Evaluating Used Solar Collectors
Tempered glass glazing
High temperature insulation (Polyisocyanurate or fiberglass)
Copper manifolds and riser tubes
Copper or Aluminum absorber plate.
AER, Energia, Grumman, Heliodyne, ITT Grinnell, NorFlo, Monrningstar, Novan, Solar Industries, Suncatcatcher, SunEarth, U.S. Solar
Check as much as you can visually. Check the inside of the manifold pipes for signs of corrosion. Check the frame etc. for damage, corrosion, ...
If you can find a label, read it for the brand and other useful material on the collector.
Chuck's procedure is to plug all but one of the manifold collections, and hook up compressor and air pressure gage to the remaining manifold connection and pressurize to 40 psi. Check after 15 or 20 minutes for leaks. If you detect leaks, make sure its the panel itself, and not your plugs.
I think that many people may find it easier to use water to pressurize the collector for the leak check. Figure out a way to attach a garden hose to one end, and attach a shutoff valve to the other end. Start the garden hose, and wait for a steady flow of water out the valve end, then shut off the valve while letting the garden hose continue to pressurize the collector plumbing. Check for leaks after a few minutes.
Chuck does not mention this, but I would be inclined to do a flow test to make sure there are not blockages in the internal collector plumbing. Maybe hook up a garden hose to one manifold with a pressure gage. See what kind of pressure it takes to produce the rated flow for the collector ( about 0.05 gpm per sqft of collector eg 1.6 gpm for a 4X10 collector).
Cost ranges for used collectors
4X8 ft $225 to $300 (new Heliodyne 4X8 is about $800)
4X10 $275 to $350 (new Heliodyne 4X10 is about $940)
Shipping used collectors may be prohibitively expensive, so best to look locally.
There is more information in Chuck's Home Power article -- you will have to pay a small fee to download that issue (112), but probably well worth it if you are buying used collectors.