BFL13 wrote:
I found my notes on testing my 230w panel with MPPT and how amps go up when Vbat goes down. Just to put some numbers on what Salvo was saying.
This was in April at 49.3N sunny, mid-day. Ambient 16C, back of panel 44C. Panel ratings: Voc 36.8, Isc 8.3, Vmp 30, Imp 7.7
At test time, panel disconnected Voc 35.4, Isc 8.77
Panel connected, voltage at panel junction box 29.3/controller input 29.0 (drop of 0.3v at 8.8ish amps)
Controller display No load- 13.4v, 15.32a, 205w
With load to drop Vbat----- 12.9v, 15.73a,201w
With load some more-------- 12.7v, 16.48a, 210w
Later some more-------------12.3v, 16.67a, 205w (was a change up in insolation by then- panel disconnected Voc 35.0, Isc 8.92!
I never saw such high amps again after April and it got warmer out in the summer so at 25C with back of panel now 51C, Voc was down to 34.0 That made a typical mid-day reading 13.5v, 13.5a, 182w
Naturally, I got annoyed at the MPPT only giving me 13.5a instead of the 15.5a I saw earlier.
Also in reply to those who say you lose panel wattage with PWM not using all of it, but MPPT uses it all, can figure out whatever happened to the 230-180 = 50w gone missing with the MPPT here! (hint-panel temperature 51C instead of 44C)
I had nothing but the 200w, 12v coffee pot to load my 230w system with and only saw 16.2a/220w peak. It will be interesting to see if a 230w poly can come close to the 17.1a peak that the 245w mono panels produce. If so the 220w mono produces 25% less than the 230w poly that can produce close to the same as a 245w mono. Sounds like another reason to pick Poly to me.
