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I am building an evacuated tube array for a solar water heater and I am selecting the materials to use for the tubing and the collectors (the places connected to the tubing that help absorb the solar radiation).

terrible schematic I can choose from copper, aluminum, or steel as they are all relatively cheap and easy to work with the tools that I have on hand. Everything else being equal, which of those three materials is best suited for collecting and transferring the heat to my 40% propylene glycol solution? Additionally, can I add a coating, such as black paint, to increase the effectiveness of this material?

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Copper sheet with an absorbing and poor emitting coating is available which is easy to solder copper pipe to the untreated reverse side. Guess why many flat plate collectors are made like this…

As for spacing you can get full details from Duffie & Beckmann Solar Thermal Engineering (can’t remember exact title, but it is a really good book) but panels I have made have about a 20cm spacing on a 1 or 1.2mm sheet which is about 90cm wide.

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  • $\begingroup$ That's exactly what I needed. I will find and read the book before I move on as will as source the coated copper. I suspected copper was the answer but did not know how to check that. I've marked your answer as the solution and when I find the book I will comment the title in for future users. Thanks a bunch. $\endgroup$
    – Mikeologist
    Commented Oct 16, 2021 at 17:35
  • $\begingroup$ The book is titled Solar Engineering of Thermal Processes. The first link I found was for a pdf of the book. $\endgroup$
    – Mikeologist
    Commented Oct 17, 2021 at 0:16

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