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Too much VOC for my 12v system?

Kirsty

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Jan 21, 2022
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I'm planning my 12v RV set up and wanting to go with +- 300 watt panels because of limited roof space. I've come across the REC Solar 365 watt mono panels that Northern Arizona Wind and Sun offer. My MPPT victron controller will be the SmartSolar MPPT 150/100 Tr. I read that its optimal to have a solar array voltage between 32v and 35v for 12 volt batteries. With these four 364w panels wired in parallel, I'll be sitting at 40.9volts. I was talking to another company (but didn't use them bc a customer had purchased all their panels that I was interested in that morning), and he said that the +- 40v is too much and will stress out my MPPT if I'm only working with a 12v system. But that doesn't seem to coincide with victron's sizing calculator.
Any helpful/directional input would be greatly appreciated.
 
They figure 40V is too much for a (MPPT, mind you) controller that's rated for 150V?
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To be the most efficient. You should configure your array to a voltage level close to the maximum of the charge controller.
 
The Victron 150/100 is good for up to 150Voc at either 12V, 24V, or 48V. Whoever said 40V is too much doesn’t understand what an MPPT SCC does.
 
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I agree with the others, sounds like misinformation. Maybe trying to steer you to another product they have?
 
There are some low end MPPT charge controllers with documentation that says they are somewhat less efficient if the panel voltage is more than 1.5 or 2 x the battery voltage. This is not the case with the Victron unit you mentioned.
 
Copy that!
He recommended I leave the 40voc stuff for home systems with 24v and 48v batteries and referred me back to 100w and 200w panels =(
With me being new to this and him dealing with them everyday, I wanted to double check before I proceeded.
Thanks so much everyone for your quick input.
 
It does not follow that manufacturers who do not publish efficiency curves have magically flat efficiencies no matter what voltage we feed the controllers.

Having said that, I suspect 95% vs 98% or whatever makes relatively little practical difference in setups with sufficient panel and sane ambient conditions.
 
Now that someone has mentioned an efficency curve, I thought I post the one for my controller, a Midnight. Looking at the curves, there is little different efficency-wise for 140V or raw solar vs only 70V.
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Get the panels that fit your roof space. Then get an MPPT to fit your panels. Many of us are putting the panels in series to get the voltage up to allow us to use smaller wire. If you put those four panels in parallel (instead of series) then you may need bigger cable, plus all the extra devices to combine/parallel everything.

A 2s2p configuration may be exactly what you need and would work well with that MPPT. In fact, you might be able to go with the 100/50 MPPT but you would likely be leaving amps on the table. You would get 50 amps of charging, but no more than that.
 
My panels are in series for about 90 volts Vmp. Works fine 10 years running my 150v Morningstar controller. No expected issues with the Victron.
 
Get the panels that fit your roof space. Then get an MPPT to fit your panels. Many of us are putting the panels in series to get the voltage up to allow us to use smaller wire. If you put those four panels in parallel (instead of series) then you may need bigger cable, plus all the extra devices to combine/parallel everything.

A 2s2p configuration may be exactly what you need and would work well with that MPPT. In fact, you might be able to go with the 100/50 MPPT but you would likely be leaving amps on the table. You would get 50 amps of charging, but no more than that.
HRTKD, you brought up a good topic that I was wondering about too. Why isn't the Victron calculator giving me the 150/70 as an option. It seems to be pushing me up to pretty high ratings with the 150/100 and no other options. The panel specs are below.

REC365NP 2 specifications:​

  • Nominal power: 365 Watts
  • Number of cells: 120 half-cut
  • Power tolerance: +5 / -0 Watts
  • Vmp: 34.3 Volts
  • Voc: 40.9 Volts
  • Imp: 10.65 Amps
  • Isc: 11.36 Amps
  • Module efficiency: 20.0%
  • Dimensions (inches): 69.1" x 40.94" x 1.2"
  • Dimensions (mm): 1755 x 1040 x 30
  • Weight: 44.0 lbs (20 kg)
So no matter if I do all 4 in parallel or a 2s2p, you'd think I'd be safe either way with the 150/70. It would save me $200
 
365 x 4 = 1460 watts / 14 volts = 100 amps. The 70 would be a bit over driven. Might be all that is needed if the panels are mounted mostly flat on the roof.
 
365 x 4 = 1460 watts / 14 volts = 100 amps. The 70 would be a bit over driven. Might be all that is needed if the panels are mounted mostly flat on the roof.
That would be my expectation with my limited experience with flat mounted panels.
 
365 x 4 = 1460 watts / 14 volts = 100 amps. The 70 would be a bit over driven. Might be all that is needed if the panels are mounted mostly flat on the roof.
Yeah you're right, I was having a brain lapse with that formula for a minute there. And I've also seen people add 20% to their number after dividing. Thanks for the brain jog =)
 
Yes, if you parallelly three or more panels, you need fuse protection for each panel.
 
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