I was wondering if anyone had any experience in this field. I am experimenting with off grid refrigeration techniques and have come across this concept. Here's a rough overview of my plans to keep the groceries cold with the sun:

Two 20 lb propane cylinders will be emptied and valves removed. One will be placed in the bottom of a 55 gallon drum and the drum burried in a hole 1 foot wider in diameter than the drum. The area between the drum and the hole will be filled with mulch to act as an insulator. The bottom of the drum will be filled with pea gravel as a frost bed, up to the top of the propane cylinder contained therein. Food will sit on the pea gravel bed.

A 1/4 inch copper pipe will run up from the cooler chest into a condenser coil submerged in water and then into the second propane tank at ground level. The second tank will be filled with activated carbon soaked with methanol. A 36" parabolic reflector will focus sunlight onto the ground level tank heating the methanol to gas during the day and sending it into the condenser.

Cold methanol will collect in the bottom tank, freezing the pea gravel bed. Overnight, the now dry carbon will begin to reabsorb the methanol as it slowly vaporizes. And then the sun rises and the cycle repeats.

The concept is similar to ammonia type systems found in RV's...

Let me know your thoughts,

Sri Oracle

[edit on 23-10-2007 by DontTreadOnMe]

Could this sort of be like the cold air duster can effect?
As the gas evaporates (or flows out) the container gets cold.

I got to brush up on my refrigerator dynamics.

A diagram and a short course in refrigeration theory would be nice here.

Sri, I think you'd be better off with one of those a 12v power cooler powered by 2 golf cart batteries and recharged by a solar cell or wind charger. Depending on where you live, an old fashioned root cellar will keep most veggies edible for weeks if not months in most areas. Any meat not eaten immediately can be smoked, cured or jerked.

There are several other more efficient methods of creating cooling like the ammonia systems you mentioned. Many of the older RV units can be bought very cheaply on E-bay. You can radically improve their performance by super insulating them, installing small circulation fans in them and placing them completely in the shade. Remember they only need a heat source to operate and not propane. A solar concentrator can produce tremendous heat and you may be able to transfer some of that heat to operate the fridge.

Originally posted by crgintx
Sri, I think you'd be better off with one of those a 12v power cooler powered by 2 golf cart batteries and recharged by a solar cell or wind charger.

Aside from surviving outside of Babylon... I seek to have little impact in my personal life. Activated Carbon, Wood Alcohol, copper pipe and two old steel propane tanks have a remarkably small metaphysical impact. Batteries and Solar Panels are generally pretty Babylonian in my eye... although I do (presently) keep such a system for off grid power tool usage for my carpentry business, etc.

an old fashioned root cellar will keep most veggies ...Any meat not eaten immediately can be smoked, cured or jerked.

That's where I am at right now... But I want to keep milk and eggs...

(mind you... when I am here chatting with you... then there's a traditional fridge in the next room; but this is far, far from home.)

Many of the older RV units can be bought very cheaply on E-bay.

I feel more comfortable working with, and teaching others to work with, pyroxylic spirit (methanol) rather than spirit of hartshorn (ammonia) as it is has a 1 rather than 3 msds/nfpa health rating and is a liquid rather than gas.

If you have access to a constantly flowing spring, you can keep eggs and dairy in a spring house. Another choice is the good old ice box.

But I want to keep milk and eggs

You can purchase can (shorter storage time) and dried milk. There are several types available including powdered whole milk. You can also purchase powdered eggs.

Keeping it simple, I think your best bet would be the root cellar. Also, dried beans, legumes and rice will keep for a very long time.

There a variety of places to purchase the items for very long term storage (approx. 30 years), one of which is: Waltonfeed.com

Need to research the potential for carbon methanol solar cycling to produce pressure for methanol vapor "steam engine"; ie convert to mechanical energy