though, the absorption stuff looks quite promising, especially when you remove the need to provide the flame directly to the refrigeration system (by transferring it via the hot water/glycol plumbing).
I'm still learning about this stuff as I go along, so take that into consideration when reading this. I don't know if my ideas will work out in reality, but I sure plan to give it a shot.