Introduction: Cheap Solar Fridge

Picture of Cheap Solar Fridge

This instructable is being entered in the Green Tech Contest so please vote.

This solar fridge is a simple and quick diy project. The reason I decided to build it was because the fridge in your house takes up a ton of energy.  This fridge is so cheap and reliable that it can be used in 3rd world countries.  It takes about 15 to 30 minutes to complete and it only cost around $15 dollars.  

Here is what you need

1 large clay flower pot
1 small clay flower pot
 sand  (I used about 1/4 of a bag) 
 clay or plumbers putty   (only needed if there is a whole in the bottom of the pot)   

Step 1: Filling Up the Holes

Picture of Filling Up the Holes

The first step is to see if you have a hole at the bottom of your pot.  If there is not a hole then you can skip this step.  If there is a hole then take your clay or putty and firmly press it into the hole and cover it.  Make sure there is no gaps for water to leak out.

Step 2: Even the Pots

Picture of Even the Pots

Fill the larger pot with a layer of sand.  Then put the smaller pot inside the larger one and level the sand until both pots are at even height.

Step 3: Finishing With the Sand

Picture of Finishing With the Sand

Fill the remaining area between the pots with sand.

Step 4: Time to Put the Water In

Picture of Time to Put the Water In

Pour water into sand to saturate it completely.  Once the water begins welling up instead of soaking in, you can stop.

Step 5: Stock the Fridge

Picture of Stock the Fridge

put any items you want into the fridge.

Step 6: Almost Done

Picture of Almost Done

Now you have to soak the towel and place it over the top of the pots. 

Step 7: Usage of Your Fridge

Make  sure you put your fridge in a shaded place.  Also return once or twice a day and refill the sand with water and dampen the towel.

Step 8: How It Works

The action that allows it to stay cool is the evaporation of the water surrounding the smaller pot.  As the water evaporates, heat draws out from the smaller pot, keeping the contents inside much cooler the the surrounding environment.


ragtimelil (author)2013-04-16

I tried this and did not have success. I think it works in a dry climate but not in a humid one.

cdrobsonjr (author)ragtimelil2017-06-27

Evaporative coolers - which this truly is - rely on, oddly enough, evaporation. When your ambient humidity is high, the differential between the wet pot and the surrounding air is small, so less evaporation takes place and hence less cooling takes place inside. Your intuition is correct.

Satrah101 (author)2017-04-11

Hello all can i ask how cool does this get.

iffee (author)2012-07-16

How it is solar???

jeffeb3 (author)iffee2012-07-16

It's not solar. "Make sure you put your fridge in a shaded place". A better title would be "Evaporative Fridge" or "No-Electricity Fridge" or "Cheap Portable Fridge".

rimar2000 (author)jeffeb32012-07-16

Yes, it is indirectly solar, bacouse the wind is due to sun.

phepner (author)rimar20002012-07-19

then it's indirectly nuclear also ... nice instructable anyway

PaulT241 (author)phepner2017-01-14

Alright! We went from low-tech to high-tech - It's a nuclear fridge. :-)

SpikeFiend (author)phepner2012-07-19

Fossil fuels are also indirectly solar energy. ;)

Would a lid on top of the center pot help keep it cooler? Assuming the evaporation takes place in the outer pot.

rimar2000 (author)SpikeFiend2012-07-20

Both you are right.

fzbw9br (author)rimar20002012-07-19

the wind is not only caused by the sun, but by pressure differences on the earth, so it could be called, an "Indirect, SolaNuclear Low Pressure EvapCooler"

AKA: InSoNuLPEC device

rimar2000 (author)fzbw9br2012-07-20

Yes, you are right.

martinbolton (author)iffee2012-08-14

Thats what I was thinking.
Confused with 'evaporative'

iffee (author)martinbolton2012-08-15

It is evaporative not solar. Think it is night time and cooling will continue in absense of sun!!!

bcavaciuti (author)2012-10-21

you could fill the bottom holes with clay mixed with fibres(grass/rope/anything fibrous to hold its strength) this is for 3rd world countries or any people that dont have putty :)

PaulT241 (author)bcavaciuti2017-01-14

Clay could be used in place of putty. Some third-world countries may not have putty, but some areas of the world have easy access to clay.

BrianB382 (author)2016-11-15

It's no joke. There are a number of names for this type of cooling system, but one is called an evaporative cooler. Check out for more info.

mobius1ac (author)2016-05-22

BTW, this is called a Zeer Pot, it is different from a Refrigerator. A fridge has to have an active element to it.

Great product, but title is misleading to those of us looking for an actual fridge

aurasolar (author)2015-04-15

You should named it "Power Free Fridge" rather than "Solar Fridge". But your work is awesome. Thumbs up.

andrewj33 (author)aurasolar2015-12-26

Yes, you're right. "Power Free Fridge" is better. And your name is interesting. too.

ValentinoM (author)2015-04-28

another variant I saw some time ago, worked like this, if I remember correctly.

put your stuff on the ground.
cover with small pot upside down, having sealed its hole.
put the big pot on top
fill the gap with sand through the hole, then water

this is less practical, but I believe more efficient.

ValentinoM (author)2015-04-28

My grandparents actually used something like this up until the 50s!! I live in northern Italy, in a zone abundant with water. They still have this concrete fountain (it had a manual pump until they dug an artesian well) which is divided in two compartments: a basin and an enclosed box. When the basin is full, the water also covers the box. And that box was their fridge! That dark, cold and moldy closet used to scare me as a child, but it also fascinated me how they had to make do with something as rudimentary as that, compared to a modern fridge.

Anyway, this is a great project! I'll use it at the next BBQ

nice gonna try it

milododds (author)2015-03-26

Not sure why people are arguing over this being solar, of course it is because the heat source which causes the evaporation is the sun and for that matter if you were to put this out in direct sunlight and were vigilant in terms of keeping water in the sand and on the wet towel it would actually work better than putting in a "cool dark place" because more heat would be drawn away from the inside because there would be a faster rate of evaporation. My only question is whether it can keep the food inside between 35-38 Fahrenheit or not? Sure this is better than nothing in an emergency situation (it's also a great demonstration), however to be really useful there needs to be some way to control the amount of evaporation so you could maintain an ideal internal temperature, at around 40 degrees the bacteria rate will begin to triple.

virginia.fryer.9 (author)2014-08-12

Hi, I just posted the blog below and would like to amend something. Because of many different accents and lingual influences the 'Chatti' is also known as the 'Tatti' !

The basic secret is water evaporation from unglazed Terra Cotta pots. Go back to school and read about 'latent heat'.


virginia.fryer.9 (author)2014-08-12

Good for the 3rd world you genius??? WOW India is going to be thrilled. They have had the 'Chatti' for over 2000 years - Innovation ?? Don't think so.

ΒίκηΕ (author)2014-08-03's very smart! i'll try it!

catfurmama (author)2014-01-18

Nice! I'm going to use this with my Girl Scouts this summer

gsteele (author)2012-10-02

Very "cool" project. I am wondering if it might be easier to use a circular egg crate foam top. It would hold more water and be less messy than a wet towel. I am imagining an eye bolt through the center of the foam, with a large plastic washer and nut on the bottom side (to keep from tearing the foam and make it easy to pull off the lid)

iffee (author)2012-08-14

More interesting material can be found if you seach in google images with the following "refrigeration without electricity"
Be sure to seach in google images.

spinlite (author)2012-07-19

How cold does this keep the items?

jackoftheforest (author)spinlite2012-07-24

I used this ancient technique when I was living in the desert, and there were a few times when ice formed. But this was only possible in the hottest, dry and windy days. And it required very regular refilling with water. But it is how nomadic people made ice in the desert ages past. Fine tuning your fabric cover, and being sure to use pots that breathe particularly well, and regular refilling, will insure cool temperatures :D
Thanks for the instructable!

static (author)jackoftheforest2012-07-26

My understanding ice can be made in dry desert conditions with heat in the water radiating to the cold deep space night sky, and has been down to be done in Persia, and the American Southwest. Respectfully I can't see water cooling to freezing by mere evaporation alone during the daylight hours. When spending time out at the lake wet burlap over the ice chest helped the ice inside last longer by cooling the outside of the chests by evaporation, during the heat of the day.

1Word (author)static2012-08-14

"Respectfully I can't see water cooling to freezing by mere evaporation alone"

That's where physics comes in. Take a college level class and you'll see that it is not only possible, thanks to α = k / ρc(p), but happens often.

maewert (author)spinlite2012-07-19

As the water in the towel and the output pot evaporates the pot cools down.  Think of evaporation as the 'faster' water molecules leave into the air first leaving behind the 'slower' molecules.  The slower molecules are the colder ones so the inner pot is cooled down slightly.  This depends on the humidity, since in high humidity, the water doesn't evaporate very fast so the cooling effect is less.

jackoftheforest (author)maewert2012-07-24

As water evaporates it draws heat with it. With sufficient evaporation, one can reach freezing temperatures. It is the same system by which we perspire. I'm not sure what you mean by slower molecules vs faster molecules. It will only cool slightly if you live in a wet and cool place, arid and hot regions can utilize this for refrigeration, provided enough water ams optimized evaporation.

Krotas (author)2012-08-14

You smile at the finished project... and the project smiles back (note: first picture in the introduction page).

Bioruffo (author)2012-07-24

This is called a "zeer pot":

databoy (author)2012-07-22

Very inefficient when compared to the Coolgardie Safe.


The Coolgardie Safe is a low-tech refrigeration unit which uses the heat transfer which occurs during evaporation of water. It was named after the place where it was invented — the small mining town of Coolgardie, Western Australia, near Kalgoorlie-Boulder.

Coolgardie was the site of a gold rush in the early 1890s, prior to the Kalgoorlie-Boulder gold rush.

For the prospectors who had rushed here to find their fortune, one challenge was to extend the life of their perishable foods — hence the invention of the Coolgardie safe.

The safe was invented in the late 1890s by Arthur Patrick McCormick, who used the same principle as explorers and travellers in the Outback used to cool their canvas water bags: when the canvas bag is wet the fibres expand and it holds water. Some water seeps out and evaporates, especially if it is in a breeze, cooling the stored water.

This technology is commonly thought to have been adopted by explorer and scientist Sir Thomas Livingstone Mitchell, who had observed the way some Aborigines used kangaroo skins to carry water.

Principles of operation.

The Coolgardie Safe was made of wire mesh, hessian, a wooden frame and had a galvanised iron tray on top. The galvanised iron tray was filled with water. The hessian bag was hung over the side with one of the ends in the tray to soak up the water.

Gradually the hessian bag would get wet. When a breeze came it would go through the wet bag and evaporate the water. This would cool the air inside the safe, and in turn cool the food stored in the safe. This cooling is due to the water in the hessian needing energy to change state and evaporate. This energy is taken from the interior of the safe (metal mesh), thus making the interior cooler. There is a metal tray below the safe to catch excess water from the hessian.

It was usually placed on a veranda where there was a breeze. The Coolgardie safe was a common household item in Australia until the mid-twentieth century. Safes could be purchased ready-made or easily constructed at home.

Ole bally (author)databoy2012-07-22

Dunno who invented it, but the 'upgrade' to your Coolgardies cooler was one we had when I was little and living off the grid! The fridge was made of panels of brandering wood and rabbit mesh filled with charcoal. The tray on the top had tiny holes in the rim at the bottom and a piece of cotton shoe lace was pulled through it to act as a wick. The wicks led onto the top of the charcoal panels.The try filled with water would then slowly seep through the charcoal panel and the wind / air flow would cool it!
The tray needed filling once a day or so ...held about 50 liters of water I think!
The charcoal stopped any odours too!

erdbewohner (author)2012-07-19

I thought about cooling my mobile home by running a perforated garden hose over the roof and pump water (from my rain barrel) to mist the roof for a certain time ( i would have to figure out the timing). The problem is that I could not find a pump yet what automatically shuts off when the water runs out. I have this on my mind since several years. (Since we have very hot summers here in Kentucky and the A/C would not run a lot less then it does) If anybody knows where to get the right pump, please post on here.

espdp2 (author)erdbewohner2012-07-20

Rather than a sump pump or "toilet float" setup as most are suggesting, you want to take a look at the siphon system from this gardening 'ible - . It will fill up more quickly on sunny days when you need more cooling, and it won't run at night when you don't need it so much.

You will need to elevate a quantity of water above your roof on a tower next to your roof (I wouldn't put it actually *on* the roof) and find a source of water (your rain barrel on the ground). Install a solar pump with sufficient head to lift it to the upper tank. When your siphon system starts working, it will drain until the tank empties and the siphon breaks, and your solar pump will continue to putter along to refill it.

This would work GREAT with a grass roofed house!

denswei (author)espdp22012-07-22

A grass roof would be good in several ways: the dirt layer as insulation & thermal mass, and the evaporative cooling as the grass transpires water. Also, the shade of the grass (keeping direct sunlight off the soil).

Ole bally (author)erdbewohner2012-07-20

A boating bilge pump would work! Or any pump that you can attach a 'float switch' to! Ask at yr local boating store or irrigation supply store!

Daveallnight (author)erdbewohner2012-07-19

try a sump pump (with a float)

dalesql (author)erdbewohner2012-07-19

Get a sump pump with a float switch. feed that power from your timer. If the water level is too low, the pump will not turn on. About 80 bucks at the orange depot when I bought one a couple years ago.

you could use the float switch off a sump pump to control the pump or a well control switch the has a low pressure cut-off

firewoods (author)erdbewohner2012-07-19

this is called 'latent evaporative cooling' and is very effective. if you go to, there's a book called 'How to Really Save Money and Energy in Cooling Your Home by George S Barton. detailed plans, the science behind it, etc. good stuff!

Google "float switch"

chuckyd (author)2012-07-22

Do you even know what "non-sequitur" means?

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