Looking for thoughts/opinions/issues on my Full Plan Set

[Jeremy3292]

I finally got my full design plan set from Tesla with 3 Powerwalls, shown below. Does anyone see any issues with stringing, design, etc.? People on this forum know more than I do about those types of items - parallel/series, wiring, etc.

My #1 question is why they gave me TWO 7.6 kW inverters for a 9.315 kW solar array size. PVWatts tells me the annual output difference between one 7.6 kW, one 7.6 kW + one 3.8 kW, or two 7.6 kW inverters is negligible (DC/AC ratio change). I've read on here numerous times Tesla used to hardcore push a very high DC/AC ratio and people had to scream and yell to get another inverter with a much larger PV array than mine. My only thought it is the Tesla inverters have been prone to failure and maybe that is due to the heavy use/heat from such high DC/AC ratios? So they realized that and are now they are oversizing inverters maybe?

I appreciate any thoughts you may have or anything I should ask my advisor to look at or change.

 

[Matt-FL]

I wouldn't be concerned about having two 7.6kW inverters. I personally would rather overkill (or the possibility of expanding) rather than overdriving.

You might want to put up a small half-fence around your Powerwalls on the side of the house. They do have breathing glow-strips all the way around (no way to turn it off), that just shouts out 'here I am'. (They 'breathe' when charging or discharging). I *think* this was omitted on the PW3s.

Overall, looks great. I know you were trying to get a few more panels overall, but it is still a great design. Look forward to seeing the completed product!

 

[Jeremy3292]

I just noticed the stringing also. 6 panels on string 1A and 6 panels on string 1B going to one inverter. 6 panels on string 2 and 5 panels on string 3 going to the other inverter. Not sure what string 1A and 1B mean though? It seems they are just wired together but don't know what that produces as a result from a practical standpoint vs doing it like the other inverter in separate strings.

 

[offandonagain]

I just noticed the stringing also. 6 panels on string 1A and 6 panels on string 1B going to one inverter. 6 panels on string 2 and 5 panels on string 3 going to the other inverter. Not sure what string 1A and 1B mean though? It seems they are just wired together but don't know what that produces as a result from a practical standpoint vs doing it like the other inverter in separate strings.

Looks like a parallel string going into one of the inverters, so you'll only have 3 wires coming down from the roof. I'm not sure why Tesla does that (conduit fill percent? / wire cost?). But you have a single panel orientation, so assuming there are no issues with shading I don't think it will affect performance.

 

[Jeremy3292]

Looks like a parallel string going into one of the inverters, so you'll only have 3 wires coming down from the roof. I'm not sure why Tesla does that (conduit fill percent? / wire cost?). But you have a single panel orientation, so assuming there are no issues with shading I don't think it will affect performance.

I do have some issues with shading from trees around, so I requested multiple strings and MPPT's. It is more of an issue now with the sun being low in the sky. I'm not sure exactly which panels they strung together, but at the very least it seems they heeded my request.

 

[Docfxit]

Since you do have shading possibilities it would be helpful for you to know what is causing lower production. It would be helpful for Tesla to know what part of your roof is being shaded so they can wire the strings to minimize the effect. You might consider a video camera to be installed so you can see what is being shaded. Of course that will change throughout the year but it would be nice to take a stab at it now.
You can get a cheap $30 wireless camera for temporary install.
Maybe this will shed some light on the subject:

Please ignore in the video the talk about optimizes and focus on the reduced production in a string.

 

[Jeremy3292]

Since you do have shading possibilities it would be helpful for you to know what is causing lower production. It would be helpful for Tesla to know what part of your roof is being shaded so they can wire the strings to minimize the effect. You might consider a video camera to be installed so you can see what is being shaded. Of course that will change throughout the year but it would be nice to take a stab at it now.
You can get a cheap $30 wireless camera for temporary install.
Maybe this will shed some light on the subject:

Please ignore in the video the talk about optimizes and focus on the reduced production in a string.

I already have numerous pictures tracking the sun across the sky/my roof from my Simplisafe outdoor camera. It isn't in one place throughout the day or time unfortunately. The sun tracks across the sky and the rays "hit" trees, thus partially soiling the panels, as the back of my property is is entirely wooded. I've been looking at this since construction and it gets worse as the sun gets lower in the sky obviously.

The only way to describe is that the closer to the top ridge the less shading that will occur (obv bc it is higher up). I pointed this out to my advisor and showed pictures, basically saying can we make sure we at least bifurcate the top 2 and bottom 2 rows of panels with different strings. I'll ask what exactly they did.

I think it is going to mostly just be a problem now before the trees shed all their leaves and allow more sunlight through. Example pics below.

Feb 18th at 10:58am during construction

Aug 10th at 5:34pm

Aug 21st at 9:30am

Oct 24th at 10:39am before time change

 

[Matt-FL]

The installers may alter the design when they arrive, so be ready to support your position with these pictures. There are many cases (mine included) where the designer had one idea, and installers a different (installer was trying to maximize production, installers were more interested in what made an easier install).

 

[Jeremy3292]

This is my confirmed stringing diagram below. As @Matt-FL pointed out, I'll need to make sure the installers follow it.

 

[yblaser]

This is my confirmed stringing diagram below. As @Matt-FL pointed out, I'll need to make sure the installers follow it.

View attachment 991371

As @offandonagain pointed out they have wired 1A and 1B in parallel. While likely not a huge impact when you consider your total yearly production it is not ideal. For example in your Aug 21st at 9:30am photo, 1B has about 2 panels shaded. While this is happening you will lose an equivalent of two panels of production from 1A since both strings must maintain the same voltage.

 

[Jeremy3292]

As @offandonagain pointed out they have wired 1A and 1B in parallel. While likely not a huge impact when you consider your total yearly production it is not ideal. For example in your Aug 21st at 9:30am photo, 1B has about 2 panels shaded. While this is happening you will lose an equivalent of two panels of production from 1A since both strings must maintain the same voltage.

I agree. I guess I could’ve asked for a 4th string and MPPT, but I think the shade is too variable for a truly optimal solution here. The sun tracks across the sky differently every day as it is higher/lower in the sky depending on the time of year. So I figured just keep the lower panels segregated and leave the top 2 rows in a string.

 

[Vines]

I agree. I guess I could’ve asked for a 4th string and MPPT, but I think the shade is too variable for a truly optimal solution here. The sun tracks across the sky differently every day as it is higher/lower in the sky depending on the time of year. So I figured just keep the lower panels segregated and leave the top 2 rows in a string.

The other PW+ uses 2 discrete of the 4 MPPT channels, so there is no reason that I can see why the first PW+ can't use 2 discrete channels and run 4 wires down to each inverter.

 

[Jeremy3292]

The other PW+ uses 2 discrete of the 4 MPPT channels, so there is no reason that I can see why the first PW+ can't use 2 discrete channels and run 4 wires down to each inverter.

The other Powerwall+ appears to not have a charge controller. I have one of each below in my plan set.

But yeah 4 MPPT's is possible for each inverter. Not sure if it is worth the hassle to change at this point as they are preparing my interconnection agreement and county permit now.

 

[Vines]

The other Powerwall+ appears to not have a charge controller. I have one of each below in my plan set. But yeah 4 MPPT's is possible for each inverter.

View attachment 991480

My understanding is that only one PW+ needs a site controller. This is the brains that coordinate with the backup switch. The second PW+ will just follow what the first says to do.

 

[Jeremy3292]

My stringing is actually the below, but not sure it makes any difference really.

 

[YRide]

As @offandonagain pointed out they have wired 1A and 1B in parallel. While likely not a huge impact when you consider your total yearly production it is not ideal. For example in your Aug 21st at 9:30am photo, 1B has about 2 panels shaded. While this is happening you will lose an equivalent of two panels of production from 1A since both strings must maintain the same voltage.

I had similar during my install, they forced a few strings that should have been separate to go parallel on same MPPT. I pushed back hard, they said nothing they could do (material cost savings...and "it wont impact your production at all"). I stood my ground, asked them (nicely) to escalate to their manager back at HQ. They got him on the phone, I went out and got sandwiches for the entire crew, and when I came back they agreed to split them all out to indepenent MPPT's...but still claimed it would not benefit me at all.

Then, later during inspection...our city inspector...that mainly did big commercial stuff, had to fill in for a residential guy that was not in...challenged Tesla due to conduit fill allowances, de-rating, etc, etc. I really wish i had this on video. Got heated for a bit, but then the inspector went back to his truck and said he would look for a way to navigate around it...came back with the code book and showed the inspector how he was going to view it and done, signed off. When he left, the Tesla inspection lead said he was still wrong...but just went with it.

It's a whole other world out there! Moral of story...always buy lunch

 

[CrazyRabbit]

Baloney sandwiches?