I really like your propane idea. Thanks. Might run some on our test equipment.
For add-ons in the co-gen area, yeah, I like the hot water for domestic and building heat, and we are looking at making stills (as in distillary) for distilled water and alcohol production.
Had considered freon but it seemed too big a PITA.
We put up a tracker last month . . 4 of them actually. About 225 ft^2 each, for solar cell arrays. They work with freon outrigger tubes that sit in the Sun and heat up and shift gas/liquid back and forth as weight to re-balance the trackers to track the Sun.
We were chatting about NH4 systems, too. I used to do air conditioning/refrigeration work and played with some of that, but am not so keen on that for leaks, etc. The idea of highly pressured hot ammonia blowing out a leak does not excite me.
But it might be good to use as a co-gen absorbtion cooling system on the back-end of a boiler.