diy solar

diy solar

Shading and solar arrays

wiseacre

Solar Enthusiast
Joined
Aug 8, 2021
Messages
492
Location
North of the Adirondacks
do I understand correctly?
say 8 panels mounted in a single row
if I have a string of 8 panels in series (8s) and one gets shaded the whole string suffers
if they're broken up say 2s4p and one panel gets shaded only the string that's shaded will be negatively affected, the other 3 will still produce full power
and so on until they're all shaded and I get bumpkins
 
do I understand correctly?
say 8 panels mounted in a single row
if I have a string of 8 panels in series (8s) and one gets shaded the whole string suffers
if they're broken up say 2s4p and one panel gets shaded only the string that's shaded will be negatively affected, the other 3 will still produce full power
and so on until they're all shaded and I get bumpkins
Yes..... and No. (How is that for a definitive answer?)
As a generic statement, your assumption is basically correct. However, if there are bypass diodesin the system, it may not be as bad as you describe when the panels are in series. If there are bypass diodes in the junction box of each panel, then if the panel is shaded, current will flow through the bypass diode and not reduce the output from the other panels in the series string. Many (Most?) name brand panels now come with bipass diodes so this is often a reduced issue for modern installs.

Some panels even come with multiple bypass diodes, each bypassing a different part of the panel, this means that even power reduction from partial shading is reduced. (Each panel acts like multiple panels, each with its own bypass diode) The most common configuration of multiple internal bypass diodes I have seen is 3 diodes, each bypassing a stripe along the long access of the panel. If you mount these panels horizontally, you start getting power in the morning when only the top 3rd of the panel has sun, then 2/3rds then the whole panel, the reverse happens when the sun sets in the evening. This is a nice way to boost the total production of a panel with minimal extra expense.

Note however, that a bypass diode means the voltage from the string may vary significantly from full sun to partial sun. Therefore, an MPPT controller is needed in order to take advantage of the changing voltage from the panels. (PWM controllers work best when the solar voltage is well matched to the battery voltage....and a changing solar voltage makes that 'difficult')

If the panels you have don't have bypass diodes, you can often add one inside the junction box. If you cant get into the junction box there are ways to add them externally but it starts to become a PITA and/or expensive.
 
Yes..... and No. (How is that for a definitive answer?)
As a generic statement, your assumption is basically correct. However, if there are bypass diodesin the system, it may not be as bad as you describe when the panels are in series. If there are bypass diodes in the junction box of each panel, then if the panel is shaded, current will flow through the bypass diode and not reduce the output from the other panels in the series string. Many (Most?) name brand panels now come with bipass diodes so this is often a reduced issue for modern installs.

ah, so that's what the diodes do in a panel. Got it
 
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