Heat 1, MPPT 0
Previously we noted that heat is hard on MPPT due to the panel's loss of voltage with increasing heat. Doesn't bother PWM though, you still get Isc or more.
This Spring, I took some measurements posting the MPPT vs PWM values, and at high noon was getting about 15.5 amps vs 14.5 for PWM.
The thought then was when it warmed up for Summer the MPPT "advantage" would not be even that much. So here we are in some hot weather (for here) so a comparison was made.
I have been noticing lately that the expected amps just aren't coming in and wondered what was the matter. Checked everything, nothing found wrong, then measured temp under panel. Oops.
So here are the Spring/Today figures in blue sky no clouds all same set-up.
Ambient temp- 16C/24C
Under panel temp- 44C/48C
Voc-35.4/34.0
Isc- 8.7/8.4
Amps output 15.71/13.88 (both at 13v battery)
Panel watts (of 230w)- 205/181
So instead of getting 1 amp more than PWM, now I am getting 1 amp less than PWM for my 230w. It seems the only difference in conditions is the temperature. The under panel temp is not that much more compared with the big jump in ambient, but it is enough to hurt the MPPT.
BTW, panel voltage coefficient is - 0.330%/degree C. Rated Voc is 36.8v got 34, diff is 2.8. Temp diff is 48-25C = 23 and 23 x .33 is 7.6 and 7.6% of 36.8v (rated Voc) = 2.8v and that minus 36.8 is 34, which us what I got for Voc so that all works out.
Bottom line us that MPPT sucks unless you use it in the Arctic :) I would do better with two 115w panels than with the single 230w. Fortunately, with the warm weather there is also no furnace to run, so the loss in solar doesn't matter, but I still get annoyed when I don't get those amps in whether I need them or not! Drat and phooey!
I can't even complain that this is a surprise, since I used to post about that before I got this set-up. I got it because the price of the 230 was better than two 115s. Now I am paying the other "price" in aggravation.
This Spring, I took some measurements posting the MPPT vs PWM values, and at high noon was getting about 15.5 amps vs 14.5 for PWM.
The thought then was when it warmed up for Summer the MPPT "advantage" would not be even that much. So here we are in some hot weather (for here) so a comparison was made.
I have been noticing lately that the expected amps just aren't coming in and wondered what was the matter. Checked everything, nothing found wrong, then measured temp under panel. Oops.
So here are the Spring/Today figures in blue sky no clouds all same set-up.
Ambient temp- 16C/24C
Under panel temp- 44C/48C
Voc-35.4/34.0
Isc- 8.7/8.4
Amps output 15.71/13.88 (both at 13v battery)
Panel watts (of 230w)- 205/181
So instead of getting 1 amp more than PWM, now I am getting 1 amp less than PWM for my 230w. It seems the only difference in conditions is the temperature. The under panel temp is not that much more compared with the big jump in ambient, but it is enough to hurt the MPPT.
BTW, panel voltage coefficient is - 0.330%/degree C. Rated Voc is 36.8v got 34, diff is 2.8. Temp diff is 48-25C = 23 and 23 x .33 is 7.6 and 7.6% of 36.8v (rated Voc) = 2.8v and that minus 36.8 is 34, which us what I got for Voc so that all works out.
Bottom line us that MPPT sucks unless you use it in the Arctic :) I would do better with two 115w panels than with the single 230w. Fortunately, with the warm weather there is also no furnace to run, so the loss in solar doesn't matter, but I still get annoyed when I don't get those amps in whether I need them or not! Drat and phooey!
I can't even complain that this is a surprise, since I used to post about that before I got this set-up. I got it because the price of the 230 was better than two 115s. Now I am paying the other "price" in aggravation.
