Series Parallel panel wiring newbie question

[Belzo]

I'm brand new to solar and have just setup my first really small setup. I have a MPPsolar PIP 2424 Inverter (off grid model, no feed to grid) with 4 Rich 200W panels wired in series going to the Inverter right now with a BigBatteries.com Mule 24v 3kwh battery. What I'm curious about is I have issues with shade on my 800w (max) panel array right now. I was considering adding another group of panels in a different spot on my roof to get morning and midday sun and I'm trying to wrap my head around maybe doing that group back there in series as well and then joining the two groups of panels into parallel. So one group would be in the current location (south) on one angle and direction and the other group would be elsewhere pointing a slightly different direction (south but maybe more south east) and angle. Would this array setup work in theory or is there a better way to do this? Thank you

 

[sunshine_eggo]

4S Vmp = 81.6

PIP MPPT range = 30-80V

You may be losing a little off the top end.

Recommend you rewire existing array as 2S2P. This would mitigate partial shading implications. Panels in parallel do not adversely affect one another when shaded. When a panel in a string is shaded, it can have a notable impact on the output of the entire string.

Given your plan, you could go 2S4P: 2S2P to South. 2S facing West and 2S facing East.

 

[Belzo]

I think I understand thank you for the suggestion. Technically is what I was thinking acceptable or would it not work?

 

[Belzo]

4S Vmp = 81.6

PIP MPPT range = 30-80V

You may be losing a little off the top end.

Recommend you rewire existing array as 2S2P. This would mitigate partial shading implications. Panels in parallel do not adversely affect one another when shaded. When a panel in a string is shaded, it can have a notable impact on the output of the entire string.

Given your plan, you could go 2S4P: 2S2P to South. 2S facing West and 2S facing East.

Here's some of the monitoring from my PV panels yesterday. I can see that in peak sunlight it looked like it was topping out on 80v like you are saying. So it would be best to put my current 4 panels into a 2S2P instead of 4S? Thank you

 

[sunshine_eggo]

Here's some of the monitoring from my PV panels yesterday. I can see that in peak sunlight it looked like it was topping out on 80v like you are saying. So it would be best to put my current 4 panels into a 2S2P instead of 4S? Thank you

Yes. I made that suggestion above a couple times.

I doubt the 80V is coming into play by much. If it is, then 2S2P eliminates it. You'll be well within the MPPT range. 2S2P is more shade tolerant, and 2S2P is more efficient. MPPT becomes less efficient converting from higher voltages by about 1-2%. This is often offset by reduced losses in wiring due to higher voltage/lower current.

Summary:
4S:
Less shade tolerant
May be impacting MPPT performance by a small amount due to high voltage
Is 1-2% less efficient than lower voltages

2S2P:
More shade tolerant
Works well within the MPPT voltage range
Is more efficient than 4S

 

[sunshine_eggo]

I think I understand thank you for the suggestion. Technically is what I was thinking acceptable or would it not work?

Your intent isn't entirely clear. It is important that any panels in series be in the same orientation/tilt. If not, the array won't perform any better than the weakest panel.

 

[rmaddy]

4S Vmp = 81.6

PIP MPPT range = 30-80V

You may be losing a little off the top end.

You need to use Voc, not Vmp, when calculating the safe range of voltage. And Voc goes up in the cold. Also, you can't exceed the max voltage input at all or you can fry the SCC. It's the controller's output current that can be clipped safely. But not the input voltage.

So a Voc of 24.3V at 4S is 97.2V. That's way over the max of 80V, and even more so as the temperature goes down.

 

[sunshine_eggo]

You need to use Voc, not Vmp, when calculating the safe range of voltage. And Voc goes up in the cold. Also, you can't exceed the max voltage input at all or you can fry the SCC. It's the controller's output current that can be clipped safely. But not the input voltage.

So a Voc of 24.3V at 4S is 97.2V. That's way over the max of 80V, and even more so as the temperature goes down.

Per the specs the OP linked:

80V is the upper limit of the MPPT operating range.
145V is the Voc upper limit.

 

[rmaddy]

Per the specs the OP linked:

80V is the upper limit of the MPPT operating range.
145V is the Voc upper limit.

Oops - I did misread that. Thanks.

 

[mactech]

Oops - I did misread that. Thanks.

I have this same unit and didn't realize the 80v MPPT range which explains why 3 panels in series didn't produce 3 x 300w - efficiency I expected. I now have 2s2P of 300w bifacial panels and routinely get 1100watts, slowly dropping with the sun.

 

[Belzo]

Yes. I made that suggestion above a couple times.

I doubt the 80V is coming into play by much. If it is, then 2S2P eliminates it. You'll be well within the MPPT range. 2S2P is more shade tolerant, and 2S2P is more efficient. MPPT becomes less efficient converting from higher voltages by about 1-2%. This is often offset by reduced losses in wiring due to higher voltage/lower current.

Summary:
4S:
Less shade tolerant
May be impacting MPPT performance by a small amount due to high voltage
Is 1-2% less efficient than lower voltages

2S2P:
More shade tolerant
Works well within the MPPT voltage range
Is more efficient than 4S

I've made this drawing based on what you are proposing I switch my current 4S panels to. I have already ordered a Renogy Parallel pair of connecters and a 15Amp in line fuse as I figured I might need them at some point anyway. One thing I would like to know is if I have the proper placement for the inline fuses for this 2S2P setup as well as if I will have any problems with the 10AWG MC4 PV wiring with the increased current with the change to series-parallel option or is 10AWG sufficient at these currents? Also with this setup will I maybe run into issues getting proper voltage to the MPPT lowest input range of 30V given that my max voltage range for this 2S2P would now be closer to 40V vs my existing 80V? Thanks!

 

[sunshine_eggo]

I've made this drawing based on what you are proposing I switch my current 4S panels to.

You have sketched a 2S2P array.

I have already ordered a Renogy Parallel pair of connecters and a 15Amp in line fuse as I figured I might need them at some point anyway. One thing I would like to know is if I have the proper placement for the inline fuses for this 2S2P setup

Yes.

as well as if I will have any problems with the 10AWG MC4 PV wiring with the increased current with the change to series-parallel option or is 10AWG sufficient at these currents?

This is something you need to confirm. 10awg PV wire is typically 30A (some are more), and some parallel connectors are rated for 50A. You may want to combine your arrays in a combiner box like an MNPV4, which would eliminate the need for the fuses in the 2S2P arrays.

Also with this setup will I maybe run into issues getting proper voltage to the MPPT lowest input range of 30V given that my max voltage range for this 2S2P would now be closer to 40V vs my existing 80V? Thanks!

Not likely. Voc is the triggering voltage, and the MPPT is going to try to work within its range. It's unlikely that the max power point will actually ever be below 30V for any significant length of time.

First light (even indirect) on a panel is what gives you its voltage. More current is available as more solar energy hits the panel, so you get voltage first, then you get current. Here's what that looks like:



As you can see, my panels hit 96.18V, and this was13 minutes before sunrise today. My Vmp is about 120V, so you can see it hits and holds Vmp from about 7:15am on. The variations were due to scattered wispy clouds. At shortly after 8am, my 3kW array is producing about 1kW - 3.5 hours before my peak solar.

You should expect similar performance.

 

[Belzo]

You have sketched a 2S2P array.



Yes.



This is something you need to confirm. 10awg PV wire is typically 30A (some are more), and some parallel connectors are rated for 50A. You may want to combine your arrays in a combiner box like an MNPV4, which would eliminate the need for the fuses in the 2S2P arrays.



Not likely. Voc is the triggering voltage, and the MPPT is going to try to work within its range. It's unlikely that the max power point will actually ever be below 30V for any significant length of time.

First light (even indirect) on a panel is what gives you its voltage. More current is available as more solar energy hits the panel, so you get voltage first, then you get current. Here's what that looks like:

View attachment 72835

As you can see, my panels hit 96.18V, and this was13 minutes before sunrise today. My Vmp is about 120V, so you can see it hits and holds Vmp from about 7:15am on. The variations were due to scattered wispy clouds. At shortly after 8am, my 3kW array is producing about 1kW - 3.5 hours before my peak solar.

You should expect similar performance.

Thank you. I appreciate your information. It's been very informative! I still am thinking about how I might add panels. I might draw up some diagrams for those ideas too and might have some questions. I think I understand now how and why switching my 4S to a 2S2P would be best. Thank You

 

[Belzo]

What do you think of this 3S2P design?

 

[sunshine_eggo]

You have sketched a 3S2P configuration with fuses in the correct location. Again, fuses aren't necessary with only two strings in parallel, but they become necessary if you parallel 3 or more.

No harm in having a fuse!

MPPT performance should be good @ 60Vmp.

 

[Belzo]

You have sketched a 3S2P configuration with fuses in the correct location. Again, fuses aren't necessary with only two strings in parallel, but they become necessary if you parallel 3 or more.

No harm in having a fuse!

MPPT performance should be good @ 60Vmp.

I just switched to 2S2P so will see have to see how it compares to what I got today in 4S. Will update.

 

[Belzo]

You have sketched a 3S2P configuration with fuses in the correct location. Again, fuses aren't necessary with only two strings in parallel, but they become necessary if you parallel 3 or more.

No harm in having a fuse!

MPPT performance should be good @ 60Vmp.

Is it possible that I would get less performance going to 2S2P vs my 4 in series before? I haven't seen the higher wattage (600w+) that I was getting before on 4 panels in series. I mean it has been overcast some of the days like normal but on the clear days I haven't seen it get as high as it was getting before switching. Is there any possible explanation for this?

 

[sunshine_eggo]

Is it possible that I would get less performance going to 2S2P vs my 4 in series before? I haven't seen the higher wattage (600w+) that I was getting before on 4 panels in series. I mean it has been overcast some of the days like normal but on the clear days I haven't seen it get as high as it was getting before switching. Is there any possible explanation for this?

Did you confirm that your battery was not in the absorption phase of charging? If you're at peak battery voltage, it doesn't matter how much the array can produce as the charger will only draw the power it needs to maintain battery voltage.

With light usage, I rarely see more than 50% of my array's output because the battery is at absorption voltage before peak solar.

On a completely clear day, when you are at your peak solar, typically noon on an optimally oriented array. Add loads that exceed your array's output. That way you can be certain that you're getting everything the panels can deliver.

 

[Belzo]

Ok, I will have to watch for that next time I have excellent sun input and if my battery is peaked out. I haven't been up to my 28.8v max for a while now since sun has not been at it's max. It's been cloudy most days with brief times of good sun but even these brief times just seem to be lower PV power getting produced. I will leave it the way it is though until I get a really clear day to do a comparison to how it was before.

 

[sunshine_eggo]

Assuming you're in the Northern hemisphere, the closer we get to the Winter Solstice, the worse our available solar becomes. If you're trying to compare what you remember to what you're seeing now, it's just not going to be reliable.

If you really think it is an issue, you can revert to 4S.