Derating 24v Solar Panels?
I'm considering running two 250w/24v poly panels; tracked/pointed during spring/fall, and flat during the summer; thru the Tracer 3215BN 30a mppt controller. I can also get 200w/24v mono panels, local...
Forum Discussion
smk,
Access to the roof, and the combiner box, won't be a problem, so any changes will be made there.
Maxing out the controller for short durations, occasionally, does not concern me so much, but at 500w, that's well above the stated rating of 390w. And yes, I've been told many times I will not see full wattage, but I have seen 150w out of my 140w panels several times now, so I have no reason to be believe I will not see over 250w out of the 250w panels. And as Jim pointed out, it will likely not be on hot summer days that it's a problem, but on mild sunny days... which is exactly when I saw 150w out of the 140's. So I feel I need to be careful about how I do things. I'm just trying to get my head around all the options, while still having the ability to utilize the system to its fullest, when necessary, without cooking it.
I may not need to de-rate, if flat, but I'd like to know how to if necessary. I think BFL's approach will work fine for me, though... just trying different cells to see what happens. Although, I would prefer to have somewhat of an idea of what to expect.
Yesterday, with ambient temps at around 80F, the charger cabinet was about 92F, even with doors open, partially shaded, and a decent breeze. So I'd prefer not to push the unit under such conditions... which could easily get much hotter. I have to keep in mind this is not a $600 unit either, so I think it best to keep things in perspective, in this regard. I'd rather error on the side of caution, until I know for sure how the 24v panels work under various conditions.
Access to the roof, and the combiner box, won't be a problem, so any changes will be made there.
Maxing out the controller for short durations, occasionally, does not concern me so much, but at 500w, that's well above the stated rating of 390w. And yes, I've been told many times I will not see full wattage, but I have seen 150w out of my 140w panels several times now, so I have no reason to be believe I will not see over 250w out of the 250w panels. And as Jim pointed out, it will likely not be on hot summer days that it's a problem, but on mild sunny days... which is exactly when I saw 150w out of the 140's. So I feel I need to be careful about how I do things. I'm just trying to get my head around all the options, while still having the ability to utilize the system to its fullest, when necessary, without cooking it.
I may not need to de-rate, if flat, but I'd like to know how to if necessary. I think BFL's approach will work fine for me, though... just trying different cells to see what happens. Although, I would prefer to have somewhat of an idea of what to expect.
Yesterday, with ambient temps at around 80F, the charger cabinet was about 92F, even with doors open, partially shaded, and a decent breeze. So I'd prefer not to push the unit under such conditions... which could easily get much hotter. I have to keep in mind this is not a $600 unit either, so I think it best to keep things in perspective, in this regard. I'd rather error on the side of caution, until I know for sure how the 24v panels work under various conditions.
