Old 06-22-2012, 11:48 AM
ralph124c ralph124c is offline
Join Date: Mar 2002
Posts: 18,476
How Do Solar Ponds Work?

A solar pond is a way of capturing thermal energy from the sun. It is basically a pool of water, with two layers:
-a high density salt water layer at the bottom
-a lower density, non-salty layer at the top.
The bottom water heats up from the sun's rays, and the top layer stays cool. You can then run a heat engine on the temperature difference between the layers. My question: why don't convection currents mix the layers?
Old 06-22-2012, 11:55 AM
Mines Mystique Mines Mystique is offline
Join Date: Mar 2003
Location: Golden,CO
Posts: 177
I am by no means an expert, but some quick googling led to this page on Wikipedia. According to the article, there are actually 3 layers, the top-most is fresh water, the middle has a salinity that increases as the depth increases, and the bottom layer has a uniform salinity. The middle layer acts as a barrier to keep the convection mixing from occurring.

The mixing is prevented because the salinity gradient makes the water denser as the depth increases, while the temperature gradient tries to make the density decrease as the depth increases. These 2 effects cancel each other out, preventing the mixing from occurring.
Old 06-22-2012, 12:01 PM
wevets wevets is offline
Join Date: Mar 2000
Location: hobgoblin of geographers
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In solar ponds there is also a salinity gradient, but in the opposite direction of what you mention. You want the high salinity water on the bottom, because it is more dense, and under the right concentration of salt and temperature it will not lose enough density to cause a convection current. Your top layer is your low-salinity layer because likewise, it will not sink due to a higher density than your bottom layer.

There's also a third layer between of intermediate salinity, that helps to separate the two.

... ETA: yes, what Mines Mystique said.

Last edited by wevets; 06-22-2012 at 12:02 PM.
Old 06-22-2012, 01:18 PM
CalMeacham CalMeacham is offline
Join Date: May 2000
Location: Massachusetts
Posts: 42,038
How Do Solar Ponds Work?

Plagiaristically like Sherlock Holmes.

August Derleth shoulda been sued.
Old 06-22-2012, 02:00 PM
billfish678 billfish678 is offline
Join Date: Jun 2006
Posts: 16,681
While I understand the basic concept I was always kinda surprised that diffusion wouldn't render the things unoperable in relatively short order. The perfectionist in me couldn't help but put a thin layer of clear plastic between the the different layers of water.

My theory is they work like magnets

Last edited by billfish678; 06-22-2012 at 02:01 PM.
Old 06-22-2012, 03:39 PM
DocCathode DocCathode is offline
Join Date: Jul 2000
Location: Philladelphia-Mummer city
Posts: 11,667
Originally Posted by CalMeacham View Post
Plagiaristically like Sherlock Holmes.

August Derleth shoulda been sued.
Curse you! I wanted to be the one to make a Solar Pons joke!

Nothing is impossible if you can imagine it. That's the wonder of being a scientist!
Prof Hubert Farnsworth, Futurama


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