Solar Panels

Installing NEMA 14-50 connector to solar breaker panel

I have Tesla solar panels and I'm hiring an electrician I've known for a long time to install the connector per Tesla's install guide. He's asking me if I want the NEMA 14-50 connector wired to a breaker in the solar panel breaker box or main panel breaker box, and I honestly don't know which is better, if either. My panels are ~7.8 kw and I also have one 13 kw Powerwall. Any advice on where to wire the 50 amp breaker for that connector?


  • Is your system wired such that the solar panel breaker box is the only set of circuits powered during a grid outage (i.e. "backed-up"), and is fed by the Powerwalls? If so, putting your 14-50R breaker there would have it available to plug in an EVSE ("charger") in order to charge an EV during a grid outage. Otherwise, you'd be out of luck charging an EV if the breaker box is on the grid side of things, and the grid failed.

    I'm not sure you want to charge an EV with nearly 10kW (Level 2 EVSE of 240V at 40A) of power out of your Powerwalls (PWs) anyway. I used plural, because it would take a minimum of two PWs to power a 40A EVSE, and charging an EV at a 40A Level 2 from your PWs would use every watt they could provide, and deplete the energy in those PWs very quickly. A useful EVSE would be one that can charge at many different power levels. I understand that Tesla sells such a device (as does other vendors).

    I have 5kW of PV and two PWs. I've also got an EVSE, that can charge an EV from ~1k (on 120V) up to 2.9kW (on 240V). When on my PWs during a grid failure, I can still slowly charge up my Bolt over several days, without severely impacting the energy available for the rest of the house. (My whole house is backed up by my PWs.) I've got a couple Level 2 EVSEs at 7.2kW. but I wouldn't use those during a grid outage.
  • I have 10kW solar plus 2 PW. My whole house is connected to the combo - no devices left behind including my car chargers. In terms of power consumption - the vehicles are set to charge mid-day during peak solar production to maximize the direct solar to vehicle connection. Since my PW generally recharge to 100% prior to noon - this works pretty well for me - YMMV.
    From the perspective of vehicle charging during a grid failure, there are a couple of factors:
    1 - My model 3 / PW combo interact such that the car will not charge unless the PW are up to at least 90%. Fully automated and supported by Tesla.
    2 - During a grid failure, I actually tend to produce more via solar than the house consumes, especially once the PW are charged. In this case, with a surplus of power, the solar is actually induced via frequency manipulation of the TEG to shut down. I am essentially throwing away available photons. If the car is plugged in - it gives me one more destination for excess power.
    3 - Keep in mind - the car batteries are simply enormous compared to everything else. Charging the car from zero to 100% consumes 100% of my solar output on an ideal production day.

    If you put the charger on the solar / PW side - you simply need to manage it either manually or using some automation. Remember - when the grid goes down, you are on EMERGENCY power.
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