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Installing Solar, HPWC, future proof Powerwall?

Discussion in 'Tesla Energy' started by swimgeek, May 14, 2018.

  1. swimgeek

    swimgeek Member

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    I bought a house and am having solar installed, along with HPWC.

    Both 4.3kW (DC rating, 4 kW AC) solar and HPWC @ 50A breaker will be in a garage sub panel, fed by 3/4” conduit, which I believe can take max 60A breaker on main panel side.

    Does the garage sub panel need to be 100A to avoid overloading bus bar?

    Also getting main panel and service upgraded to 200A. In the future, I could add max 8-9 kW solar on the house roof feeding the main panel.

    Should I get a 200A main panel with higher rated bus bar or “solar-ready”?

    Finally, I may want to add Powerwall in the future. I would hope to add in the garage, but assume that would require digging up and increasing the conduit and wire size to the garage. Alternatively, could wire into the main panel. Would that also go against the main panel back-feed allowance, in addition to the solar?

    Thanks, trying to learn all of the potential intricacies. Maybe I shouldn’t worry too much about future proofing, but I’d rather get the right panels now to make it easier if/when I get more solar and Powerwall.
     
  2. swimgeek

    swimgeek Member

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    #2 swimgeek, May 14, 2018
    Last edited: May 14, 2018
    Updated - garage sub panel will be 125A, still fed by 60A breaker.

    200A panel could be upgraded to 225A pretty reasonably and then support 70A backfeed - might be best to do that?
     
  3. Shygar

    Shygar Member

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    My 7.5kW solar is on a 30 amp breaker, and my single powerwall 2 is also on a 30 amp breaker. I have a 60 amp breaker for my Tesla HPWC.
     
  4. GenSao

    GenSao Member

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    Based on your 2nd message, 125A is plenty for your inital planned use. For a 4.3kW (DC rating, 4 kW AC) solar system, you are looking at (conservatively) a 20A breaker for solar. So 20A (solar) + 60A (line in) = 80A < 150A (125A * 1.20%) OK

    If you left the charger in there upon installing a whole home backup (2 power walls), then 125A panel is also adequate. 20A (solar) + 30A (PW) + 30A (PW) + 60A (line in) = 140A < 150A (125A * 1.20%) OK

    The charger could be moved to your new load panel, then the existing panel can be used as a "generation" sub-panel. Tesla likes to keep the powerwall connection (breakers) as close to the solar breakers. This can be done in the new load panel Tesla will install or a separate "generation" service panel.

    Where is your main panel located? Other than the 125A garage-sub panel, are there other sub-panels?

    In general, there is no need to increase your main service panel above 200A. What is more important is your sub-panel for your backup or whole home loads. I suggest 225A at least for growth. I have a 200A load panel, but am limited in growth: 25A (solar) + 30A (PW) + 30A (PW) + 150A (line in) = 235A < 240A (200A * 1.20%) OK. Only 5A to spare for added solar and max of 150A from utility.

    Going 225A would let me do the flowing: 25A (solar) + 10A (more solar) + 30A (PW) + 30A (PW) + 175A (bigger line in) = 270A = 270A (225A * 1.20%) Added 10A to spare for solar and max of 175A from utility.

    Be mindful that Tesla would need to install a Gateway between your meter and electrical panel with your loads (backup or whole home). Being in California, your main panel may be directly connected to the meter and it may be difficult to add the Tesla gateway and reuse the existing panel, forcing a new sub-panel. Perhaps if you are upgrading to 200A service, consider making sure there is room for a future Energy Gateway to intercept your home load panel. If you are able to do this, there would be less rewiring. Your main load panel should be 225A if not greater.

    How far is your garage to your main panel? Could all your home loads be moved to the panel in the garage?

    If you want to be proactive, have your electrician install a higher gauge wire for say a 100A service and maintain the 60A breaker. You can always upside the panel and/or breakers in the garage as needed afterwards.
     
    • Informative x 1
  5. SoundDaTrumpet

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    I had 4.2kW solar installed up here in Northern California. I had the Powerwall v1 AND EV charging in mind when guiding the design. As you know, Powerwall V2 is completely different. Just stating here that Tesla Energy products could change down the road. It behooves me to think that there is a "perfectly adequate" DC-AC inverter already in built into today's Powerwall. When Tesla comes back to install the Powerwall, they are basically tearing out everything the previous contractor AND original panel. Home is circa 2003.

    I would also advise against adding solar to an existing system, it is not cost effective to add-on, unless you are like doubling solar. With Powerwall, sizing doesn't have to be perfect as having oversized solar just doesn't just dump back to the grid for pennies, but instead couples well a power backup strategy. I would saying being undersized to 80%, I estimate the Powerwall can arbitrage the 20% with its charge and discharge cycle assuming you have a EV type of rate schedule.

    About your garage subpanel... I assume it's being added. This seems to indicate that your solar installer cannot add the 20A PV breakers into the main. Due to 6-throw rule for main lug only (MLO) panel and they can't add a main breaker, or your panel is full. I mention this because my installer did the same and Tesla is planning to change the main panel anyway. It is tough to coordinate two different contractors/installers (even if they are both Tesla for EV and Powerwall) as they have different goals/interests/methods. I also found the solar friendly meter-load center combo panels to be not that helpful because at all because the solar attached directly to the meter. The PV is supposed to be behind the gateway which Tesla provides.

    The gateway is unique in that there are only 3 lugs: one to generation (PV+PWs), one to the house load, and one to the grid.

    As for overloading the busbars:
    1. The garage subpanel is fine for solar only and EV. The solar PV breaker will have to be relocated to the generation "combiner panel" anyway. So the garage subpanel will be decoration. The garage subpanel serves simply as a local disconnect if you are going >60A for EV charging (HWPC).
    2. The main panel will be derated via a smaller breaker. In my case they are using a 150A to provide up to 120A of backfeed. (225-150 + 225*20%). The backfeed is sum of the solar and Powerwall breakers. In my case 20A+30A+30A=80A. (I forget if the bus bar is 225 or 200... either way I am covered.)

    I hope this helps.
     
  6. swimgeek

    swimgeek Member

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    No other subpanels. Main panel on the house - garage is detached, and conduit is run under/through concrete driveway, so painful to increase beyond 60A 6gauge wiring.

    Interesting point, thanks for the heads up

    Currently, would need to either keep max 60A rated going back and forth garage to house, or demo driveway and install new conduit.

    Thanks for your thoughts, really helpful. Still not sure I have easy solutions without tearing up the driveway to tie solar/powerwall on garage and possibly home together, but it is what it is.
     
  7. swimgeek

    swimgeek Member

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    Currently have 60A subpanel in the garage, no solar at all. Subpanel connected through conduit through driveway to main panel.

    This is interesting, will have to ask what main panel is.

    This helps, thanks much for your thoughts!
     
  8. GenSao

    GenSao Member

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    I assume your solar panels would be installed in the garage. Tesla likes to keep the powerwall connection (breakers) as close to the solar breakers thus they would be installed in the garage as well.

    You do have a few options:
    1) See if the existing 60A circuit will work for solar, batteries, and ev charging. (Doubtful)
    2) Run a new 100A to the main panel. Keep the Ex 60A Circuit for the ev charger or as a spare.
     
  9. swimgeek

    swimgeek Member

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    I will have a 200amp service, 225amp busbar, meter combo panel for the main now.

    I asked about separating meter and main panel, but there's only so much future-proofing that makes sense now. Also, looks like you can potentially turn a main panel into a subpanel in the future if need be.

    Not sure what will happen, but I will have plenty of upgradeability for future solar on main home, and going full home backup with powerwalls will be kind of a pain to rewire and get that all worked out if I go that way eventually.
     
  10. SoundDaTrumpet

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    The main panel upgrade from Tesla Energy have my house specified with the similar 200A service / 225A bus meter combo panel.

    With your garage panel limited by the 3/4" conduit, looks like you are limited to your solar panels plus a single (1) Powerwall, which won't get you the full home backup you desire (as two (2) minimum are required to support whole home backup). You could go double Powerwall on your main house, but your garage loads will affect recorded generation data which will affect data recording for SGIP, or other incentive programs. Tesla would have to come up with a way to transmit power data for the solar panels and sync with the rest of the system.
     
  11. swimgeek

    swimgeek Member

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    Interesting -- what's the rest of your system look like? Is the gateway connected between panel and meter somehow, or to a sub-panel off of that main meter combo panel?
     
  12. SoundDaTrumpet

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    The gateway is a sub-panel off of the combo meter/load center.
     
  13. swimgeek

    swimgeek Member

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    Thanks for all your thoughts.

    Install starts tomorrow!

    For main panel - going to leave longer wire so that in the future we can blank out the meter, put jumpers to the box, and turn it into a sub panel attached to a gateway. It is a 200A breaker, 225A bus bar, so can triple the current solar before running into backfeed issues (which is the max solar I have roof space for)

    I think I am relatively well future proofed, and excited to get charging and solar going!
     
  14. swimgeek

    swimgeek Member

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    Quick update - old buried conduit is not allowing old wires to budge, so going to have to dig and put in new stuff. They’re going to drop 1 1/4” to support 100A, which seems fine. At least I will now max out the Model 3 charging ability!
     
  15. BrokerDon

    BrokerDon Member

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  16. GenSao

    GenSao Member

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    Since you are trenching, do consider a bigger sized conduit for prehaps a bigger conductor. There should be a marginal cost increase to allow for growth.

    You can still downsize the breaker to 100 amps.
     
    • Like x 1
  17. SoundDaTrumpet

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    #17 SoundDaTrumpet, May 21, 2018
    Last edited: May 21, 2018
    Put in a 3" conduit and be done with it. It can handle 320A service. Keep in mind the PANEL must MATCH the service. (i.e. cannot install a 400/320A panel whatsoever on a 200A service). Panels >225A are beasts (bigger) and they have to be 3ft away from gas services.

    Background: I explored upgrading service to 320A (aka 400A) with PG&E. Engineer site visit. Great experience. Local PG&E guy handled the local area. One man job... three day turnaround. Good job PG&E. Minimum $1000 with PG&E just to initiate engineering, and estimate $3000 for PG&E to only pull wire in my existing 3" conduit. The only risk is if their the conduit is blocked by a tree root or other obstruction then trenching is additional. I did not pursue upgrading electrical service.

    Time for my question: Anyone here invoke (pay for) the "main panel upgrade" and decided to go with 400/320 service? I am thinking maybe pay Tesla Energy extra and pay PG&E for the upgrade for the fun of it. I am curious if the 400/320 main panel option is available through Tesla. I am not interested about the anticipated 400A gateway, but talking about increasing EV charging capacity.
     
  18. miimura

    miimura Active Member

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    PG&E used to have a subsidy program that would discount the service upgrade cost if it was needed for EV charging installation. You should ask about that. I haven't heard anything about it in more than 3 years, so it may not exist any more.

    When I had my house built in 2012 I also had the privilege of talking directly to the PG&E service engineer. He was very knowledgeable and agreed that with EVs and solar that I should get the 320A service. He also discussed the alternatives for how to provision separate metering for EV charging. At the time there was no Net Metering Aggregation, so I didn't do anything to allow for a second meter. Weeks after talking to the PG&E engineer I found out that the electrical contractor had installed a 200A panel and I had to twist his arm that it was insufficient and got him to put in a larger panel that could accommodate 2 200A main breakers.
     
  19. swimgeek

    swimgeek Member

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    Another update - got my Permission To Operate!

    Panels are turning the meter backward (slowly due to SoCal June gloom), and I’m excited to see how the current system does with my usage.

    Also have HPWC going; it’s great to have max charge speed ability. Don’t really need the full 48A charge rate of model 3, but it will come in handy. Also it’s on a 100A breaker so if we get another Tesla we can dual charge superfast. Unnecessary but no additional cost from 60A breaker given how close to panel it is and leftover wires could be used.

    Plan to see how usage compares to solar over the next couple of months and figure out if I want more panels and/or Powerwall, depending on availability etc.
     
    • Like x 2
  20. GenSao

    GenSao Member

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    Congratulations!
     

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