Reverse Bias due to shading and Bypass Diodes

Rogli

New Member
Interesting information here in this thread. I have a relating issue that seems to be unresolved, or I understood it differently. Could anyone please take a look at my query regarding bypass diodes? I want to bypass an entire solar panel from a string of solar panels attached in series. I shared a picture and would like to know where to place those diodes. Remember, I aim to bypass an entire solar panel upon shading so that the string consisting of panels connected in series does not drop the power to near zero. Below is the link to the thread I started.

 

mike95490

Solar Enthusiast
Any commercial manufactured panel should have 3 bypass diodes built into it's J-Box at the factory. If the entire panel is shaded, the 3 diodes activate ( or as many as needed to bypass the shaded solar cells ) and the panel is completely bypassed. Now if you get enough panels or sections of panels shaded / bypassed , you may not have enough system voltage to run .

Blocking diodes are built into nearly all charge controllers ( even the $7 ones ) so there really is no installer that adds any diodes, they are either built into the panels at the factory (bypass) or in the charge controller (blocking)

Now the other half of the story. Panel mfg's are cheap and use the cheapest parts, and when bypass diodes are worked hard by shaded panels, the diodes often overheat and fail. So there is some market for repair parts for bypass diodes, but Shade is the problem. If you have too much shade, you should relocate the panels, not try to mess with some weird diode scheme that isn't going to work.
 

Rogli

New Member
Thanks a lot. I am very confused since, in my experience, shading on one panel connected in series with other panels of similar configuration, shuts down the entire system.

This doesn't happen in parallel connection though. However, my inverter is designed so that it operates mainly on voltage. Hence, connecting panels in series is a requirement.
 

Hedges

I See Electromagnetic Fields!
Thanks a lot. I am very confused since, in my experience, shading on one panel connected in series with other panels of similar configuration, shuts down the entire system.

This doesn't happen in parallel connection though. However, my inverter is designed so that it operates mainly on voltage. Hence, connecting panels in series is a requirement.

You experienced system shutting down? The PV string should just lose the voltage of the one shaded panel. If remaining panels add up to enough voltage to feed SCC or GT inverter, system should keep running. Assuming your panels had diodes. If the string is barely enough voltage, then yes it shuts off.

I had a GT inverter with 18 "24V" PV panels wired 9s2p. I tried shading a single panel, and inverter reported wattage about 17/18ths of what it did unshaded.

Another setup used to have "12V" panels wired 24s. When I rewired with additional panels as 16s2p, voltage was so close to lower end of MPPT range that slight shading shut it off.

With parallel panels, if one panel is partially shaded so 1/3 or 1/2 of it doesn't produce power, its Vmp drops so low it produces zero current and the other parallel panels are all that's left. In series, you only lose the 1/3 or 1/2, not all of the panel.
 
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