Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register

Tesla system design size leading to violation of PG&E NEM2 guidelines?

IamMark

Member
Dec 31, 2019
52
17
SF Bay Area
I do not yet have my solar panels installed; in fact, I still haven't accepted the design. Based on my usage, which is currently about 9,500 kWh per my last 12 months, Tesla recommended a medium size system with 24 panels. In my configuration this design has an estimated annual production of 12,243 kWh, which is about 129% of our usage.

I read somewhere that PG&E's Net Energy Metering program requires that you don't size your system more than 5-10% over your usage. I looked into this a bit more last night and found their NEM2 Agreement and Customer Authorization form. According to Part II of their agreement, "NEM2 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." Given this, I have some questions:

1) Tesla's recommended system sizes seem like they will always be oversized, and in some cases significantly. Doesn't this mean that a good portion of their PG&E customers will be violating the NEM2 guidelines?

2) What happens if your production is greater than 110% of your usage? What are the consequences of violating their NEM2 guidelines?

3) While the panels will generate more than 110% of my usage initially, as they degrade over time, they will eventually be producing less than 110%. Does PG&E take that into consideration at all?

Thanks.
 

jboy210

Supporting Member
Dec 2, 2016
5,094
3,165
Northern California
I do not yet have my solar panels installed; in fact, I still haven't accepted the design. Based on my usage, which is currently about 9,500 kWh per my last 12 months, Tesla recommended a medium size system with 24 panels. In my configuration this design has an estimated annual production of 12,243 kWh, which is about 129% of our usage.

I read somewhere that PG&E's Net Energy Metering program requires that you don't size your system more than 5-10% over your usage. I looked into this a bit more last night and found their NEM2 Agreement and Customer Authorization form. According to Part II of their agreement, "NEM2 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." Given this, I have some questions:

1) Tesla's recommended system sizes seem like they will always be oversized, and in some cases significantly. Doesn't this mean that a good portion of their PG&E customers will be violating the NEM2 guidelines?

2) What happens if your production is greater than 110% of your usage? What are the consequences of violating their NEM2 guidelines?

3) While the panels will generate more than 110% of my usage initially, as they degrade over time, they will eventually be producing less than 110%. Does PG&E take that into consideration at all?

Thanks.

Not sure how they do it, but if you are concerned they will reject your larger system just tell them you are planning on getting an EV. That will definitely make your system fit under "... and projected future increase" clause.
 
  • Like
Reactions: bkp_duke

SoCal Dave

Member
Jul 30, 2020
420
317
California
Not sure for PG&E, but for SCE, Telsa had me sign a form stating:

I have compared the estimated annual production of my Generating Facility with my most recent 12-month usage history. I am aware that my Generating Facility is expected to produce more energy than I used in the last 12 months. However, I affirm that I expect to increase my usage accordingly in the upcoming year. My Generating Facility was sized to meet this expected increase.
We will definitely use the AC more and I just added a pond pump which is 500W x 24 hours a day.
 

holeydonut

Supporting Member
Jun 27, 2020
1,501
880
East Bay NorCal
I sized my system to 120% of previous annual consumption. Variables driving more usage include COVID sheltering and a future EV purchase. The PG&E form you linked has a section Part II, B, (6) that my installer let me complete with an anticipated increase to future consumption.
 

IamMark

Member
Dec 31, 2019
52
17
SF Bay Area
I get that there are valid reasons for having oversized systems, such as increased future usage. However, there will be people who purchase through Tesla and get a system that is oversized with no anticipated increase in energy consumption. What happens when their system is generating more than 110% of their usage?
 

Uncle Paul

Well-Known Member
Nov 1, 2013
6,286
6,826
Canyon Lake,CA
Most new owners with Solar tend to use more than before, because of economics and the desire to live more comfortably. Adding an EV will of course add more usage. Guess that in an emergency (producing too much) you could simply cover a panel or two to reduce production. Currently, more people are working from their home offices, and children are staying home. Customers are not going on as many vacations away and generally spending more of their time sheltering in place. All this tends to increase consumption.
 

holeydonut

Supporting Member
Jun 27, 2020
1,501
880
East Bay NorCal
I get that there are valid reasons for having oversized systems, such as increased future usage. However, there will be people who purchase through Tesla and get a system that is oversized with no anticipated increase in energy consumption. What happens when their system is generating more than 110% of their usage?

PG&E pays you something like $0.03 per kWh for your excess generation. This is basically the wholesale price of surplus energy in the open market.

In the past they used to pay more but it's gone done a ton since California has an over-supply of energy already. So they really don't want residential solar adding even more surplus.
 

tikhipoodi

Member
Aug 2, 2020
6
0
NJ
I get that there are valid reasons for having oversized systems, such as increased future usage. However, there will be people who purchase through Tesla and get a system that is oversized with no anticipated increase in energy consumption. What happens when their system is generating more than 110% of their usage?

I don't have the panels yet, but am speaking with Tesla and others for an upcoming purchase. My understanding is that although Tesla simplifies the purchase into a small/medium/large category, the actual design and purchase will be tailored to your home and forecasted usage. I don't believe the utilities will allow something greater than 120% (this may be on the high end) of past usage.

Your second question is an important one which I myself would like to know the answer to. What happens if you are consistently producing more than you use. Will you still get credit from the utilities for the excess, or will they cap this at some point? What happens if you have an EV and your historical usage is indicative of that, but then you sell the EV and no longer have the same consumption levels? This scenario would result in excess production. Same question applies here.
 

BrettS

Active Member
Mar 28, 2017
2,109
2,512
Orlando, FL
I don't have the panels yet, but am speaking with Tesla and others for an upcoming purchase. My understanding is that although Tesla simplifies the purchase into a small/medium/large category, the actual design and purchase will be tailored to your home and forecasted usage. I don't believe the utilities will allow something greater than 120% (this may be on the high end) of past usage.

Your second question is an important one which I myself would like to know the answer to. What happens if you are consistently producing more than you use. Will you still get credit from the utilities for the excess, or will they cap this at some point? What happens if you have an EV and your historical usage is indicative of that, but then you sell the EV and no longer have the same consumption levels? This scenario would result in excess production. Same question applies here.

There is no global answer to this. It depends on your specific utility. It can range from full retail value all the way down to nothing at all. I even saw one poster who said that his utility won’t give him any credit for excess production, but will apply those credits to people who are experiencing a hardship and unable to pay their bill.
 

miimura

Well-Known Member
Aug 21, 2013
6,254
5,878
Los Altos, CA
This thread is specific to PG&E. I have never heard of them refusing a system that produces more than historical consumption, unlike some other utilities and co-ops. That said, overbuilding your solar with no plan to use all the generation is not very smart financially. PG&E pays so little for Net Surplus Compensation that it's just not worth it.
 

IamMark

Member
Dec 31, 2019
52
17
SF Bay Area
This thread is specific to PG&E. I have never heard of them refusing a system that produces more than historical consumption, unlike some other utilities and co-ops. That said, overbuilding your solar with no plan to use all the generation is not very smart financially. PG&E pays so little for Net Surplus Compensation that it's just not worth it.
The main reason for me wanting to oversize my system is to make sure that I'm still generating enough when the panels have degraded due to age. I still want to make sure my usage is covered 15-20 years down the road after the panels are only generating 85% of what they used to.
 
  • Like
Reactions: RabidYak

BGbreeder

Member
Jun 19, 2020
233
128
Bay Area
Given the rapidly decreasing cost of solar, it might make more (better?) financial sense to add panels at the point in the future when you feel that your production has dropped below your magic number of "just right".

We substantially overbuilt ours based on upgrading to two EVs. PG&E hasn't said anything. The whole shelter in place has caused a significant drop in our demand, but we can always crank the AC up if we get bad wildfires again, or use more electric heating.

YMMV, of course.

BG
 

tkizzy

Member
Jun 8, 2015
206
63
Napa, CA
It seems downright evil to push people not to produce clean renewable energy in excess....if that is the case somebody needs to get the aclu or someone else to sue the crap out of PG&E. as a utility monopoly, it’s not ok to think of electricity in terms of a commodity to limit because the surplus cheapens the price. As long as there is a single fossil fuel plant producing electricity for the state of California, solar production should never be limited.
 
  • Like
Reactions: RabidYak

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
8,812
9,758
Riverside Co. CA
I don't have the panels yet, but am speaking with Tesla and others for an upcoming purchase. My understanding is that although Tesla simplifies the purchase into a small/medium/large category, the actual design and purchase will be tailored to your home and forecasted usage. I don't believe the utilities will allow something greater than 120% (this may be on the high end) of past usage.

Your second question is an important one which I myself would like to know the answer to. What happens if you are consistently producing more than you use. Will you still get credit from the utilities for the excess, or will they cap this at some point? What happens if you have an EV and your historical usage is indicative of that, but then you sell the EV and no longer have the same consumption levels? This scenario would result in excess production. Same question applies here.

I signed that form mentioned earlier stating I was expecting an increase in usage in 12 months, in 2015. I was expecting to be able to buy an EV in 2015, but then life happened, and I didnt buy it till 2018. I had "excess" solar production 2015, 2016, 2017 and 2018 (didnt buy the EV till december of 2018). SCE didnt do anything except pay me wholesale rates for the over production when I was a net producer each of those years. Like $400 to %550 worth of "credit on my account" turned into around $40-50$.

Thats one persons experience, and not with PGE but with SCE... but saying that, I cant see why they would really care too much except they dont want to compensate people for being "powerplants".


Also, OP wont have to have a NGOM because the system itself is sized lower than 10kW, regardless of actual production, its the system specs that matter for that, I am almost positive. My "8.7" kW sized system generates between 12,000 and 13,000 kWh a year, for example.
 

SMAlset

Well-Known Member
Mar 4, 2017
9,058
9,783
SF Bay Area
Not sure for PG&E, but for SCE, Telsa had me sign a form stating:

I have compared the estimated annual production of my Generating Facility with my most recent 12-month usage history. I am aware that my Generating Facility is expected to produce more energy than I used in the last 12 months. However, I affirm that I expect to increase my usage accordingly in the upcoming year. My Generating Facility was sized to meet this expected increase.
We will definitely use the AC more and I just added a pond pump which is 500W x 24 hours a day.

I've been wondering the same thing and interesting to see how SCE handled it. The last few months I've been charging my car at the nearby supercharger to make use of the 1K miles I got as a referral (since I'm not going anywhere, SIP). Husband on WFH since March has free supercharging on his car and has been primarily doing the same for the time being. Also because we switched to the EV timed plan for midnight to 3pm a while back, we've been trying to use less A/C etc until we get connected to our solar/PWs. We looked back at our electrical usage a few years back and definitely were using more then so don't think it will be a concern for us.
 

SoCal Dave

Member
Jul 30, 2020
420
317
California
It seems downright evil to push people not to produce clean renewable energy in excess....if that is the case somebody needs to get the aclu or someone else to sue the crap out of PG&E. as a utility monopoly, it’s not ok to think of electricity in terms of a commodity to limit because the surplus cheapens the price. As long as there is a single fossil fuel plant producing electricity for the state of California, solar production should never be limited.

Unfortunately, solar does have the significant limitation of only generating energy during the day and mostly around noon. My understanding is California does have a big problem where we are fine during peak solar production but the evenings when solar is dropping off but AC usage is cranking up we don't have enough power.

The power companies either need to have fossil fuel, battery or some other alternative power source during these times.

This video was pretty interesting talking about the problem and some of the planned expensive solutions:
 

About Us

Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.

Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


SUPPORT TMC
Top