Tesla Inverter MPPT

[houser2021]

What is the min number of panels you can put per string on the 7.6kw tesla inverter? I have 20 panels facing same direction and there is some shade to 4 of them next to the chimney. Does it make sense to put those 4 on its own string?

 

[arnolddeleon]

What is the min number of panels you can put per string on the 7.6kw tesla inverter? I have 20 panels facing same direction and there is some shade to 4 of them next to the chimney. Does it make sense to put those 4 on its own string?

According to the Tesla installers that recently installed my system (4 kW Tesla solar install (with existing solar) and Powerwall addition and what I learned) the answer is apparently 5.

The specs says 60V is the minimum input voltage. A string that is too short may have trouble reaching the the minimum voltage.

I think you want to read this thread, Solar layout - Does this need optimizers?, on the question of putting them on their own string.

 

[s0schen]

According to the Tesla installers that recently installed my system (4 kW Tesla solar install (with existing solar) and Powerwall addition and what I learned) the answer is apparently 5.

The specs says 60V is the minimum input voltage. A string that is too short may have trouble reaching the the minimum voltage.

I think you want to read this thread, Solar layout - Does this need optimizers?, on the question of putting them on their own string.

On the Cell Q6 spec sheet, Min performance at standard test condition is 33.6 V / panel at MPP and at Normal operating conditions 31.97 V / panel at MPP. I would guess you need at least two panels in a string based on this but this puts you at risk being below 60 V if there is shading?

On another note, my design diagram shows 13 panels on one string. I'm wondering if that is too many in one string. There is partial shading on 1 panel on that string.

 

[s0schen]

On the Cell Q6 spec sheet, Min performance at standard test condition is 33.6 V / panel at MPP and at Normal operating conditions 31.97 V / panel at MPP. I would guess you need at least two panels in a string based on this but this puts you at risk being below 60 V if there is shading?

On another note, my design diagram shows 13 panels on one string. I'm wondering if that is too many in one string. There is partial shading on 1 panel on that string.

On the Cell Q6 spec sheet, Min performance at standard test condition is 33.6 V / panel at MPP and at Normal operating conditions 31.97 V / panel at MPP. I would guess you need at least two panels in a string based on this but this puts you at risk being below 60 V if there is shading?

On another note, my design diagram shows 13 panels on one string. I'm wondering if that is too many in one string. There is partial shading on 1 panel on that string.

Correction. There is group of 13 panels physically, but design is 12 panel string. Not sure how they are splitting it up. There is one string of only 3 panels on the electrical diagram though. This is for the Powerwall+

 

[arnolddeleon]

Should this be a single string of 12 or two strings of 6 on different MPPT inputs? @nwdiver?

 

[nwdiver]

Should this be a single string of 12 or two strings of 6 on different MPPT inputs? @nwdiver?

If they're not facing the same direction then they can't be on the same string.

 

[arnolddeleon]

If they're not facing the same direction then they can't be on the same string.

That's what I was thinking. I started doubting my understanding.

 

[arnolddeleon]

If they're not facing the same direction then they can't be on the same string.

Would it matter if they were paralleled? If they did parallel them then they could just as easily just run a second pair of lines down to the second input.

I had asked the installer about the strings and he said it was ok because they were on the same azimuth. I was not looking at the roof at that time and now either my understanding of azimuth is wrong or they were misspoke when they said they were the same azimuth.

 

[nwdiver]

Would it matter if they were paralleled?

A little. Ideally strings that aren't identical should be independent but I have 5 strings on my toy system facing different directions paralleled and they seem to do ok. Series means the current through all panels in a string WILL BE the same. Parallel means the voltage across the strings WILL BE the same. The voltage of the panels in series can vary and the current between two parallel strings can vary A LOT. Current changes mostly due to sunlight and voltage varies mostly due to temperature.

.... ideally ALL strings should be independent. There's really no reason to install a system going forward with strings in parallel. I don't plan to ever install another system without independent strings.

 

[arnolddeleon]

A little. Ideally strings that aren't identical should be independent but I have 5 strings on my toy system facing different directions paralleled and they seem to do ok. Series means the current through all panels in a string WILL BE the same. Parallel means the voltage across the strings WILL BE the same. The voltage of the panels in series can vary and the current between two parallel strings can vary A LOT. Current changes mostly due to sunlight and voltage varies mostly due to temperature.

.... ideally ALL strings should be independent. There's really no reason to install a system going forward with strings in parallel. I don't plan to ever install another system without independent strings.

Thanks!

I'll need to verify that in parallel not in series. in this case they were parallel the only savings is they had to run 2 few wires down. The inverter already had a second MPPT input. Trying to get over voltage startup would be the same whether they used one or two MPPT inputs. The string length is still 6 in either case.