Serial vs Parallel Solar Panel Shading
I was asked if a post in another thread if this "Serial is actually better for shading (than parallel) if that is a concern for you." was a typo. It is not a typo but panel shading is not always understood on this board.
What is overlooked is the bypass diodes and how they operate. All 24V 6x10 or 6x12 cell panels have 3 bypass diodes. Some 12V 4x9 cell panels have 2 bypss diodes. The diodes bypass 2 rows each, ie 2x9, 2x10 or 2x12 cells in what I’ll call a panel section. The diodes are installed to protect the serial panels from shade which can damage them which is why virtually all 24V panels have them. BUT they also allow the panel to produce more output in shaded conditions than parallel panels.
While there are various online articles on the need for bypass diodes to protect the panels (which I’ll skip) and articles on the shading/power effects, I’ll provide my own experience.
My 60 cell panels have 3 diodes each and each one can and does bypass 1/3 of a panel voltage in shading conditions. One key to understanding is that while shading on one section reduces the voltage by 1/3, the amps from the other 2 is the full amps from that panel for the given light conditions. Or to express it another way the panel produces 2/3 of its power. This is a dream made in heaven for MPPT controllers because by design they can harvest that 2/3 power from that panel plus all of the power from other series panels.
The same shading scenario for parallel panels means that the reduced panel voltage doesn’t contribute to the total power that the CC can harvest.
My 3 series connected panel’s means that I have 9 panel sections. Shade on one section means that I have 8/9 of the panel power for the MPPT controller to harvest. If 2 sections are shaded with either the same or different panels means that I now have 7/9 of the panel power. And so forth all the way to 2/9, with 1/9 being about 10V for my panels.
My panels are 30V (rounding) panels so I have 90V in series. Each shaded section that activates a bypass diode reduces that voltage by 10V down to 20V and the MPPT is happy as a clam to continue charging the batteries. Ie At high noon if I had 7 shaded sections the panel output would be 20V at 8A or 160W/14.8V = 10A bulk battery charging at 14.8V.
This picture shows the morning leafy shade 10V voltage changes due to shading. This is a graph of the Morningstar MPPT 60 CC and represents any MPPT controller. The thread is Click.
What is overlooked is the bypass diodes and how they operate. All 24V 6x10 or 6x12 cell panels have 3 bypass diodes. Some 12V 4x9 cell panels have 2 bypss diodes. The diodes bypass 2 rows each, ie 2x9, 2x10 or 2x12 cells in what I’ll call a panel section. The diodes are installed to protect the serial panels from shade which can damage them which is why virtually all 24V panels have them. BUT they also allow the panel to produce more output in shaded conditions than parallel panels.
While there are various online articles on the need for bypass diodes to protect the panels (which I’ll skip) and articles on the shading/power effects, I’ll provide my own experience.
My 60 cell panels have 3 diodes each and each one can and does bypass 1/3 of a panel voltage in shading conditions. One key to understanding is that while shading on one section reduces the voltage by 1/3, the amps from the other 2 is the full amps from that panel for the given light conditions. Or to express it another way the panel produces 2/3 of its power. This is a dream made in heaven for MPPT controllers because by design they can harvest that 2/3 power from that panel plus all of the power from other series panels.
The same shading scenario for parallel panels means that the reduced panel voltage doesn’t contribute to the total power that the CC can harvest.
My 3 series connected panel’s means that I have 9 panel sections. Shade on one section means that I have 8/9 of the panel power for the MPPT controller to harvest. If 2 sections are shaded with either the same or different panels means that I now have 7/9 of the panel power. And so forth all the way to 2/9, with 1/9 being about 10V for my panels.
My panels are 30V (rounding) panels so I have 90V in series. Each shaded section that activates a bypass diode reduces that voltage by 10V down to 20V and the MPPT is happy as a clam to continue charging the batteries. Ie At high noon if I had 7 shaded sections the panel output would be 20V at 8A or 160W/14.8V = 10A bulk battery charging at 14.8V.
This picture shows the morning leafy shade 10V voltage changes due to shading. This is a graph of the Morningstar MPPT 60 CC and represents any MPPT controller. The thread is Click.
