I remember seeing a documentary a number of years ago around charcoal refrigeration. Basically, the building structure has the walls filled with charcoal mesh on inside and outside. Water is fed into the charcoal, heat on outside evaporates the water. This sucks the heat from inside the building, which cools the inside. In the documentary I originally saw, I believe they were able to go below zero, or at least very close. Was unable to locate the original documentary, but here is a clip showing it being used in the real world, with very basic construction. Would this be of use for anyone, for keeping veg cool, or even incorporating it into house construction ?

Here's a link: http://www.postharvest.org/images/CharcoalcoolstoragePNACQ751.pdf

This would work best in very dry climates where the rate of evaporation would be very high. I am not sure how they would physically be able to get temps below zero, because evaporation decreases as the temp goes down, you are dripping water down that is above zero, and there would be other factors. There are a lot of things you can do to a house to keep it cool without using power. These techniques would vary with climate so I would recommend looking at those that are geared towards a monsoonal climate. For veggies you could do like the ancient Egyptians and take one of the large water jars and wrap it in wet burlap and keep it in the shade. I imagine it would be more practical to get a solar cell to operate a refrigerator.

I have used sprinklers on top of my quail barn when it was very hot to help keep it cool, but it takes power to get the water up there. It would be very interesting to see the original video

Looks good for brewing beer, which needs temperatures of around 23°C. I'll look into that but it looks like a lot of work to get ready.