Again, TED Talks offers a wealth of fabulous information, "ideas worth spreading". This video of this design for the world without electricity and refrigeration. I won’t explain the science of this except to say one can heat a small thing (size of an iron) and let it cool, put it in something else (3 gal. vessel) and it keeps things cool for 24 hours. They are on the 5th prototype and creators believe they can produce it for $25-$40.
Today, I am making the decision whether to eliminate my refrigerator. Stay tuned . . .