Solar Panel Configuration

[rvtyme]

I am now trying to determine my best configuration for the 8 190w HQST Solar panels (Voc 24.3, Isc 10.15A)
I have (2) Victron MPPT 150/100 SCC along with 618ah Lithium Batteries @ 12V

Various configurations I am looking at:
(A) Use the two SCC and use 4 panels on each controller in a 2S2P configuration. Just splitting them across the two controllers.
(B) Use only 1 of the 150/100 SCC and use all 8 panels 2S4P configuration. Sell the other 150/100 MPPT

These panels will be on a 5th wheel trailer. I have heard that it is best to have a higher voltage so you can maximize the sun earlier in the morning?? Still much to learn. Thoughts on best way to configure this - I don't plan on expanding beyond these 8 panels.

 

[NVS]

You can do a 4s2p setup on one scc. That way you'll be at 97.2v with 20.3a input and can use 10gauge wire.

 

[rmaddy]

A 100A controller with a 13.5V battery can handle 1350W. You have 8 190W panels for a total of 1520W. But your panels will be flat mounted so you will rarely see the full 1520W. The roof of your 5th wheel probably has lots of things that will cause shading issues meaning you'll typically see even less total wattage.

Given all of this, and the expense of a 100A SCC, I would go with your 2nd option. Put all 8 panels on one SCC. Given the specs you could do either 4S2P or 2S4P. The 4S2P can give better lower light performance but shading issues could easily make it much less useful.

Most likely you would get better overall performance with a 2S4P setup. Try to ensure none of the 4 series pairs will get partial shading to help maximize the performance. If you don't actually have much on the roof that can cause shading issues then 4S2P would be good. But you need to avoid partial shading across 4 panels in series and that can be very difficult on an RV roof.

Do note that with the 4P setup you need to fuse each of the 4 parallel strings. The result will be about 41A so you likely need a combiner box since most MC4 connectors are only rated for 30A. Plus, depending on the length of wire from the combiner box to the SCC, you might need up to 4AWG. That's too large for most MC4 connectors.

 

[rvtyme]

You can do a 4s2p setup on one scc. That way you'll be at 97.2v with 20.3a input and can use 10gauge wire.

Ah yes... that's true. Thanks for the input! Much appreciated.

 

[rvtyme]

A 100A controller with a 13.5V battery can handle 1350W. You have 8 190W panels for a total of 1520W. But your panels will be flat mounted so you will rarely see the full 1520W. The roof of your 5th wheel probably has lots of things that will cause shading issues meaning you'll typically see even less total wattage.

Given all of this, and the expense of a 100A SCC, I would go with your 2nd option. Put all 8 panels on one SCC. Given the specs you could do either 4S2P or 2S4P. The 4S2P can give better lower light performance but shading issues could easily make it much less useful.

Most likely you would get better overall performance with a 2S4P setup. Try to ensure none of the 4 series pairs will get partial shading to help maximize the performance. If you don't actually have much on the roof that can cause shading issues then 4S2P would be good. But you need to avoid partial shading across 4 panels in series and that can be very difficult on an RV roof.

Do note that with the 4P setup you need to fuse each of the 4 parallel strings. The result will be about 41A so you likely need a combiner box since most MC4 connectors are only rated for 30A. Plus, depending on the length of wire from the combiner box to the SCC, you might need up to 4AWG. That's too large for most MC4 connectors

Everything has trade offs... You have given me plenty to think about for sure! Added to that, I am trying to decide if I add tilt brackets for the panels and if I would want to climb the ladder every time to actually use it! Thanks again!

 

[rvtyme]

A 100A controller with a 13.5V battery can handle 1350W. You have 8 190W panels for a total of 1520W. But your panels will be flat mounted so you will rarely see the full 1520W. The roof of your 5th wheel probably has lots of things that will cause shading issues meaning you'll typically see even less total wattage.

Given all of this, and the expense of a 100A SCC, I would go with your 2nd option. Put all 8 panels on one SCC. Given the specs you could do either 4S2P or 2S4P. The 4S2P can give better lower light performance but shading issues could easily make it much less useful.

Most likely you would get better overall performance with a 2S4P setup. Try to ensure none of the 4 series pairs will get partial shading to help maximize the performance. If you don't actually have much on the roof that can cause shading issues then 4S2P would be good. But you need to avoid partial shading across 4 panels in series and that can be very difficult on an RV roof.

Do note that with the 4P setup you need to fuse each of the 4 parallel strings. The result will be about 41A so you likely need a combiner box since most MC4 connectors are only rated for 30A. Plus, depending on the length of wire from the combiner box to the SCC, you might need up to 4AWG. That's too large for most MC4 connectors.

So after some more thought. If I run 4 parallel strings of (2) panels each to a combiner box (2s4p). I would need to place (1) 30amp MC4 fuses on the positive of each of the strings for a total of (4). The combiner box would have a total of 8 10awg wires (4 positives/4 negatives) connected onto their perspective bus bar within the combiner box. I would then have 4awg (do I really need 4awg?) from the combiner to a dc breaker and then onto the SCC 250/100.

I have the combiner box and the 4awg/10awg wires so I have been thinking this may be the best route.

Sound correct?

 

[rmaddy]

You only need 15A fuses for each parallel string since each pair in series is about 10A. Many combiner boxes will have breakers for each string. So you could put 4 15A breakers in the combiner box instead of using MC4 inline fuses.

The output of the combiner box will be about 48V at 41A. The gauge wire you need depends on how long it will be from the combiner box to the SCC. 4AWG would be good for up to about 60'.

 

[rvtyme]

You only need 15A fuses for each parallel string since each pair in series is about 10A. Many combiner boxes will have breakers for each string. So you could put 4 15A breakers in the combiner box instead of using MC4 inline fuses.

The output of the combiner box will be about 48V at 41A. The gauge wire you need depends on how long it will be from the combiner box to the SCC. 4AWG would be good for up to about 60'.

Gotcha. The distance from the combiner box to the solar charge controller would be no more than 15'. I have the inline fuses already as I didn't have room in the combiner box to house them. Thanks for all your help! This has definitely been a learning experience.

 

[rvtyme]

Gotcha. The distance from the combiner box to the solar charge controller would be no more than 15'. I have the inline fuses already as I didn't have room in the combiner box to house them. Thanks for all your help! This has definitely been a learning experience.

I have a double pole breaker between the Combiner box and the SCC. Since I am pulling in about 41amps, what do you suggest for a dc breaker size? I figured I would also have a 100 AMP DC Breaker between the SCC and the positive bus bar. So I am protecting both the input and output of the SCC. Sound correct?

 

[rmaddy]

The DC breaker for the PV disconnect isn’t there to protect anything so it must be rated for more than the 40A as well as the 48V. Anything over 50A should be fine.

Since you have a 100A SCC then the fuse between the SCC and bus bar should be 125A, not 100A.

 

[rvtyme]

The DC breaker for the PV disconnect isn’t there to protect anything so it must be rated for more than the 40A as well as the 48V. Anything over 50A should be fine.

Since you have a 100A SCC then the fuse between the SCC and bus bar should be 125A, not 100A.

Thanks for all your help. Much appreciated!

 

[DerpsyDoodler]

Thanks for all your help. Much appreciated!

disregard.

 

[rvtyme]

Also note that when he said "4awg would be good for up to 60'": that is a 60' round trip, meaning the combined length of the positive and negative cable.

Gotcha. My run is only 15' tops so that won't be an issue. Thanks for checking!

 

[rmaddy]

Also note that when he said "4awg would be good for up to 60'": that is a 60' round trip, meaning the combined length of the positive and negative cable.

Nope. I actually meant 60' one-way in this case. I should have made that clear.