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Can you help with Tesla Powerwall+ Invertor MPPT Questions?

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Hey everyone, I am getting 20.4kW Solar, 2 Powerwall+, and 1 Powerwall2. I have questions before I approve the final design.
  1. What does the Powerwall+ Input Connectors per MPPT: 1-2-1-2 mean?
  2. Tesla's design shows 8 strings to the 2 PW+ but is only using 5 of the 8 MPPTs? Any valid reason?
  3. Tesla says that every 3 panels are isolated with an MCI Mid-Circuit Interrupters so MPPT isolation for shade does not matter?
  4. Tesla says that an MCI functions like an optimizer or microinverter. Really?
From reading this forum, I get that the Powerwall+ is basically a Powerwall2 plus an 7.6kW inverter.
I think I understand what an MPPT Maximum Power Point Tracking does.
I did ask to see the Plan Set as other have encouraged. Wow, did that show a lot of install problems.
 
Tesla is saving on wire and conduit fill at the expense of your system performance.. so is that a smart decision? Perhaps on some systems…
MCI’s are not optimizers.
@CrazyRabbit, Thanks! But if Tesla is already wiring up 8 strings back to the 2 PW+ inverters, they are already putting in the wire and conduit? 3 MPPT will have two parallel strings, 2 MPPT will have one string each. So the wiring is already to the inverter. It makes no sense unless I am missing something.
Any help with what this spec means: What does the Powerwall+ Input Connectors per MPPT: 1-2-1-2?
 
@CrazyRabbit, Thanks! But if Tesla is already wiring up 8 strings back to the 2 PW+ inverters, they are already putting in the wire and conduit? 3 MPPT will have two parallel strings, 2 MPPT will have one string each. So the wiring is already to the inverter. It makes no sense unless I am missing something.
Any help with what this spec means: What does the Powerwall+ Input Connectors per MPPT: 1-2-1-2?
They have been paralleling on the roof and running one home run and then jumping mppt’s together.
Post a picture of your engineering..
they are paralleling your homeruns, tell then NO.
 
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So they can jumper mppt one to two, one run the home run to two. That way they can run twice the current down from the roof.
True, but I would have phrased it as they are saving running two wires down from the roof. (Reduced labor and reduced wiring errors would be my guess as to why.)

Tesla does it frequently. Read other threads here if you want a sense of the pros/cons, but I wouldn't expect Tesla to change anything.

All the best,

BG
 
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As panels age, two similar strings will be come non equal. And output will only be as high as the lowest string.
For parallel strings, that would only be true if the degradation behavior is that V_mpp changes significantly, which I would not expect to be the case. And then you'd also need to have uneven degradation between strings, so that one string's V_mpp is quite different from the other's. Since dP/dV = 0 at V_mpp, a small shift in voltage away from V_mpp gives a near-zero change in power output.

Cheers, Wayne
 
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My design is for 19KW array with 2 PW+. If each PW+ has a 7.6KW inverter, then 2 have 15.2KW, and my AC to DC ratio is 1.3, which is not bad, but a little on the high side. The part I need help making sense of, like OP, is the string table, which looks like this:
Screen Shot 2022-12-13 at 3.11.33 PM.png

Any red flags here?
MCI/String are all 3 or less, is that ok?
What is a good maximum number of modules/string? Mine go as high as 25.
Should I be concerned that 8 strings go to one of the PW+, and only 6 to the other? Or should I be more focused on the total load per PW+?

I want to come across as an informed consumer, but I really have no idea what a lot of the FULL PLANS I requested actually mean, so any links to how to interpret proposed plans would be much appreciated!