[Mikesolar]

It really depends on a couple of things whether you need copper all the way. The first is the angle, as we discussed, and the second is the specs of the panel, the absorption and emission characteristics of the panel.

On this I have a big bone to pick with the SRCC way of representing the performance of a panel. The rest of the world states absorption as No 0.750 (for example) and is an absolute value. Then it states the major collector losses as W/(m2K) such as 4.50 W/(m2K). The lower the losses the better. But SRCC (aside from changing it to btu), presents the numbers as BTU delivered on a cloudy day, sunny day etc. I feel that this is all people look at and they don't learn what the other terms mean. It dumbs down the process.

Anyway, back to your issue. A DIY collector will typically not have the good loss number (poor- 6W, good 3.5W, for example) and the higher the loss numbers, the lower the stagnation temperature, or the lower the maximum collector temp will be with no fluid flow at 1000w/m2 of sun shine.

A really good flat panel will sit there in these conditions at over 200C and a lesser efficient one will sit at 150C. Even 150C is too hot for PEX as it is rated for 80C temps (although this is only the CSA test procedure, they can go much higher. Especially PEXa tubes such as REHAU and UPONOR), but 150C is not good.

At the very least there needs to be copper for the first 2-3M from the panel with a DIY panel, but copper all the way is a way better bet.

This is not to say that a manufactured panels with a higher losses number is bad panel. Remember that the vast majority of the time we need collectors temps of 50-80C and not 150C (a pump won't run at this temp anyway, the control won't let it). This is why I would rather see an extra panel or two than pay to have a higher efficiency panel.