We just got our PTO from PG&E on our system last week, and because our gas hot water heater just failed, I would like to add a 30A circuit for a heat pump hybrid water heater. I need some help to understand what type of load calculation I may need to show the building department to add another circuit. My primary concern is that the backup load center has a bright red placard stating “Caution do not add new loads”, and I’m just not sure how that affects how an inspector evaluates an additional circuit.
Specifics:
6.46 kW solar, two Powerwall system, whole home backup (Square D panel fed by 125A breaker)
No AC, gas-fired furnace, gas dryer (for now), gas water heater (RIP). Our only 240V load is the mobile charger for our Model 3.
We basically maxed out our S and W facing roof area with panels knowing that we would initially be a net exporter, but planned to electrify NG appliances over time to export less. I let our project advisor know that the only reason I was willing to go with the Tesla plan of filling our roof was because we were planning on this electrification of more appliances. In the PG&E PTO application, Tesla included their estimate of 20% increase of electricity usage (though I think that Tesla includes whatever they need to get an oversized system approved by PG&E without really considering the implications of a usage increase with a whole home backup).
We plan on running the water heater in heat pump only mode (1.2 kW). We’re replacing our 50 gallon gas heater with a 65 gallon model because of the longer recovery time for operating in this mode. We will also use a higher tank temp. with a hot water tempering valve to further minimize the effects of the heat pump-only mode recovery time. If this still isn’t enough, we may need to operate it in “Energy Saver” mode (4.5 kW), but I never see us needing to operate it in “High Demand” mode (5.7 kW)
Our background level usage is around 0.7 kW, with spikes up to approx. 2 kW. Outside of charging activity, I’ve only seen a single short spike over 3 kW in the last two weeks. Since that the two PowerWall configuration provides 10 kW continuous, with 14 kW peak, I don’t see any problem with adding this load. I realize that during an outage we may have to manage our usage a little more carefully, but given our excess solar production and the ease of adjusting the energy usage of the hot water heater via app control, I don’t see our energy demands even remotely approaching system limits.
Given the difficulty of getting our project advisor to return calls while our project was active, I’m not confident that I can get information from Tesla in a reasonable time frame. I was hoping folks in this forum might have gone through a circuit expansion, or have other experience that could provide guidance on what calculation or information our AHJ might want to see at inspection that would allow them to be comfortable with an additional 30A circuit in the panel (given the placard warning).
Specifics:
6.46 kW solar, two Powerwall system, whole home backup (Square D panel fed by 125A breaker)
No AC, gas-fired furnace, gas dryer (for now), gas water heater (RIP). Our only 240V load is the mobile charger for our Model 3.
We basically maxed out our S and W facing roof area with panels knowing that we would initially be a net exporter, but planned to electrify NG appliances over time to export less. I let our project advisor know that the only reason I was willing to go with the Tesla plan of filling our roof was because we were planning on this electrification of more appliances. In the PG&E PTO application, Tesla included their estimate of 20% increase of electricity usage (though I think that Tesla includes whatever they need to get an oversized system approved by PG&E without really considering the implications of a usage increase with a whole home backup).
We plan on running the water heater in heat pump only mode (1.2 kW). We’re replacing our 50 gallon gas heater with a 65 gallon model because of the longer recovery time for operating in this mode. We will also use a higher tank temp. with a hot water tempering valve to further minimize the effects of the heat pump-only mode recovery time. If this still isn’t enough, we may need to operate it in “Energy Saver” mode (4.5 kW), but I never see us needing to operate it in “High Demand” mode (5.7 kW)
Our background level usage is around 0.7 kW, with spikes up to approx. 2 kW. Outside of charging activity, I’ve only seen a single short spike over 3 kW in the last two weeks. Since that the two PowerWall configuration provides 10 kW continuous, with 14 kW peak, I don’t see any problem with adding this load. I realize that during an outage we may have to manage our usage a little more carefully, but given our excess solar production and the ease of adjusting the energy usage of the hot water heater via app control, I don’t see our energy demands even remotely approaching system limits.
Given the difficulty of getting our project advisor to return calls while our project was active, I’m not confident that I can get information from Tesla in a reasonable time frame. I was hoping folks in this forum might have gone through a circuit expansion, or have other experience that could provide guidance on what calculation or information our AHJ might want to see at inspection that would allow them to be comfortable with an additional 30A circuit in the panel (given the placard warning).