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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) 
 towel 
 water
 clay or plumbers putty   (only needed if there is a whole in the bottom of the pot)   

 
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Step 1: 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 4: 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 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.



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'.

Merci.

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.

ΒίκηΕ4 months ago

mmm...it's very smart! i'll try it!

catfurmama11 months ago

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

ragtimelil1 year ago
I tried this and did not have success. I think it works in a dry climate but not in a humid one.
bcavaciuti2 years ago
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 :)
gsteele2 years ago
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)
iffee2 years ago
How it is solar???
Thats what I was thinking.
Confused with 'evaporative'
It is evaporative not solar. Think it is night time and cooling will continue in absense of sun!!!
jeffeb3 iffee2 years ago
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".
Yes, it is indirectly solar, bacouse the wind is due to sun.
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
Yes, you are right.
then it's indirectly nuclear also ... nice instructable anyway
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.
Both you are right.
iffee2 years ago
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.
spinlite2 years ago
How cold does this keep the items?
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!
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 static2 years ago
"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.
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.
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.
Krotas2 years ago
You smile at the finished project... and the project smiles back (note: first picture in the introduction page).
Bioruffo2 years ago
This is called a "zeer pot":
http://en.wikipedia.org/wiki/Zeer_pot
databoy2 years ago
Very inefficient when compared to the Coolgardie Safe.

Wikipedia:

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.
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!
erdbewohner2 years ago
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.
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 - http://www.instructables.com/id/Vermiponic-Garden/ . 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 espdp22 years ago
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).
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!
try a sump pump (with a float)
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
this is called 'latent evaporative cooling' and is very effective. if you go to knowledgepublications.com, 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"
iffee2 years ago
It works better in dry weather.
kc8hps iffee2 years ago
I'm sure solar doe not play into this equation. We are talking here about evaporation cooling.

YES you are correct this will function in more efficiently in dry climates.
The real model here resembles how a swamp cooler functions.

Swamp coolers as most of you know do not work in humid climates, just like refrigeration air conditioning is less efficient in dry climates.
denswei kc8hps2 years ago
I've wondered why more refrigeration AC systems don't gain some of the efficiencies of evaporation cooling by spraying cooling water over the compressor coils. It seems like window units reuse the condensate from the evaporator coils to haphazardly splash onto the compressor coils, but I haven't seen it done for other domestic systems.
The only problems I can see is that using tap water will cause mineral deposits on the condenser coils, while reusing the clean condensate could be complicated if there are separate evaporator and condenser units (since it would have to be pumped)
chuckyd denswei2 years ago
Water cooling is not efficient for home cooling. However, evaporative coolers are used for commercial and industrial sized cooling.
denswei chuckyd2 years ago
(removed by author or community request)
chuckyd denswei2 years ago
Do you even know what "non-sequitur" means?
denswei chuckyd2 years ago
Yup. Your comment logically "does not follow" the previous comments (other than the use of a couple of words).
Not sure how I posted the same thing twice though...
denswei chuckyd2 years ago
??? non-sequitur...
J-Ri denswei2 years ago
I've seen refrigerators (couldn't tell you what brands) that have a spiraled section of the compressor discharge line that is mounted in a trough that 's filled with cool water from the evaporator drain. It cools the refrigerant a bit before passing through a finned cooler.
jimluschen2 years ago
How cold? That depends on the outside temperature and the outside humidity, as well as how much wind is blowing. But whatever the answer is, don't store meat or milk or some other perishable food item in it. It might cool a couple of sodas and a banana somewhat, but it will not prevent bacteria growing in food.
arty jimluschen2 years ago
...But neither does an electric frig. ;)
arty2 years ago
I would suggest not plugging the hole in the outer pot, then placing the whole assembly in a shallow pan. It would be easier to add water to the shallow pan (not so likely to flood the food storage area), and the pan could keep the towel damp by wicking. Depending on the capacity of your pan, you might be able to reduce the servicing period to once a day or every other day. In any event, it would make a visible indicator to tell whether or not your frig needed water. A very nice Instructable. Thank you.

PS: If your pan was large enough, you could keep it wet with a self-waterer made out of a liter bottle; fill the bottle with water, up-end it into the pan, then adjust the height so that air leaks into the bottle when the water drops below your desired level.
ibrent2 years ago
Beware: this only works well in dry climates. The coolest that it will get is determined by the 'dew point' which is how cool the atmosphere has to be before water vapor condenses out. If the humidity is 100%, then the dew point is equal to the current ambient temperature and this device won't cool at all. Where I live, today's forecast high temperature is 81 degrees, and the high dew point is forecast to be 70 and the low dew point is 66. This means that in the peak of today's heat, this device will at most cool down to 70, which may not be sufficient to prevent food spoilage, or even feel terribly cool.
fzbw9br ibrent2 years ago
the relationship of DP to actual temp is not linear. I'll have to check at work as we use electronics now to calculate the DP, but from memory, I think the DP is actually lower than the WetBulb...

I'll check it out, and try to reply here...
ibrent fzbw9br2 years ago
You're exactly right, the dew point is always lower than the wet bulb, see the various psychrometric charts running around. There's all kinds of factors like barometric pressure, etc. In my example, with a dew point of 70, and dry bulb of 81, the wet bulb reading would be 73. So 73 would be the maximum cooling one could expect from an evaporative refrigerator such as this. So is it worth the fuss for an 8 degree cooling, which is what I'd get where I live? Probably not. In dry climates it's very effective. Of course, in dry climates getting the water for this may be the real trick.
Tumunga ibrent2 years ago
I betcha Bear Grylls, if in a desert, would be able to get some "water" for it...if you know what I mean.
Gotta say it, he's a terrible survivalist if he thinks drinking his own urine is a means of retaining water in dire situations...

Still, that joke will forever follow him to his grave.
heheheh! Lots of little blunders in his programs! Swimming at night in the Zambezi when crocs are sleeping?!!!
I kind of like the other guys approach better where he chats with the locals to see how they live on the land before making his program...Bear would benefit a lot by asking around too! I think he eats some of that stuff just for the 'gross' factor! :)
He's made a good living by grossing people out...
I do agree with you and your explanation is very informative. More the air is dry better it works. The traditional water cooler uses a a porous ceramic (botijo in Spanish) suspended in a shadowed place with lots of wind. There are several techniques for cooling for example fruits.
The same principle was used in Iran for cooling the houses with a wind tower.
DavidM452 years ago
Idea: buy a clay pot dish that would fit over the small pot top, wet it to increase cooling/sealing at the top where you loose most of your cool.

nice & simple cruzer
chamy2 years ago
Yeah, I was thinking the same thing. I wanted the pots to turn solar heat into ice cold banana smoothies.
peabody19292 years ago
Suggested improvement to make it really solar powered. Get a small fan that is driven by a small solar array. Place the fan to blow air at the wet surface. It will increase the evaporation rate, cooling things faster.
SunDanzer is a brand of DC powered refrigerators and freezers. They work pretty well and you can reduce your power requirements for a solar installation because you don't have large ac loads when the motor of a regular appliance turns on.
Alphageek632 years ago
A sump pump will drain your barrel in minutes. You want something smaller, like a pond pump with a float switch to cut it off at low water level. You can get simple float switches that are used inside Poly tanks.
LeanDean2 years ago
Nice use of the old evaporative cooler concept. Well worth it to keep the picnic lunch cool.
kmartin-12 years ago
Not really fridge so much as a cooler. Not come down on it, I like this, I might give it a try tomorrow at work, to keep my lunch cooler than normal.
GLFaria2 years ago
I (and a lot of others...) often used the same principle when in jungle war in Africa 40 years ago. Before leaving for the day's er... let's say walk, we would dip our water canteens, which had a fabric cover (US Army type), in water. Not comfortable for the first couple of minutes, until you got used to having your sides/back wet, but it sure kept the water inside cool until mid-morning, at least during the dry season.
digitalia2 years ago
This would be great to take to the lake. I'd get it there dry and sandless, and assemble it on the beach, using an old beach towel. Great idea!
Yep, and use your bubble gum to seal the pot holes. LOL.

Actually, the air at the beach might be a bit too humid to allow this method to work well.

Now, if you were to bury a barrel deep in the sand with inlet and outlet ports, and connect that to a solar chinney above ground, the sun-heated hot air above would rise... thus drawing cool air from the barrel to the surface. You could keep your food as cool as 56 degrees F... much cooler! Still not the 40 degrees you want to avoid spoilage though. :(
Peter Angel2 years ago
Can you put this in the fridge or freezer overnight and then remove it and use it as a portable fridge?
BOBCAPATAZ2 years ago
NICELY DONE..! -- (detractors aside)
virginnyb652 years ago
Maybe there are some who didn't see the first one.
justrelax2 years ago
isnt it heavy to carry ? :)
You could say the same thing about your regular fridge.
I bet you carry that around with you...
Good idea, I did much the same thing when I was in Africa. No electricity but wanted cool drinks. So I just pulled up a cotton athletic sock around the soda then kept the sock wet while the drink was placed in the window with the breeze passing. With humidity at about five percent it cooled the drink. Friends thought I was nuts until they found it worked. Next day they were doing it too.
I'm sorry, but your instructable should be removed. As Tim_N showed, this has already been done http://www.instructables.com/id/Garden-Camping-Festival-no-electricity-Fridge/

Further, you have not significantly added too, nor improved the original Instructable. The title is quite misleading as well.

I applaud your effort, but this is a conflict and the original instructable poster should have full credit. I don't think that you would want to put up an instructable and have someone post the very same thing.

Cheers
If you could post a nice chart or table that shows how cool your "fridge" can get based on different temperatures and dew-points, that would be awesome!
Why is it called "solar" if it needs a shaded place?
Anotar2 years ago
I would be interested in knowing if any measurement was taken of the temperature differential? If an indoor/outdoor thermometer were used, the probe could be put into the pot and after a couple hours you could simply read the two temps (of course it would be reversed and outdoor would mean "inside the pot" ha ha ha...) But then there would be some actual data that would be useful.

I could see making something like this if it can drop the inside temp 15 degrees when it is 90 outside, but if it only drops it 4 degrees that is a different story, and some actual measurements can answer that for me and any other readers who might consider constructing one.
motleyjust2 years ago
It definitely qualifies as "Green Tech", but why did you feel it necessary to claim it is solar (defined as "Using or operated by energy derived from the sun")

I think the name needs to be corrected.
YES!
mehendalek2 years ago
A Clay lid could make any difference?
Maybe just use the saucer that usually comes with the terra cotta pots? I'd glue a knob or handle on it.
cstandley2 years ago
Hmmm...........would this work for keeping potted plants a little cooler outdoors in dry climates?? Is this the principle of the Oregon ice caves?
kintekobo2 years ago
This is similar to what we used to call a 'desert cooler' in Saudi. You get a trough with water in it and hang some gauze so it dangles in the water and the water 'wicks' up the gauze. Place this in front of your bedroom window and as the breeze blows through it evaporates the water and cools the air. Far quieter than air-conditioning and it doesn't dry the air.
timwhite92 years ago
Would it not be really an evaporation fridge since it doesn't depend upon direct sunlight?
Also, what temperature drop could you expect?
you would not want this in direct sunlight

put it in the shade, where wind can get at it

When baling as a kid, my Grampa had a 1gal water bottle wrapped and wired up tight in burlap. Kept damp, this water was always cool to drink.
mayelamingi2 years ago
Very cool Project. Have you measured what temperature it holds?
I have to admit, I'm curious about this as well.
pvrmack2 years ago
Check out this link (or search "mitticool reffrigerator") for a guy in India who is making a low-cost, non-electric "fridge" for cooling water and small amounts of fresh foods using a similar "technology"...very interesting!

http://www.greendiary.com/entry/mitticool-indian-craftsman-creates-clay-refrigerator-that-works-without-electricity/
danzo3212 years ago
would sealed cans or bottles do even better if embedded in wet sand, in any vessel that allowed evaporation?
danzo3212 years ago
At this point it looks like inner pot has risen higher than outer pot
tim_n2 years ago
*cough*

http://www.instructables.com/id/Garden-Camping-Festival-no-electricity-Fridge/

oh well :) it's not solar, it's an evaporation fridge. If it was solar, you'd be putting it in the sun, not the shade!

The terracotta wicks the water to the outside of the pot and evaporates. In dry windy conditions it works a treat.
lime3D2 years ago
I like it. I wonder if we could increase efficiency if we buried it in the soil (leaving the top open, of course).
t.rohner lime3D2 years ago
Since it uses water evaporation for cooling, the more outer pot surface is exposed to dry air, the better it cools.
Moving air (wind) also helps tremendously.
mehmeh2 years ago
Well, when I was young, my parents chopped ice from the lake in the winter, and they kept it all summer, by placing it in sawdust, and covering it with a layer of sawdust as well. That was the only way we could cool anything in the summer, because we had absolutely no electricity, plumbing, running water, (except for the hand pump), or any other modern conveniences.
sitearm2 years ago
@cruzer28; Hi! Nice article. I am curious were you able to measure the temperature inside vs. outside? Cheers! Site
BudBump2 years ago
This is the same design concept used with evaporative coolers favored in the US southwestern states during the summer where air conditioning is too expensive and too dry. Evap coolers work VERY well and so does this pot design for a food chiller. In geographic regions with a desert character, this design for a chiller has been used for centuries by those who manage the heat so they can enjoy quality of life without dying from the heat. The Roman public baths were also designed using this same natural design and excellent effect.
Ortiz2 years ago
look for "botijo"
heathbar642 years ago
I would like to know what temperature you achieved. also what was the ambient temperature and humidity.
rrkrose2 years ago
I love solar powered products but rarely try them because they require a lot of technology know how that I don't have. This looks like a really fun project. I am on vacation right now but when I get back I will be off to the store to buy some pots!
I love solar, everything, excluding nuclear and geothermal and tidal motion and few others, is solar. Technically even these are solar (well... stellar) since they are (some theorize) the product of an ancient supernova ejecta. Even fossil fuels which were once living tissue that got their energy (sugars, protein etc) ultimately from the sun (plants). I think any project that makes use of the energy tension created by the sun (heat, wind, photons, stirling etc) is a good one, like this one. Nice project, simple. Thank you for sharing
macrumpton2 years ago
It would be nice if you included some measurements of the temperature inside and outside the fridge to show how well it works.
rimar20002 years ago
Good work, cruzer28.

Evaporation of water is surprisingly refrigerant. Once I drank water from a boot that had been exposed for an hour to the wind and the water seemed taken from the refrigerator.
Drakekay2 years ago
I think the solar part comes into play when u consider evaporation. but true, its not that solar ;D
Nifty :)