3 inputs 2 strings south one string west

[philatio]

New member here.
I have searched the internet to try and get an answer to my question to no avail.

My apologies if this is the wrong place to post this.

I just had a 7.4kw system installed consisting of:

20 x REC 370 Alpha Black panels
20 x TS4-R-SMA optimizers
1 x SMA Sunny Boy 7.7 (SB7.7-1SP-US41) string inverter.

The 20 panels were mounted on a south facing roof with 2 strings of ten in 2 of the 3 inputs on the inverter.

I am thinking about expansion already as I plan a battery back up a few years from now.

I can add 4 more panels to my south roof and the panels/inverter can take up to 13 panels per string per the contracted company.

I was thinking that for the 3rd input I could also add panels to the west facing roof. I understand this roof will see 15% reduction in output vs south facing.

Will this affect the output of the panels on the south facing roof that are on the first 2 inputs?

Any information you can provide would be greatly appreciated.

 

[snoobler]

Welcome to the forum.

Each input is independent of the others, i.e., you could have 1 on the first and 13 on the second, and your net would be 14.

You must pay attention to any paralleling you do on a single input. Any parallel strings on a given input must have the same or highly similar series Voc. Looks like your inverter has a 10A limit on each input, so parallel on the same input isn't an option:

https://files.sma.de/downloads/SBxx-US-DS-en-38.pdf?_ga=2.245694787.650397328.1622658412-1294820493.1622658409

Assuming you would add 2 panels to each of the strings for 12 in series on inputs 1 and 2, and all of these panels are in the same orientation, that's fine.

All panels on the west facing roof should be mounted in the same orientation.

Your 20 panels are already at 7.4kW, which is just under the inverter limit at 7.7kW. 24 would put you at 8.88kW and the West face would just add to that. Lets say you can get 8 on the West roof. Now your total is 11,840. Not a big deal, but your production will be clipped to 7.7kW, but it will produce that for as long as the array can support that level.

The linked datasheet shows that it can handle 12,320W, so don't exceed that.

This post has a graphical representation of clipping:

Solar Charge controller, how many amps?

I want to install 600 watts of solar on my van. After performing a basic calculation of 600/12 = 50, it seems that I would need at a minimum a 50 amp charge controller. I am a little confused as I am looking at starter kits from Grape solar and Rich solar 3 X 200-watt panels with only 40 amp...

diysolarforum.com

Blue is essentially your existing array. The entire parabola is your new array. You will gain the green, but you will lose the red.

It's about how much you want to spend, and graphically, at this point, you're only going to gain about 50% for every Watt you purchase vs. your existing panels; HOWEVER, considering that you're adding panels to the West roof, as your South array drops off, you will harvest solar notably later into the day, so it might be worthwhile in spreading out power throughout more of the day.

 

[philatio]

Wow, thanks for such a detailed answer. I didn't even think about limits.

So much to learn, so little time.

But now I have my answer.

Thanks again.