Solar-Panel to Controller Loss

Salvo wrote:
You realize you have an improbable scenario. The maximum power point voltage is 27.5V while the battery is 30V. I doubt you'll see any current.

BFL13 wrote:

EG at 800 and 45C (NOCT list of specs), you get INPUT 185w, (no line loss) (27.5v x 6.71a) and if controller is 95% eff then OUTPUT watts is about 185 -9 = 176w and divide that by 30v = 5.87 amps

Why can't 5.87 amps charge the battery at 30v ?

The question is why can't the 24v battery get any current at 30v as long as "panel voltage" is higher than 30.0 volts?

If the controller is PWM, panel voltage will be Vbatt plus line loss, so the 'real' panel voltage we are talking about must be (the same as when you take) Voc. ??? There is no Vmp with PWM.

The Voc for the 65C IV curve is about 32v so why won't the 30v battery get any current at 65C? I admit I am very confused!

But if the controller is an "MPPT" now you have the buck converter in there, which changes how you get any amps out to the battery. So if now the input voltage has to be higher than 30 by 1 volt you need 31 volts input. Input is Vmp in Bulk, and with Vabs set to 30, you will be in Bulk till you get there.

The specs say the panel's Vmp at STC is only 30.2 with a 25C panel so how can you have Vmp at 31 at even higher panel temps?

Does this mean I can get to 30v with the 60 cell panel with PWM (which I did), but not with MPPT? Meanwhile Morningstar is saying you need MPPT to the rescue because PWM can't do it! Huh? ( It turns out they really mean any controller that can handle two 60 cell panels in series for the Voc input limit)

I suppose I could just test for how far up the MPPT controller can get the 24v batts , comparing Vmp which I can measure easily, and Vbatt to see when there is a cut off in amps. All work and no play! (except for swimming up at the lake of course :) )