Shade effect on series panels.

Mismatched panel Vmp: Unlike batteries in series panels have non linear voltage which is shown on the IR curves for the panels. Since a MPPT controller maximizes the total power by adjusting the (panel) load some serial panels produce less amps then their irradiance would indicate. And they may not be at their Vmp since the total series string is not optimized and can’t be optimized for every individual mismatched panel.

There seems to be little information on this subject. Possibly because solar arrays tend to use matched panels vs DIY projects which often evolve over time.

red31 wrote:

BFL13 wrote:

The amps is what it is, so the controller must fiddle with R to change V. R being a "load".

Yes, one can make an IV curve with a bunch of resistors and light.
Isc is max resistance, Voc is zero resistance, various values in between define the iv curve. Mppt imposes a resistance/load and makes constant adjustments to find/keep mppt, via computer control.

PWM in abs pulses panel current and no current, panel current is at batt V and no current is at Voc. 50% duty cycle would be 50% @ 14.6v and 50% @ ~20v (Voc). 14.6+20 / 2 = ~ 17v. With more OFF time (Voc) the average V goes up. I believe mine does this at 60hrz.

Thanks for the clarification that in PWM it is the current that goes on and off, to make the voltage whatever, and that it is between Voc and batt V. So it passes through batt V to the panel same as any PWM controller.

Makes it interesting when batt v can be 12 and panel 24 instead of 12-12, but why not? Harder with a 24v panel to keep the average above Vmp with 12v batt though.

BFL13 wrote:

The amps is what it is, so the controller must fiddle with R to change V. R being a "load".

Yes, one can make an IV curve with a bunch of resistors and light.
Isc is max resistance, Voc is zero resistance, various values in between define the iv curve. Mppt imposes a resistance/load and makes constant adjustments to find/keep mppt, via computer control.

PWM in abs pulses panel current and no current, panel current is at batt V and no current is at Voc. 50% duty cycle would be 50% @ 14.6v and 50% @ ~20v (Voc). 14.6+20 / 2 = ~ 17v. With more OFF time (Voc) the average V goes up. I believe mine does this at 60hrz.

Had a glimmer. The string is in series and so are the cells in each panel, so for the voltage it doesn't matter how the cells are grouped by panel as in "mixed sizes" of panel. It is a string of howevermany cells. One big panel that the controller "sees". The cells are not all the same size though, but they still just add up regardless of grouping.

It does matter how the cells are grouped by panel watt size for the amps, where the lowest amp grouping (panel size) is the "string amps".

. I read that the MPPT "adjusts the load" on the panel to get the voltage for the max watts. Where the controller is a load that pulls down the array voltage. (from what?)

The amps is what it is, so the controller must fiddle with R to change V. R being a "load".

Anyway, back to the OP and regular programming----

PWM operates at the battery voltage. So if you put on a load big enough to cause that to sag, even fewer watts go into the system.

BFL13 wrote:
I think the panel voltage is the voltage of whatever it is connected to.

Who started this anyway?

i think you did

2oldman commented on panel shading

you brought in the off-side comments about voltage etc.

Woo hoo! Just arrived. That's 3M 5200 Marine adhesive. Hope it holds!



Nice and light.. I love it. Now I need to figure out how to support the 4" overhang over the existing panel. Some kind of metal bracket I guess.

As for your statement about a panel's voltage being the same as what it's connected to...If you mean they will adjust between Vmp and Voc, yeah, they can do that.

The 'load' is the controller. As that changes, so do the panels. The controller doesn't change the panels, the panels change themselves, just as a battery adjusts itself.

2oldman wrote:

BFL13 wrote:
I think the panel voltage is the voltage of whatever it is connected to.

I'll hook up my new panel to a flashlight battery and see if you're right. No I won't.

Hmmmm. If you go panel-direct, the voltage on the wires is battery voltage, but that voltage is rising from the current flow. However, there is a limit to how high that voltage can go I believe.

I did that test (but with an MPPT controller) to see if my 60 cell panel could recharge a 24v battery bank and it got the batts to 31 volts and stalled out. Supposedly a 72 cell panel would get the batts to a higher voltage. (more cells in series in the panel)

The panel voltage limit is not its Vmp (but I have to check on that) because with MPPT in Float, the panel voltage displayed is higher than rated Vmp. But that is the controller's voltage not the panel's?

Who started this anyway? :(

BFL13 wrote:
I think the panel voltage is the voltage of whatever it is connected to.

I'll hook up my new panel to a flashlight battery and see if you're right. No I won't.