1) Been there, almost done that in 1929: The Crosley Radio Corporation introduced a water-ammonia mixture refrigerator in 1929: "The Icyball is an intermittent heat absorption type of refrigerator. A water/ammonia mixture is used as the refrigerant . Water and ammonia combine easily. So, they combine in the hot ball at room temperature. When the hot ball is heated, for about 90 minutes, the ammonia evaporates first because it has a lower boiling point than water. The other cylinder is in water to help condense the ammonia in the cold ball. When the balls are fully charged, the cold ball is placed in the insulated box, as the ammonia evaporates to recombine with the water in the hot ball it removes heat, cooling the inside of the refrigerator for 24+ hours." They are still found in garage sales and junk stores. ::Crosley Ice Ball and you can build your own, ::Instructions here. Add a solar hot water heater and you are set.
2) Doing it right now: The Energy Concepts Company designed and built the ISAAC Solar Icemaker, acronym for Intermittent Solar Ammonia-water Absorption Cycle. Designed for third world use, we learn from Sustainable Village:
During the day the solar collector focuses the energy of the sun onto the ammonia generator in the collector trough. Solar heat distills pure ammonia vapor from the water-ammonia solution in the generator. The vapor condenses in the cooling coils and collects as liquid ammonia in the receiving tank in the evaporator.
At the end of the day, the user switches three valves from the Day to Night position to allow the ammonia to evaporate in the ice compartment, providing the refrigeration to freeze the water. The resulting vapor is absorbed back in the generator. Critical to the operation of Isaac is a passive thermosyphon that operates in the Night mode to remove the heat from the generator and allow the ammonia vapor to absorb into the solution at lower pressure and temperature.
At the beginning of the day, the operator harvests the ice from the ice trays, operates a drain sequence to remove traces of absorbent from the evaporator, and places the unit back into Day mode to begin the next cycle.
This was designed for third world use: "Energy Concepts has adopted this technology to a machine which uses the sun as the only energy output. The particular advances in the design and configuration have resulted in a low cost and reliable method of making significant quantities of ice in areas without electricity." the biggest unit, at costing $ 17,000 can make 150 pounds of ice per day.