Condensation inside flat plate

DD_5

I installed two Caleffi NAS10406 - Flat plate collectors six years ago. The customer was cleaning the roof and noticed condensation inside the collector. What might be the cause? What should I look for when I go to check it out?

matt_sunwaysolar

I've used a lot of AET's AE-Series and Solar Skies's SS-Series Collectors, which those Caleffi Collectors' design is based off of. (Really the exact same collectors.) Condensation inside these collectors is usually going to be one of two things:

1) The boxes are not watertight. "Neither are anyone elses'.) Especially after a few years, they can begin to take on moisture after rain, snow or heavy humidity. Normal condensation will typically evaporate after and hour or two of sunlight, with minor effects on production. I wouldn't be too worried about this unless it's staying all day and having a dramatic effect on system production.
You could try things like replacing the glazing gasket, but the backsheet and the mitered framewalls of those collectors take on water too and are more likely to be the cause of moisture entering the box.
If the collector box or frame is damaged and allowing water in, that's another story, it may need to be repaired or replaced. Some manufacturers well sell collector boxes without the absorber or glazing for a much cheaper price.

2) A brazing joint could have failed between the header and the riser tubes, letting heat transfer fluid (HTF) into the collector box. Depending on your HTF, you can look for signs of discoloration and sediment on those braze joints without removing the glazing (typically). Propylene glycol will usually look a turquoise color an the absorber plate/braze connection. Water will typically have a white-ish scale an sediment buildup on the joint. You should check your system pressures, fluid levels and operating characteristics to see if you've been losing any HTF. If this is the case and the collectors are still under warranty, you can typically braze them yourself and collect a labor allowance from the manufacturer or be sent a replacement collector.

hot_rod

Notice on the back side the two small black "button" vents. Should be one near the top and bottom. These allow the collector to "breathe' so the surround ambient conditions temperature, moisture, etc will always be "traveling" thru the collector. The collector is not an air tight assembly.

Depending on dew point, etc you will see some condensation inside the box from time to time, just as you car windows fog up

As soon as the absorber plate warms inside the collectors should clear up.

As Matt mentioned, a leak inside the tubing will also cause clouding. if you suspect a leak, monitor the system fill pressure.

Generally it is low in the morning, rises a bit as the sun hits the collector, and falls a bit as it cools. It should not go to zero, that could indicate a leak, or perhaps it was not pressurized when installed.

Gasket leaks around the glass are rare, unless the collector was dropped or damaged, or the glass has been replaced. Sometimes rough handling during shipping or installation can damage the glass mounting channel, causing a leak around the glass gasket.