This article does not pretend to be an exhaustive dissertation on solar ponds, but it should be enough to wet the appetite of anyone who is searching for a relatively simple almost passive way of collecting the sun's heat and energy.


Brenda H. Nelson

This article does not pretend to
This article does not pretend to be an exhaustive dissertation on solar ponds, but it should be enough to wet the appetite of anyone who is searching for a relatively simple almost passive way of collecting the sun's heat and energy.
Brenda H. Nelson,

I first became aware of Solar Ponds back around 1980, from an architect who who was building them in adjunct to his houses. I spent a long afternoon with him and his wife in their Orr's Island home near Brunswick, Maine. Listening to him rhapsodize about solar ponds, I quickly became deeply impressed and still, almost 30 years later, I remember much of what he told me--except his name, alas.

Over those 30 years I have tried to Johnny Appleseed the idea, but most people dismiss it as too simplistic. Or they say, "Well, if it worked so well, we'd see a lot of them around wouldn't we?" This sort of reasoning parallels the "Build a better mouse trap and the world will beat a path to your door"--school of thinking--and is a myth of equal magnitude. The statements should be rephrased in the following manner, in order to be accurate: "Build a mousetrap that makes more money and the world will beat a path to your door;" and likewise "Build a solar energy production method that makes more money, and there will be lots of them around."

Unfortunately, solar ponds really require little money and there is very little to manufacture and sell in association with them--except for the turbine generator one could attach to them if one wanted to produce electricity as well as heat.

I will now explain the basics of what a solar pond is--and forgive me if I am insulting your intelligence, but in the course of researching this article I spoke with many solar "experts" and none of them knew about solar ponds. It was an idea which enjoyed a lively surge of interest around the late seventies and early 80's--an energy that quickly evaporated along with the rest of the simple living experiments of that era.

However, it is an idea that deserves a resurgence of interest--in my humble estimation. I have not yet uncovered a basic problem with the concept that should stop anyone from utilizing them--or at least doing some serious experimentation with them. And I would love to see them dotting the rural landscape and perhaps even dotting the city landscape--laid out on flat roofed buildings (that can carry the load--water weighing 9800N/cu meter or about 558 lbs./cu. yard)

There is some use of them in the American SW--fairly large ones being used in association with research and small manufacturing. And the Israelis use large ones extensively for public electricity production.

Again, back to exactly what is a solar pond. A residential solar pond might have a perimeter measurement of 12 X 12 feet, with a depth of about 3 feet This would be sufficient to supply the annual heating needs of a single family throughout a Northeast winter- according to my architect friend.

In the North East, where I live, they are practical as well. Even in Canada an experimental solar pond was started in November and was boiling by January! This was actually too much heat as you want the three salination layers to remain more-or-less distinct for the best heat absorption.

The pond should be lined with an impervious material--and an insulating one is better yet. So the 12 foot square pond (or whatever shape you like) could be lined with several inches of extruded styrofoam and then it should be painted black. Then black water pipe could be baffled back and forth across the bottom--or a spiral design might work nicely in a round pound--and run to the house and back to the pond in a closed loop. If the pipe is insulated or buried below the frost-line it can be filled with water. If not, a heat exchanger fluid is used--but in either case it can run through baseboard or radiant floor copper pipes--or whatever piping material releases the heat the most efficiently and resists corrosion.. The only interruption in the flow is a thermostat and possibly a pump. Convection and siphon effect are possibilities if the house and pond are not at two untenably disparate levels. Another interruption in the flow might be a small turbine engine for the production of electricity. This might require a larger pond. I have no figures on this and in an e-mail response, Ormat Corporation, manufacturers of large solar pond turbine engines in Israel said that small solar ponds were not practicable for electricity production. I, however, have yet to be convinced of that.

The pond is then filled with water and great quantities of salt are added--until it is precipitating out on the bottom and there is a dense layer of precipitate about a foot deep. Finally a screen is placed on the surface of the water to keep children, animals and leaves out (it should be cleanable). It produces 160-212F (71-100C) water or heat exchanger fluid to circulate as heat or to run a turbine for electricity. The pond still functions effectively even when the top layer of water is frozen.

I don't know exactly how much salt should be added, but some simple experimentation or or research should answer it easily. I had found one booklet on line which sounds promising--"Design Guide for Shallow Solar Ponds" by A. B. Casamajor, which was put out by the National Institute of Standards and Technology back in 1979

In warmer climates or in summer time you could use water in the pipes, but in colder climes antifreeze or other nonfreezing heat exchanger should be used. Then simply add an thermostatic valve and voila! -- cheap renewable heat from the sun.

According to Wikipedia's excellent brief description there are more efficient ways of producing heat --e.g. concentrating solar collectors, but none-to my mind are simpler, except for perhaps a south facing window.

As mentioned above, if you want to generate electricity as well, the architect told me that an Israeli company called Ormat Ltd produces a small Rankine-cycle turbine generator for generating electricity from low heat sources: that can run off the pond. In 1980 it cost about $5000. If you had several houses built in a cluster you could make one 20' X 20' pond (according to the architect 3-4 homes could be supported by this) and spread the cost of the generator and pond construction out.

This article (click here) has more on Israeli solar ponds in general and the Rankine turbine generator made by Ormat Ltd. in particular.

In an excellent article about larger communities and solar pond power production, authors Allen S Krass and Roger LaVialle III designed a solar pond for North Hampton, MA's 30,000 residents.

I ordered the previously mentioned publication , entitled "Design Guide for Shallow Solar Ponds" by by A. B. Casamajor, through the reference desk at my local library. It was put out by the National Institute of Standards and Technology back in 1979. You can try calling the Canadiana Collection of the Canadian Institute for Historical Microreproductions (CIHM) at (613) 2355-2628, FAX - (613) 235-9755552).

I tried to get it directly from them--but no go. Luckily one of our Maine libraries had a copy stashed away in its stacks--but when it arrived it was on illegible microfiche! Even my library's brand new microfiche reader could not bring it into focus. I have just discovered and ordered a used copy of the 59 page pamphlet for $24.99. I will write an addendum to this article if it has anything new to say.

Another solar Pond article from a Science News 1977 article by Carl Neilsen discusses his successes with experimental solar ponds at the University of Ohio. It also discusses the problems of algae growth and loss of heat through wave action caused by wind--which it seems to me could be reduced by stretching chicken or sheep wire over the surface.

Here is an article on large solar ponds in Victoria Australia with a nice little diagram.

Or, for the same project you can look up:

Solar Pond Project Leader, RMIT University


Dr John Andrews:(03) 9925 6085
Professor Aliakbar Akbarzadeh:(03) 9925 6079

Or you can read about the worlds largest solar pond (in 1984) in Popular Science; Sep84, Vol. 225 Issue 3, p38, 1p, 1bw

So I do hope someone will give this a try and let me know how it works. I do not have the wherewithal to do it myself, but my dream home has one installed already.


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