Solar-Panel to Controller Loss
Much has been made of the lower losses on the panel to controller path with MPPT because the amps are less. So once you have your loss measured, how valuable is it to improve on that if you don't like the loss amount you have?
EG, before I changed it all, I had a 1% loss on that path, but now I have a 2% loss. It can be reduced with a lot of bother, but is it worth it? Others with a similar problem might be interested in the calculations here.
At the time, the Vmp at the panel end was 29.0 and at the controller it is 28.5, so loss is 0.5/29 = 1.7% so with some work in my case this could be reduced to half that, say.
So what? Panel rated watts 255w. At Nominal Operating Cell Temperature (NCOT) of 45C (and today it came to 45C with the IR gun) and ambient 20C, you get a spec -0.43%/C drop in power for a total of 8.6% at NOCT so 8.6% of 255 is 22 so now you are down to 233w. Add line loss of 1.7% so now you are at ( 1.7% of 233 = 4w) so input to the controller is say 233-4 = 229w
Output from the controller was 215w at the time (12.7v x 17a) so loss in the controller is 229-215 = 14w/229 = 6%. (Reasonable mid-90s controller efficiency)
So what would the amps to the battery be if only that lousy 1.7% line loss on the panel to controller path could be cut in half?
Still starting at 233, now subtract 2 instead of 4w = 231w to controller with same 94% efficiency, loss is 13.86 instead of 14w Output is 217 instead of 215w
So with same batt v, you get 217/12.7 = 17.1a instead of 17a.
Hmmm. How much bother is worth 0.1 amp when you are already getting 17?
BTW, yes, I have a new 255w panel instead of the 230w panel for the 5er, and I will post some test results when the sky is right to allow testing someday soon. :)
EG, before I changed it all, I had a 1% loss on that path, but now I have a 2% loss. It can be reduced with a lot of bother, but is it worth it? Others with a similar problem might be interested in the calculations here.
At the time, the Vmp at the panel end was 29.0 and at the controller it is 28.5, so loss is 0.5/29 = 1.7% so with some work in my case this could be reduced to half that, say.
So what? Panel rated watts 255w. At Nominal Operating Cell Temperature (NCOT) of 45C (and today it came to 45C with the IR gun) and ambient 20C, you get a spec -0.43%/C drop in power for a total of 8.6% at NOCT so 8.6% of 255 is 22 so now you are down to 233w. Add line loss of 1.7% so now you are at ( 1.7% of 233 = 4w) so input to the controller is say 233-4 = 229w
Output from the controller was 215w at the time (12.7v x 17a) so loss in the controller is 229-215 = 14w/229 = 6%. (Reasonable mid-90s controller efficiency)
So what would the amps to the battery be if only that lousy 1.7% line loss on the panel to controller path could be cut in half?
Still starting at 233, now subtract 2 instead of 4w = 231w to controller with same 94% efficiency, loss is 13.86 instead of 14w Output is 217 instead of 215w
So with same batt v, you get 217/12.7 = 17.1a instead of 17a.
Hmmm. How much bother is worth 0.1 amp when you are already getting 17?
BTW, yes, I have a new 255w panel instead of the 230w panel for the 5er, and I will post some test results when the sky is right to allow testing someday soon. :)
