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HPWC Install with Powerwall

holeydonut

Supporting Member
Supporting Member
Jun 27, 2020
2,225
1,611
East Bay NorCal
My project advisor responded back to me stating that their engineer is confident that 50A can be added into my backup panel, and nothing into the main service panel. All of the electricians I contacted so far are refusing to add anything into the backup panel, stating my load calculation is already at 89A and adding anything will overload the panel.

Is there a list of Tesla recommended electricians who may have more knowledge of powerwall backed up system?


I don't think the 50A in the backup side is overloading the panel rating, it's just overloading the 100A breakers that Tesla somehow put in over the top.

Maybe you can search your local solar companies that at one time tried to get Powerwalls only for Tesla to tell them to sod off with zero inventory. Those installers would have been trained to do the Powerwall, so they'll be able to get your HPWC in since the Powerwalls won't be so scary for them.

I had Sunrun as my PV+ESS installer and also had difficulty getting a HPWC in. I had to find a smaller solar shop to add in my HPWC on the backup side. The guy spent all the money to get ready for selling Powerwalls and did all the Training, but then Tesla cancelled the deal. So he seemed much more comfortable adding the HPWC than the normal electricians. But I didn't have the problem you have of a throttled backup loads panel. Sunrun put in many 200A breakers all over my system so my backup loads panel could get 200A easy.
 
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UGS88

Member
Sep 15, 2021
10
0
Inland Empire, CA
I don't think the 50A in the backup side is overloading the panel rating, it's just overloading the 100A breakers that Tesla somehow put in over the top.

Maybe you can search your local solar companies that at one time tried to get Powerwalls only for Tesla to tell them to sod off with zero inventory. Those installers would have been trained to do the Powerwall, so they'll be able to get your HPWC in since the Powerwalls won't be so scary for them.

I had Sunrun as my PV+ESS installer and also had difficulty getting a HPWC in. I had to find a smaller solar shop to add in my HPWC on the backup side. The guy spent all the money to get ready for selling Powerwalls and did all the Training, but then Tesla cancelled the deal. So he seemed much more comfortable adding the HPWC than the normal electricians. But I didn't have the problem you have of a throttled backup loads panel. Sunrun put in many 200A breakers all over my system so my backup loads panel could get 200A easy.
Thanks for the input. I have very little understanding of the code requirements, but will upgrading my service panel up to 200A allow me to add more breakers (load) on to the service panel, and not affect my current system setup? I assume if I upgrade the panel and would like to add more load into the backup panel, the 100A breaker and the wirings between the gateway and MSP will need to changed as well.
 

yblaser

Member
Aug 4, 2018
84
57
South Bay Los Angeles
Thanks for the input. I have very little understanding of the code requirements, but will upgrading my service panel up to 200A allow me to add more breakers (load) on to the service panel, and not affect my current system setup? I assume if I upgrade the panel and would like to add more load into the backup panel, the 100A breaker and the wirings between the gateway and MSP will need to changed as well.
I would guess that since they relocated all the loads from the service panel they are using the internal energy metering within the gateway 2. For full functionality you would need to have an external energy meter / CTs installed in the service panel and the gateway configured to use it. Without this addition the Tesla system would never see the power drawn from circuits in your service panel. This would mean that the data in the Tesla app would be inaccurate and more importantly the powerwalls would never discharge to cover those loads.
 
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UGS88

Member
Sep 15, 2021
10
0
Inland Empire, CA
I would guess that since they relocated all the loads from the service panel they are using the internal energy metering within the gateway 2. For full functionality you would need to have an external energy meter / CTs installed in the service panel and the gateway configured to use it. Without this addition the Tesla system would never see the power drawn from circuits in your service panel. This would mean that the data in the Tesla app would be inaccurate and more importantly the powerwalls would never discharge to cover those loads.
Thanks for the input. If I upgrade my service panel, I would have to ask how much it would cost to upgauge the wiring within the backup system and see if it worth the cost. Otherwise, I am fine with having the HPWC not installed in the backup panel.

On the otherhand, is it feasible to have a HPWC breaker (40 or 50A) installed in my current 125A service panel even though the sum of CB will exceed the bus ampacity and still have a permit approved? There is one electrician who is willing to do so but it will be violating the 705.B.2.3.C sticker placed in the panel, and I would assume permit request will be denied because of it.

Realistically, there is zero chance it will cause an overload on the service panel since I'll only be charging my car at during midnight when there is minimal load demand in my house.
 

xelaca

New Member
Sep 8, 2021
4
2
San Diego, CA
This design doesn't make any sense. You already have a 200A main panel, so you don't need an upgrade. The 90A connections between the main, Gateway and backup panel make no sense -- those should be 200A, with correspondingly larger wire. The comment about upgrading the load center to 125A also does not make sense since it is shown as 125A already (and I wonder why they are using an external load center rather than the optional internal 200A panelboard in the Gateway)

More physical space could be obtained in the backup panel using some tandem breakers for the 15A and 20A circuits.

An advantage of having the EV charger on the backup panel is that if the grid goes down you can soak up the excess solar by charging the car rather than having the solar shut down when the Powerwalls get full. But if power rarely goes out, that may not matter much. The advisor's concern about draining the Powerwalls to charge the car can be valid depending upon what battery strategy you choose. But if you choose a strategy such that the home it taking power from the grid during the time (say, after midnight) that you charge the EV, then it is not a problem

With only a 90A breaker in the main panel you could certainly add a 60A breaker for the EV charger there.

13kW solar roof on one 7.6kW inverter does seem like a stretch unless a lot of your tiles are on the north slope.
Thanks for the reply. That is what some of my confusion was there. I have written up a long email asking for escalation as their solutions don't match up with reality... I am sitting on it for a bit to re-read later on.

I have learned way more than I ever wanted to know about this stuff over the past week and a half.
 
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