Copper vs aluminum diy solar water heater

[Fordguy64]

Well as I slowly get closer to getting my roof done I plan to build a new shed and add some solar to it. I've been looking into the diy "1000$ dhw set up that people have been making on builditsolar. My question is why not use copper as the collector fins other then price? I was doing a little digging today and ran across this copper flashing now it is a bit pricey but with copper being twice as conductive as aluminum wouldn't it make more cents? I haven't seen anyone try it so I was thinking about doing some small scale testing to see if it make a difference

Thoughts? Something I missed?

[greif]

Test would be a great service to everyone, would like to see the results

[Mikesolar]

This one is easy. Until 10 years ago, copper was used for 99% of all fins and the thickness was roughly .2mm+-. The biggest problem was the copper tube, aluminum fin connection which corroded a lot. It might have been good for a few years but the average panel with aluminum fins only lasted a few short years.

Now, with ultrasonic welding and laser welding, better aluminum (less reactive alloy) the joint is "supposed" to last as long as long as a copper fin. The thickness needed to have the same overall heat transfer for the same standard 150mm fin width is around .45-.5mm.

The surface prep is a bit different as well. The aluminum MUST be roughed up lightly and cleaned of any oxidation even more so than copper and just before the coating is put on.

Here is a spec by a company that makes both products. I toured their plant back in 05 in Germany. Interesting anecdote is that the head of the company took me out to lunch and we had fish from a river that used to have a NUC plant on it. 5 years after the NUC plant was decommissioned (thanks to solar PV, wind and Thermal), the fish were deemed safe to eat.

Note the absorption curve. This is with the coating, of course and it will be different from a painted coating that DIYers will have.

[Fordguy64]

I only got a quick glance at the info you posted but it looks like there is only a slight difference between the copper and the aluminum? Probably not worth it then?

[NiHaoMike]

The thermal conductivity difference means almost nothing in most solar applications .(1kW/square meter is much smaller than the 100W/a few square centimeters typical of high power semiconductors, and the difference is small even there.)

As for coating them, maybe a really cheap way would be to smoke them over a wood fire? (Spray water on the reverse side to prevent it from melting.) In physics, it's pretty common to make a "perfect absorber" by smoking a piece of metal or glass over a candle.

[nitro-nige]

Sorry to hijack, I'm in the planning stage for a solar heater/pop can heater.
I had been wondering if using copper pipe would be better than Aluminium cans/pipe.
But if I understand NiHaoMike's comment for solar it's more about convection than conduction, is that correct?

[Mikesolar]

There s another thread about pop can solar. Thicker metal doesn't make it any better with air heating. It is all about surface area and having thin metal which is why the pop cans are so good. You want the heat to transfer as quickly as possible through the metal and the thinner it is, the faster it will move.

[AC_Hacker]

Originally Posted by Fordguy64

...My question is why not use copper as the collector fins other then price?...

I think your query might have gotten off track...

Your question was about using copper fins, right? Copper is a better conductor by twice compared to aluminum, but that doesn't mean that you'll get twice the heat.

Gary over at Build It Solar did some experiments using copper tubes, and he found about a 7% increase, which he thought was negligible. I agree with him in that case, because you can apply your bigger 'copper budget' to an alternative method and get bigger collectors and more heat per buck.

However, if size was constrained, for instance if you were talking about radiant floors, it may not be possible to make your floor bigger, so copper and its 7% advantage might be very attractive especially in the long term.

* * *

On a slightly different tack, there are hundreds of thousands of splendid all-copper solar collectors that are not being used (who would want to screw around with solar when gas is only 63 cents per gallon?) and will eventually end up in the scrap yard, which is the last stop before being sent to China... yes, China is the worlds largest buyer of copper.

If you look around you'll be able to find top quality solar collectors for a song. I did it, Daox did it, and you can too. Be resourceful, check CraigsList in your area and any other resource you can think of. Also a little patient, and you'll have those collectors of your dreams quicker and cheaper and better than you can build them.

Best,

-AC

[greif]

Side note, I would expect copper prices to rise after last week copper mine landslide in utah , nearly mile deep open pit mile is mostly closed and may be for a long time for them to dig out

Utah Copper Mine Landslide Will Hurt State Economy - ABC News

[AC_Hacker]

Originally Posted by greif

...I would expect copper prices to rise after last week copper mine landslide in utah...

All-Copper solar collector found in
less than 1 minute of searching...

All the better reason to re-double your search for the used copper solar collectors.

Best,

-AC