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PowerWall 2 Interface with a Generator

Discussion in 'Tesla Energy' started by shs1, Aug 1, 2017.

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  1. shs1

    shs1 Member

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    Mariposa CA
    We have a grid-tied all electric home plus an MS, and hopefully soon a 3, powered by 11.4 kW of solar PV, and during power failures, a Kohler 18 kW propane generator. In the next few days we be getting a PW2, and likely soon thereafter, a 2nd one.

    The question is how the PW2 gateway interfaces with the generator. I am familiar with how the Sunny Island works during a power failure to fire up the generator if either the battery bank needs charging or the demand in the house exceeds the battery backup capacity in kWs, as would likely be the case with the PW2s when the cars are charging.

    I have been assured by my installers that the PW2 gateway will also use the generator in an intelligent way, but have seen no evidence so far that an interface exists. The only thing that is needed for control of the Kohler generator is a contact closure; I currently I have a line running to the house and a switch there so that I can turn the generator off during periods of low usage to save propane. While I am certain Tesla must have considered this need and has designed the gateway appropriately, it would be nice to hear from anyone with direct knowledge of this capability.
     
  2. pilotSteve

    pilotSteve Member

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    I would like to know the answer to this as well. We have a 20kW Kohler nat gas gen with a transfer switch currently installed and would like to understand how to interface that with a PW and solar.
     
  3. dhu1

    dhu1 New Member

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    No answer yet. I put in an order for a PW2. The site surveyor came out and took a look. They said their designers are still figuring out how to interface with my generac transfer switch. It has been a month already--the latest update was that it was with their lead engineer to figure out a solution. will update once I hear more.
     
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  4. miimura

    miimura Active Member

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    If I had to guess, I would say that they would put their transfer switch inside the Generac one so that the generator would look more like the grid when it is turned on. This will give them time to sync to it just like they do when they reconnect to the actual grid after an outage. The key point would be to keep the Generac from starting as soon as the grid failed, but instead start when the PowerWall wants it to.
     
  5. shs1

    shs1 Member

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    Location:
    Mariposa CA
    As to keeping the generator from starting when the grid fails, that is pretty easy with my Kohler generator at least, as when the transfer switch detects a power failure, it closes a contact and returns a 12V start signal to the generator. This start signal can be broken by an open contact closure or simple switch inserted in the signal path. In my case, I have routed that start signal to a switch in my house and back to the generator and thus can turn the generator off when it is not needed to save propane during a power failure. It is certainly possible to automate this control via a WiFi controlled contact closure device such as the Wemo Maker (silly name, smart device).

    Ideally, we can find some logic signal, TTL or contact closure, on the gateway or PowerWall that indicates that the PW is in discharge mode and use that logic to kill the generator when it is not needed. There also seems to be some concern about the ability of the PW to sync with the generator so preventing simultaneous generator and PW discharge might also be a good idea from that standpoint as well.

    The really surprising thing is that Tesla has apparently not worked this all out, or at least isn't saying, but seems to allow customers and local installers to figure these things out for themselves. Tesla seems to feel that generators are not really necessary, but in our case, we have been without power for a week at a time during and after a winter storm, heat the house with a geothermal heat pump and need to charge our Tesla(s). I don’t think it is practical to rely on solar and battery storage only in this case. Plus we already own the generator! Of course charging the car from a generator is a whole different subject.
     

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