Mottled shade on solar panels not good?

BFL13 wrote:
I see what you mean, but if your example started with the two 12v panels in parallel with an MPPT controller, then the type of controller would be the same in each case.

Not much point paying for MPPT then using parallel panels, though. I was talking about common, real world systems.

I see what you mean, but if your example started with the two 12v panels in parallel with an MPPT controller, then the type of controller would be the same in each case.

BFL13 wrote:

mike-s wrote:
It won't damage the diodes. They're there to bypass shaded strings of cells. But, especially if you use a PWM controller, shade on even a single cell can stop all power output from that panel for as long as it's shaded. But nothing gets damaged.

What does PWM vs MPPT have to do with it?

Simple, with PWM shading on a single cell will take out that whole column, the voltage for that panel will drop below what's needed to charge the battery, so you effectively lose the power from the whole panel.

With MPPT (assuming you have 2 or more panels in series, or a higher voltage panel), losing a string just results in a partial loss from the panel, the remaining columns continue to contribute.

e.g. 2x 100W "12V" panels wired in parallel to a PWM controller. Shade one cell, you lose the output from the entire panel, and instead of 200W you now have 100.

The same 2x 100W "12V" panels wired in series to a MPPT controller. Shade one cell, you lose 1 column (commonly 3 per panel). The diode bypasses that column, but the other 2 continue to contribute because the voltage is still above the minimum needed by MPPT. You only lose 1/6 of the potential power, and instead of 200W you get 167.

(I probably should have said "column" in my first response, "string" more often refers to series panels)

mike-s wrote:
It won't damage the diodes. They're there to bypass shaded strings of cells. But, especially if you use a PWM controller, shade on even a single cell can stop all power output from that panel for as long as it's shaded. But nothing gets damaged.

What does PWM vs MPPT have to do with it?

There was something about cells in panels being damaged by some light effect, can't remember what that was (not the water one either), but it wasn't mottled shading or the diodes. Where a cell got too hot ISTR.

It won't damage the diodes. They're there to bypass shaded strings of cells. But, especially if you use a PWM controller, shade on even a single cell can stop all power output from that panel for as long as it's shaded. But nothing gets damaged.

won't hurt anything, let alone any damage to the diodes, but it can affect your panel output significantly.