Are my strings correctly set up?

[SeBas42]

Hi there. I had my install today and when I asked the project lead on site about the way my system is configured I didn’t get a straight answer. Here’s my question. Can someone help me understand this wiring diagram? I have two arrays of panels. 9.6 kW system with 15 panels facing east and 9 facing west. Based on the diagram it looks like they’re combined into two strings of 6 and 18 panels. Shouldn’t it be 9 and 15? Doesn’t make sense to me to wire 3 of the west facing panels with 15 east facing panels in the same string. Am I missing something? I reached out to my PA about this but would like to get some feedback from this group. TIA.

 

[power.saver]

Hi there. I had my install today and when I asked the project lead on site about the way my system is configured I didn’t get a straight answer. Here’s my question. Can someone help me understand this wiring diagram? I have two arrays of panels. 9.6 kW system with 15 panels facing east and 9 facing west. Based on the diagram it looks like they’re combined into two strings of 6 and 18 panels. Shouldn’t it be 9 and 15? Doesn’t make sense to me to wire 3 of the west facing panels with 15 east facing panels in the same string. Am I missing something? I reached out to my PA about this but would like to get some feedback from this group. TIA.

Your interpretation is correct, and it isn't a good design. The reason they did it is because they paralleled two strings to two MPPT inputs, and that requires an even number of panels. So they added 3 west panels to the 15 east panels to get 18, with 9 in each of the paralleled strings.

The better design would be to use all three MPPT inputs without paralleling any strings: one for your 9 west panels, and two for your east panels, with 7 and 8 panels in each of those strings. But that would have required more wire in the conduit which seems to be something Tesla doesn't want to do.

 

[SeBas42]

Your interpretation is correct, and it isn't a good design. The reason they did it is because they paralleled two strings to two MPPT inputs, and that requires an even number of panels. So the added 3 west panels to the 15 east panels to get 18, with 9 in each of the paralleled strings.

The better design would be to use all 3 MPPT inputs without paralleling any strings: one for your 9 west panels, and two for your east panels, with 7 and 8 panels in each of those strings. But that would have required more wire in the conduit which seems to be something Tesla doesn't want to do.

Thank you. Exactly my thought. Is that so something I should push them on to come back out and correct? Running another wire through the conduit doesn’t seem like too much to ask. I thought they’d go for optional performance and not trying to save a few bucks on wiring.

 

[power.saver]

Thank you. Exactly my thought. Is that so something I should push them on to come back out and correct? Running another wire through the conduit doesn’t seem like too much to ask. I thought they’d go for optional performance and not trying to save a few bucks on wiring.

I would do that. It's not optimal having panels that face different directions on the same string.

 

[SeBas42]

Thank you. Is that something I should push them on to come back out and correct? Running another wire through the conduit doesn’t seem like that big of an ask. I’m baffled that they’re trying to save a few bucks on wiring instead of going for optimal performance.

 

[el-guapin]

...... I thought they’d go for optional performance and not trying to save a few bucks on wiring.

Not Tesla!...savings, savings!

 

[SeBas42]

I would do that. It's not optimal having panels that face different directions on the same string.

 

[SeBas42]

Not Tesla!...savings, savings!

Wish I had seen the wiring before the install.

 

[power.saver]

Wish I had seen the wiring before the install.

Yes, it's always best to review the plans before installation to know what you're getting. Tesla doesn't make this easy, and not everyone understands solar well enough to pickup on these details.

 

[yblaser]

Your interpretation is correct, and it isn't a good design. The reason they did it is because they paralleled two strings to two MPPT inputs, and that requires an even number of panels. So they added 3 west panels to the 15 east panels to get 18, with 9 in each of the paralleled strings.

The better design would be to use all three MPPT inputs without paralleling any strings: one for your 9 west panels, and two for your east panels, with 7 and 8 panels in each of those strings. But that would have required more wire in the conduit which seems to be something Tesla doesn't want to do.

It took me a few times looking at the design but that's not quite what they did. There is 15 East panels, a string of 6 on their own inverter input and a string of 9 that is wired in parallel with the West string of 9.

@SeBas42 while running the strings in parallel is not optimal it really doesn't have a huge impact unless you have shading on the strings. Tesla seems to like to run parallel strings to save a few dollars.

 

[SeBas42]

It took me a few times looking at the design but that's not quite what they did. There is 15 East panels, a string of 6 on their own inverter input and a string of 9 that is wired in parallel with the West string of 9.

@SeBas42 while running the strings in parallel is not optimal it really doesn't have a huge impact unless you have shading on the strings. Tesla seems to like to run parallel strings to save a few dollars.

Thanks. Shading is not really the issue. I was more thinking that in the morning and evening hours the string isn't really optimized since only half of the panels have direct exposure. It's a 4/12 pitch roof and I'm in Florida.

 

[yblaser]

Thanks. Shading is not really the issue. I was more thinking that in the morning and evening hours the string isn't really optimized since only half of the panels have direct exposure. It's a 4/12 pitch roof and I'm in Florida.

With parallel strings both strings have to be at the same voltage and the optimum voltage on a string doesn't strongly depend on the intensity of sunlight hitting the panels.

I tried to explain some of the issues with parallel strings here mostly pertaining to shading:

Should I request Power Optimizers?

I'm trying to learn about Power Optimizers to see if they would be a good idea to add to my array design or not. Does anyone have any experience with them and Tesla solar/inverter/powerwalls? I've heard they're typically only added when there's a good amount of shade on your array, but I'm...

teslamotorsclub.com

 

[SeBas42]

With parallel strings both strings have to be at the same voltage and the optimum voltage on a string doesn't strongly depend on the intensity of sunlight hitting the panels.

I tried to explain some of the issues with parallel strings here mostly pertaining to shading:

Should I request Power Optimizers?

I'm trying to learn about Power Optimizers to see if they would be a good idea to add to my array design or not. Does anyone have any experience with them and Tesla solar/inverter/powerwalls? I've heard they're typically only added when there's a good amount of shade on your array, but I'm...

teslamotorsclub.com

Once again thank you for taking the time and pointing me to this post. Sounds like the the performance of 2 strings of panels wired parallel is mainly impacted by shading but not as much by azimuth and resulting level of illumination. Given that it's probably not worth requesting an update to the strings. Sounds like I'd be losing a lot more time and energy waiting for the redesign than what it's worth.

 

[SeBas42]

Found some additional resources that explain why having opposite facing panels (east/west) wired in parallel on the same string might not be that big of an issue under the following conditions:

1. The two sets of panels must be identical in number.
2. They must be on a gently sloping roof.
3. No partial shading of different panels on same string.

East West Facing Solar Panels On A Single Inverter Input Can Work Well

Wondering if you can put east and west facing solar panels on a single input inverter? The good news is you can - in certain conditions.

www.solarquotes.com.au

https://www.energymatters.com.au/images/news/2013/east-west-solar-paper.pdf