Panels shorting in series

[ILFE]

I just read a thread on running panels in series. I am considering doing this as well, creating a 24vac system.

My question is, if you have one panel that shorts, or has any other issues - perhaps not producing power any longer, will the other panes in the array continue to provide voltage to the controller? Or, will one panel failing cause the entire array to stop functioning?

[inetdog]

I just read a thread on running panels in series. I am considering doing this as well, creating a 24vac system.

My question is, if you have one panel that shorts, or has any other issues - perhaps not producing power any longer, will the other panes in the array continue to provide voltage to the controller? Or, will one panel failing cause the entire array to stop functioning?

1. When a panel shorts out (from its + to its - lead) it will not produce any power but will not get much hotter than it would just from the sun shining on it anyway. (The panel will be converting at most 20% of the solar energy to electrical energy anyway.) And it will allow current from the rest of the panels in series to flow through it.

2. When a panel open circuits (a break in the wiring or the panel itself, then the entire array will stop sending current to the controller. Unless there is a bypass diode in the junction box. (*) more about this later.

3. When one panel is shaded or partially shaded, it will continue to contribute to the Voc of the string, but the maximum current will be limited to that produced by the shaded panel (*)

4. When a panel output decreases with age, you can expect that to apply equally to all of the panels in the series string. If you add a new panel to an old series string (especially if the panels are amorphous) you may not get the full rated output from the new panel.

5. If the voltage of the string is lowered enough, it may no longer be enough to allow your PWM or MPPT controller to charge the batteries. This is more likely to be a problem with a PWM controller. (As when you use only 2 12 volt panels in series to charge a 24 volt battery bank.)

*: Bypass diodes allow current to bypass (make sense, doesn't it) a section or entire panel which cannot produce as much current for any reason as the rest of the series string. The string voltage will drop to about 1 volt below what the voltage would have been if the panel had not been in the string at all. See 5.