Solar Cooler in a Can




About: Currently pursuing a degree in Mechanical Engineering. contact: jamesrpatrick(at)

It's been getting really hot up in the Northern Hemisphere lately, so here's a way to combat the heat by making a cooler that stays cool. Just add water!

This project is based on the recent invention of Emily Cummins, originally designed for impoverished families in Africa to keep meat and milk from going bad. The beauty of the cooler is its simplicity. It can be made from scrap materials that can be found in almost any home, sometimes in the trash. The Evaporation Fridge consists of an inner and outer tube, with a wet material in between the two layers. Perishable items are kept in the inner tube in a sealed container. As the water in the wet material evaporates, it removes heat from the inner tube and lowers the temperature. The whole process can be compared to the human perspiration system. Think of the fridge as a cooler that sweats, except less gross.

UPDATE: Check out the new version here:

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Step 1: Tools and Materials

I found all of my materials in my garage. If you can't find something, feel free to substitute similar object. My materials are as follows:

1 empty paint bucket
1 empty lantern propane tank(small)
2 plastic tank caps(from full or empty propane tanks)
4-6 rags/washcloths(anything that holds water: sand, sponge, wool, ShamWOW)
2 mesh gutter covers
1 can of spray paint
steel wool

The tools that I used are also very common:
drill press
1" hole saw drill bit
small drill bit
hacksaw with blade for metal
tin snips
hot glue gun

Step 2: Prepare Your Bucket

I wanted my cooler to be portable, so I used a paint bucket with a convenient handle. A larger five gallon bucket would also work. I chose a plastic one because it won't rust. The first thing to do is remove all of the paint from the bucket. Just get the sludge out and rinse it off. Mine was latex so after it dried it just peeled off. If the bucket has rust on the rim, use some steel wool to scrub it off. Lastly, mark drilling points for 12 holes in the side of the can.

Step 3: Drill Your Bucket

Use the hole saw to drill the twelve 1" holes in the wall of your bucket. Try to make them even and consistent. These will be the "pores" of the system, letting water evaporate from them.

Step 4: Add a Screen

You'll want to add a screen behind the pores so that the towels don't stick out and collect dirt. Simply roll up one of the gutter guards and stick it in the bucket. Then maybe make sure it sits flush against the edges.

Step 5: Make the Inner Screen

The inner screen helps keep the absorbent medium in place. It's made from a smaller section of the same gutter guard. If you bend the exposed barbs, you can lock them into the opposite end of the screen and create a tube shape.

Step 6: Create an Absorbent Bucket

Now it's time to finish the bucket part of the bucket. Wrap 4 to 6 towels around the inner screen that you just created and insert the sushi roll into the bucket. Stuff the edges of the towels below the surface of the bucket. Your cooler is now ready to accept a food capsule.

Step 7: Prepare the Propane Tank

DO NOT PERFORM THIS STEP WITHOUT ADULT SUPERVISION! This step is NOT safe and I am not responsible if you blow yourself up. Proceed at your own risk.

Now, the propane tank must be completely empty. Make sure you release all of the propane from the tank by attaching a blowtorch attachment,  opening the valve, igniting any gas, and leaving the torch open after the flame goes out. Then carefully drill a small hole in the top dome of the tank. Next, use a hacksaw to cut the top off of the tank, making sure you rotate the tank as you go. There are two valves that protrude below the top of the tank and they make cutting more difficult.

Now sand down all of the sharp edges you just made and give the whole thing a nice new coat of paint.

Step 8: Finish the Capsule

The only thing it's missing is a lid. It turns out that some propane tanks come with plastic bottoms that fit perfectly. You might also want to plug up any holes with hot glue to prevent rust.

Step 9: Assemble Your Solar Cooler

This solar cooler is just about ready to go for a test drive. To use it, simply put your food/drink into the capsule, close it up, and put it into the bucket. Then pour water over the capsule until the absorbent medium is full, and take the cooler outside with you. After enough water evaporates, your capsule will be sufficiently cool and ready to eat out of!

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    107 Discussions


    9 years ago on Step 7

    Coleman made a plastic bit called the Green Key that they included with their propane cylinders. Once the tank was "empty" you inserted the Green Key into the cylinder's valve. This allowed the last of the propane to slowly escape out of the cylinder so it was safe to recycle.

    I just checked Coleman's site and it says that the idea didn't catch on so they aren't including the Green Key with their cylinders anymore. That doesn't mean a person couldn't locate one or two if they wanted to try this project without fear of fire/explosion.


    1 reply

    Reply 8 years ago on Introduction

    As an alternative method of "safeing" a propane can before cutting it, someone here at Instructables suggested filling it with water to displace and absorb any traces of gas. Maybe the author or someone else will recognize which -ible talks about using water to make an empty propane tank safe for cutting.


    8 years ago on Introduction

    I wouldn't say evaporator based coolers are new, for they have been around for sometime using wicker baskets and such.

    2 replies

    Yeah they've been around at least since Egyptian times but this is a new design with more modern materials.


    Reply 8 years ago on Introduction

    James R Patrick-
    Yeah I'll say evaporative cooling has been around since Egyptian times, even thin sheets of ice were made at night using the method! (Sorry I have no URL reference for that factoid, but I did read it in a book many years ago.)

    Nice -ible, keep going with these.   :)



    8 years ago on Introduction

    I'd like to share my experiences with evaporative coolers hoping someone may improve on this design.

    I think it could spur some ideas with all the brilliant people on this site

    Lectric Wizard

    9 years ago on Step 9

    Nice instructable but wouldn't it be easier to use a coffee can or similar to make the food capsule ? Then you wouldn't have the possibility of your food tasting like propane odorant . It is a great idea though !!

    3 replies

    My original plan called for a coffee can and I spent about an hour looking for one, but nobody in my house drinks coffee. It would probably work better though. As for the propane odorant, there was no scent left in the tank after it was fully drained.


    Reply 8 years ago on Step 9

    yes, i was thinking this while reading. Great inst. & I think I'll try it with a coffee can. I always by metal ones just to keep for storage.


    9 years ago on Introduction

    I've been seeing this concept for 10+ years but no web site ever provides hard info on how well it works. Like, if it's the ambient (air) temperature is 90F, how cool is the inside of the pot? Does it cool more in shade or sun? Inquiring minds want to know. If it's 90F in the outside sun, and the inside of the pot is 80F, 80F is not conducive to food preservation.

    4 replies

    Reply 8 years ago on Introduction

    I'm sorry I can't give you the hard facts that you want, but as you probably already suspect, there are a lot of variables. Yes, it definitely works better in the shade. The cooling varies with the materials used for both the inner and outer containers and what you use for the packing material. This idea has been around since the 1800's at least, probably longer. My Grandma used a big crock that she kept filled with lemonade or water for the field hands. She kept it in the barn and the heat caused the crock to sweat which pulled the heat from the liquid inside the jar. It was quite a bit colder than the outside temperature, but if it was 100 degrees out, the liquid could not be called cold. Whatever you put inside the container should already be cold for the best results.
    A filling of damp sand or crushed charcoal works very well for a filling between the two containers. You could also use sawdust, moss, straw or leaves, as long as you have water to dampen them. Using a porous container for the outer layer increases the cooling (for example a large unglazed flower pot) or sink your container into the ground with pebbles around it and keep them damp. In the old days, people often dug out a hole and put a wooden keg into the ground with a wooden box sitting on top. They back filled around the keg with small stones, wet them down and filled in around the barrel with dirt, which was mounded up around the box to allow rain to run away from the keg. The box was the 'lid' of this under ground cooler. A stick was fastened to the box and containers of food were tied to the stick and hung in the keg below. This kept food from spoiling for several days.
    Just a little note of interest: In the middle east they made ice by pouring water in shallow trays and placing them where the wind would blow over them. The water would develop a thin layer of ice which would be collected before sunup and stored in tall jars, kept in a cool corner. Their houses were cooled naturally by woven mats hung across the small windows on the windward side of the house. These mats were kept damp by ladeling water across them. Natural swamp coolers!


    Reply 9 years ago on Introduction

    This is a variation of a Zeer pot. when working at optimum efficiency, 80 degree dry day, you may get 60F inside the cooler. never tried it at 90, but should still work there. The design is not so much to refrigerate, as to cool. As for sun vs shade, it doesn't matter much, but the sun will add heat to the whole setup, so shade is better. What makes a bigger difference is local humidity. In the desert, these things work GREAT. In a rain forest, it wouldn't work at all. All depends on how well water is evaporating in your exact location. To that end, wind helps. I've used the clay pot/sand version, and was able to keep lunch meat edible for several days during the summer. Without the cooler, it would have lasted several HOURS. For me though, this style cooler works best to take HOT water, and give you COOL drinking water. You can fill the interior container with half your water, dump the other half onto the sponge/towel pad, and in an hour or two, have cool drinking water. To do this tho9ugh, I'd advise a stainless steel inner container. Used propane tanks tend toward not being food safe.


    9 years ago on Step 7

    make shur u clean out the inside bc there would be gas residue and u put food in ther soo yea....


    9 years ago on Introduction

    Great idea. I am looking into adapting this concept to make a portable cooler for keeping perishable foods in while camping. Basically using evaporation cooling to enhance a traditional cooler / icebox. Does anyone have any thoughts on materials? For eample is the outer shell best made of metal (ie a good onductor) or plastic? Also, could it be finned to increase surface area?

    Then the inner liner. If the food is put in chilled plus some ice blocks would it be best to use an insulated inner to keep the heat out or would that be counterproductive in that colling would not be efficient?