NEM-PS Annual True-Up Calculation [PG&E example]

[YRide]

Assuming your solar is what your installer told PG&E it is, I think the only way to exceed their estimated production would be to use a lot of Grid Charging and Export Everything. So maybe they found it wasn't worth the extra paper and postage.

Hmmm. I think this is an issue, because as we get into winter my ratio goes way up.

Actually, might depend on one key thing (I think I asked this before and someone likely answered but i forgot)…is monthly export limit an actual export limit (one way) or is it net export/generation?

Below you can see in Oct I generated 944kWh from PV. Oct was not all blue sky, so let’s say 1,000kWh was ideal/theoretical PV max generation (and would be the limit for Oct by PG&E on BWbill).

Of that amount the PV exported 255kWh to the grid.

Then below, you can see my ESS’s exported 1,062kWh to the grid. NOTE: 1st half of month I lost 1of4 PW’s, so it’s lower GC and lower EE. That got fixed then it went back to the full 54kWh of ESS capacity in second half of month.

So if the PG&E limit is pure export only, then 255+1062=1,317kWh and I’ve exceeded my hypothetical 1,000kWh export limit.

This is (really) bad because 1) I’ve disallowed high-earning NEM credits at peak rates for low-earning off-peak, and 2) I unnecessarily imported many kWh’s driving up my NBC’s.

On the other hand, if it’s a net export limit, then I exported 255+(1062-1404)= -87kWh.

So I really need to know the export limits by month if the policy is the former, in order to tune my system (prob by increasing my ESS SOC reserve to >0%).

 

[miimura]

On Paired Storage accounts, PG&E tracks total export and compares it to Estimated PV Generation. If Total Exports are higher than Estimated PV, they start subtracting from your Peak credits, then when those are exhausted, they subtract from your Part-Peak credits.

This is the danger of Grid Charge + Export Everything. PG&E will eviscerate your NEM credits if you over do it. If you never use Grid Charge, you are never in danger unless PG&E doesn't know about all your solar.

 

[YRide]

On Paired Storage accounts, PG&E tracks total export and compares it to Estimated PV Generation. If Total Exports are higher than Estimated PV, they start subtracting from your Peak credits, then when those are exhausted, they subtract from your Part-Peak credits.

This is the danger of Grid Charge + Export Everything. PG&E will eviscerate your NEM credits if you over do it. If you never use Grid Charge, you are never in danger unless PG&E doesn't know about all your solar.

Well, I definitely don’t have a bill yet that is indicating my limits…so it’s kind of hard to tell if I’m over, close or not.

This is why the Charge On Solar (CoS) is pretty important. It allows me to have have all daytime production prior to 3p go to the car, instead of the grid.

However, it would be much more advantageous if the Powerwall would do a better job at anticipating solar production next day and not using GC to 99% SoC each night. It used to only do 85-90% SoC. And it really could go to just 75-80% and be fine. And then maybe if it’s low at 230p…do a final import for like 30min…it could get 11kWh if it needed to, so even if there’s literally no sun.

That would also reduce my NBC’s slightly too.

Anyone have experience really affecting GC behavior?

 

[Redhill_qik]

Well, I definitely don’t have a bill yet that is indicating my limits…so it’s kind of hard to tell if I’m over, close or not.

This is why the Charge On Solar (CoS) is pretty important. It allows me to have have all daytime production prior to 3p go to the car, instead of the grid.

However, it would be much more advantageous if the Powerwall would do a better job at anticipating solar production next day and not using GC to 99% SoC each night. It used to only do 85-90% SoC. And it really could go to just 75-80% and be fine. And then maybe if it’s low at 230p…do a final import for like 30min…it could get 11kWh if it needed to, so even if there’s literally no sun.

That would also reduce my NBC’s slightly too.

Anyone have experience really affecting GC behavior?

If you are not using the Powerwall Export Everything option AND not charging the Powerwalls from the grid than you won't hit the export limit.

It does appear that you are grid charging, but why are you enabling that feature?

 

[miimura]

I have only started using Grid Charge this month because I recently got it enabled by my installer. I only personally see a use for it when I'm not generating enough to recharge to 100% before 3pm. I have only turned it on 3 times and that was when I could see that peak solar time had passed and I wasn't going to make it to 100% because it was an overcast day. Before, I used to just crank up my Reserve (up to 75%) so that my expected generation would be able to recharge from my small solar system. It was always going to hit the Reserve every day anyway, so why not retain a higher base? Now that I've increased my solar and enabled GC, I leave the Reserve relatively low (40%).
I never pushed to have GC enabled before because I took the original Federal Tax Credit that required 100% renewable charging. I interpret that rule to apply for 5 years and my system is now over 5 years since install. This is not tax advice.

 

[swedge]

So I really need to know the export limits by month if the policy is the former, in order to tune my system (prob by increasing my ESS SOC reserve to >0%).

You won't know exactly PG&E's estimate until you have full year of B&W bills, if they ever do share the info with you.

In the mean time, as you suggest, you could increase your backup reserve so that your exports don't exceed you solar production. This will decrease both your EE exports and your grid charging imports, I think.

The limit is on total exports. PG&E does not want us to buy from them at off peak and sell back at peak prices. Only PG&E are allowed to do that with their own batteries, even though us doing so reduces peak grid load and generation costs. As Steve Martin said in The Jerk, "Oh, I get it! It is a profit deal." NEM does obligate them to buy kWh you produce and loan to them till you need them. Since all such energy is sold at the same instant to some other customer at the same retail price plus NBCs, it has only a small net positive effect on their revenue.

Anyway, the limit is on all exports, not the net of exports minus imports.

 

[swedge]

I’m trying to think if NBC’s change with tariff changes? I think they do, it actually looks like NBC’s went down from 3.541¢/kWh to 3.271¢/kWh in Sep tariff change…does that align with your understanding?

NBCs are the sum of four components of the bundled charges, and so they might or might not change with each update to the tariff.

The last published EV2 effective as of 9/1/2023 is here: PDF, and only the Generation and Distribution components change with season and time of use.

The NBC Components effective 9/1/2023 were, power kWh:

Public Purpose Programs (PPP): $0.02578​

Nuclear Decommissioning (ND): $0.00135​

Wildfire Fund Charge (WFC): $0.00530​

Competition Transition Charge (CTC): $0.00030​

​

Total: $.03273 on each kWh imported, not credited on exports.​

Again, these do not change with season or TOU, but may change when the rates are changed. I don't know when they were last changed, but for simplicity and since they are small, for estimation purposes I assume they are constant all year.

 

[swedge]

Dude, how will you put your PHD in PG&E Bill Reading to use if they nix the black and white bill?

My dad used to say that we all know what the BS in a bachelor's degree stood for. He had one, so perhaps he knew. Anyway, he always told us that "PhD" stands for "Pile it Higher and Deeper."

My "study" of the B&W bills is to be sure I understand the true-up calculation so that I can operate my PW so as to minimize my costs.

Under NEM1, our solar w/ PowerWall covererd our home needs almost perfectly, so the true-up was only a few bucks. (I did use a hack to grid charge on a few cloudy winter days, this was before the GC feature was introduced.) Then we got a Tesla Model Y, which uses almost as much as the house, which meant we'd need more solar. But how much more? Along came Export Everything and legit Grid Charging which would help leverage the solar, but enough more solar also meant we'd loose our NEM1 grandfathering and have to deal with NBCs. So it was Excel time. Based on all this, we added 6 panels to our old 14, and switched to NEM2.

When our first full year of NEM2 and car charging true up came around, we were charged only $67 at true-up, cool! But my Excel model said it would be around $300, hmmm. Hence the dive into the B&W morass. Turns out PG&E wrongly used my NBCs rather then the HIGHER NEM charges, contrary to everyone's understanding of the rules. Hence the depth of the dive.

NEM2 creates some non-linearities in the cost vs net-consumption functions. NEM vs NBC vs MDC, and Imports vs Exports all matter. The best settings for PowerWall depend on these cumulative totals, which we won't know till year end. So, getting the setting right requires estimates in advance, especially during our first year after any significant change in production, PW or consumption. The B&W true-up bills provide most of the numbers needed to fine tune one's settings.

Of course one could just invest in enough solar to have significantly more production than consumption, hence simplifying the issues. However, spending thousands of $ to save tens of $ works only for those with extra zeros in their net worth, lucky bastards!

Anyway, it was PG&E, not I who piled it higher and deeper.

 

[YRide]

If you are not using the Powerwall Export Everything option AND not charging the Powerwalls from the grid than you won't hit the export limit.

It does appear that you are grid charging, but why are you enabling that feature?

I have both GC & EE. The purpose being to maximize NEM credits to offset the fact that I am a significant net importer (3EV's).

 

[YRide]

I have only started using Grid Charge this month because I recently got it enabled by my installer. I only personally see a use for it when I'm not generating enough to recharge to 100% before 3pm. I have only turned it on 3 times and that was when I could see that peak solar time had passed and I wasn't going to make it to 100% because it was an overcast day. Before, I used to just crank up my Reserve (up to 75%) so that my expected generation would be able to recharge from my small solar system. It was always going to hit the Reserve every day anyway, so why not retain a higher base? Now that I've increased my solar and enabled GC, I leave the Reserve relatively low (40%).
I never pushed to have GC enabled before because I took the original Federal Tax Credit that required 100% renewable charging. I interpret that rule to apply for 5 years and my system is now over 5 years since install. This is not tax advice.

My strategy is not quite this. Close, but still different. Aim is to maximize NEM credits which is up to max 4x PW (54kWh/day, with 0% reserve) and then adding any PV between 3p-9p (very little in winter). PV from 9p-3p should first go to PW/ESS (this is not working great at the moment), and then second go to CoS (one of the three EV is usally plugged in) to ensure no daytime PV goes to grid via GC, eating away at my monthly export limit.

They key I have still to figure out in this "algorithm" is how to force the PW to stop GC at like 75% or 80% so that PV can prioritize taking it to 100% SoC during the day. It's a little strange this setting (max SoC) doesnt exist. Intuitively, it doesn't make sense, but with PG&E (prob one of the biggest consumer of PW/PV and in the backyard of their R&D folks) Tesla should be aware of this monthly max export limit.

Lucky enough I did my install after 1/1/2023 where the FTC limitation on GC no longer applies.

 

[YRide]

In the mean time, as you suggest, you could increase your backup reserve so that your exports don't exceed you solar production. This will decrease both your EE exports and your grid charging imports, I think.

Yes, if I raised my backup reserve to 50% (from 0% today) then I would reduce my EE exports by 50% each day, at 4p peak it would only export 54*50%=27kWh (plus anything that went straight for PV to grid, which might go up if there is no ESS to fill and the cars charge to their limit) instead of the full 54kWh. And yes, it would also reduce my GC import by 27kWh from 54kWh down to 27kWh.

It's probably the best mechanism I have to control right now, short of maybe doing some intricate custom rate tables per my "algorithm" comment in previous post.

It would be kinda cool if Tesla would create two reserve level's, kinda like Charge on Solar, but in reverse. A "home load reserve %" and a "export everything reserve %". Home Load Reserve % would be the stop limit for consuming the powerwall for home and vehicle charging needs. Export Everything Reserve % would be the stop limit for if I exported to grid. Setting the former low would ensure I still dont pull anything from the grid to power house, and setting the latter higher would allow me more fine grained control to manage hitting PGE export limits and invalidating valuable peak NEM credits.

Anyway, the limit is on all exports, not the net of exports minus imports.

Noted, thanks for confirmation.

This is important as the net import/export numbers are aggregated by the hour, but the NBC imports are aggregated by 5 (or maybe 15) minute intervals. This leads to a higher NBC import number when it captures sporadic high current usage from equipment like an A/C condenser turning on for less than 5 minutes. Must months there is less than 10 kWh difference between hourly and the 5/15min interval, but during the summer I see increases of 40-80 kWh.

@Redhill_qik I just was looking up for documentation on the NBC's, and came across this table. It would indicate that for NEM2 residential that NBC's are only metered on 1hr intervals.

NBCs are the sum of four components of the bundled charges, and so they might or might not change with each update to the tariff.

The last published EV2 effective as of 9/1/2023 is here: PDF, and only the Generation and Distribution components change with season and time of use.

The NBC Components effective 9/1/2023 were, power kWh:

Public Purpose Programs (PPP): $0.02578​

Nuclear Decommissioning (ND): $0.00135​

Wildfire Fund Charge (WFC): $0.00530​

Competition Transition Charge (CTC): $0.00030​

​

Total: $.03273 on each kWh imported, not credited on exports.​

Again, these do not change with season or TOU, but may change when the rates are changed. I don't know when they were last changed, but for simplicity and since they are small, for estimation purposes I assume they are constant all year.

@swedge where did you confirm the NBC's per above? I was of the impression that the 4 were: PPP, ND, CTC and DWR Recovery Bond. Couldn't find DWR referenced anywhere...but then saw this buried in the tariff. It doesn't say NBC explicitly, but i guess the last sentence implies that? They really do make this way more complicated then it needs to be!

 

[holeydonut]

My dad used to say that we all know what the BS in a bachelor's degree stood for. He had one, so perhaps he knew. Anyway, he always told us that "PhD" stands for "Pile it Higher and Deeper."

My "study" of the B&W bills is to be sure I understand the true-up calculation so that I can operate my PW so as to minimize my costs.

Under NEM1, our solar w/ PowerWall covererd our home needs almost perfectly, so the true-up was only a few bucks. (I did use a hack to grid charge on a few cloudy winter days, this was before the GC feature was introduced.) Then we got a Tesla Model Y, which uses almost as much as the house, which meant we'd need more solar. But how much more? Along came Export Everything and legit Grid Charging which would help leverage the solar, but enough more solar also meant we'd loose our NEM1 grandfathering and have to deal with NBCs. So it was Excel time. Based on all this, we added 6 panels to our old 14, and switched to NEM2.

When our first full year of NEM2 and car charging true up came around, we were charged only $67 at true-up, cool! But my Excel model said it would be around $300, hmmm. Hence the dive into the B&W morass. Turns out PG&E wrongly used my NBCs rather then the HIGHER NEM charges, contrary to everyone's understanding of the rules. Hence the depth of the dive.

NEM2 creates some non-linearities in the cost vs net-consumption functions. NEM vs NBC vs MDC, and Imports vs Exports all matter. The best settings for PowerWall depend on these cumulative totals, which we won't know till year end. So, getting the setting right requires estimates in advance, especially during our first year after any significant change in production, PW or consumption. The B&W true-up bills provide most of the numbers needed to fine tune one's settings.

Of course one could just invest in enough solar to have significantly more production than consumption, hence simplifying the issues. However, spending thousands of $ to save tens of $ works only for those with extra zeros in their net worth, lucky bastards!

Anyway, it was PG&E, not I who piled it higher and deeper.

Nah I said PHD. That’s not a PhD.

PHD means PG&E Hating Degree.

 

[swedge]

@swedge where did you confirm the NBC's per above? I was of the impression that the 4 were: PPP, ND, CTC and DWR Recovery Bond. Couldn't find DWR referenced anywhere...but then saw this buried in the tariff. It doesn't say NBC explicitly, but i guess the last sentence implies that? They really do make this way more complicated then it needs to be!

Good point! There are differences depending on where you look. I suspect the DWR was changed after those fires, but who knows.

This is a screen shot from a recent B/W bill, which is what I quoted:

A friend's recent blue solar only true-up says the same.

Here is what the NEM2 tariff says:

And on PG&E website there is a sample solar bill:

The most recent EV2A tariff includes the wildfire fund charge, but lacks a DWR charge:

 

[swedge]

@Redhill_qik I just was looking up for documentation on the NBC's, and came across this table. It would indicate that for NEM2 residential that NBC's are only metered on 1hr intervals.

That chart is not quite correct.

• NEM1.0 had no NBCs,
• NEM2's credits were at import rates minus NBCs,
• NEM2 NBCs are charged on all imports, not net energy consumed.

I would not trust the "interval" info either. I think the smart meters simply continuously accumulate imports and exports, and report the hourly totals.

A slightly off topic observation: Some of the billing reports the monthly kWh with three decimal places of precision, meaning down to the individual Watt-hour. I don't know where the rounding happens in the billing process, but they show only whole kWh and cents, with no rounding errors totals due to rounding.

 

[holeydonut]

That chart is not quite correct.

• NEM1.0 had no NBCs,
• NEM2's credits were at import rates minus NBCs,
• NEM2 NBCs are charged on all imports, not net energy consumed.

I would not trust the "interval" info either. I think the smart meters simply continuously accumulate imports and exports, and report the hourly totals.

A slightly off topic observation: Some of the billing reports the monthly kWh with three decimal places of precision, meaning down to the individual Watt-hour. I don't know where the rounding happens in the billing process, but they show only whole kWh and cents, with no rounding errors totals due to rounding.

 

[YRide]

That chart is not quite correct.

• NEM1.0 had no NBCs,
• NEM2's credits were at import rates minus NBCs,
• NEM2 NBCs are charged on all imports, not net energy consumed.

I would not trust the "interval" info either. I think the smart meters simply continuously accumulate imports and exports, and report the hourly totals.

A slightly off topic observation: Some of the billing reports the monthly kWh with three decimal places of precision, meaning down to the individual Watt-hour. I don't know where the rounding happens in the billing process, but they show only whole kWh and cents, with no rounding errors totals due to rounding.

It’s on the CPUC website?!?!

Customer Generation

www.cpuc.ca.gov

 

[Redhill_qik]

It’s on the CPUC website?!?!

Customer Generation

www.cpuc.ca.gov

The written and approved NEM2.0 regulations take precedent over a web page. I'm not terribly surprised that this discrepancy exists as wording on NBC metered interval does not explicitly say 5 min, 15 min or 60 min. I think it was done this way to allow some variance for existing installed meter capability.

My NBCs are definitely sub 60 min and likely 5 min intervals based on the variance for net hourly kWh versus billed NBCs kWh during the summer months when my AC is running for about 5 mins at at time.

 

[YRide]

The written and approved NEM2.0 regulations take precedent over a web page. I'm not terribly surprised that this discrepancy exists as wording on NBC metered interval does not explicitly say 5 min, 15 min or 60 min. I think it was done this way to allow some variance for existing installed meter capability.

My NBCs are definitely sub 60 min and likely 5 min intervals based on the variance for net hourly kWh versus billed NBCs kWh during the summer months when my AC is running for about 5 mins at at time.

Do you have the link for the approved NEM2 document?

 

[YRide]

My strategy is not quite this. Close, but still different. Aim is to maximize NEM credits which is up to max 4x PW (54kWh/day, with 0% reserve) and then adding any PV between 3p-9p (very little in winter). PV from 9p-3p should first go to PW/ESS (this is not working great at the moment), and then second go to CoS (one of the three EV is usally plugged in) to ensure no daytime PV goes to grid via GC, eating away at my monthly export limit.

They key I have still to figure out in this "algorithm" is how to force the PW to stop GC at like 75% or 80% so that PV can prioritize taking it to 100% SoC during the day. It's a little strange this setting (max SoC) doesnt exist. Intuitively, it doesn't make sense, but with PG&E (prob one of the biggest consumer of PW/PV and in the backyard of their R&D folks) Tesla should be aware of this monthly max export limit.

Lucky enough I did my install after 1/1/2023 where the FTC limitation on GC no longer applies.

Very weirdly…since this post, my Powerwall has stopped GC to 99-100% SoC each night…and instead only goes up to 83-86% SoC for the last few days.

So Tesla Energy R&D team that is watching this thread… hi , thank you, and if you could tune it a bit more to get my to only 75% via grid charging each morning that would be ideal. PV should be able to top it off during the day.

 

[wwu123]

The written and approved NEM2.0 regulations take precedent over a web page. I'm not terribly surprised that this discrepancy exists as wording on NBC metered interval does not explicitly say 5 min, 15 min or 60 min. I think it was done this way to allow some variance for existing installed meter capability.

My NBCs are definitely sub 60 min and likely 5 min intervals based on the variance for net hourly kWh versus billed NBCs kWh during the summer months when my AC is running for about 5 mins at at time.

Question about net metering calculations (NEM2 in California)

Previous discussion in another thread on the interval duration says it's definitely 15 minutes

.... or 60 minutes...

... apparently it's a subject everyone agrees to disagree...