Stuck with 100amp Service from PG&E. HELP!!

[who177e]

Hi all,

I am new to the forums but I have enjoyed reading everyone's experiences. Sorry but this will be a long post.

Background Info
Union City, CA (PG&E is provider)
Single Family House 1,855 sq ft (completely renovated 5 years ago when we bought the house)
Original House Built: 1972
Underground Power Lines: 100 amps only (nearest power distro box is across the street and down the block, about 130ft)

Current loads: All LED lights in the house, electric - AC / frig / washer / dishwasher / garbage disposal / Microwave / small radiant in floor heat in master bath (on timer) / gas - range / furnace / tankless water heater / dryer

Goals
2 Phase Project
Phase 1 - Add solar to cover current electric costs ($90 per month) and any additional infrastructure needed for Phase 2 and to future proof.
Phase 2 - Buy Model 3, add EV Charger, add powerwall/s and maybe more solar

I shopped around for the PV system and most likely going to go with Tesla Energy. We are currently going back and forth trying to figure out the design on the electrical side. They proposed a (12) 315w panel system (3.78kwh) with solaredge HD wave and power optimizers. This will cover more than what we are currently using.

CHALLENGES
Main Panel Upgrade
I want and am pretty sure a Main Panel Upgrade to 200 amps is needed. But PG&E says that I would be responsible for the trenching costs. I have quotes from $18 - $20k! On PG&Es EV webpage they make it seem as if they would consider "facility upgrade charges" as "common facilities" so the homeowner would not be responsible for those charges. However, they are only waiving the PG&E charges which doesn't include trenching. So that is a no go.

My current 100A main panel only has space for the 100A breaker that powers a sub panel that is in the garage where all of the house loads are, there is no space in the main panel to tie in the PV. PG&E doesn't allow line side taps.
PG&E will let us swap out the "a like for like" panel meaning a new 100A rated panel (they will not allow us to put in a 200A panel and derate it down to 100A with a breaker). However, Tesla is having a hard time finding a main panel that:

• rated for 100A
• branch breaker rating to meet panel rating (100A) (need this to still power my subpanel with the home loads)
• able to backfeed in the PV
• Space to support a future 40A EV Charger
• support for future powerwall

After doing some additional research will the below work / pass inspection / PG&E allowed?
In this scenario we would NOT need a MPU but would be putting in a derated subpanel.
Can the new subpanel support more PV in the future, future 40A EV charger, and future powerwall? Would it and could it be rated for 200A and derated to 100A?
Does anyone know of a main panel that fits the requirements?
The PV ready panels I found have a breaker of 100A but a rating of 125A (so PG&E would not allow it), also Tesla said that those panels would not be compatible with a powerwall in the future. Not sure why.

I don't have a clear understanding of how a Powerwall and all of it other components (gateway, etc) tie into everything, but for Phase 1, I want to make sure that I put in the right equipment to support Phase 2.

Any insight / ideas / thoughts / recommendations / etc. would HELP!

Thanks

 

[Haxster]

I have the early identical house situation here in the South Bay, except no central A/C...but our range and oven are both electric. We have both gas and 240V connections in our laundry room but are using a gas dryer.

Since we're not using the 30 Amp 240V to the dryer, I figured adding a 50 Amp breaker to the panel for the 40 Amps going to the charger wouldn't be pushing things very much. Over the last nearly two years, I've not had any issues with this set-up. And the cost was basically the 50 Amp circuit breaker, a wall socket (right next to the panel) and some wire.

Just to be safe, and to avoid extra juice wasted by the car to cool it down in a hot daytime garage during charging, I usually charge at night and often set the charge rate to 20 Amps. It runs fine at 40 Amps in a hot garage, but wastes some energy and could be an issue (i.e. 100 Amp main circuit breaker) if I maxed out our major appliances.

This could be a Phase 0.1 to get you started.

For our relatively low energy use, it's the most cost-effective solution. As appealing as solar is, at projected PG&E rates, the amortization period for us makes no sense.

Here's a little more info on my setup:

 

[who177e]

Thanks @Haxster . Sounds like we have the same house situation.
Thanks for the insight and to know that our home loads can support an EV charger.

 

[Tam]

...Any insight...

I don't think I am of any help but I thought Tesla would take care of all the design, planning, permits...

I would do everything at once instead of dividing it into 2 phases. It's easier for Tesla to figure it out once it has everything: all the loads including your future Electric Cars...

Since an increase in your amperes cost too much from PGE, I would stay with current 100A.

100A panels are very popular and houses that have 100A are also numerous so I can't understand why Tesla can't find one for you!

If your whole house current loads can't accommodate an EV charging, maybe you can connect a manual toggle switch that allows

.either A/C or Charging (only 1 can be fed live at a time)
.or instead of the above: either 30A dryer or Charging (only 1 can be fed live at a time)...

So instead of paying $20,000 for a 200A trenching, maybe you can use that fund to get:

1) an Electric car
2) more solar panels
3) more PowerWalls...

 

[miimura]

PG&E used to have some subsidy if you needed a service upgrade because of an EV. You should ask about that. Obviously, paying $18k for trenching a new service line is prohibitive.

When you install solar, it is very common to have a higher rated panel with a smaller main breaker. This is because the solar is also contributing supply which could overload the bus. This is one reason that they force you to install solar breakers at the bottom of the panel, opposite the main breaker - the supply is coming from both ends of the bus.

Also, if you do have a Powerwall installed, it will require a third "generation panel" for the solar and Powerwall on the backed up side of the Backup Gateway. This is what it would look like. You would probably only need a 150A main panel. Sorry for the poor quality mod of your diagram.

 

[who177e]

Thanks @miimura for drawing this up. It is very helpful.

PG&E used to have some subsidy if you needed a service upgrade because of an EV. You should ask about that. Obviously, paying $18k for trenching a new service line is prohibitive.
View attachment 339340

I did ask PG&E about this and have been going back and forth about how their website reads regarding this. Unfortunately after digging deep into the documentation, it does specify that trenching costs aren't included....

In your experience, will PG&E let you have a higher "rated" main panel than the service wires but with an appropriate sized main breaker to protect the service wires?

When you say I only need a 150A panel, are you referring to the subpanel that has the Future EV Charger? No issues derated that to 100A?

@Tam Telsa is responsible for the design and permits but they are really slow and then communicating with them I have to go through many layers and can't talk directly with the electrical engineer.

 

[wwhitney]

From your diagram, it looks like you have a combo meter main with just one breaker in it. In which case if you are limited to a 100A service, there's no need for that combo meter main to be rated any higher than 100A. With just one line coming in (the service), and one line going out (the feeder to the rest of your wiring), and a 100A breaker, there's no way to overload that panel during normal operation.

Downstream of the combo meter main, if you have multiple sources (PV, Powerwall, or utility) feeding separately into a panel that also has loads connected to it, then that panel may need to be rated more than 100A. Miimura's diagram is a good option if you don't want the EV charger to be backed up by your Powerwalls. [That avoids the possible issue of a night-time power failure while your car is charging leading to the Powerwalls being drained.]

In Miimura's diagram, the "(N) Subpanel" does not require a main breaker, as it is protected by the 100A breaker in the combo meter main. That panel requires a minimum 125A bus rating, as long as the 100A breaker feeding the gateway is at the opposite end of the panel from the supply. [120% rule: 100A (service) + 50A (generation panel) <= 120% * 125A (bus rating)] Load breakers in that panel would then be unlimited.

The "(E) Subpanel" would need a 100A main breaker as shown, or else the feeder from the Backup Gateway to that panel would need to be rated for 150A, and the panel would need a 150A bus. The generation panel would need to have a bus rated 100A, or else it would need to have a main breaker in it to protect the bus at its rating.

Hope this helps.

Cheers, Wayne

 

[mblakele]

Phase 1 - Add solar to cover current electric costs ($90 per month) and any additional infrastructure needed for Phase 2 and to future proof.
Phase 2 - Buy Model 3, add EV Charger, add powerwall/s and maybe more solar

Not an electrician, but I'd think you'll be fine with a 100A panel for these goals. Max solar for your service should be about 4 kW, which would probably offset your usage just fine with NEM2. Without heavy EV charging it's probably overkill, and PG&E won't pay you much of anything for excess generation. That said I'd think you'd want to max out the solar in phase I, and include any batteries then too. That's because retrofitting is expensive, kind of a PITA, and depending on what happens you could lose NEM status or other incentives.

Even if an electrician limits your EV circuit to 30A, I can tell you that's plenty for a 70-mi round-trip commute.

You may need to switch utility plans to maximize the benefits of solar. Consider joining a CCE program if that's an option: I see EBCE – A Bright Choice will pay you a penny over retail for your excess solar power.

 

[who177e]

Thanks @wwhitney and @mblakele !

This is super helpful!

@wwhitney

From your diagram, it looks like you have a combo meter main with just one breaker in it. In which case if you are limited to a 100A service, there's no need for that combo meter main to be rated any higher than 100A. With just one line coming in (the service), and one line going out (the feeder to the rest of your wiring), and a 100A breaker, there's no way to overload that panel during normal operation.

Yes we have an existing combo meter with only one breaker in it.
My initial idea was to replace the main combo meter with a new 100A combo meter (PG&E says I can do this since its a like for like) that has more breaker spaces in it so that I can 1 - back feed the PV, 2 - feed my 100A subpanel that feeds the home loads, 3 - add a future EV charger, and 4 - add a future powerwall (but now i have a better understanding of the powerwall system, so that probably won't work).

@mblakele

Even if an electrician limits your EV circuit to 30A, I can tell you that's plenty for a 70-mi round-trip commute.
You may need to switch utility plans to maximize the benefits of solar. Consider joining a CCE program if that's an option: I see EBCE – A Bright Choice will pay you a penny over retail for your excess solar power.

My commute is exactly 70 miles everyday. Union City to Richmond.......painful.
I was just looking at the EBCE website yesterday, as we just got notice that we are getting switched over. Will they really pay a penny OVER retail for excess solar??? Based on TOU isn't that like $0.27+ ?? That would be huge.
However, with (12) 315w panels (3.78kwh) (of PV I would already be maxed out on the 100A service.

I see other homes in my neighborhood that have a lot more panels than (12) and I'm pretty sure we all only have 100A services. I saw on the Tesla website where it shows all of the other PV systems in my area and many of them have systems larger than 4kw. I wonder how they accomplished that?

 

[mblakele]

I was just looking at the EBCE website yesterday, as we just got notice that we are getting switched over. Will they really pay a penny OVER retail for excess solar??? Based on TOU isn't that like $0.27+ ?? That would be huge.
However, with (12) 315w panels (3.78kwh) (of PV I would already be maxed out on the 100A service.

According to Net Energy Metering with EBCE – EBCE "New Low Income and Municipal Customers after 6/1/18: Retail + $0.01". I'm not sure what a municipal customer is: maybe it means you have to be inside the city limits? You could email or call them and ask.

For maximizing solar, panel count may not tell the whole story. I have 15 x 320W panels, but I've seen the inverter clip generation to around 4-kW near solar noon on cool days in midsummer. I was told my 100A service was the limiting factor, and so a larger inverter wouldn't make sense. After I thought about it, I realized that it shouldn't bother me to lose that little bit of peak power. Having more panels means I get more power over a longer period, and that's probably a good ROI trade-off with NEM2.

 

[wwhitney]

Yes we have an existing combo meter with only one breaker in it.
My initial idea was to replace the main combo meter with a new 100A combo meter (PG&E says I can do this since its a like for like) that has more breaker spaces in it so that I can 1 - back feed the PV, 2 - feed my 100A subpanel that feeds the home loads, 3 - add a future EV charger, and 4 - add a future powerwall (but now i have a better understanding of the powerwall system, so that probably won't work).

There's no need to replace your existing combo meter main, and no real upside. And the downside as you have learned is that PG&E places restrictions on the first piece of equipment on your premises, the service disconnect (rating has to match your service size.)

So instead just add new equipment between your existing combo meter main and your existing subpanel, as miimura suggested in his diagram. That way PG&E doesn't care about the specs, and you can size the equipment as required to do what you want to do.

If, BTW, you want your EVSE on the backed up side of the gateway, you don't even need the subpanel between the backup gateway and your existing panel.

However, with (12) 315w panels (3.78kwh) (of PV I would already be maxed out on the 100A service.

A 100A 120V/240V service can support 24 kW of power (100A * 240V) flowing either to or from the grid. [Edit: solar production is considered continuous and so would be limited to 80% of this, or 19.2 kW.] In practice PG&E's upstream equipment may limit your backfeed to less than 24 kW [edit: 19.2 kW], but I don't think it would be as low as 3.78kW. And the tariffs probably limit you to installing a system that would cover 100% of your anticipated demand.

Cheers, Wayne

 

[who177e]

@wwhitney
So could I have (15) 315W panels (4.72kw) system on my 100A service? What about the 120% rule? Does that only apply to the panel that the PV is backfed to? So if I'm not backfeeding into my main 100A combo panel and into a subpanel we should be ok?
So in my case, if I included the EVSE on the backed up side, would the following work and pass code?

 

[wwhitney]

Any panel that can be supplied with power via more than one connection needs to meet one of the criteria listed in the NEC 705.12(B)(2)(3). The most common option is the so-called 120% rule, which says that a panel bus can be connected to supplies totalling 120% of the bus rating, as long as those supplies are connected only at the ends of the panel bus, with the total supply at one end no more than the panel bus rating.

Another option allows the backfeed as long as the sum of the breakers in the panel, excluding the main breaker, does not exceed the rating of the panel bus. So if your service panel has only the (1) 100A breaker in it, it automatically complies with that rule.

For completeness, the last option is simply that the panel bus rating is at least as great as the sum of the supplies feeding the panel. In that case there is no restriction on the locations of the supply breakers within the panel.

Cheers, Wayne

 

[who177e]

@wwhitney
Ok so if I am understanding correctly, it's not my 100A main SERVICE that is limiting the amount of PV I can add to my home, but rather it depends on bus bar rating on the panel (main or sub) that the PV is backfeeding into.

Sooo......in theory if I had a 200A rated subpanel being fed by the 100A breaker coming from my 100A main combo panel, and connected to the 200A rated subpanel I had 60A of PV and 30A of powerwall that would work and pass inspections?

If this is true in theory couldn't you just put in a 400A subpanel and connect boat loads of PV to that?

Thanks for baring with me, just trying to fully understand what I can do.

 

[miimura]

According to my understanding, Panel N 200A rated, could have the 60A solar and 30A Powerwall and still meet all the requirements. In the extreme, I don't think you can have more than 100A total breakers for solar generation when you have 100A service. However, @wwhitney is more of an authority on these two items.

Also, in your diagrams, you picture what looks like 100A breakers at both ends of wires connecting panels. You only need a breaker in the feeding panel. So, Panel E does not need a "main breaker" it could just terminate the feed line to the lugs at the top of the panel. Same with Panel N. The cables from the Main Combo Panel 100A breaker could terminate on the panel lugs.

Edit: changed / added "could" in two places.

 

[who177e]

Also, in your diagrams, you picture what looks like 100A breakers at both ends of wires connecting panels. You only need a breaker in the feeding panel. So, Panel E does not need a "main breaker" it would just terminate the feed line to the lugs at the top of the panel. Same with Panel N. The cables from the Main Combo Panel 100A breaker terminate on the panel lugs.

Yes on "Panel E" we do have an existing 100A breaker that feeds the bus bars in the panel. I think that is it just convenient / safe to have a way of cutting power to the bus bar at the panel that you are working on. It also helps that is tells whoever is working on that panel that is is derated to that amperage.

 

[miimura]

Ok. I agree it's convenient. The sub-panel in my house does not have one.

 

[wwhitney]

PG&E will have its own restrictions on how much solar you can connect to a 100A service. There are two issues:

1) They probably don't want you to be a net exporter over the course of the year (and it doesn't pay for you to be one, either). So they may limit your PV size based on your historical usage, or if you are getting an EV, based on an estimate of your future usage with EV.

2) If you put too much PV on your service, they will have to upgrade their equipment, and so they might either restrict the amount of PV, or want to charge you for the upgrades.

As a simple example, suppose your 100A service is on its own transformer, not shared with any other customers. A 100A service is nominally good for 24 kVA (24000 volt-amps), but it will not be served by a 25 kVA transformer, it would be, say, a 10 kVA transformer.

That is because NEC load calculations (used to size equipment you own) are very conservative, and prior to the advent of EVs and PV, there were basically no residential continuous loads. So even if your load calculation comes to 100A and you need a 100A service, actual monitoring of that service might show that your average current is only 10A, with very rare excursions above 40A. The 10 kVA transformer can handle intermittent overloading as long as it has time to cool down in between excursions above 40A (40A * 240V = 10 kVA, approximately)

But now if you put 60A of PV on your service, or if you get an EV and want to charge it at 60A, your demand profile has changed and you are actually trying to use your 100A service at 60A continuously for multiple hours. The 10 kVA transformer may no longer handle that, and PG&E would have to upgrade to a 15 kVA or 25 kVA transformer.

If your transformer is actually shared with other residences, then it is likely to have more reserve capacity, as long as you are the only customer on that transformer with an EV or PV.

Cheers, Wayne

 

[wwhitney]

Edit: when I say 80A of PV, I mean 19.2 kW worth of inverters. Such inverters would have to interconnect via a 100A breaker, because they are treated as continuous sources.

@wwhitney
Ok so if I am understanding correctly, it's not my 100A main SERVICE that is limiting the amount of PV I can add to my home

With the above caveat about PG&E's limits, a 100A service is limited to 80A of PV connected to it. That's because a 100A breaker is only rated for 80A continuously, and if you connect more PV the main breaker may trip.

but rather it depends on bus bar rating on the panel (main or sub) that the PV is backfeeding into.

Not just the panel the PV is connected to, but every panel that can get power simultaneously from two different connections, the PV and the utility. The point is that if the 100A service panel has only two connections to it, the utility and the rest of the house, that panel can't be simultaneously receiving power from both connections during normal operations.

Sooo......in theory if I had a 200A rated subpanel being fed by the 100A breaker coming from my 100A main combo panel, and connected to the 200A rated subpanel I had 60A of PV and 30A of powerwall that would work and pass inspections?

Yes, if PG&E would OK it.

Cheers, Wayne

 

[wwhitney]

Also, in your diagrams, you picture what looks like 100A breakers at both ends of wires connecting panels. You only need a breaker in the feeding panel. So, Panel E does not need a "main breaker" it could just terminate the feed line to the lugs at the top of the panel. Same with Panel N. The cables from the Main Combo Panel 100A breaker could terminate on the panel lugs.

That is true for the configuration drawn. It is worth noting, however, that when you insert a Backup Gateway into one of those feeders, and you use both of its load side lugs, one to connect the existing load panel, and one to connect a new generation panel, then it is required that the existing load panel have a main breaker. That is because the feeder segment from the Backup Gateway to the existing load panel (and that panel's bus) can now be fed from two different sources, the utility and the generation panel, and so it could be overloaded otherwise.

Also, while a main breaker is a convenient way to kill all the circuits in the panel, when doing electrical work in the panel it is safer to kill the upstream breaker feeding the panel, so that there are no energized parts within the panel.

Cheers, Wayne