The following data was collected from my 3x250W flat mounted solar panels on 1/16/15 in my storage area in the Phoenix area. The graph shows the significant transition as the sun just covers the 3rd rear most panel while the front 2 panels are in full shade. The Vmp is 92V for the 3 panels in series. Prior to the transition the sun is covering 2/3rds of rear panel which is producing about 17V and the remaining section is in bypass mode as are the other 2 panels. Then at the transition the 3rd panel is producing its full power while the other 2 panels remain in bypass mode. This shows an advantage of series panels with bypass diodes and an MPPT controller. For a compatible situation with parallel panels and PWM there would be no power for the batteries prior to the transition. After the transition the graph shows the MPPT60 controller adjusting for Vmp to obtain maximum power to the batteries. Ie Array voltage is being reduced and array current is increased.Solar Controller Graphs - Updated and date of test correctedStorage area overviewSun transition on the 3rd panel

Hi CaTraveler,Thanks for the information. What are the units on each graph?

Oops - The battery amps was showing on the wrong scale. Graph updated above and now showing time scale.

Good post. Some of my panels in partial shade will partially shut down, others will completely shut down.

Kyocera panels (and perhaps others?) have multiple bypass diodes that will allow portions of the panel to continue to operate when partly shaded. Many of the really cheap panels have no bypass diodes, or only have one for the whole panel.

CA Traveler wrote:...This shows an advantage of series panels with bypass diodes and an MPPT controller. For a compatible situation with parallel panels and PWM there would be no power for the batteries prior to the transition. ...Don't understand this statement.When all panels are under full shade, what does parallel versus serially connected panels have to do with power output? Or bypass diodes?EDIT: Never mind, I get it, finally. That one panel was initially not under full shade. Rather it was under partial shade allowing the bypass diodes to do their thing.I understand that mppt can be better in full shade.

Solar Panel Shadows and Bypass Diodes | Good Sam Community

jrnymn7
Explorer
Jan 21, 2015
CA Traveler said;

"For a compatible situation with parallel panels and PWM there would be no power for the batteries prior to the transition."

Is this an accurate statement? Wouldn't the panels just put out less amperage?
mena661
Explorer
Jan 21, 2015
Missed this one entirely. Great post!
pianotuna
Nomad III
Jan 18, 2015
Hi brulaz,

If the panels have bi pass diodes and are poly or amorphous then some power is going to go to the controller.

For example, at solar noon in June in rain, I sometimes get 3 amps of output from the controller. Under perfect conditions with loads on the battery bank I get 17 amps. The panels are in series parallel for a vmp of 33 volts. This allows the controller to output some current 30 minutes after sunrise.
12thgenusa
Explorer
Jan 18, 2015
I recently (before Christmas) went over to check my trailer in storage after a snow storm. Before I checked the panels I loaded up the electrical system and found that it would only produce about 91 watts. I went on the roof and found that one panel was completely snow covered and the other was about 1/3 to 1/2 covered. I swept off the snow and went back down to check production again. It was now at 198 watts. This is about spot on for my panels currently mounted flat, with 5 degree roof slope to the South at about 30 degrees F. Panels are wired in parallel.

Here is a nice tutorial on bypass diodes. Their primary function is to prevent hot spots and damage to the panels, but a nice benefit is partial production in partial shade.
brulaz
Explorer
Jan 18, 2015
CA Traveler wrote:

...
This shows an advantage of series panels with bypass diodes and an MPPT controller. For a compatible situation with parallel panels and PWM there would be no power for the batteries prior to the transition.
...

Don't understand this statement.

When all panels are under full shade, what does parallel versus serially connected panels have to do with power output? Or bypass diodes?

EDIT: Never mind, I get it, finally. That one panel was initially not under full shade. Rather it was under partial shade allowing the bypass diodes to do their thing.

I understand that mppt can be better in full shade.
atreis
Explorer
Jan 18, 2015
Kyocera panels (and perhaps others?) have multiple bypass diodes that will allow portions of the panel to continue to operate when partly shaded. Many of the really cheap panels have no bypass diodes, or only have one for the whole panel.
2oldman
Explorer II
Jan 17, 2015
Good post. Some of my panels in partial shade will partially shut down, others will completely shut down.
CA_Traveler
Explorer III
Jan 17, 2015
Oops - The battery amps was showing on the wrong scale. Graph updated above and now showing time scale.
pianotuna
Nomad III
Jan 17, 2015
Hi CaTraveler,

Thanks for the information. What are the units on each graph?

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