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PG&E/EBCE interconnection agreement question regarding system size vs. actual usage

funkadelic

Member
Oct 24, 2018
30
27
Fremont, CA
Hi all,

Have a solar roof install scheduled for install later this month and trying to understand the interconnection process with PG&E so that I can minimize any back and forth.

Reading through the PG&E net metering interconnect agreement and it states "NEM systems should be sized with an estimated annual production no larger than 110% of the Customer’s total previous 12 months of usage (annual usage) and projected future increase"

I will have a 11.2kW solar roof (estimated 15,367 kWh production in the 1st year per the tesla docs) and my trailing 12 months of electrical usage is a hair under 12,000 kWh. 15,367 kWh / 12,000 kWh = 128%, so I'd be generating an extra 18% over the 110% limit before considering that I'm charging my Model 3 at home now instead of at work and plan on getting a hot tub installed next year.

For those that that have solar connected through PG&E (and East Bay Community Energy, which my city, Fremont, is part of) did you have issues getting approval when your generation is expected to exceed 110% of usage? I plan on filling in the "I plan to increase my annual use by" field to account for the hot tub and additional home charging (which should easily cover the 18% difference over the 110% limit) but is PG&E a stickler for that field?

Also, how does PG&E determine what the annual production is? The pdf mentions "Solar CEC-AC rating" but does anyone know how I get that value? The footnotes say:

California Energy Commission Alternating Current, refers to the inverter efficiency rating (Quantity of PV Modules x PTC Rating of PV Modules x CEC Inverter Efficiency Rating)/1000

That value that gets multiplied by 1664 to arrive at the total energy production in kWh.

tesla_solar_roof_layout.png


thanks,
-norm
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
8,223
9,068
Riverside Co. CA
PGE should be like SCE, so whoever is working on your interconnect agreement should send you a form to fill out as part of that where you state you will be increasing your consumption next year. Its not that big a deal because you are fairly close to it already, and adding an EV.

Its a 1 page form in SCE land, so I would imagine its similar in PGE. If you were trying to double up your consumption or something you might have more to worry about.
 
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hayhayday

Member
Dec 8, 2020
25
20
94952
I think PGE formula assumes panels are\ mostly are south. PTC ratings of my panels is 90 and 93% of name plate, not sure what ptc for solar roof tiles are but might get you in right ballpark. Delta inverter cec efficency 99%. 11.2kw*.9*.99*1664 =16600 KWH
 
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openx1282

New Member
Dec 10, 2020
2
1
SF Bay Area
PGE should be like SCE, so whoever is working on your interconnect agreement should send you a form to fill out as part of that where you state you will be increasing your consumption next year. Its not that big a deal because you are fairly close to it already, and adding an EV.

Its a 1 page form in SCE land, so I would imagine its similar in PGE. If you were trying to double up your consumption or something you might have more to worry about.

Thanks for the response.

I have a similar question. Our solar was installed last week, waiting now for PTO from PG&E.

We oversized the solar system by 2X. Current annual usage is around 5,500 kwh. We went with 6.8KW system with anticipated annual production of 10,200kwh - anticipating more usage with a new electric car in 2021 and more AC usage in summer. I was not aware of the PG&E sizing "requirements" until I saw the interconnection paperwork filed with PG&E earlier this week. Neither Tesla (nor Sunrun who I talked to before Tesla) told me anything about not oversizing beyond 110%.

Could this be an issue if the usage is significantly less than the production next year?

Thanks.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
8,223
9,068
Riverside Co. CA
Thanks for the response.

I have a similar question. Our solar was installed last week, waiting now for PTO from PG&E.

We oversized the solar system by 2X. Current annual usage is around 5,500 kwh. We went with 6.8KW system with anticipated annual production of 10,200kwh - anticipating more usage with a new electric car in 2021 and more AC usage in summer. I was not aware of the PG&E sizing "requirements" until I saw the interconnection paperwork filed with PG&E earlier this week. Neither Tesla (nor Sunrun who I talked to before Tesla) told me anything about not oversizing beyond 110%.

Could this be an issue if the usage is significantly less than the production next year?

Thanks.

Not once they give you PTO. Its possible for it to be an issue in processing your interconnect agreement, but I dont think you would have much problem when you get PTO... especially with the relative "small size" of your system.
 

Redhill_qik

Member
Aug 16, 2020
186
99
South SF Bay, California
Thanks for the response.

I have a similar question. Our solar was installed last week, waiting now for PTO from PG&E.

We oversized the solar system by 2X. Current annual usage is around 5,500 kwh. We went with 6.8KW system with anticipated annual production of 10,200kwh - anticipating more usage with a new electric car in 2021 and more AC usage in summer. I was not aware of the PG&E sizing "requirements" until I saw the interconnection paperwork filed with PG&E earlier this week. Neither Tesla (nor Sunrun who I talked to before Tesla) told me anything about not oversizing beyond 110%.

Could this be an issue if the usage is significantly less than the production next year?

Thanks.

You should have electronically signed a PG&E interconnect agreement that Tesla provided. If you go back into your account you should find this and you can see how Tesla justified the sizing which is 99% likely to be that the owner/you are planning on increasing your electric usage in the future. This is true as you are planning on getting an EV.
 
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openx1282

New Member
Dec 10, 2020
2
1
SF Bay Area
Thank you all for the conformation.

Receive the PTO from PG&E about an hour ago. Super excited to turn on the system in the morning :)

Overall I am impressed with Tesla's efficiency (so far) and the speed of the process. Here is my timeline

Early Nov: Placed the order online, while still on the fence about solar, having just begun the research on the project
Nov 17: Home inspection
Nov 18: Layout ready. I requested a change - remove 4 panels as they are not in a good spot
Nov 23: Updated layout ready. I approved and signed the documents.
Nov 25: Called the scheduling department. They offered to install the next working day Nov 27th. I wasn't ready, so asked to schedule on December 4th.
Nov 30: Receive a Call from Tesla asking if I am OK with install next day Dec 1st. I said OK.
Dec 1: Installation, completed in about 7 hours total
Dec 7: City inspection complete. Received invoice same day
Dec 8: Made the payment. Tesla submitted the interconnection application to PG&E
Dec 10: PTO email from PG&E

Install to PTO in 9 days...
 
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funkadelic

Member
Oct 24, 2018
30
27
Fremont, CA
I think PGE formula assumes panels are\ mostly are south. PTC ratings of my panels is 90 and 93% of name plate, not sure what ptc for solar roof tiles are but might get you in right ballpark. Delta inverter cec efficency 99%. 11.2kw*.9*.99*1664 =16600 KWH

a quick googling didn't turn up anything specific for the PTC ratings for the tiles, but the example from your panels is helpful in seeing which numbers go where...now if I can only find out the PTC ratings of the solar tiles....
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
8,223
9,068
Riverside Co. CA
a quick googling didn't turn up anything specific for the PTC ratings for the tiles, but the example from your panels is helpful in seeing which numbers go where...now if I can only find out the PTC ratings of the solar tiles....

Unless you enjoy digging into stuff like this, this isnt something you really need to worry about. It more comes into play if they need to upgrade a transformer or something, and gives them an out.. or you normally consume 6500 kWh a year but want to install a PV system that has a yearly generation of 18000 kWh or something.
 
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h2ofun

Active Member
Aug 11, 2020
2,175
336
auburn, ca
Unless you enjoy digging into stuff like this, this isnt something you really need to worry about. It more comes into play if they need to upgrade a transformer or something, and gives them an out.. or you normally consume 6500 kWh a year but want to install a PV system that has a yearly generation of 18000 kWh or something.

I have heard of two cases.

One was their transformer could not handle the load so they were forced to pay for a new one, not cheap

A second was a person who have installed tons of solar and after the install, tried to get PGE to approve. They would not because the infrastructure could not support so he had to remove a whole bunch of it.

So if you are just planning to use what you produce, nothing to worry about. BUT, if you are trying to game the system by becoming a big generator, well, ...
 

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