More MPPT Confusion and Question
Still trying to understand my MPPT set-up and what would be the effect of changing things a bit. My 230w (30.0 Vmp x 7.7 Imp) poly panel has a Vmp of 30.0v with a measurement tolerance of +/- 3% S...
Forum Discussion
EDIT--re the above, I was getting 44C back of tilted up panel with 16C ambient. and 51C panel at 25C ambient.
It is true I have never measured the current input to the controller, only taken the voltage there. I know that the Isc at the controller's input is the same as at the panel and is at or above rating so I believe insolation is good.
AFAIK, the input current is whatever it comes to with the power there divided by the Vmp and that is the Imp of the moment.
Working backwards, knowing output power is say 200w and controller efficiency is say 93%, then input power would be 215w. Measured voltage is 29.3 at panel and 29 at controller input. 215/29 = 7.4 amps while rated Imp is 7.7a
If something is wrong with the controller so that it's efficiency is 85% instead of 93, then with 200w output (actual) then input would be 235w, which is too high. (Panel Voc at 34 instead of rated 36.8 due to heating so its power must be down from 230w too)
So that indicates the controller efficiency at 93% when panel is near max power rating of controller is reasonable. So again, I don't think the controller is the problem.
I think what I am seeing must be fairly normal. It would be good to get comparable figures for a $600 MPPT controller in the same situation and see if they are any better.
In the comparison, if the $600 controller were rated for 500w instead of my 250w one, then it would be higher on the efficiency curve using the 230w panel. Have to fudge for that, and then see.
It is true I have never measured the current input to the controller, only taken the voltage there. I know that the Isc at the controller's input is the same as at the panel and is at or above rating so I believe insolation is good.
AFAIK, the input current is whatever it comes to with the power there divided by the Vmp and that is the Imp of the moment.
Working backwards, knowing output power is say 200w and controller efficiency is say 93%, then input power would be 215w. Measured voltage is 29.3 at panel and 29 at controller input. 215/29 = 7.4 amps while rated Imp is 7.7a
If something is wrong with the controller so that it's efficiency is 85% instead of 93, then with 200w output (actual) then input would be 235w, which is too high. (Panel Voc at 34 instead of rated 36.8 due to heating so its power must be down from 230w too)
So that indicates the controller efficiency at 93% when panel is near max power rating of controller is reasonable. So again, I don't think the controller is the problem.
I think what I am seeing must be fairly normal. It would be good to get comparable figures for a $600 MPPT controller in the same situation and see if they are any better.
In the comparison, if the $600 controller were rated for 500w instead of my 250w one, then it would be higher on the efficiency curve using the 230w panel. Have to fudge for that, and then see.
