Connection Issue on Grid-Tied PV Array??

rocmor

Greetings.

I have a 24 panel PV array sitting on my garage roof that is wired to a junction box of sorts (also on the roof) via 4 cables. This box, in turn, feeds the GTI inside the garage. After a recent snow, I was checking the GTI display: though it was sunny, the output was only 1300+ W at a time of day when I would have expected more like 2kW. The next day, about the same time, I checked it again. Though there was cloud cover, the output display read almost 1800W. Both days, the DC volts were reading in the 320 - 340 V range, and all the panels were totally clear of snow. The only difference, other that cloud cover, between the two days is that, on the first day, the junction box was covered with snow, the second day, it was clear and dry. This is the second winter for this system. It was professionally installed by a reputable and "certified" installer. Otherwise, it performs to spec. Could the connections at the junction box be leaking or shorting somehow? Thanks for your help.

BB.

Re: Connection Issue on Grid-Tied PV Array??

If your output is 1/2 what you would expect--Then it is definitely having problems.

If you can get to the individual cables on the roof--A DC Current Clamp Meter would be a good place to start. Measure the current in each string--The values should very close (less than +/- 10%, if no shading). If you have more variation, then cabling, connections, or even bad panels, are suspects for the problem.

It is still possible to have "bad panels" if the failures are distributed among all strings. A problem with the inverter is also a possibility--But probably not my first guess (more likely the inverter is working or not, partial reduction in output may be less likely).

-Bill

RCinFLA

Re: Connection Issue on Grid-Tied PV Array??

Voltage reading is primarily a function of panel temp and not a good indication of output level.

Assuming the first day the panels were not covered in snow fall blocking sunlight, the next logical reason would be one four string not functioning, or worse, loading down other three good strings.

Get youself an AC/DC capable clip-on ampmeter (Sears has one for about $60) and check output on each of four string during good illumination. If the strings have different orientation or one or more strings have just a small area of shading at a given time of day it will effect output from that string. Something like a shorted bypass diode in one of the panels can bring down that whole string.

niel

Re: Connection Issue on Grid-Tied PV Array??

rc,
that doesn't seem to fit from my way of thinking as the next day it had its output up closer to his expected 2kw. if water is leaking into some of the connections and shorting out part of the current then he's got a big problem with that combiner box.

do check all of the strings for proper output anyway, but do look inside that combiner too.