Fishermen in the village of Maruata, which is located on the Mexican Pacific coast 18 degrees north of the equator, have no electricity. But for the past 16 years they have been able to store their fish on ice: Seven ice makers, powered by nothing but the scorching sun, churn out a half ton of ice every day.

There's a global scramble to drive down emissions of carbon dioxide: the electricity to power just refrigerators in the U.S. contributes 102 million tons annually. Solar refrigeration can also be inexpensive and it would give the electric grid much-needed relief. Electricity demand peaks on hot summer days—150 gigawatts more in summer than winter in the U.S. (A gigawatt equals on billion watts.) That's almost 1.5 times the generating capacity of all the coal-fired power plants west of the Mississippi River. Further, solar is plentiful. The solar energy hitting 54 square feet (five square meters) of land each year is the equivalent of all the electricity used by one American household, according to data from the National Renewable Energy Laboratory and Energy Information Administration, both part of the U.S. Department of Energy.

Making cold out of hot is easier than one might think. A group of students last year at San Jose State University built a solar-powered ice maker with $100 worth of plumbing and a four-by-eight-foot (1.2-by-2.4-meter) sheet of reflecting steel. No moving parts, no electricity but give it a couple hours of sunshine and it can make a large bag of ice.

The key is the energy exchanged when liquids turn to vapor and vice versa—the process that cools you when you sweat. By far the most common approach, the one used by the refrigerator in your house, uses an electric motor to compress a refrigerant—say, Freon—turning it into liquid. When the pressure created by the compressor is released, the liquid evaporates, absorbing heat and lowering the temperature.

Absorptive chillers like solar refrigerators use a heat source rather than a compressor to change the refrigerant from vapor to liquid. The two most common combinations are water mixed with either lithium bromide or ammonia. In each case, the refrigerating gas is absorbed until heat is applied, which raises the temperature and pressure. At higher pressure, the refrigerant condenses into liquid. Turning off the heat lowers the pressure, causing that liquid to evaporate back into a gas, thereby creating the cooling effect.

As with most technologies, the efficiency of such absorptive refrigeration depends on the degree of engineering (and expense) brought to bear. Single-effect devices have a coefficient of performance of 0.6 to 0.7—that is, they create 60 to 70 Btus (British thermal units) of cooling for every 100 Btus of input heat. That low level of efficiency can be achieved with something as crude as some pipe, a bucket of water, some calcium chloride (as absorbant), ammonia (as refrigerant), and a sheet of shiny metal (the solar collector).

If what you want to do is heat or cool, using solar energy this way is probably more efficient—and certainly cheaper—than converting it first into electricity. "That approach ought to be comparable to photovoltaics, or a little better," said Tom Mancini, program manager for solar power at the Sandia National Laboratories in Albuquerque, N.M.

It would take a fair-size collector—86 square feet (eight square meters), assuming 40 percent panel efficiency—just to deliver the cooling of a small (6,000 Btu per hour or half-ton) window air conditioner. And central air-conditioning units are often 30,000 Btu or more; few homeowners could spare the space for that.

32 Comments

1. 1. SunDanzer 05:12 PM 10/20/08

   I'm not sure the claims that this technology is cheaper than PV powered refrigeration are correct. Today, you can buy a turnkey PV powered refrigerator of 8 cu.ft. for about $1,500. This includes the fridge, PV panel, battery, charge controller, and wire. A freezer version is about $2,500.
   
   I'll believe the claims of lower cost for absorption machines when I see them for sale on the internet.

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2. 2. Off-Gridder 08:48 PM 10/20/08

   The concept is valid as I am in the business of absorption refrigeration and many of the refrigerators in RV's are 12v dc power equipped which is essentially a heating element to power what is usually run by a propane, or kerosene gas burner to start the absorption process. Any heat producing element will provide the desired result as long as it get's hot enough. There is also a brand of DC powered refrigerators and freezers that can be purchased for around $1000. Propane refrigerators and freezers are now manufactured in the US up to a whopping 22 cubic feet of capacity.
   Ben Campbell www.BensDiscountSupply.com

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3. 3. clustertim 07:46 AM 10/21/08

   Now this seems like a great idea and one thats long overdue!
   
   JIff
   www.privacy-center.be.tc

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4. 4. frgough 09:36 AM 10/21/08

   For crying out loud. Filling the world with lithium bromide and ammonia is better for the environment than putting millions of tons of plant food into the atmosphere?
   
   SA needs to change it's name to SA-Pravda.

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5. 5. macrumpton 10:06 AM 10/21/08

   40% efficient seems low for solar thermal panels. Also 86sq ft is just over 9'x9', which does not seem that big to me.

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6. 6. link05n 11:23 AM 10/21/08

   it needs heat for the freon to compress. what do you do in the winter

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7. 7. link05n 11:23 AM 10/21/08

   it needs heat for the freon to compress. what do you do in the winter

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8. 8. boris555 04:46 PM 10/21/08

   so, how about some directions, or a LINK to directions on how to build one of these?
   
   I see stuff like this all the time. "Save thousands in energy and waste with only a few bucks worth of parts" articles. But there's never any meat. I've been googling for an hour and haven't seen any plans yet.
   
   Sci-Am readers are tinkerers. Help us get started!

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9. 9. chumpmeister 06:24 PM 10/21/08

   I second that... Sci-Am readers are tinkerers. They're also bloggers that record their experiments, stimulating practical improvements, generating industries that respond to market needs... eventually. Come on Sci-Am, give us a link. Real science quotes repeatable experiments, or it's not a far cry from conspiracy theory. Maybe I could build a cooler with an efficiency of 1.1+ ;-)

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10. 10. chumpmeister 06:32 PM 10/21/08

    ..but Google is my research friend & here's a start:
    http://dvice.com/archives/2008/08/solar_icemaker.php

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11. 11. chumpmeister 11:14 PM 10/21/08

    If you think about the job of providing Solar AC in hot, humid places like Florida, how would a PV electric based Solar AC work at night... with expensive batteries. If you read the details of how this system works, it could be adapted to provide your night time cooling, while the PV system provides the day time cooling.

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12. 12. seekingzeroeneryuse in reply to chumpmeister 02:21 PM 10/22/08

    here is a good link
    http://www.solarhaven.org/AmmoniaAbsorptionIcemaker.pdf

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13. 13. footware 10:49 PM 10/22/08

    This solar electronic is awesome.I hope people can invent more and more solar related stuff.Does anybody heard of http://www.shinesolar.net ?

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14. 14. footware 10:50 PM 10/22/08

    This is cool solar stuff.I hope we can invent more solar electronics.Have you heard of this company:http://www.shinesolar.net ?

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15. 15. Jan Jitso 03:32 AM 10/23/08

    If the sun is not shining perhaps there is wind and its kinetic energy may be converted directly into heat or cooling by a Dareus mill (vertical axes), which has holes in its wings to get inside the reduced pressure caused by flowing air on the surface of the wings. The mill drives a compressor and the process is comparable with the heating up of a pump for a bicycle tyre.
    A simple model could be tried out for warming seats at a bus stop.

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16. 16. Jan Jitso 04:12 AM 10/23/08

    I like to add that to the suggested operation of the Darrieus mill a trick may be needed to overcome centripetal forces and flow inside the wing, perhaps with help of a liquid which is slower than air so that intermittently the proper conditions wil show up.

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17. 17. jeanlan02 06:12 AM 10/23/08

    i wish to see a drawing/picture of a device applying this theory if someone has it. thx.

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18. 18. jeanlan02 06:19 AM 10/23/08

    if someone has a drawing/picture of a divice that applies this theory -- refrigeration by using water + calcium chloride + ammonia + sun heat -- i wish to see it. according to the description in the text, it should be very simple. many thx

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19. 19. Off-Gridder 10:07 PM 11/2/08

    Hmm I'm not sure the tinkerer could whip up an absorption refrigerator - lot's of welding and tube bending to do. I'm working on it myself. I think you could convert any refrigerator with an aftermarket replacement type absorption cooling unit but they are really expensive. For solar you have to have battery backup storage and a good location. I'm sure things will get cheaper as demand grows.
    Ben
    [URL]http://www.BensDiscountSupply.com[/URL]

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20. 20. DSF 09:29 PM 7/9/09

    keep Googleing and you will find sets of plans for calcium chloride and Icyball ammonia and water systems. But anywhere one uses pure ammonia caution, safety, and ventilation are coins of the realm.

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21. 21. alishabrown 02:39 PM 7/20/09

    How much is this refridgerator? and where can i get one?

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22. 22. shiva 12:20 AM 1/8/10

    Ya. Its very good idea to reduce pollution and increse the use of solar energy. We can do a project in our own on this topic. I wanna made a solar refrigerator. I need some suggestions from u those who are interested to give.

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23. 23. shiva 12:22 AM 1/8/10

    Enter Your Comment Here.

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24. 24. shiva 12:24 AM 1/8/10

    Enter Your Comment Here.

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25. 25. rotimi 10:54 AM 5/5/10

    Please, i am so green about solar energy and its products. Can i get tutorials from you. The objective is i live in a rural area where electricity is and will always be an issue. Can you be of any help?

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26. 26. tuprox in reply to boris555 01:06 PM 7/21/10

    Look up Einstein Refrigerator. He came up with the idea for this process and it may help you find what you are looking for (uuggghhh, today's grammar...)

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27. 27. tuprox 01:15 PM 7/21/10

    I also envision automobiles as mobile ice machines, or any internal combustion engine for that matter anything with a radiator! Right now we vent all the heat from combustion of fossil fuels to the environment around us but it could be used in this cycle. You could either use the heat for AC or even to make ice if you have a long enough trip. The ice could be stored and used to keep the inside of the car cool while you are inside w/o running the car, or it could be used for other things.
    
    

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28. 28. tuprox in reply to tuprox 01:31 PM 7/21/10

    As I said above about the combustion engine there is even more heat available from a number of places such as the exhaust manifold on back, much energy/heat is released upon braking (which is why hybrids work, they turn the energy into electricity though).
    
    There is so much wasted energy all around us which could be harnessed and/or stored with the right technologies. As fuel gets more expensive these technologies will become more attractive.

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29. 29. chmac 11:46 AM 7/26/10

    I found some good articles discussing this type of technique. Here's one PDF file that covers the technology in some detail:
    http://www.solarhaven.org/AmmoniaAbsorptionIcemaker.pdf

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30. 30. solarch 11:22 PM 10/26/10

    This solar electronic is awesome.I hope people can invent more and more solar related stuff.Does anybody heard of http://www.solar-ch.com ?
    
    cearmic mugs oem ceramic color chang mugs
    http://www.ceramic-mug.cn
    
    

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31. 31. integrity 02:15 PM 9/28/11

    I might be more impressed if I saw some plans somewhere?

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32. 32. john.d 07:07 AM 11/15/12

    Now lets take this concept a little further: lets make a cooling unit for a data center which would use the high temperature of the used cooling air to cool the room down. About 80% of the power used in a computer becomes heat.

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