Open Circuit Voltage?

RogerD

Solar Enthusiast
Joined
Sep 26, 2019
Messages
97
I found a good deal on 200w panels. $606 for 4.

Specs
  • Maximum Power Voltage(Vmp): 20.4V
  • Maximum Power Current(Imp): 9.80A
  • Open Circuit Voltage(Voc): 24.3V
  • Short Circuit Current(Isc): 10.2A
I'll be using (8) 280ah cells configured as a 24V battery.

I've heard you want your PV voltage to be at least 20v over your battery bank voltage.

With the above panels if I do 2s2p that's only 40.8v. Is this not OK?

If I put them all in series, I'll obviously be well over. However, the Voc will be 98.8.

I was looking at using Victron 100/30 controller, but I keep seeing posts that you want to keep the Voc quite a bit below what the controller is actually rated for.

Why?

What Voc is acceptable for 100v controller?

I'm looking at some other 200w panels and the Voc would be 90.8 (4 in series) and 87.44 (2s2p -24v panels) are these too high as well?

I could just get the Victron 150/35 it's only $36 more. So no big deal.

I'm just curious why a controller that is rated for 100V, it seems everyone thinks you should stay quite a bit below it.
 

upnorthandpersonal

Administrator
Joined
Dec 25, 2019
Messages
2,616
Location
63 degrees North, Finland
Because Voc changes quite a lot with temperature. I've made a calculator some time ago. Also, just because a charge controller can accept 100V, does not mean this 100V is within its working range, just that it can handle it without breaking. Check the manual on the charge controllers for these details.
 

RogerD

Solar Enthusiast
Joined
Sep 26, 2019
Messages
97
Because Voc changes quite a lot with temperature. I've made a calculator some time ago. Also, just because a charge controller can accept 100V, does not mean this 100V is within its working range, just that it can handle it without breaking. Check the manual on the charge controllers for these details.
None of the panels I'm looking at list a Pmax/Voc temperature coefficient.

I couldn't find anything in the victron 100/30 manual that says anything other than the max voltage is 100.
 
Top