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DIY Nanofluid Solar Collectors

 
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Liquid with black particles suspended in it can adsorb solar thermal energy with great efficiency.
Nano particles avoid the problems of sedimentation and abrasion.

Nanofluids in solar collectors

Luckily, a little bit will go a long way, because nanotubes are not so cheap, and  diy nano particles might not have the same properties.

I envision a simple collector like this:




Only made with clear tubing like this:





This would lead to a storage tank of dark fluid for space heating, or a coil of dark fluid in a preheating tank for DHW.


Alternatively you could build a collector like this :




It uses a black lining to adsorb the solar heat energy.
Our version would use black liquid instead.
A very thin, flat version of this panel could top an insulated tank,with a a small solar powered pump slowly circulating the dark liquid.
This would  allow maximum solar penetration  of the dark liquid, and outdoor storage of the heat tank.
With a DHW coil passing through the insulated tank of dark liquid, rather than a coil of dark liquid  passing through a DHW tank, we avoid exposing pipe to abrasion from rapidly moving particles , so we can probably use cheaper home made, not necessarily nano particles.








 
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Charcoal from a sufficiently hot process might not be nanoparticle-sized, but they will have a greater surface area than a ground mineral source of similar grade. For a homestead DIY-scale experiment, I think it would certainly qualify.

-CK
 
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Careful about plastics that have not been designed for high temps.      They give off nasty dioxins when heated to high temps.      Pex can be used if is the high temp kind...
 
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Nanoparticles have tended to get a bit of side-eyeball from people who are concerned about toxins, because there has not been a ton of research done on their health effects.  The concern is that nanoparticles of substances we consider benign at the usual particle sizes might have unforeseen effects on the chemistry and biology of humans, pets, and livestock.   I haven't been keeping up, though, on what the best current thinking about this is.

I realize that you are proposing closed loops and contained systems, but every system has the potential for leaks, spills, and end-of-life disposal issues.  So it might be something to consider.
 
Chris Kott
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That's a lot of the reason I suggest charcoal suitable for biochar. Granted, if you grind it to a fine powder, you won't want to inhale it, but for reasons of disposal and accidents, I think it a safe alternative.

-CK
 
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I would try for soot. A much finer particle then most biochar.
 
William Bronson
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Excellent points about the nano particles
Looking into it more, I think that all suitable solids will probably to contain potentially dangerous nano sized particles, but graphite is probably a good choice for many reasons.

Here is something on graphite as a wet/dry lubricant.

This is something on graphite for solar heat storage.


Graphite liquid mixtures are a fairly complex topic it seems.
A simple diy material has been hard to find.
Graphite/Propylene Glycol mixture would be great, if it can work.

Mart, the temperatures of standard solar batch heaters do seem to be 160 F or higher, close to the limits of standard vinyl tube, so a flat panel/ storage tank type collector is probably the better idea.

This is better depiction of the storage  tank/collector idea:



In the diagram, the EPDM Adsorbing layer could be eliminated, as that role would be covered by dark liquid.
The pump, depicted in diagram with the big P could be a solar powered air lift pump, offering the benefits of no moving parts, low energy use, and circulating settled particles.



I feel like this could be built with a chest freezer, sheet of insulation, double pane window, coil of PEX.
Maybe some reflectors.
 
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Back when I was experimenting with my a-frame mini greenhouses I tried milk jugs with (a) used motor oil and (b) plain water with rit dye as a solar absorber+thermal mass.  Despite being very different materials, I was surprised that both worked out about the same.

Given those results, I'm not convinced that nano-particles would be significantly different either.  It's just that they're the "hot new thing" right now. (no pun intended)

Of course, the DIY recipes proposed would be less toxic than oil and (probably) cheaper than dye, so those would be the real advantages.
 
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You might want to check out the MOST (Molecular Solar Thermal Storage Technology) that has the same objective; collecting energy from the sun, yet has the advantage of being able to store said energy in molecular form for up to 18 years. The molecule , suspended in fluid) changes when exposed to the sun (currently just the blue & UV spectrum) and when exposed to a catalyst, changes back and releasing energy in the form of heat (currently 180 F). They anticipate commercial application within 10 years. Here is a Youtube of Kaspar Moth-Poulsen - "A liquid fuel with the ability to store solar energy" - Boma France Campfire discussing his technology and a related window film that can get energy from light and release it as heat on demand. Interestingly he was studying nano tech when he started on the liquid solar fuel idea at Berkeley. The system as it is developing uses primarily carbon, nitrogen and hydrogen, forgoing rare or expensive elements. Early versions used toluene as part of the system but they were able to switch to a non-toxic, cleaner carrier for the molecules.
 
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Solar Components claim their tubes have increased heat storage if you fill the tubes with water and add a dye.  Anyone know if this actually does that?

 
Graham Chiu
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This guy determined that black dyed water tubes increased heat by 20% over light blue.
In the comments it says if he added salt to the water that would have given him possibly a further 5% heat storage capacity.
 
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I wonder what would happen id copper particles were added to the water? They would quickly tarnish and go black, but then again, copper has an affinity for heat transfer so maybe a person would get some really interesting thermal dynamic properties???
 
Travis Johnson
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I have always had an out of control fetish for Active Solar Heat, and I once say a parabolic solar set up that cast the reflected light upon a tube. But this arrangement was long and curved so that it followed the arc of the sun. It was done that way so there was no moving parts, just a pump to push the brine through.

I wondered what would happen if you dyed a salt brine and then pumped it through the arced solar array?

I always liked Active Solar only because a person has much, much more control of the heat, because with simple controls you can send the heat when and where you want it to go.
 
Travis Johnson
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I talked with a solar heat hot water guy at a fair one time, and he told me the secret to getting efficient BTU's...it is how the sun transfer heat across miles of space...VACUUM.

I know MAINTAINING a vacuum is hard to do, but what if a vacuum was on a timer and when the pressure increased, the vacuum system kicked in to maintain the vacuum? It would be a easy do it yourself workaround. A person could even go out and buy a woodworking vacuum system and just put it on a timer so that every hour, on the hour, it would come on and maintain a vacuum. Amazing homemade solar heating arrays could be made then. The efficiency would quickly pay for the vacuum and timer.
 
Graham Chiu
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I'd think it'll be easier to purchase evacuated solar tubes.  Vacuum already established.
 
Travis Johnson
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Graham Chiu wrote:I'd think it'll be easier to purchase evacuated solar tubes.  Vacuum already established.



Perhaps???

It all depends upon the cost of them. I like to do as much as I can myself because when you keep the overall cost of the project down, the return on investment is so much quicker. And I have a wife and (4) daughters and so the amount of money I have to spend on these projects is marginal because I always hear the dreaded, "you spend how much money on this idea of yours?" By keeping the cost down, projects such as these might actually be carried out instead of just being a discussion of theory.

I think a lot of people on this site are in that situation, so I try to think of do it yourself solutions, then share those ideas with others. They can accept or reject them, but I like exercising my brain, thinking, "how can I do this myself", rather then just make a list of expensive parts I have to save up and buy.
 
Graham Chiu
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Well if you can come up with a working solution that would be great. When all my solar evacuated tubes failed the efficiency dropped to almost nothing yet from the outside nothing was obviously wrong.i presume the vacuum had broken. Likely movement over the years had broken the glass with fractures. Luckily it was only at 8 years and the warranty was for 10 so they've all been replaced.

They say nature abhors a vacuum which means it's difficult to obtain and maintain as in my experience. I've never heard of anyone attempting this on a domestic site. Here a single tube costs about NZD 36. If you can beat that, you won't have to worry about money in the future!
 
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