(Please) rate my setup - how does this look?

[EightBitWhit]

Hi everyone - I'm in the final stages of negotiations with my solar installer and before I commit to hard dollars, I'd appreciate some feedback on the proposed system I'd be installing.

Here's some level-set on the house configuration and consumption:

• 400A service split across two 200A panels with a single meter
• panels are Leviton Load Centers with smart breakers with LDATA data collection hubs
• House is 100% electric (stove, water heater, etc.) with Geothermal for HVAC (also electric). All of these circuits are on one of the 200A panels.
• Currently have 2 Teslas, both with dedicated wall connectors. They are both energized by two 50A circuits on the second 200A panel.
• The balance of the lights/utilities/etc. are spread relatively evenly across the two 200A panels
  
  
• 12-month total home consumption: 33,905 kWh
• 12-month Average monthly consumption: 2,825 kWh
• 12-month Average utility rate: 0.117 / kWh - the actual monthly rate fluctuates due to a "Fuel cost adjustment" and an "environmental surcharge" added to the 0.0896 / kWh base rate

Here's the system my installer has spec'd out and the numbers they provided:

• 31.1 kW in size
• Qty. 84 370W Silfab panels
  • estimated to product 36.1kW per year
  • projected ~104% energy offset over the course of the year
• Qty. 4 Tesla Powerwall + (2 per panel)
• Qty. 2 Gateways

Here's a few questions I'd have for the collective here:

What other information should I be looking at to know whether this system is truly sized properly for 100% offset for my daily needs?​

My Geothermal pulls anywhere from 3-4kW when it's running (which is not continuously), the water heater does the same when it's running, the stove pulls about 2.5kW, etc. Each of the Tesla's pull ~10kW when charging, but I rarely charge them both at the same time... it happens occasionally, but it's the exception rather than the rule. I also wouldn't expect to charge the Teslas from the Powerwalls when the house is running on battery.

When "idle" (with none of the above running) the house pulls roughly 950W per panel to run TV's, computers, lights, refrigerator, freezers, etc.

When I do my own math, it seems to be sized well, but I'm neither an engineer or solar installer by trade, so I need some input here on how to really look at this properly.

What's my best Powerwall installation location?​

Would it be best to install the Powerwalls in my insulated (but not climate controlled) outbuilding and then run their output across the trenched line to the gateways at the house or would it be best to install the Powerwalls inside my house (on the basement foundation wall; within 20 ft. of my electric service)? I figure the answer there will be related to the the efficiency of pushing the DC from the panel array to the Powerwall's over a distance, but am considering both options and would like some guidance. All of my research says the better spot would be in the basement in the house. The storage room where they would be installed there isn't climate controlled, but it never gets as cold (or as hot) there as it would in the outbuilding.

Using the Powerwall + integrated inverters, what's the best way to monitor proper panel operation and to know when I have a panel that's not performing or having an issue? ​

Having Powerwalls are a necessity for me making this type of investment, and the installer wants to install Powerwall + with integrated inverters. My research shows these to be string inverters and not micro, so I'm curious as to how best to troubleshoot/diagnose the solar array as time goes by.

Whole panel vs individual breaker protection with the Powerwalls? ​

The installer is telling me that the system can be wired to back up the entire panel and I then manage the house load myself when on battery. Other prior quotes from other installers have told me that I'd have to select individual breakers in each panel for the Powerwalls to back up and I'd have limited flexibility on what can stay on when running on battery. What's the general consensus here?

Thank you in advance - I know it's a bit to read through, but I do appreciate any/all feedback.

 

[jjrandorin]

Using the Powerwall + integrated inverters, what's the best way to monitor proper panel operation and to know when I have a panel that's not performing or having an issue? ​

Tesla does not offer any panel level monitoring itself, so you wont be able to see whether "a panel" is working properly through Teslas information. If panel level monitoriing is a requirement you will want to discuss that with your installer and see what non Tesla monitoring the panels you are installing might offer.

While I know a little bit, I am not the most Technical member here so I dont have much opinion on your other questions.

 

[CrazyRabbit]

Split system (2 gateways) may not be optimal for off grid as one system will deplete the batteries first. Since you have a years data, what is your peak consumption in Kw? If less then 48Kw I would put both loads panels on one gateway, and install another Leviton panel as non backup (I would do it now as it may not be available in future) and install non backed CT on it so gateway knows about it.
I prefer powerwalls in temperature controlled space, keeping temperature below 82, so in garage with mini split system installed.
What orientation are panels. Run thru pvwatts (nrel) for production estimate.

 

[EightBitWhit]

Split system (2 gateways) may not be optimal for off grid as one system will deplete the batteries first. Since you have a years data, what is your peak consumption in Kw? If less then 48Kw I would put both loads panels on one gateway, and install another Leviton panel as non backup (I would do it now as it may not be available in future) and install non backed CT on it so gateway knows about it.
I prefer powerwalls in temperature controlled space, keeping temperature below 82, so in garage with mini split system installed.
What orientation are panels. Run thru pvwatts (nrel) for production estimate.

I appreciate the visual there - very helpful.

As far as my utility reporting goes, my highest month consumption-wise over the past 12 months was 3,955 KwH. I'm not sure what time factor to use in the forumula to convert that back to peak Kw.

The panels are in vertical orientation, side-by-side, so changing the circuit layout is going to be difficult as the Romex for each circuit is run just long enough for where it goes in the original layout... I've wanted to move things around and the only way I've been able to accomplish any kind of reorganization is by swapping a few circuits up/down the vertical stack where it makes sense and when I've ran new circuits I allowed some extra Romex so I had some flexibility later on. The house is 30yo and fully-furnished so I don't feel like I have a lot of options without tearing it all out - which I have no appetite for... I did that once with the Load Center install and it was a job.

Copy that on the Powerwall installation location - in the basement seems to be the best place to me as well.

Regarding the question for system sizing... I realize that the goal is to export more energy every year than you consume to be 100% self-sufficient, per-se. With net-metering helping to buffer for the months where I don't product as much and the system overall producing more than I use over a 12-month period, is it safe to say I'm OK in that regard as far as sizing goes? I read it as I will be.

I did the PVWatts calculator and this is what I got back - looks encouraging!

 

[EightBitWhit]

Tesla does not offer any panel level monitoring itself, so you wont be able to see whether "a panel" is working properly through Teslas information. If panel level monitoriing is a requirement you will want to discuss that with your installer and see what non Tesla monitoring the panels you are installing might offer.

While I know a little bit, I am not the most Technical member here so I dont have much opinion on your other questions.

Understood. I'll look into what Silfab provides - if anything.

The "Tesla Pro" app looks like it provides some additional data and monitoring - have either of you used that?

 

[CrazyRabbit]

I would use 3/0 wire. You might not need all the 200 amp breakers depending where equipment is installed. Feeder rules and emergency disconnect rules.
Edit: can’t you mine your usage thru your Leviton panel monitoring?

 

[CrazyRabbit]

Understood. I'll look into what Silfab provides - if anything.

The "Tesla Pro" app looks like it provides some additional data and monitoring - have either of you used that?

You can monitor your string data thru that, also through powerwall dashboard.
I would definitely wire as I indicated, you will regret it later. Everyone thinks two gateways are better, it is not. Do a loads calc, download Mike holts electrical toolbox. If you did wire one gateway, I would consider putting both chargers on one circuit using load sharing.

 

[CrazyRabbit]

Why not powerwall three?

 

[BGbreeder]

If you are worried about power losses from an out building, you can upsize the conductor to reduce the resistance and losses. (But more cost in wire, larger conduit, and labor)

If I were you, I would not try to back up the second panel with the Teslas, at least initially. That would greatly simplify life. It would cut one gateway, and enable all four poweralls to be on one gateway. I would have Tesla put CTs on the panel feeds at the meter, so the gateway can send your solar to the cars when you are on grid. If you foresee a need to charge in the middle of an extended outage with lots of sun, I might install one (additional) charger on the backup panel for emergency use.

All the best,

BG

 

[miimura]

If the system will use Powerwall+ or Powerwall-3, then the Powerwalls should be installed on the same building as the solar. You can only practically do standalone Powerwall-2's in a remote building, and even then it's a big hassle with higher installation costs.

31kW of solar is also a lot for 4 Powerwalls. It would be better to put 3 Powerwalls on each Gateway, but that adds significantly to the cost. If you care about runtime and living normally during a grid outage, especially with heat pump HVAC, I would recommend the additional Powerwall capacity for both power and energy reasons.

 

[EightBitWhit]

I would use 3/0 wire. You might not need all the 200 amp breakers depending where equipment is installed. Feeder rules and emergency disconnect rules.
Edit: can’t you mine your usage thru your Leviton panel monitoring?

I can get instantaneous (Watts each circuit is using) and historical consumption (kWh) information for each circuit and the entire panel through the Leviton LDATA hub, but that's the extent as it currently sits. I wish the LDATA hubs would expose more information, and maybe they do, but I'm limited to what Leviton allows us to see and there's no way to export it for historical use - we can only see it graphically in the Leviton app and that's it - currently.

What do you mean by "feeder rules and emergency disconnect rules"?

 

[EightBitWhit]

You can monitor your string data thru that, also through powerwall dashboard.
I would definitely wire as I indicated, you will regret it later. Everyone thinks two gateways are better, it is not. Do a loads calc, download Mike holts electrical toolbox. If you did wire one gateway, I would consider putting both chargers on one circuit using load sharing.

I appreciate the input... I'll show it to the installer and talk about it with them.

You mention the "Powerwall dashboard" - is that part of the Tesla app itself or is it available directly via the software on the inverters and/or gateways that I'd log into separately?

 

[EightBitWhit]

Why not powerwall three?

I asked the installer the same question and I was given a response that they've had "teething issues" (mainly reliability) and very little time in market and wouldn't be widely available until mid/late 2024, so their reasoning was the Powerwall + was a mature product at this time and wouldn't present any installation or service issues, comparatively.

 

[EightBitWhit]

If you are worried about power losses from an out building, you can upsize the conductor to reduce the resistance and losses. (But more cost in wire, larger conduit, and labor)

If I were you, I would not try to back up the second panel with the Teslas, at least initially. That would greatly simplify life. It would cut one gateway, and enable all four poweralls to be on one gateway. I would have Tesla put CTs on the panel feeds at the meter, so the gateway can send your solar to the cars when you are on grid. If you foresee a need to charge in the middle of an extended outage with lots of sun, I might install one (additional) charger on the backup panel for emergency use.

All the best,

BG

Appreciate the input. My only hesitation in doing that is losing the ability to run the other circuits in the house on the second panel (outside of the 2 chargers) and some of those are critical circuits (sump pump, radon fan, food freezers, etc.). I really need to run a mix of circuits from both panels in an outage and want the flexibility of having the whole house "on" and then I go back and pare it down as needed by turning down loads naturally from wtihin the house - or absolute worst case - I ad-hoc turn off breakers as needed during an extended outage to increase run-time.. but I get to make that decision as I go.

Regarding the CT clamps - are you meaning to do that in lieu of gateways or powerwalls on the backup panel or is this something you'd do in addition to the system, regardless of configuration? Also, is the "backup" panel what you're referring to as the panel with Powerwall backup or just the second panel in what I'm describing?

 

[jjrandorin]

I asked the installer the same question and I was given a response that they've had "teething issues" (mainly reliability) and very little time in market and wouldn't be widely available until mid/late 2024, so their reasoning was the Powerwall + was a mature product at this time and wouldn't present any installation or service issues, comparatively.

Thats fair, at least to me it is.

I would also suggest trying to have one of your 200amp panels being a "backup loads" panel, and one being non backed up loads, with one Tesla gateway (not 2) and all your powerwalls on one gateway. I would see if there is anyway possible to get everything "important" on one panel.

Having two systems at once house that dont talk to each other (and cant provide power back and forth) would seem to be pretty frustrating.

I also second the suggestion to consider having the Tesla wall connectors setup for power sharing and using (1) 60 amp circuit, which would allow you to still charge both cars at 24amps or if only 1 needs to be charged, it would charge at 48amps.

That may let you put them both on the backup loads side. Both of my wall connectors are setup for load sharing but on the non backed up loads side, with a CT monitoring them so if the grid is up, I can use powerwall power for them if desired.

Anyway, If it were me I would be doing everything I could to avoid the (2 gateway / 2 system) setup.

 

[EightBitWhit]

If the system will use Powerwall+ or Powerwall-3, then the Powerwalls should be installed on the same building as the solar. You can only practically do standalone Powerwall-2's in a remote building, and even then it's a big hassle with higher installation costs.

31kW of solar is also a lot for 4 Powerwalls. It would be better to put 3 Powerwalls on each Gateway, but that adds significantly to the cost. If you care about runtime and living normally during a grid outage, especially with heat pump HVAC, I would recommend the additional Powerwall capacity for both power and energy reasons.

When you say 31kW of solar is a lot for 4 Powerwalls, are you meaning that it's near the edge of what they can cumulatively accommodate or that 4 Powerwalls isn't really enough to service that load?

I'll ask the installer about the remote building comment as well!

 

[jjrandorin]

When you say 31kW of solar is a lot for 4 Powerwalls, are you meaning that it's near the edge of what they can cumulatively accommodate or that 4 Powerwalls isn't really enough to service that load?

Each powerwall can take 5kW of power, so (4) powerwalls = 20kW of power they can take together (if they were in one system). It gets complicated for me if they are not in one system because I dont know how your solar will be divided between your systems.

Anyway, if your 31kW of solar never generates more than 20kW of power at any given time (entirely possible, depending on if its roof mounted and angles of roof, angle of sun, etc) then thats fine. If it does peak over 20kW however, if there is no grid, and the solar is generating more than the powerwalls can take at once (20kW) it would shut down "the system" (meaning no powerwall power).

Its important to remember that 2 gateways = 2 separate systems. Even if they are both at your home, for practical purposes it wouldnt be any different than having one system at your home and one at a vacation home across the country. No interaction between the 2 separate gateway systems.

Having (2) buckets of 27kW of power when your home uses all that power is less flexible than one bucket of 54kW.

@CrazyRabbit and @h2ofun have the largest powerwall installations of our regular members that I am aware of here, they could both talk more about it.

 

[buckets0fun]

If it does peak over 20kW however, if there is no grid, and the solar is generating more than the powerwalls can take at once (20kW) it would shut down "the system" (meaning no powerwall power).

It’ll only shut down the solar inverters, the backup side stays online and continues until 9x% or so and inverters are commanded on, fill the pw set, and then the cycle repeats.

This amount of PV is likely for the winter months, solid plan, but I’d likely go with more PV if able. You can always add more PW later to “hold” it when you decide that you need in a few years.

 

[h2ofun]

Each powerwall can take 5kW of power, so (4) powerwalls = 20kW of power they can take together (if they were in one system). It gets complicated for me if they are not in one system because I dont know how your solar will be divided between your systems.

Anyway, if your 31kW of solar never generates more than 20kW of power at any given time (entirely possible, depending on if its roof mounted and angles of roof, angle of sun, etc) then thats fine. If it does peak over 20kW however, if there is no grid, and the solar is generating more than the powerwalls can take at once (20kW) it would shut down "the system" (meaning no powerwall power).

Its important to remember that 2 gateways = 2 separate systems. Even if they are both at your home, for practical purposes it wouldnt be any different than having one system at your home and one at a vacation home across the country. No interaction between the 2 separate gateway systems.

Having (2) buckets of 27kW of power when your home uses all that power is less flexible than one bucket of 54kW.

@CrazyRabbit and @h2ofun have the largest powerwall installations of our regular members that I am aware of here, they could both talk more about it.

Yes, having 2 GW's and solar and PW's and ATS split is not idea.

If I were to do over again, I would have did the load cals such that most of my house, if not all, would be on 1 GW, with a 600amp panel to handle all the solar and 7 powerwalls. This 600 amp panel is VERY expensive, but would give me all the PW's as back.
I then would have run the EV wall connectors on a seperate 200 amp line, without worrying about them being able to be
used in a power outage. Just does not happen often enough. Vines is the expert on this setup.

 

[CrazyRabbit]

Yes, having 2 GW's and solar and PW's and ATS split, is not ideal. (Edit)

If I were to do over again, I would have did the load cals such that most of my house, if not all, would be on 1 GW, with a 600amp panel to handle all the solar and 7 powerwalls. This 600 amp panel is VERY expensive, but would give me all the PW's as back.
I then would have run the EV wall connectors on a seperate 200 amp line, without worrying about them being able to be
used in a power outage. Just does not happen often enough. Vines is the expert on this setup.

This is the way! I tried to get Tesla to do this and they wouldn’t. I did the load calc and can get by with just 200 amps for house. Tesla can back and suggested I replace one 40 circuit panel with 80 circuit panel. I thought about it and accepted that solution just so we could move forward. It didn’t have to go that way, but I wanted powerwalls.

To OP, feeders don’t have to be individually current protected. But do to emergency disconnect rules you might requir a breaker as a disconnecting means….
You jurisdiction should take a years worth of data in place of a loads calc, so pull you maximum instantaneous power from your panel. Can you down load each panels data, put in spreadsheet and add both panels together and find the peak…

I put my chargers on the non-backup panel, but I have a 50A/240V receptacle in garage connected to the backed up loads panel and have the Tesla mobile cable I can use to charge from solar during a grid down event if needed.