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Don't I need a new panel?

GoGoGoMach5

Member
Mar 11, 2020
17
4
Southern California
Tesla says I don't need a new panel for our solar glass roof. Besides it being old and original, it is completely used up. I will probably replace it before the roof is installed, but I found it strange they didn't recommend an upgrade. Am I missing something?
IMG_4452.jpg
 

bob_p

Active Member
Apr 5, 2012
3,705
2,815
Our installers removed our breaker panels to review what was inside prior to the installation.

The only changes they made relative to the breaker panels:
  • Moved wiring connection from the grid to the new Tesla Backup Gateway (required replacing the power cabling going to the breaker panel)
  • On one panel, we added a 14-50 outlet so we could charge our Tesla vehicles off the PowerWalls/solar panels if we were operating off-grid (after a hurricane)
Otherwise all of the changes were made with new panels and cabling on the outside of the house.

As long as they can get all of the circuits on your existing panel to work off the new solar system (including PowerWalls, if you are getting any), they shouldn't need to change out the breaker panel.
 

jboy210

Supporting Member
Dec 2, 2016
5,179
3,228
Northern California
Tesla says I don't need a new panel for our solar glass roof. Besides it being old and original, it is completely used up. I will probably replace it before the roof is installed, but I found it strange they didn't recommend an upgrade. Am I missing something?
View attachment 531329

They are going to feed that panel from the boxes they install, same as your power company does. As long as they can make the hookup correctly they are happy. After all, all they doing is feeding your panel power. What happen to the power after that is your problem.
 

GoGoGoMach5

Member
Mar 11, 2020
17
4
Southern California
Where is the backfeed breaker going to go if there's no more room?
I have no clue about a backfeed breaker. I assume you feel I need a bigger panel.

What's your solar roof output rated at, and what's your main feed rating?
The current plan we've been presented is 6.5kW, though I'm hoping to squeeze another .5kW out of our roof. We have 100 amp service.
 

GenSao

Member
Aug 3, 2017
550
938
Pleasant Hill, CA
Tesla says I don't need a new panel for our solar glass roof. Besides it being old and original, it is completely used up. I will probably replace it before the roof is installed, but I found it strange they didn't recommend an upgrade. Am I missing something?
View attachment 531329

Your Cutler-Hammer electrical panel has 22 slots. Tandem circuit breakers may be used to make room. The existing Slots 12, 15, and 17 are tandem breakers (and I assume your panel has capacity to convert some of the existing circuit breakers). The 120 volt circuits in Slots 14, 16, 18,19, 20, 21, and 22 may combined to make room. Even the 240 volt circuits in the top half of the panel can be combined. See below picture of my home loads panel during installation with tandem circuit breakers on most of the circuits. Note, solar and powerwalls are installed at the bottom.

20171115_125754_HDR.jpg


A back feed circuit breaker is the circuit breaker(s) solar and/or Powerwalls are connected to in the panel. They back feed solar and battery power into the panel. A breaker does not care which direction current flows. It works the same if your using it normal or back feeding it. As in the above photo, Per code, Tesla prefers to install the back feed circuit breaker at the exact opposite of the main load on top.
 

GoGoGoMach5

Member
Mar 11, 2020
17
4
Southern California
Your Cutler-Hammer electrical panel has 22 slots. Tandem circuit breakers may be used to make room. The existing Slots 12, 15, and 17 are tandem breakers (and I assume your panel has capacity to convert some of the existing circuit breakers). The 120 volt circuits in Slots 14, 16, 18,19, 20, 21, and 22 may combined to make room. Even the 240 volt circuits in the top half of the panel can be combined. See below picture of my home loads panel during installation with tandem circuit breakers on most of the circuits. Note, solar and powerwalls are installed at the bottom.

View attachment 531799

A back feed circuit breaker is the circuit breaker(s) solar and/or Powerwalls are connected to in the panel. They back feed solar and battery power into the panel. A breaker does not care which direction current flows. It works the same if your using it normal or back feeding it. As in the above photo, Per code, Tesla prefers to install the back feed circuit breaker at the exact opposite of the main load on top.

Thank you for the explanation, GenSao! So my panel isn't really "used up". It's just old and ugly. o_O But, hey, if I can save 2 or 3K by not upgrading, I'll take it.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
9,554
10,754
Riverside Co. CA
Thank you for the explanation, GenSao! So my panel isn't really "used up". It's just old and ugly. o_O But, hey, if I can save 2 or 3K by not upgrading, I'll take it.

The thing I would be thinking about in relation to upgrading is, 100amp service seems very low for "todays" world, especially if one is planning on getting an EV at some point. My house came with 200 amp service (built in 2007), and that is fairly common where I live for homes around the same age.

If I was planning something like a solar roof, I would want 200 amp service (also because I would likely be trying to run as many electric items off my "pre paid for" solar as I could, and would want to minimize "no we cant do that because the load calculation says...."

Upgrading it "just because?" maybe not... .but definitely if you are "getting work done" electrically at least, anyway.
 

destructure00

Active Member
Mar 2, 2019
1,473
1,625
Scottsdale, AZ
Aren't main busses limited on how much you can backfeed? In my case I have a 200 amp panel and could only backfeed 20%, or 40 amps. I originally ordered a large system (60 amp backfeed breaker) and had to change to medium (40 amp backfeed) to avoid a panel replacement. Can't remember if that was a local regulation or NEC.
 

GenSao

Member
Aug 3, 2017
550
938
Pleasant Hill, CA
Aren't main busses limited on how much you can backfeed? In my case I have a 200 amp panel and could only backfeed 20%, or 40 amps. I originally ordered a large system (60 amp backfeed breaker) and had to change to medium (40 amp backfeed) to avoid a panel replacement. Can't remember if that was a local regulation or NEC.

Yes, typically a 20% back-feed is allowed per the 120% rule. So a 200 A panel would be permitted to have 40 A of solar (240 A total). A solution would be to de-rate the main feed into a 200 A panel to say 150 A. Then you'll have the capacity for 90 A back feed (240 A - 150 A). Assuming 150 A is most you actually need.

If the OPs existing panel is 100 A, de-rating the main breaker is not advised.
 

destructure00

Active Member
Mar 2, 2019
1,473
1,625
Scottsdale, AZ
I appreciate all the information that’s been shared thus far.

So will a 20 amp backfeed breaker handle a 7.3 kW system that we've recently signed off on?
P=IV (power = current x voltage)

7300 watts = I x 240 volts
I = 30.4 amps

Breakers need to be rated at 125% of continuous load (or continuous load can only be 80% of breaker capacity), which is 38 amps in your case. 40 amps is the next available size that works.

All of this is assuming your panel hasn't already been derated I guess, do you know anything about that?

Might be beneficial to get a more detailed explanation on why they say you don't need an upgrade. I can't imagine they'd miss the things we're talking about in this thread.
 

GoGoGoMach5

Member
Mar 11, 2020
17
4
Southern California
Well, I was prepared for a panel upgrade, but not a service upgrade. The latter would result in some landscape rearranging (if you know what I mean.)

I've reached out to my utility to confirm if my service/panel can handle a 7.3kW system. Whatever information they can provide, I will pass on to Tesla.

As soon as I know something, I'll update the thread.
 
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Eveque Fou

Member
Nov 29, 2018
8
1
Cincinnati, OH
In our install (not by Tesla, but Tesla-authorized), the Gateway feeds two panels, each with a 200A breaker. One is our existing panel, unchanged. The other has the solar and Powerwall breakers, with a sticker saying not to add any circuits to it. (Not totally sure why you couldn't, though; perhaps that's where back-feed would come in?)

Net result, there's no back-feed in the main panel. The main panel always has energy coming in the main breaker and doesn't care where it comes from. The PW and solar panel is almost always exporting energy, not consuming it.
 

bob_p

Active Member
Apr 5, 2012
3,705
2,815
The panel with the solar panel and PowerWall breakers is a generation panel. In our configuration, that panel is connected to a large generation switch that disconnects the solar panels/PowerWalls from the Gateway, something that is required for solar installations (at least in our area). While the solar panels only generate electricity, the PowerWalls both consume and generate electricity (which is different than a house panel, which only consumes electricity).

Our solar installers did install one 110 circuit to the generation panel, powering the solar power monitor gateway - which communicates to the solar panels over the powerlines - and was installed in that panel at the recommendation of the microinverter supplier.

The Gateway is capable of feeding two house breaker panels (we have two 150A house panels connected to our Gateway) plus the generation breaker panel.
 

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