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Design Question

Dear Community

This Tesla Solar project will make me an electrician soon, I read all the posts but still couldn't figure out some items, also I am trying to optimize my investment. Any suggestion or help will be appreciated. I am in N. California , PG&E

Situation:
-We have a 125a main panel, with 40 amp going to HVAC compressor and 90 amp going to sub panel in the second-floor bedroom, which is full (Electric Range, Electric Dryer, Gas Heater, Tankless Water Heater, and regular stuff for a 1900 sqft home). Currently consuming 400kwh monthly on average
-I want to install EV charger after solar is completed since all the electricians recommend a subpanel near the main service panel or load balancer I decided to wait until the solar project is completed. So I want my solar to EV charger ready with minimum cost

We are installing 6.8kwh Solar panels and 1 Powerwall. (we started with 4.4kwh and 1 powerwall+ and at that time it was all house backup)

This is the latest design document from Tesla, but I am confused.
1-This will be partial home back up, I can accept separating the 40a HVAC compressor out but is this means something my home will be also included?
2-Not to have all house back up: will this effect
-Nem 3.0 requirements? if any
-Can I still to time of cost use? What I mean, can I use the electricity I produce from solar in the day time, when peak hours 4pm-9pm, use it from the battery and then use grid? Will that mean only part of my home will use the powerwall and the rest will still use the grid even on pick hours?
-Should I increase it to 2 powerwall to optimize the cost?
3-If they will decide which items on my current subpanel hooked up to the powerwall, how this will work, currently only one cable going to subpanel and subpanel divide its to different circuit, how they will will split it to powerwall vs non powerwall
4-In previous design document there was something called 125A distribution panel but this design do not have it. what does it mean?
4- Future EV Charger, where this EV charger will be connected? Before electricians said, once Tesla put a subpanel outside, they can hook up the EV charge to it so it can be less costly. does it still make sense?

Thank you



Screen-Shot-2022-01-11-at-4-34-10-PM.png
 

Ampster

Active Member
Supporting Member
-Nem 3.0 requirements? if any
If the Proposed Tariff gets approved on January 27th as is, you will have until May to get under the wire on NEM 2.O. As to the question of a second Powerwall the Proposed Tariff may have incentives but that is a moving target. All you can do to optimize that decision is to stay informed as this evolves. The other tactical issues are less important in the long term.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Moderator
Nov 28, 2018
15,748
20,436
Riverside Co. CA
Dear Community

This Tesla Solar project will make me an electrician soon, I read all the posts but still couldn't figure out some items, also I am trying to optimize my investment. Any suggestion or help will be appreciated. I am in N. California , PG&E

Situation:
-We have a 125a main panel, with 40 amp going to HVAC compressor and 90 amp going to sub panel in the second-floor bedroom, which is full (Electric Range, Electric Dryer, Gas Heater, Tankless Water Heater, and regular stuff for a 1900 sqft home). Currently consuming 400kwh monthly on average
-I want to install EV charger after solar is completed since all the electricians recommend a subpanel near the main service panel or load balancer I decided to wait until the solar project is completed. So I want my solar to EV charger ready with minimum cost

We are installing 6.8kwh Solar panels and 1 Powerwall. (we started with 4.4kwh and 1 powerwall+ and at that time it was all house backup)

This is the latest design document from Tesla, but I am confused.
1-This will be partial home back up, I can accept separating the 40a HVAC compressor out but is this means something my home will be also included?
2-Not to have all house back up: will this effect
-Nem 3.0 requirements? if any
-Can I still to time of cost use? What I mean, can I use the electricity I produce from solar in the day time, when peak hours 4pm-9pm, use it from the battery and then use grid? Will that mean only part of my home will use the powerwall and the rest will still use the grid even on pick hours?
-Should I increase it to 2 powerwall to optimize the cost?
3-If they will decide which items on my current subpanel hooked up to the powerwall, how this will work, currently only one cable going to subpanel and subpanel divide its to different circuit, how they will will split it to powerwall vs non powerwall
4-In previous design document there was something called 125A distribution panel but this design do not have it. what does it mean?
4- Future EV Charger, where this EV charger will be connected? Before electricians said, once Tesla put a subpanel outside, they can hook up the EV charge to it so it can be less costly. does it still make sense?

Thank you



Screen-Shot-2022-01-11-at-4-34-10-PM.png

I can not advise you on any of the technical questions. I can Advise you on, however, getting the EV charger done at the same time if possible (designed into your current design) instead of "later".

There is no circumstance I can think of where it would be cheaper to do this proposed EV charger "later" than it would be to do it at the same time the electricians are there configuring everything.

Also, if tesla is your installer, they dont tend to design for expansion later, and you will not be able to get the on site electricians to add anything that is not on the plans they have, when they are on site doing your install. Meaning, you wont be able to say "hey I bought this EV charger, can you throw this in while you are here?" or "I bought this 14-50 outlet, can you throw this in while you are here?".

if its not on the plans, they likely wont want to do it, "separate in cash payment" or not, as they will be concerned about it not passing inspection.

If you want an EV charger, get it designed in there now, not later. Adding "later" can be slightly annoying, or supremely difficult, in almost no case is it "easy".
 

h2ofun

Active Member
Aug 11, 2020
3,856
941
auburn, ca
I can not advise you on any of the technical questions. I can Advise you on, however, getting the EV charger done at the same time if possible (designed into your current design) instead of "later".

There is no circumstance I can think of where it would be cheaper to do this proposed EV charger "later" than it would be to do it at the same time the electricians are there configuring everything.

Also, if tesla is your installer, they dont tend to design for expansion later, and you will not be able to get the on site electricians to add anything that is not on the plans they have, when they are on site doing your install. Meaning, you wont be able to say "hey I bought this EV charger, can you throw this in while you are here?" or "I bought this 14-50 outlet, can you throw this in while you are here?".

if its not on the plans, they likely wont want to do it, "separate in cash payment" or not, as they will be concerned about it not passing inspection.

If you want an EV charger, get it designed in there now, not later. Adding "later" can be slightly annoying, or supremely difficult, in almost no case is it "easy".
Yep, I am dealing with trying to add after and so far, no one wants to touch!! So yep, get it done at same time or may not be able to get done at all
 
1-This will be partial home back up, I can accept separating the 40a HVAC compressor out but is this means something my home will be also included?
2-Not to have all house back up: will this effect
-Nem 3.0 requirements? if any
-Can I still to time of cost use? What I mean, can I use the electricity I produce from solar in the day time, when peak hours 4pm-9pm, use it from the battery and then use grid? Will that mean only part of my home will use the powerwall and the rest will still use the grid even on pick hours?
-Should I increase it to 2 powerwall to optimize the cost?
3-If they will decide which items on my current subpanel hooked up to the powerwall, how this will work, currently only one cable going to subpanel and subpanel divide its to different circuit, how they will will split it to powerwall vs non powerwall
4-In previous design document there was something called 125A distribution panel but this design do not have it. what does it mean?
5- Future EV Charger, where this EV charger will be connected? Before electricians said, once Tesla put a subpanel outside, they can hook up the EV charge to it so it can be less costly. does it still make sense?
1) Question unclear
2) If Tesla installs an additional CT to monitor the usage by the 40A service disconnect for your HVAC unit, then the Powerwall+ can potentially offset that usage during peak periods.
3) Everything in the subpanel supplied by the 90A feeder will be backed up. If any of those items are on breakers bigger than a 30A breaker (e.g. the electric range) it would likely overload the PW during an outage when the sun isn't shining if you tried to use it at full power (so don't turn on all the burners at once in that event). But there would be lots of other ways to overload the PW in that situation.
4) Not really a distinction to be worry about. But if you switch to 2 PWs, the project will definitely end up needing an additional panel, rather than just the Backup Gateway as in the diagram you posted.
5) With the latest diagram, your choices would be to put the EVSE on a breaker in your 90A subpanel, in which case it would backed up. Or to change out the 40A breaker to something larger, put a "non-backed up loads" panel next to the meter/main, and put two breakers in it: the 40A breaker for your HVAC, and the breaker for your EVSE.

Cheers, Wayne
 

slcasner

Active Member
Supporting Member
Feb 20, 2011
1,536
1,078
Sunnyvale, CA
@coffeci, if your existing subpanel is already full with several large loads, how does Tesla propose to add a 2-pole 50A breaker? Are there enough 15A and 20A circuits that could be doubled-up with tandem breakers?

As @wwhitney said, if you elect to add another Powerwall, then another panel would be needed. The easiest and cleanest addition would be to add the internal 200A panel into the Backup Gateway that will hold three 2-pole breakers providing room for a 50A breaker for the Powerwall+ and a 30A breaker for the Powerwall plus another 90A or 100A breaker to feed your existing subpanel.

@wwhitney, what load calculation would be used for the 125A main panel? Would it even be possible to add the EVSE there? @coffeci, do you have the whole design document from Tesla? Can you show the page with the load calculation?
 
@wwhitney, what load calculation would be used for the 125A main panel? Would it even be possible to add the EVSE there? @coffeci, do you have the whole design document from Tesla? Can you show the page with the load calculation?
That 125A panel with the meter is not really a main panel, it doesn't have a main breaker. Rather, it's two different service disconnects on a common bus.

The load calculation is just the standard load calculation for the dwelling unit. That determines the minimum size of the bus of the service disconnects panel, as well any service conductors after the service point. The load calculation is also the only thing that protects those service conductors/bus from overload; it's fine for the sum of the service disconnects to exceed the size of the service conductors, as they presently do in that panel. 90A + 40A = 130A > 125A.

Cheers, Wayne
 
Thank you all for the comments, it is really helpful, more helpful than Tesla actually.

In my latest communication, Tesla told me that, all the loads on my 90amp sub panel will be backed by powerwall+ in their design, they will only exclude the 40 amp on my main panel directly going to the HVAC compressor.
I talked to several electricians, two of them I trusted they recommended the same thing,
Can you share your ideas on that, please?

After Tesla complete the project
They will replace the 40 amp on my main panel to a 40-50 or 30-50 quad breaker. My HVAC unit was recently replaced and their max Amp is listed as 32.
and they will have a dedicated line to nema 14-50 to connect my car, it is ok if it is out of powerwall as well.
Do you think is it feasible?


@wwhitney my 90amp solar panel as 50 amp breaker and Range on it, so in one powerwall, if I use the range on total blackout, will it work? or will it only consume more power/electric from the power wall.


And tesla installers, when I talked to them on the phone, they don't want to install the EV charger, so I need to hire a separate electrical to install once they complete. do you think any chance tesla might accept to install the EV charger as a part of the project?
 
They will replace the 40 amp on my main panel to a 40-50 or 30-50 quad breaker. My HVAC unit was recently replaced and their max Amp is listed as 32.
and they will have a dedicated line to nema 14-50 to connect my car, it is ok if it is out of powerwall as well.
Do you think is it feasible?
Using a quad breaker in your MLO service panel would avoid the need to add another panel, as long as the correct quad breaker is available and listed for use in the service panel. If the 14-50 receptacle for the EVSE is outside, you'd need to check whether it requires GFCI protection under the 2017 NEC (which California uses); I know it would under the 2020 NEC. That would mean using a small spa disconnect next to the receptacle to provide the GFCI protection; it won't be possible to get a quad breaker with GFCI protection. Hardwiring the EVSE would avoid this concern, and I don't really see the upside to using a receptacle, particularly not one with an unnecessary neutral conductor (14-50 vs 6-50).

As to the HVAC side of the quad breaker, your new unit should have a label on it says "MCA X / MOCP Y" for some values of X and Y. MCA = minimum circuit ampacity, it tells you what size wire to use. MOCP = maximum overcurrent protection, it tells you the largest breaker you can use, and may be larger than MCA. The breaker can be any size between MCA and MOCP. So if MCA = 32A and MOCP = 40A, you could use a 35A or 40A breaker.

50 amp breaker and Range on it, so in one powerwall, if I use the range on total blackout, will it work? or will it only consume more power/electric from the power wall.
With a Powerwall+ the range will likely work fine off-grid. The case where it might not would be after dark, if you turn on all the burners and the oven, and you have some other significant loads running. You could do a test after installation to see what happens then. Or just avoid that use case when off-grid.

Cheers, Wayne
 

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