Solar Panel Voc-MPPT?
Wondering if there is any relationship between measured Voc and MPPT performance with a 24v panel. My 12v panel has a Voc rating of 21.9 and Isc of 8.2, but I often see 8.2ish when Voc is only 20....
Forum Discussion
red31 wrote:
Solar insolation victoria, I'd assume flat panel so sin or cosine correction needed for direct (tilted perp to sun)
Closest NREL live data and calendars, 40 degree 800 miles south.
Thanks. We do get sunshine here and I do get rated Isc so IMO we do get 1000 Irr at least sometimes. :)
To follow up, the three graphs at the bottom of this page are good at showing what I am trying to understand. It seems that change of irradiance has little effect on Voc but has a big effect on Isc while change of temp has little effect on Isc but has a big effect on Voc.
Of course P change is with the V or I component that moves the most.
http://www.windturbine.ca/sun_panels.html
What you get in an actual panel measurement would be a combo effect of temp and irradiance off 1000 and 25C either way. I can't figure how you get slightly lower Voc and full Isc at 15C with lower Irr too.
The suggestion was that it is due to lower Irr reducing Voc with the new panel having higher than rated Isc.
I am worrying about P in this kind of situation, since that is what MPPT is all about. Imp is a sort of accidental number that is whatever the amps happen to be at Vmp.
Isc is not a real number at all, but if you are getting than many amps (as I see at the battery when I also can get Isc) then that amps amount is real. So (I hope!) with Voc only being down a bit, and Isc being where it belongs (either from new panel effect or from getting 1000 Irr) that means P will not be down much. (I hope!)
Am I delusional in that? If so what is the correct way to look at it, using those three graphs in the explanation so we are all looking at the same thing. Thanks.
