Tesla Says I Can Only Get *ONE* Powerwall bc of my Utility's Rules

[Matt-FL]

There is the possibility that the installers will alter the plans, not to fit your best energy strategy, but to make for the simplest install. I had shared shading timelapse with my designer who altered strings based on the information I provided. The installers looked at the plans and made their own. What the installer said made sense at the time, but now that I've had time to read through many posts here and research, I know why the installers adjusted.
I still have really good production, but that is mostly due to a large southern facing roof. But, I'd probably have another 5-10% production if they had installed the way the designer had it laid out.

 

[GateFather]

There is the possibility that the installers will alter the plans, not to fit your best energy strategy, but to make for the simplest install. I had shared shading timelapse with my designer who altered strings based on the information I provided. The installers looked at the plans and made their own. What the installer said made sense at the time, but now that I've had time to read through many posts here and research, I know why the installers adjusted.
I still have really good production, but that is mostly due to a large southern facing roof. But, I'd probably have another 5-10% production if they had installed the way the designer had it laid out.

What did they say to you that made you agree with them in the moment? Any tips for avoiding this? I’d much prefer the designers plans be what is installed, but can see it being difficult to argue with installers on site who come up with a reason I may not fully understand for changing the plans. Especially if it’s to make the install easier vs actually netting a benefit to me.

 

[Matt-FL]

There was several, but one was around how the inverters are designed to run consistently at 125% output. They also said that running two strings in parallel would serve better across the south facing roof. I thought I knew enough, but the wonderful people on this forum have helped me learn so much more since then. What was designed was 6 strings across 59 T400 panels. What I ended up with was 4 strings, but two parallel.
What I have in the end is 32 panels, all south facing in 2 strings on one inverter, 7 south facing + 12 east + 12 west on the second inverter. So I have one inverter always overdriven, and the other just cruising.

I'm still well over Tesla's estimates, so I haven't made any complaints. I figured it is working, better than expected, so if it isn't broke, I'm not going to have them come out and break/fix it.

 

[GateFather]

There was several, but one was around how the inverters are designed to run consistently at 125% output. They also said that running two strings in parallel would serve better across the south facing roof. I thought I knew enough, but the wonderful people on this forum have helped me learn so much more since then. What was designed was 6 strings across 59 T400 panels. What I ended up with was 4 strings, but two parallel.
What I have in the end is 32 panels, all south facing in 2 strings on one inverter, 7 south facing + 12 east + 12 west on the second inverter. So I have one inverter always overdriven, and the other just cruising.

I'm still well over Tesla's estimates, so I haven't made any complaints. I figured it is working, better than expected, so if it isn't broke, I'm not going to have them come out and break/fix it.

Ah got it. My understanding is that shading on a single panel or small few will decrease DC output for all panels connected to those panels in the same string. Therefore, it’s better to have more strings with panels grouped by areas where it’s likely the majority of panels in that string will be shaded or not shaded together. Or, to minimize the size (number of panels) of strings Where there is known shade.

 

[Matt-FL]

There are bypass diodes in each panel to reduce this. When researching this last year, I found this video helpful:

 

[GateFather]

Ugh of course this would come out today: Tesla releases more details on Powerwall 3, confirms cheaper stack coming

So now I have to decide if I want to wait for the DC Expansion PW3 models to be available. I assume they could do 1 PW3 with inverter and a separate Tesla 7.6kW Inverter to get me to close to what the current system is spec'd as.

 

[Jeremy3292]

Yep that’s what we’ve been waiting for. Wouldn’t hold your breath on availability anytime soon though.

 

[Matt-FL]

Yep that’s what we’ve been waiting for. Wouldn’t hold your breath on availability anytime soon though.

When you hear Tesla saying 'it's coming soon', just think... Cybertuck.

 

[GateFather]

When you hear Tesla saying 'it's coming soon', just think... Cybertuck.

Yeah I found out since yesterday that the "DC Expansion" packs are purely storage and provide no incremental power output. So 1PW3 and 3 DC Expansion would only provide 11.5kW output. So in my case where my utility will not allow more than 21kW total output from the installed Inverter potential (not activated AC output), I still could not get 2 PW3 and 2 DC Expansions. So it looks like the only way for me to go this route will be to use 2PW2 and 2PW+ with an additional 5.7kW AC Inverter.

 

[Jeremy3292]

Honestly it sounds like you’re at the same spot now that I was 6 months ago. Looks like I made the right decision too as you *maybe* will see these expansion packs available 6 months from now, but even then they don’t seem to work for you how you need. PW2/+ combo is a solid product and available today.

Also the more I see and read it seems like PW2/+ is more customizable. The PW3 seems like an out of the box solution that’s cheap and just works for a lot of homes but maybe not for everyone. Ironically, I’ll have more power output with my 2 PW+ and 1 PW2 then I would with the PW3 due to my 20 kW AC utility limit.

 

[GateFather]

Honestly it sounds like you’re at the same spot now that I was 6 months ago. Looks like I made the right decision too as you *maybe* will see these expansion packs available 6 months from now, but even then they don’t seem to work for you how you need. PW2/+ combo is a solid product and available today.

Yep. I’ve made my peace with it. The issue, I realized, is not Tesla, it is my utility. Tesla has all the modularity in their PW3 system to allow for derating/disabling of inverters on their PW3s and would do so if my utility allowed. But, given my situation, their solution of 2PW2 + 2PW Plus + extra 5.7kw AC inverter looks like the way to go. There's also something to be said for these being battle tested and real-world used products which have a lot of data to support them working well (well the batteries, maybe not so much the inverters). I have a call with my advisor at 11am ET today and plan to give the green light verbally and finish signing the forms/approving the design at that time. Next steps for me will be to get the license and liability insurance info for my HOA submission, then permits, then likely as in your case, a long wait for the actual install.

 

[CrazyRabbit]

Ask duke if they will accept export/software limit of 20kw.

 

[GateFather]

Ask duke if they will accept export/software limit of 20kw.

Not sure if this was directed at me but I have Atlantic City Electric and heard back from them that they don’t allow more than installed 21kW AC inverter capability regardless of whether it’s all being used/disabled/derated. If it’s there and available, it counts.