PV Panel Shading

pogonippogonip New UserPosts: 14Registered Users
I was wondering if a solar panel had 20% shading how much that would decrease it's output?

If one panel in a 10 panel string we shaded by 20% how would that affect the output of the string?



  • nielniel Solar Shotgun Posts: 10,309Solar Expert ✭✭
    Re: PV Panel Shading

    i don't know the exact degradation, but my guess would be it might nullify the whole pv's usable output depending on where and how that shading occurs.

    that pv placed into a string will have its bypass diodes active and allow the current and voltage of the rest of the string to pass. basically a shaded pv is a wasted pv.
  • BB.BB. Just some guy Posts: 23,914Super Moderators admin
    Re: PV Panel Shading

    Adding to Niel's comment... Shading a panel in a string (or partial shading) does depend on the system configuration.

    Shading will reduce the output of a solar panel to zero current/volts...

    If you have a 17.5 volt panel charging 14.5 volts into a 12 volt battery bank, shading will reduce the output voltage to less than 14.5 volts and therefore, no current will flow into the battery bank.

    If you have 20 panels in series for ~Vmp=350 volts and shade 2 panels for ~Vmp=315 volt array voltage and the GT inverter accepts from 200-600 VDC, then you will have ~a 2/20 or 10% reduction in output for your system (there are bypass diodes that let the current flow around the shaded panel).

    Solar electric panels are very sensitive to shade and it is worth while to work hard at preventing shading, especially during the prime hours of 9am to 3pm (moving vent pipe on roof, trimming back trees, etc.).

    If you have, for example, power lines that cast a shadow across your roof most of the day, just those little shadows from wires can easily kill 50% off of your power production.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • GlovesGloves New User Posts: 65Solar Expert ✭✭✭
    Re: PV Panel Shading

    yeesh, phone lines... Never thought about that.

    I know that one of my panels gets about 1 PV square into the shade from my
    chimney around 4:30pm in the winter. The 2 panels are in parallel so the other
    stays in full sun.
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