'hard shading' causing panel failure?

15 Posts
Dec 13, 2011 02:46 pm
'hard shading' causing panel failure?

I have had a 3kw grid tied system on my house for 8 years. Two parallel strings of 9 panels on either side of a dormer to a Sunnyboy inverter. The installer decided to use two strings to deal with a dormer on the center of the roof.

Recently, one string (west) has stopped producing power because of a panel with burn marks and a local technician theorizes that hard shading from a dormer has caused this failure. Has anyone heard of hard shading causing either a cell or diode to burn up and open the circuit? The only proposed fix is to rewire the whole system, including retrofitting 8 panels that have a few hours of shading with Enphase inverters for about 9 or 10 grand. Any thoughts on this burn out problem? The local technician said that the other 7 panels that have hard shading for a few hours per day will eventually burn out also.

Any thoughts would be much appreciated!

462 Posts
Dec 14, 2011 11:14 am
Re: 'hard shading' causing panel failure?

James, you should be able to disconnect the one panel that has damage in order to verify that all the othe panels are in good working order.  The logical first step would be to simply remove the wires from the one panel in the junction or combiner box and then check the status. Having one bad panel in the string may reduce the power of the entire string.  Removing the panel, if it is in parallel with all the others, will only show a small reduction in amps out from the array.
« Last Edit: Dec 14, 2011 11:37 am by Tom Mayrand »
15 Posts
Dec 14, 2011 11:22 am
Re: 'hard shading' causing panel failure?

One panel is definitely dead.  I am just wondering if this shading  caused the burn out or if it just was flawed and died prematurely.    If it was the shading, I have 7 more (of 18 total) panels in the same type of situation.  If I just remove the bad panel, the voltage would be below my inverters minimum, so I need to decide between replacing the bad one (if can find a BP 5170)  and hope that the others hold, or alter the wiring of the whole system and add Enphase inverters.  THe major change and adding the mini inverters would make the whole system work more efficiently and I would get much more production, but it would be quite expensive (9-10k).
462 Posts
Dec 14, 2011 11:54 am
Re: 'hard shading' causing panel failure?

James, is this panel 24 volts? If so, and the rest of the system is designed for 24 volts, then removing the bad panel will have no effect on the voltage of the array.  When  same voltage panels are connected together  in parallel, through a combiner or junction box, the current is added,

(eg. 9 -170 W - 24 volt panels combined together, all + and -  leads combined, the total amperager would be around
170W/24V x 9 panels =60+/- amps)

 so removing a single panel will only cause the current to be reduced from that part of the array by 170 W/ 24 V =7 amps.

If you are feeding 9 X 24 or 220 volts into your inverter, then yes you MAY have to replace the single panel
« Last Edit: Dec 14, 2011 12:26 pm by Tom Mayrand »
15 Posts
Dec 14, 2011 12:12 pm
Re: 'hard shading' causing panel failure?

Yes, these are 24 volt panels, but my system is two parallel strings of 9 panels each.  So one of my strings is open because of the dead panel.  Each string is 216vdc.  If I remove the bad panel then my voltage will be below the Sunnyboy's minimum input voltage of 208vdc.
462 Posts
Dec 17, 2011 12:50 pm
Re: 'hard shading' causing panel failure?

  I would swap out one panel from the working array, if easily done,  for test purposes, just to make sure the rest of the underperforming array is okay.
   Is there any way to adjust the input voltage minimum on the inverter?
  Even with one missing panel, voltages can vary, and the array may still produce with the bad panel removed. (If one array gets more sun than the other, make that the 8 panel array) Then you can monitor the array until you find a new panel. 
15 Posts
Dec 19, 2011 07:53 pm
Re: 'hard shading' causing panel failure?

I don't think there is a way to adjust the input minimum threshold of the inverter.  An electrician or engineer might be able to, but not me.  I don't have an extra panel to swap in to the string in order to test it.  I'd love to find a replacement one, but as with most technology purchases,  the current models are old news quickly and even more quickly taken off the shelves.   My model panel BP 5175 is impossible to find now.
462 Posts
Dec 20, 2011 12:10 pm
Re: 'hard shading' causing panel failure?

James, I know you don't have an extra panel, my suggestion was to remove one panel from the other, working array, (the array with no shading), and use that panel to replace the bad panel on the other array to ensure that there are no other problems with the shaded array. 
 I also took a quick look at the sunnyboy literature. It shows that the input wattage is over a range so I am not sure if it has to meet the maximum in order to produce.

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