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

brulaz
Explorer
Jan 23, 2015
MrWizard wrote:
the voltage per solar cell is pretty uniform across the industry
BUT the larger the individual cells the more current per cell

all my unisolar panels have the same Number of cells and the same voltage
but i have THREE sizes, and three different wattage ratings

the individual cells are different sizes in each of the three different wattage's

could be the same thing with the 72 195w vs your 60cell 250 watt
your 60 cell panels have bigger cells
what is the dimensions of the cells and the panel
this is where the "efficiency" rating of more expensive higher efficiency panels comes into play, producing more amps/power per cell

Would mono cells be smaller?
My 6x12 195W panels are mono.
From their spec sheet:
125x125mm cells (4.92"x4.92")
1610x808mm total (63.4"x31.8")
Cell efficiency: 17.9%
Module Efficiency: 15.6%
brulaz
Explorer
Jan 23, 2015
CA Traveler wrote:
I removed the cover from the junction box to see the diodes. It would be common for a 6xnn cell array to have 3 bypass diodes (assuming it has any). The reason is that for every 2 rows both wires are near the junction box so there is only a small amount of wire needed to provide connections for the 3 diodes. Hope this helps but there are other arrangements.
...

Thanks. If I'd known I would have checked before mounting the panels. But don't think I'll pull one off now to check.

Will rather try covering sections of the panel and see what happens to output.

So with three diodes, and a 6x12 array, you would expect each diode to control a 2x12 group of cells? Not a 6x4 group?

How I try to partially shade the panel depends upon how the cells might be grouped.

And here's a photo of one of the panels. Think that's 72 cells?
MrWizard
Moderator
Jan 23, 2015
the voltage per solar cell is pretty uniform across the industry
BUT the larger the individual cells the more current per cell

all my unisolar panels have the same Number of cells and the same voltage
but i have THREE sizes, and three different wattage ratings

the individual cells are different sizes in each of the three different wattage's

could be the same thing with the 72 195w vs your 60cell 250 watt
your 60 cell panels have bigger cells
what is the dimensions of the cells and the panel
this is where the "efficiency" rating of more expensive higher efficiency panels comes into play, producing more amps/power per cell
CA_Traveler
Explorer III
Jan 23, 2015
I removed the cover from the junction box to see the diodes. It would be common for a 6xnn cell array to have 3 bypass diodes (assuming it has any). The reason is that for every 2 rows both wires are near the junction box so there is only a small amount of wire needed to provide connections for the 3 diodes. Hope this helps but there are other arrangements.

I agree 195W seems inconsistent with 72 cells. My 60 cell panels are 250W.
BoonHauler
Explorer
Jan 23, 2015
brulaz wrote:
So is there anyway to tell if your panel has bypass diodes other than going up on the roof and shading parts of the panel?

I may end doing that as the panel literature doesn't mention bypass diodes at all.

My panels have 72 cells of mono, arranged 6x12.

How many independent sections (if any) would you expect to find?
How would each independent section be arranged?

Sunny Power:
• Module Type: SPM195W Mono
• Maximum Power at STC (Pmax): 195W
• Maximum Power Voltage (Vmp): 36.72V
• Maximum Power Current(Imp): 5.31A
• Open-circuit Voltage (Voc): 44.00V
• Short-circuit Current (Isc): 5.45A
• Cell Efficiency: 17.94%• Module Efficiency: 15.56%

195 watts and 72 cells??......something doesn't sound right to me :h
mena661
Explorer
Jan 22, 2015
I would email the manufacturer.
brulaz
Explorer
Jan 22, 2015
dupe
brulaz
Explorer
Jan 22, 2015
So is there anyway to tell if your panel has bypass diodes other than going up on the roof and shading parts of the panel?

I may end doing that as the panel literature doesn't mention bypass diodes at all.

My panels have 72 cells of mono, arranged 6x12.

How many independent sections (if any) would you expect to find?
How would each independent section be arranged?

Sunny Power:
• Module Type: SPM195W Mono
• Maximum Power at STC (Pmax): 195W
• Maximum Power Voltage (Vmp): 36.72V
• Maximum Power Current(Imp): 5.31A
• Open-circuit Voltage (Voc): 44.00V
• Short-circuit Current (Isc): 5.45A
• Cell Efficiency: 17.94%• Module Efficiency: 15.56%
jrnymn7
Explorer
Jan 22, 2015
O.K, so perhaps it would be more accurate to say "panels in parallel would not have provided enough power for the batteries" rather than "no power". But yes, either way, mppt/series has the advantage in such a situation.

Thanks!
MrWizard
Moderator
Jan 21, 2015
remember each cell is approx .5v ( i think )
36 cells equal 18v

shaded cells produce NO voltage, its very easy, to have a panel producing voltage too low to charge a battery, say only 10v or even 12~13v, won't charge anything unless that battery is near dead

but two panels in series making 10v each at DAWN, equals 20v into the controller
this means the controller can start charging the battery, even if its only an amp or two
this requires bypass diodes internal to the panel around the cells, so the amps go around the non producing cells
this is the morning "low light", tree shade , advantage of series panels,
your not going to get mPPT gains in morning, but you get the controller "waking up" before it would do so with PWM and parallel panels all showing 10v

or under a canopy, or trees

the disadvantage is when a series panel in the shade shuts down a whole string, because they are wired multiple panels for high voltage

i think i stated all that correctly
i know somebody will..be sure to let me know i got it wrong