Post #9
9)With series connected panels what is the effect of shading on one of the panels?
I forgot about this question in my initial test list, so I wasn’t able to run an experiment till October 16th about 10AM PDT. Rather than looking at detailed power out, I concentrated on what the effect was on battery charging current.
My expectation was that the charging current would drop roughly in half, maybe a little more than 50%.
So with both panels in the direct sun, adjusted the best I could, I checked charging current, 9.4A. Then I moved one panel into the shade between two trailers. Looked at the panel current, it was 4.1A with both panels in direct sun and stayed at 4.1A even with one panel in the shade.
Just what I expected. Current should remain basically the same, voltage would drop.
Went back in and looked at the trimetric. Now you quickly can see the tracking effect of a MPPT controller. It was seeing probably about 30V @4A or so, and now it is down to about 15V @ 4A, but the conversion algorithm is based on 30V. Trimetric showed charging current less than an amp. HOLD ON, actually I expected something like that until the controller did another search. So I watched. After what seem like an eternity, but really was only a minute or so I could watch the controller doing a search. Interesting, charge current would go up several amps, bounce up and down, and then go up again, bounce around, go up repeat, and in about 30 seconds was up to 4.4A. So a drop of slightly more than 50%. So then I went back out and placed the panel in the sun to verify current. Went in and watched. Current 4.4A, and again after a minute or so the search started, went down to about 2A and then started climbing and settled in a 9.4A. But then we have those pesky wispy clouds messing stuff up today.
Conclusion:
Shading panels in series reduces current by the % of panel shaded related to total panel area.
But it also takes a some time for the MPPT controller to search and find the new Max Power point.
Hum.... wonder what happens when clouds are sporadic and the panel quickly and constantly going in and out of shade. can the controller track fast enough, or does it get appiplexy and give up and not do a decent job of tracking max power point???
Another "I'll leave it to the reader" to investigate!!
