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Generator support

Discussion in 'Tesla Energy' started by fresnoboy, Apr 11, 2019.

  1. fresnoboy

    fresnoboy Member

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    Folks, are there any updates on generator support? We're finishing up building a new house, and I'd love to add powerwalls to the solar design, esp. now that the supply seems to be available. However I have a 30 KW generator (it's a big house) for backup power, as well as the associated transfer switch, and it doesn't appear anyone knows of a way to use powerwalls in this setup.

    I had heard that tesla had be fielding a beta capability for generator support, but my installer hasn't heard of any. It would also be nice if the gateway had 400A support, but I can work around that if the generator issue was dealt with.

    I wish Tesla would design their stuff to work with other people's gear rather than requiring vertical integration and then not support a diverse set of configurations.

    mike
     
  2. Lloyd

    Lloyd Well-Known Member

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    They used to say "works in conjunction with a generator" also. I can't find that statement anymore.
     
  3. shs1

    shs1 Member

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    #3 shs1, Apr 11, 2019
    Last edited: Apr 11, 2019
    I have a single Powerwall 2 installed with 11 kW of solar and an 18 kW Kohler generator. I hope to get a 2nd PW2 any day now. This installation was blessed by Tesla, albeit after considerable discussion with my local installer. See the attached diagram I drew about a year and a half ago. My installer said that he has seen this diagram on the Tesla website, but I am not sure where, and don't know the current status of Tesla generator support. I am very glad I have the generator incorporated into my system.

    With my set up, during a power failure the PW2 will power the house until either it either runs out of charge, or the load from the house exceeds the single PW2's output. When that happens, the PW2 will shut down and the generator will automatically start and run until grid power is restored. Alternately, I can use a remote switch in the house to manually switch the generator transfer switch to the generator position and start the generator. If I manually selected the generator mode, I need to (remotely) manually switch the generator transfer switch back to the other position to later on run the house off of the PW2 or the grid.

    During early testing of the system I was able to charge the PW2 from solar while the house was being powered by the generator, but recently with all the 66 Hz nonsense going on, I am not sure how dependable that will be. Tesla has indicated that there was a recent firmware fix that addressed this 66 Hz problem, but I can't comment on that at this time.
    PowerWall 2 with Generator.png
     
  4. fresnoboy

    fresnoboy Member

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    shs1, thanks for the note. Can you attach the diagram of how your system is wired? I can have my installer go to Tesla and see if they can support it for me as well. Does your PW or gateway run with a different firmware release than anyone else?

    You don't describe particularly good support, but certainly better than nothing.

    I have seen comments in the other threads about "jump" terminals on the gateway that could jumpstart the PW when it's been drained completely but the sun is out. Have you looked at that option?

    thx
    mike
     
  5. shs1

    shs1 Member

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    Sorry about forgetting the attachment, but it should be there now. The "support" issue that you may be referring to had to do with getting Tesla to agree to allow a generator in the PW2 install. They resisted at first, but since I already owned the generator and was convinced that there would be circumstances, e.g. 10 days without grid power or sunshine like we had a few years ago, 2010, IIRC, I insisted and working through my local installed we got Tesla to agree to the scheme that is depicted in picture I attached above.

    As I suggested previously, while the house in running off of the generator, the PW2 can and will accumulate charge from the solar as long as it is not completely dead and I can switch back to PW2 operation when it makes sense. Since I have the generator in the system to run the house when necessary, and I can likely avoid the situation where the PW2 is completely drained, I haven't looked into jump starting it.

    Mike, I think we are neighbors. We may have met at an early Fresno Tesla owners event. I have had my Model W since early 2013 and my Model 3 for more than a year now.
     
  6. fresnoboy

    fresnoboy Member

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    Thanks for the drawing. I don't think we met as I'm from the valley but live in the SF Bay area now...

    The wiring diagram makes sense but doesn't work for me as I have a 400A feed, and Tesla doesn't support more than 200A. What a PITA the whole gateway product is...

    Thanks,
    Mike
     
  7. miimura

    miimura Active Member

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    The 200A Gateway just means that you can't have the whole house backed up. However, since you already have a 30kW generator and whole house transfer switch, it makes the system design more complicated. In theory you could divide it into two 200A feeds, but I doubt Tesla even wants to go down that road with you.
     
  8. nyprepper

    nyprepper Member

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    i have 2 Powerwalls and PV and also a gas generator for backup to backup. i have a sub-panel with my essential circuits (well pump, fridge, etc.) with a master switch. i can flip that switch and use my generator to power the sub-panel. This was approved by Tesla. It's just a matter of wiring. The PV and Powerwalls can be completely isolated in my setup.

    The limitation is that you can't charge the Powerwalls using your generator.
     
  9. fresnoboy

    fresnoboy Member

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    It may be possible to have the whole house transfer switch flip to emergency power (isolating the grid) but not start the generator unless the powerwall was couldn't handle the load. The ATS provides a generator start signal that could be interrupted. You could do a dual generator setup (primary and secondary emergency power), and have the PWs as a secondary, but that would isolate them and solar during the grid connected case.

    If they provided more of an open system that wouldn't be that hard. They could automatically take over in case of an outage and use a pair of contacts on the gateway to trigger generator start and shutdown. But I don't think the gateway is designed to operate that way now.

    Mike
     
  10. miimura

    miimura Active Member

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    Actually, if you just use a third party transfer switch rated for the full service size in place of the switch inside the Gateway, then you can follow the diagram provided by @shs1. Since most automatic transfer switches actuate when they lose power, you just run a small 120V circuit through Tesla's switch to actuate the switch that is actually opening the grid feed.
     
  11. fresnoboy

    fresnoboy Member

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    I have a Kohler 400A industrial transfer switch, and it's quite programmable. I don't understand what you are saying about the 120v circuit though. The ATS switches as grid power is lost, isolating the grid feed,. The ATS then starts the genset, but it doesn't have to do that. It will stay in the emergency position until the grid comes back. I think the genset can be connected to the house feed with the PWs active as long as the it isn't started.

    The genset doesn't do 400a though, so the gateway could handle the generator feed, but wiring it that way wouldn't be connected to the grid in the normal operation.

    Could you draw what you are thinking about? If the gateway was designed to work with abittrary transfer switches this would be easy.

    Thank you
    Mike
     
  12. miimura

    miimura Active Member

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    My idea is to use the Tesla Gateway transfer switch to activate another larger switch that is actually carrying the electrical load. If you look at the diagram provided by @shs1 earlier in this thread, the Powerwall + generator setup needs two transfer switches that can each carry the full grid load. When the grid fails, the switch controlled by the Powerwall Gateway simply opens to isolate the house from the grid. The generator transfer switch on the other hand is a double throw switch that connects the loads to either the generator or the Powerwalls and grid if available. In order to get more detailed than that, I would need to know how the 400A transfer switch is actually wired.

    Anyway, all this may be moot because Tesla may not want to get involved with anything that uses a third party transfer switch instead of their own.
     
  13. shs1

    shs1 Member

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    My Kohler 18 kW generator was installed when I built the house 10 years ago and used a Kohler Automatic Transfer Switch (ATS). To make it work with the PW2 as indicated in the diagram posted above, we needed to replace the logic board in the Kohler ATS, but not the whole ATS. What Tesla seemed to care about was the the PW2 would never see the generator and this scheme accomplished that.
     
  14. fresnoboy

    fresnoboy Member

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    Thanks guys for all the info. I have Kohler 400A transfer switch with the MPAC 1500 controller. That controller is very programmable, but it sounds like I'd need a 2nd 400A transfer switch to act as a "prosthesis" for the Gateway? There are cheaper transfer switches from Kohler and others - presumably those with direct relay control instead of the serial bus control that goes to some of their gas units?

    I am still not getting how to hook up the gateway to make a 2nd transfer switch act as it's prosthesis. Where does the the 120v feed come from? The main service panel or routed through the generator ATS? Sorry for being dumb here.

    Does the gateway have any relay inputs or outputs for control?

    Mike
     
  15. reardencode

    reardencode Member

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    I wish they would add a generator _input_ to powerwall, so that a small generator (too small to handle peak loads) could be used to charge the powerwall during low load times.
     
    • Like x 1
  16. miimura

    miimura Active Member

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    Let me think about this and I will see if I can make a diagram to show how to use a high current 3rd party transfer switch with simple relay control as a slave to the Gateway's switch.
     
  17. miimura

    miimura Active Member

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    Okay, here's my simple drawing of how to implement the slave switch. The power flow is the same as the one at the top of this thread posted by @shs1 except I show a main panel instead of "utility meter" and I'm showing the two poles L1/L2 instead of single line drawing. Obviously, neutrals and grounds are required but not shown.

    Gateway Slave Switch.jpg

    The assumption is that the input on the slave switch is a Normally Open type. That switch will only close and pass power from the grid when there is power in the main panel and the Tesla Backup Gateway switch is closed. The relay in the slave switch is assumed to have a 120V coil. That is why a single hot line is shown connecting from the bottom of the Gateway switch to the slave switch input. The Powerwalls and solar inverters are connected to the Generation Panel. The breaker size in the main panel is an arbitrary size, but this setup only makes sense if you need more than the 200A the Tesla Backup Gateway switch can handle. I show both poles of the Tesla Backup Gateway connected because I assume that the voltage sense in the Gateway needs to see the grid voltage from both L1 and L2. I also assume that power from the generation panel to the Gateway is needed so that it can power the Gateway computer when the grid is down and synchronize the power waveform before reconnecting the grid. However, you cannot land that line on the bottom terminals of the Gateway switch like you normally would because you would have a circular circuit when the switches are closed. You would have to cut or disconnect the existing tiny wires that the Gateway uses to sense the voltage at the bottom of the switch and connect the wires coming from the generation panel.

    Do not try to implement this without Tesla's blessing. I don't work for Tesla and there may be technical considerations that I am unaware of.
     
    • Like x 1
  18. power.saver

    power.saver Supporting Member

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    I think the problem with this is the CTs in the Gateway won't see the house load, and the PW won't charge or discharge properly.
     
  19. miimura

    miimura Active Member

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    You would obviously extend the Grid CTs to the main panel and the Solar CTs to the Generation panel. You will already have a conduit going to each location, so this is not a big deal. My installation is already like this, even without the slave switch.
     
  20. power.saver

    power.saver Supporting Member

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    So you have your Gateway CTs in your main panel. Does the house load still go thorough the Gateway transfer switch? How much of what you showed do you have? And why did you install it that way?
     

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