Noob question: parallel and series set up for 4 panels

[kaizday]

so, i have 4 mixing panels that I need to keep below 100v. with the follow specs, does it matter how my 2S2P should be (2S small panels in series vs 1 large 1 small in series)? i assume no since the wattage would be the same, right? but would like a confirm in case i miss something.

tia

	Set 1	Set 2
Pmax	260	315
Vmpp	31.17	36.5
Impp	8.35	8.63
Voc	38.56	46.2
Isc	8.82	8.9

 

[MisterSandals]

Voc

38.56

46.2

Is this per panel or per set (as labeled)?
Is a set 2 identical panels?

 

[kaizday]

Is this per panel or per set (as labeled)?
Is a set 2 identical panels?

yes, 2 of the same panels per set. and that spec is per panel.

 

[MisterSandals]

To stay below 100V (assuming its your temp compensated SCC max input voltage) you may need to pair a 38.56V panel with a 46.2V panel in series. This would give you 84.76Voc. Depending on your panel temp coefficient and the coldest temps your array will be exposed to, this should stay below 100V.

So lets see how it produces in this configuration using Vmp and Imp:

31.17V + 36.5V = 67. 67V
67.67V x 8.35A = 565W x 2 = 1130W

This actually works really well, mostly because the Imp is nearly identical.

 

[kaizday]

To stay below 100V (assuming its your temp compensated SCC max input voltage) you may need to pair a 38.56V panel with a 46.2V panel in series. This would give you 84.76Voc. Depending on your panel temp coefficient and the coldest temps your array will be exposed to, this should stay below 100V.

So lets see how it produces in this configuration using Vmp and Imp:

31.17V + 36.5V = 67. 67V
67.67V x 8.35A = 565W x 2 = 1130W

This actually works really well, mostly because the Imp is nearly identical.

perfect!! that's what i hope to hear. thanks so much for confirming. and yes, the voltage limit is set by my Renogy mppt.

thanks again

 

[Just John]

I would like to highjack this thread for a minute:

If I have 4 Renogy 100W independent panels, all with the same Voltage and Amps ratings (roughly 20.1V/5.7A) and I can connect them any way I want, how should I connect them? Assume I plan on running them via 8AWG to a Victron 100-30 controller, and eventually to a LFP bank.

And, feel free to abuse me for stupidity, but my working assumption is I am better off connecting them in series, and getting ~ 80V x 5.7A, than I am connecting in parallel and getting ~ 20V x 24A simply because I arrive at the same watts, but with much less cabling.

The only problem with connecting them all in series is that shading on a single panel affects all the panels.
Certainly, if you don't have a shade problem, you will be better off at a higher voltage. Just be careful you don't exceed the MPPT limit during a cold day.

 

[chrisski]

31.17V + 36.5V = 67. 67V
67.67V x 8.35A = 565W x 2 = 1130W

EDIT: I originally thought this was slightly off, but its perfect.

 

[Plecoptera]

Much thanks.
I think I am safe either way, because:

Series I limit the panels to 4 x 100 (21V max each), so 84V x 5.7A on a 100V controller.

Parallel I limit the panels to 4 x 100 (5.7A max each), so 21V x 22.8A on a 30A controller.

I get confused somewhat on the Ohms. I have the belief that if I have choice I am better off increasing Volts rather than increasing Amps. But if I crunch numbers I get equivalents. At the same time, if I run my numbers thru one of those cabling calculator apps, higher Volts lower Amps always comes back with I need much smaller gauge cables if I push up Volts. So series "seems" to be a better way of connecting panels.

 

[Just John]

Much thanks.
I think I am safe either way, because:

Series I limit the panels to 4 x 100 (21V max each), so 84V x 5.7A on a 100V controller.

Parallel I limit the panels to 4 x 100 (5.7A max each), so 21V x 22.8A on a 30A controller.

Solar panels will exceed their stated voltage in cold weather, that's why I said "Just be careful you don't exceed the MPPT limit during a cold day."

 

[Plecoptera]

perfect!! that's what i hope to hear. thanks so much for confirming. and yes, the voltage limit is set by my Renogy mppt.

thanks again

I added this, deleted this, am re-adding it because I didn't delete it fast enough. Was going to start a separate thread. Continuity gets a little wonky.


I would like to highjack this thread for a minute:

If I have 4 Renogy 100W independent panels, all with the same Voltage and Amps ratings (roughly 20.1V/5.7A) and I can connect them any way I want, how should I connect them? Assume I plan on running them via 8AWG to a Victron 100-30 controller, and eventually to a LFP bank.

And, feel free to abuse me for stupidity, but my working assumption is I am better off connecting them in series, and getting ~ 80V x 5.7A, than I am connecting in parallel and getting ~ 20V x 24A simply because I arrive at the same watts, but with much less cabling.

 

[Plecoptera]

Solar panels will exceed their stated voltage in cold weather, that's why I said "Just be careful you don't exceed the MPPT limit during a cold day."

I did not know that... so how much?. I fuse the line from the panels to the controller with an inline 30A fuse. I could easily drop the fuse threshold.

 

[Just John]

I did not know that... so how much?. I fuse the line from the panels to the controller with an inline 30A fuse. I could easily drop the fuse threshold.

Fuses work on amps (current) not voltage. The voltage on your panels will rise in cold weather, you don't want them to rise above the 100v limit of your MPPT controller. You are right on the borderline, do you get very cold weather? Changing the fuse will do nothing, assuming the fuse is rated for the voltage (100 volts in this instance).

 

[Plecoptera]

Solar panels will exceed their stated voltage in cold weather, that's why I said "Just be careful you don't exceed the MPPT limit during a cold day."

Fuses work on amps (current) not voltage. The voltage on your panels will rise in cold weather, you don't want them to rise above the 100v limit of your MPPT controller. You are right on the borderline, do you get very cold weather? Changing the fuse will do nothing, assuming the fuse is rated for the voltage (100 volts in this

Okay, again my ignorance is at work, but I thought my cables just carry Watts.

Weather temps here 'bouts will drop to -20F. Not often, but -10F a least once a winter (Colo Rockies). My system is to support RV boondocking, and I try not to be out in -10F.

 

[Plecoptera]

Actually, thinking about it, it has to be I moved by V, so forget the Watts thing.

 

[Plecoptera]

So, next question is whether a panel can ever exceed its maximum Open Circuit Voltage (22.5 for the Renogy)?

 

[Plecoptera]

Renogy has a sort of good discussion on this on their education pages, but there are gaps...

 

[MisterSandals]

So, next question is whether a panel can ever exceed its maximum Open Circuit Voltage (22.5 for the Renogy)?

Yes, it can and will exceed that when the panel gets colder than the testing conditions (25 deg C).
Your panel may have a listed thermal coefficient. It may be around .3-.4%.

Weather temps here 'bouts will drop to -20F.

Thats -28.9C which is 53.9 deg difference.

22.5Voc x 53.9 x .0035 = 4.24 deg increase
22.5V + 4.24V = 26.74V

26.76 x 4 = uh oh!

 

[Plecoptera]

Yeah, I'm reading about bandgaps now. Confused at a higher level. Simple solution is to drop to 3 panels when it drops to 0F. It takes idiocy to boondock at <= 0F, but I've done it.

 

[cosmicosmo4]

@Plecoptera, I would arrange those panels in 2S2P because the charge controller will be less stressed if you use 50% of the voltage rating and 50% of the current rating than to use nearly 100% of the voltage rating and only 25% of the current rating. And that's still only ~11 amps, so the required wiring is still no huge deal.

 

[Plecoptera]

Interesting. I'm using Victron MPPT 100-30. Is it possible for one of those to get stressed? I can make my own cables, so some simple storebought 2x unions and a few short pigtails is no biggy. But I just would expect the micro electronics to be more durable than that.