Optimizing NEM2.0 for PG&E EV2-A rate

[YRide]

I think you are right, that grid charging will probably help you.

Much of your PW discharge is due to Exporting Everything, i.e. discharging to the grid. Since grid charging should be done during off-peak, and PW export during peak, that extra export will reduce your NEM Charges, aka Cumulative Energy Charges and Credits. However, if you do so much of this that your cumulative is negative, i.e. a credit balance when true-up comes around, that will be ignored, and you will pay for the NBCs. So, if you do too much grid charging, the benefit goes away but the smaller NBC costs continue.

My theory is that they made this hard to predict so that we can't figure out the optimum approach. Off optimum means more $ for PG&E while the total solar and consumption are gonna be what they're gonna be.

If you can do a year long estimate of your solar production and house/car consumption, you may be able to estimate your true-up. I did this once, using monthly history data including breaking it down into TOU periods, but I don't really recommend it. Back of the envelope probably makes more sense. First you want to know if you are going to be a net generator or are going to owe a bunch at true-up.

In my case, while the NEM and NBC balances matched my projection pretty well, and was expecting a few hundred $ of true-up adjustment. But PG&E surprised me by truing up based on the NBCs even though the NEM balance was larger, adjusting only $67. Good news for me, but if they are going to do the same thing next time, I maybe should reduce the NBC's rather than strive for more NEM credits. This would suggest I do more car charging during the day directly from solar, and less grid charging, even though this latter would mean less peak period export. I am still trying to sort out the implications and cause of my strange NBC true-up, though. We all thought they true up to the largest of the NEM, NBCs, MDCs, and maybe Minimum Energy Charges. But that is not what they did for me, so confusion reigns when true-ups are near zero.

Are you saying the NBC’s are like your AMT taxes? You pay the the worse one to the gov’t, not both cumulatively? I thought those were all additive costs on top of your NEM2 net $ balancing.

It’s kinda a balance of several things (at least) it seems…

1) NEM net $ balancing, where I can use almost my peak generation credits to offset almost 2.15x $ off-peak in summer (1.68x $ in winter)….and not having excess $ credit that is “wasted”

2) minimizing grid pull , thus NBC’s

3) managing max grid export on a monthly basis to make sure you don’t exceed PVWatts total (limit also on your B&W Bill which I can’t find still, I think I read it takes 3-4mo?)…but as I understand PG&E disallows the peak NEM credits first until you fit the max generation for the month..pretty sneaky as I would easily exceed this if I don’t pay attention to grid charging.

So it seems ideal to leave grid charging on, but if Tesla could allow me to set a guaranteed PW SoC for each day, say like 50%, to use grid charge by a certain time. Then let PV fill it up. Then send excess to the grid (or to EV via CoS). So kinda like a CoS + scheduled departure feature for the PW itself.

Btw, hope everyone saw EV-2A rates went up again. Though in theory that is a good thing, more $ for NEM peak credit.

@swedge how do you calculate the NBC’s?

I wanted to refine my pricing table a bit more to take those into account. I might just extend peak from 9p-12a to see if this forces the PW to conserve a little more for planned household usage…but want to make sure the math is at least close.

I can’t see myself ever worrying about MDC’s, I’ll never be close as a net importer.

 

[Redhill_qik]

Are you saying the NBC’s are like your AMT taxes? You pay the the worse one to the gov’t, not both cumulatively? I thought those were all additive costs on top of your NEM2 net $ balancing.

How NBCs are handled at your annual true-up depends on if your TOU energy charges are negative or positive. This is because the NBCs are four of the unbundled components that make up the transmission costs and have already been included in the net energy charges. These four components are Public Purpose Programs (PPP), Nuclear Decommissioning (ND), Wildfire Fund Charge (DWR/WF) and Competition Transition Charge (CTC).

• If your energy charges are $0 or negative then you haven't paid any of these components, so your total NBCs are used.
• If your energy charges are positive then some of the NBCs are included in that total and you owe roughly the NBCs on the net kWh
  • Roughly if you imported 11,000 kWh and exported 5,000 kWh then your NBCs are based the difference or 6,000 kWH
  • There is more complication to this due to changes in NBC costs over the year and prioritizing Peak vs Off-Peak, but the simple method gets you 95% of the way there

 

[YRide]

How NBCs are handled at your annual true-up depends on if your TOU energy charges are negative or positive. This is because the NBCs are four of the unbundled components that make up the transmission costs and have already been included in the net energy charges. These four components are Public Purpose Programs (PPP), Nuclear Decommissioning (ND), Wildfire Fund Charge (DWR/WF) and Competition Transition Charge (CTC).

• If your energy charges are $0 or negative then you haven't paid any of these components, so your total NBCs are used.
• If your energy charges are positive then some of the NBCs are included in that total and you owe roughly the NBCs on the net kWh
  • Roughly if you imported 11,000 kWh and exported 5,000 kWh then your NBCs are based the difference or 6,000 kWH
  • There is more complication to this due to changes in NBC costs over the year and prioritizing Peak vs Off-Peak, but the simple method gets you 95% of the way there

Thanks @Redhill_qik! So does that mean for the current period of EV-2A (until rates adjust again) the NBC’s are:

Peak = 0.02578 + 0.00135 + 0.00030 + 0.00530 = $0.03273 / kWh (Peak, Part Peak and Off-Peak all are the same it appears during this period).

Also, you said on the “NET” amount. Is that right? I was under the impression that NBC’s are calculated on total amount of grid pull, aka “delivered”?

For example…if for an annual period I hypothetically had a net grid import of 11,000 kWh (1000 peak, 3000 part-peak and 7000 off peak) and an export of 6,000 kWh (4000 peak, 1000 partpeak and 1000 offpeak)…

Are my NBC’s either:

A (Net):
0.03273 * (1000 - 4000) +
0.03273 * (3000 - 1000) +
0.03273 * (7000 - 1000) =
0.03273 * 5000 = $163.65

Or B (delivered):
0.03273 * 1000 +
0.03273 * 3000 +
0.03273 * 7000 =
0.03273 * 11000 = $360.73

Since peak, part-peak and off-peak all seem to be the same, I doesn’t have an impact from Net calculations I’m that sense.

But if it was the former (net), then there would be no negative impact for me TOU arbitrage and charge up the powerwalls via the grid (except for the 10% round trip loss “tax”), because the energy I pull from the grid I would place back on it later.

In the latter (NBC based on delivered power) then it disincentives me from excessive grid pull, because I’m paying an extra 3.2 cents per kWh…

If I look at my June bill, was pre-PTO so didn’t do any grid charging, was basically running self powered…0.57MW. So if I napkin math that, it’s 12mo = 6.84MW * 1000 * 0.03273 = $223/yr for NBC.

However, still using import/generated from grid, for July, where I started playing with grid charging, TOU arbitrage, etc…I shot up to 3.6MW * 12mo * 1000 * 0.03273 = $1,413 NBC’s for the year.

So I have to be a little careful with the grid charging. Even the higher amount might make sense depending how I am zeroing our NEM $’s, so need to model that.

 

[swedge]

Are you saying the NBC’s are like your AMT taxes? You pay the the worse one to the gov’t, not both cumulatively?

Right.

I thought those were all additive costs on top of your NEM2 net $ balancing.

No, because the NBC's are included in the monthly Energy Charges or Credits. More on this below.

Thanks @Redhill_qik! So does that mean for the current period of EV-2A (until rates adjust again) the NBC’s are:

Peak = 0.02578 + 0.00135 + 0.00030 + 0.00530 = $0.03273 / kWh (Peak, Part Peak and Off-Peak all are the same it appears during this period).

Also, you said on the “NET” amount. Is that right? I was under the impression that NBC’s are calculated on total amount of grid pull, aka “delivered”?

For example…if for an annual period I hypothetically had a net grid import of 11,000 kWh (1000 peak, 3000 part-peak and 7000 off peak) and an export of 6,000 kWh (4000 peak, 1000 partpeak and 1000 offpeak)…

Are my NBC’s either:

A (Net):
0.03273 * (1000 - 4000) +
0.03273 * (3000 - 1000) +
0.03273 * (7000 - 1000) =
0.03273 * 5000 = $163.65

Or B (delivered):
0.03273 * 1000 +
0.03273 * 3000 +
0.03273 * 7000 =
0.03273 * 11000 = $360.73

Since peak, part-peak and off-peak all seem to be the same, I doesn’t have an impact from Net calculations I’m that sense.

But if it was the former (net), then there would be no negative impact for me TOU arbitrage and charge up the powerwalls via the grid (except for the 10% round trip loss “tax”), because the energy I pull from the grid I would place back on it later.

In the latter (NBC based on delivered power) then it disincentives me from excessive grid pull, because I’m paying an extra 3.2 cents per kWh…

If I look at my June bill, was pre-PTO so didn’t do any grid charging, was basically running self powered…0.57MW. So if I napkin math that, it’s 12mo = 6.84MW * 1000 * 0.03273 = $223/yr for NBC.

However, still using import/generated from grid, for July, where I started playing with grid charging, TOU arbitrage, etc…I shot up to 3.6MW * 12mo * 1000 * 0.03273 = $1,413 NBC’s for the year.

So I have to be a little careful with the grid charging. Even the higher amount might make sense depending how I am zeroing our NEM $’s, so need to model that.

View attachment 964163

NBC's are charged on all imports (which PG&E calls consumption) and are not credited on exports. NBC's are included in the monthly Energy Charges (which they used to call NEM ). Since all the other bundled costs are included in the export credits, at true-up it is possible for those credits to offset the "non-bypassible" NBCs. So, if the cumulative NBC's are larger than the cumulative Energy Charges, you are billed based on the NBC's rather than the Energy Charges. You have already paid the small monthly minimums, so these are deducted from the NBC amount to determine what you still owe.

This all stems from the problem with bundled rates under NEM. Since bills are based on kWh multiplied by the rates, if someone nets out to zero kWh they would pay PG&E nothing. Getting paid noting is something PG&E does not like, so they found different plausible minimums, and charge us the largest of them: minimum monthly charges, NBC's, or Cumulative Energy Charges or Credits (and maybe Minimum Energy Charges, I'm not sure on this one.) (They wanted NEM3 to bill us for the solar we consume ourselves, anything to keep the $$$ coming.)

 

[swedge]

If, over the entire true-up year, you are a net exporter (PG&E call this Net Generator), you will probably have a negative cumulative Energy Charges or Credits, i.e. a net credit. But in this case, your NBC's will still be owed, and will be the basis of your true-up adjustment. Grid charging will make your Energy Charges lower still, more credit, but will also increase you NBC's. No the other hand, the Net Generation Compensation may offset that somewhat, depending on your total imports, your net exports, and the difference between the NBC and net generation compensation rates. h2ofun is in this category, with ample excess generation.

If, instead, you accumulate more Energy Charges than credits, and this total is larger than the NBC's we expect you true-up will be based on the Energy Charges. Like you said, whichever is more is what you pay.

For those of us who do consume more than we produce, the best case would be if NBC's and Energy Charges are less than what we already paid in monthly minimums, i.e. around $120. In this case, the adjustment would be zero. To do this, total NBC's would need to be under $120. At $.032 per kWh, this would mean less than around 3,700 kWh of imports over the year.

There may be some more edge cases, as I found in my recent first NEM2 true-up. But most customers owe a lot, and a few others get net generation compensation as Net Generators.

An explanation of PG&E NEM2 true-up was posted a while back here: NEM-PS Annual True-Up Calculation [PG&E example]

 

[RichardCullip]

If I'm reading these posts correctly I see that PG&E handles the billing differently than SDG&E. Down here in SDG&E territory I am billed for NBCs in addition to the minimum daily charge. The NBCs are now a separate line item charge and are not part of the MDCs anymore.

 

[miimura]

If I'm reading these posts correctly I see that PG&E handles the billing differently than SDG&E. Down here in SDG&E territory I am billed for NBCs in addition to the minimum daily charge. The NBCs are now a separate line item charge and are not part of the MDCs anymore.

I believe you pay the NBCs every month with PG&E (not sure because I'm still on NEM 1 and don't pay them) but you get credit back for MDCs in true-up in most circumstances.

 

[swedge]

If I'm reading these posts correctly I see that PG&E handles the billing differently than SDG&E. Down here in SDG&E territory I am billed for NBCs in addition to the minimum daily charge. The NBCs are now a separate line item charge and are not part of the MDCs anymore.

PG&E are masters of obfuscation. Here is my favorite example, their explanation of my 2021 NEM1 true-up. I was billed $45.09, and here is where they calculated that amount. Note that there are no entries to explain, just numbers:

The document was 11 pages of calculations, many indecipherable. Thankfully I had the .pdf and so was able to search for each number to find where it came from. Oh, and the column labeled Trueup History Amount does not total to the $0.00 shown in the Totals row at the bottom.

It is hard to believe that SDG&E could do this any worse...

 

[swedge]

I believe you pay the NBCs every month with PG&E (not sure because I'm still on NEM 1 and don't pay them) but you get credit back for MDCs in true-up in most circumstances.

Under PG&E's NEM2, NBC's are included in the monthly Energy Charge or Credit, and so are accumulated for the true-up but not paid monthly. NBC's are also tracked separately so that ture-up can assure that they have not been credited away by export credits, NBCs being "non-bypassible". Under NEM3, who knows? That is still being litigated as far as I know.

but you get credit back for MDCs in true-up in most circumstances

I think I know what you meant here, but you don't exactly get credit back for MDCs because they are never paid back. Just like a non-solar account, the MDC's are not a fee, but rather a minimum floor on the monthly bill, which is otherwise based on the kWh's. So, if the kWh charges exceed the minimum, there is no MDC charge. Under NEM, the MDC amount is paid every month, so at true up that portion of the kWh charges has been paid already. If the kWh charges (aka Energy Charges or NEM Charges under NEM1) exceed the MDC, then only the difference is billed as the True-Up Adjustment.

The only real credit, i.e. a credit actually paid out to the customer, is the Net Generation Compensation. This can appear as a $ credit on your true-up. In this case, the Cumulative Energy Charges are typically negative and so ignored, but the NBC's are still positive and so will be charged if they are lager then the MDCs, with the MDC's reducing the amount still owed.

I just had an unusual one-month true up where this happened. The True-Up Adjustment was $5.71, the difference between the $16.99 of NBCs and the $11.28 of Minimum monthly. This was offset somewhat by the $4 of Net Surplus Compensation.

As for why they did a true-up for only one month, that is whole other story.

 

[miimura]

Under PG&E's NEM2, NBC's are included in the monthly Energy Charge or Credit, and so are accumulated for the true-up but not paid monthly. NBC's are also tracked separately so that ture-up can assure that they have not been credited away by export credits, NBCs being "non-bypassible". Under NEM3, who knows? That is still being litigated as far as I know.

I think I know what you meant here, but you don't exactly get credit back for MDCs because they are never paid back. Just like a non-solar account, the MDC's are not a fee, but rather a minimum floor on the monthly bill, which is otherwise based on the kWh's. So, if the kWh charges exceed the minimum, there is no MDC charge. Under NEM, the MDC amount is paid every month, so at true up that portion of the kWh charges has been paid already. If the kWh charges (aka Energy Charges or NEM Charges under NEM1) exceed the MDC, then only the difference is billed as the True-Up Adjustment.

The only real credit, i.e. a credit actually paid out to the customer, is the Net Generation Compensation. This can appear as a $ credit on your true-up. In this case, the Cumulative Energy Charges are typically negative and so ignored, but the NBC's are still positive and so will be charged if they are lager then the MDCs, with the MDC's reducing the amount still owed.

I just had an unusual one-month true up where this happened. The True-Up Adjustment was $5.71, the difference between the $16.99 of NBCs and the $11.28 of Minimum monthly. This was offset somewhat by the $4 of Net Surplus Compensation.

View attachment 964361

As for why they did a true-up for only one month, that is whole other story.

I should have been more clear in my statement. You will never get MDCs back on their own. As you showed above, if your situation results in your true-up billing being based on NBCs, you will be credited for the MDCs against the NBCs that you owe. That is what I meant.

If your true-up has a Net Energy Charge that is higher than the NBCs, then you will be billed for the Net Energy charge and not the NBCs and you will get credit for the MDCs already paid.

 

[swedge]

If your true-up has a Net Energy Charge that is higher than the NBCs, then you will be billed for the Net Energy charge and not the NBCs and you will get credit for the MDCs already paid.

This was my understanding too. That is until my June NEM2 true-up came in with Net Energy Charge higher than the NBCs, but the true-up adjustment was billed for the NBCs (minus the MDCs), not the Net Energy Charges. It is still not clear to me why PG&E did that. Nor do I know if that was just a mistake, or just an edge case of some sort. We discussed this in another thread: PG&E NEM2PS True-Up Calculation?

 

[swedge]

Sorry, yes, this is what I meant. As an overall net consumer of kWh on an annual basis (3x EV vs only 10.8kW PV)…I’m thinking I can substantially equalize that kWH imbalance toward $ parity leveraging NEM2 benefits from time shifting my PV + using grid charging to cover my usage deficit during peak and part-peak. Basically I should have the full usage of the 4x PW’s (well, 95% of them, 51.3kWh) to generate peak credits, while ensuring I take no peak or part-peak imports. So I require GC to offset house & EV loads during those two windows (technically I shouldn’t have EV loads then). Ideally, PW would only GC just enough to allow PV during the day to get it to 100% SoC, but it’s going all the way with GC in early AM, so I’m accruing more NBC then I want at the moment.

I'm posting this into your thread to try and keep the discussion mostly in one place.

I think you are on the same track as I am, using EE and GC to leverage your solar and PW to reduce, but not eliminate your eventual true-up adjustment. My full year true-up adjustment was $67, and was based on NBC's. You situation is quite different, but if you manage to come close to this, bravo!

Your monthly B&W detail bills will (when they eventually become available) show your Energy Credits and NBCs history for each month and the to-day cumulative, so you can see how you are doing and so as not to be too suprised by the true-up when it rolls around next year. I do seem to recall a substantial and annoying delay in those detailed bills after my PW PTO. Seems like they could guess at the monthly minimum for your blue bill, counting days probably being within PG&E's capabilities.
;-). In any case, if you'd like a preview of what they look like, PM me your email if you'd like a copy of one of mine.

I agree that your PW doing all that grid charging is not optimum. Play around with the settings to see if you can figure out why it is doing that. With GC off it should not. With EE off, it probably should not need to either. Messing with the schedule should change the discharge behavior too, such as setting peak to run from 3 to midnight without EE should make it cover your house load for the entire period.

So at this point you have a couple things to get under control: those solar drop outs and the midnight grid charging.

 

[YRide]

I'm posting this into your thread to try and keep the discussion mostly in one place.

I think you are on the same track as I am, using EE and GC to leverage your solar and PW to reduce, but not eliminate your eventual true-up adjustment. My full year true-up adjustment was $67, and was based on NBC's. You situation is quite different, but if you manage to come close to this, bravo!

Your monthly B&W detail bills will (when they eventually become available) show your Energy Credits and NBCs history for each month and the to-day cumulative, so you can see how you are doing and so as not to be too suprised by the true-up when it rolls around next year. I do seem to recall a substantial and annoying delay in those detailed bills after my PW PTO. Seems like they could guess at the monthly minimum for your blue bill, counting days probably being within PG&E's capabilities.
;-). In any case, if you'd like a preview of what they look like, PM me your email if you'd like a copy of one of mine.

I agree that your PW doing all that grid charging is not optimum. Play around with the settings to see if you can figure out why it is doing that. With GC off it should not. With EE off, it probably should not need to either. Messing with the schedule should change the discharge behavior too, such as setting peak to run from 3 to midnight without EE should make it cover your house load for the entire period.

So at this point you have a couple things to get under control: those solar drop outs and the midnight grid charging.

Seeing as my bills were $800+/mo prior to installing PV/ESS, I will definitely take a true up in that realm! Obviously it will be more with all the import, but still way less then where things were going.

I did confirm with GC off it does not import.

But EE is more important (valuable) to me then reducing the extra NBC’s by doing a little too much GC.

My next test on the GC to see if I can get it to not go to 100% SoC early each AM…is to set the buy prices for peak and part-peak to the same…so in theory it should now see the entire window from 3p-12a as a bad time to import. I guess this should more effect the import for home load I was seeing at 830p and then from 9-12a. And so I’ll have less grid import then.

Maybe I’ll wait a few days / week to see if it’s adjusts the early AM PW charging.

It may be that the algorithm just doesn’t understand the negative impact of NBC, so it would naturally think import as much as possible off-peak, because I could the export a full PW + all the solar on peak/PP.

Tesla is coming (rescheduled early to 8/31) for the inverter issue. Let’s see how that goes.

Btw, should be really interesting when I get those first two B&W…June and July were wildly different (pre and post PTO)

 

[swedge]

Here is another trick to try. Turn of grid charging one evening, and turn it back on after the solar has mostly recharged the PW, but in time for the gird to bring it up to 100%. Maybe 1 or 2 pm.

If that makes it behave the way you want, and you don't find a simpler fix, it might be possible to automate it. Do you speak Python by any chance? There may be third party apps or services to fine tune PW behavior.

The Tesla App talks to Tesla's servers, not the PW (gateway to be precise) directly. PW then gets it settings from Tesla's servers over your home network. But the software interface between PW and the servers has been at least partially documented, and so third parties and owner's own software can communicate with the server to make changes and read PW status.

Before spelunking that labyrinth though, I still suggest you first figure out why your PW thinks it needs to grid change so much before sun up. There may be a more practical solution once you understand what your PW is thinking.

For example, if you turn off Export Everything, does it still grid charge so much? Or, if you don't car charge for a few days? Or both? You have plenty of solar and PW to cover the house, I think. So maybe all you need is a way to hide the car charging from the PWs, which may be easier than rewiring them. On the other hand, if it is all the Exporting that is confusing it, yet a different strategy might work.

My sense is that it grid charges to the extent it thinks it won't have enough solar to fill up. And it tries to do this during low price times. But it has to decide before the rate change, so it has to estimate your upcoming use and your solar production. Mine appears to even take weather forecasts into consideration, by the way. So even a bad zip code in the configuration could be a culprit, who knows?

My point is that there are many possible solution paths, and the sane approach is to experiment with what is easy to control to see if you can understand why it does what it does.

I found screen shots (all views) of the graphs very helpful, but they don't show what the settings are, so you have to take notes, or screen shots of those as well. Science 1A, keep a lab book.

I did what you are trying. I doubled my annual consumption by adding an EV. I estimated that with EE and GC I needed only ~60% more solar to nearly cover the doubled total, so that is what I added. It meant loosing my NEM1 grandfathering, sigh, but I estimated that trade-off to be advantageous. My $67 true-up is the proof it worked. But I am wishing I had got 2 PW's when I had the chance, and am jonesing for heat pumps and still more solar to run those. Budgets have me dead stopped, though, sigh.

Once you get your inverter fixed and this weird grid charging issue under control, I think you'll have done all you can with what you've got. And the solar is what saves the big bucks. All this other fine tuning is icing on the cake. Like h2ofun says, if you have enough solar, all this other stuff doesn't matter.

 

[Redhill_qik]

Thanks @Redhill_qik! Also, you said on the “NET” amount. Is that right? I was under the impression that NBC’s are calculated on total amount of grid pull, aka “delivered”?

This is definitely confusing, but both are correct depending on what you are looking at

• NBCs are owed on all kWh that is imported/delivered and are reported in this way
• NBCs are also included in the Energy Charges and are not explicitly reported

You don't have to pay these amounts twice, so you remove the NBCs that are included in the Energy Charges from the total accumulated NBCs.

Examples:

• Energy Charges are negative, you have paid no NBCs so the annual true-up NBCs is 100% of the NBC total
• Energy Charges are positive and you exported 0 kWh (self-powered/solar died), all of your NBCs are included in the Energy Charges and you owe no additional NBCs
• Energy Charges are positive and you export #### kWh, some of your NBCs are included in the Energy Charges and you owe roughly net kWH * NBC rate

For example…if for an annual period I hypothetically had a net grid import of 11,000 kWh (1000 peak, 3000 part-peak and 7000 off peak) and an export of 6,000 kWh (4000 peak, 1000 partpeak and 1000 offpeak)…

Are my NBC’s either:

A (Net):
0.03273 * (1000 - 4000) +
0.03273 * (3000 - 1000) +
0.03273 * (7000 - 1000) =
0.03273 * 5000 = $163.65

This is the one that is roughly correct as what you owe as NBCs in addition to NBCs that are already part of the Energy Charges.

 

[Redhill_qik]

I should have been more clear in my statement. You will never get MDCs back on their own.

Right, MDCs are Minimum Daily Charges and you can never pay less than this. Well except for people that are net producers in which case the net surplus compensation may exceed the annual MDCs that were paid, but that is kind of a different calculation.

As you showed above, if your situation results in your true-up billing being based on NBCs, you will be credited for the MDCs against the NBCs that you owe. That is what I meant.

Right, in the posted case the Energy Charges were negative and the full NBC amount applies.

If your true-up has a Net Energy Charge that is higher than the NBCs, then you will be billed for the Net Energy charge and not the NBCs and you will get credit for the MDCs already paid.

This is not correct or is only correct the very rare case that 0 kWh was exported. The Energy Charge total includes some of the NBCs that are owed, but not all of them. You owe the difference between the total NBCs and the NBCs amounts that are included in the Energy Charge total in addition to the Energy Charge total.

 

[swedge]

You owe the difference between the total NBCs and the NBCs amounts that are included in the Energy Charge total in addition to the Energy Charge total.

I assume we are talking about PG&E NEM here. I understand that other utilities do this differently.

Looking several detailed bills, mine and friends', all of the NBC's are included in the Energy Charges. (example below) If you look at the Rate Application in the monthly bill, you will see that the NBC components are charged on the imported kWh, but are not credited on the exported kWh. The total of those NBC components is logged in the monthly summary and included in the Cumulative NBCs.

So, in the case of the energy charges being larger than the NBCs and the MDC, because the Cumulative Energy Charges already include all of the NBCs, no NBCs are added to the true-up adjustment. The true up adjustment will be the Cumulative Energy Charges minus the MDCs which have already been paid.

I believe that miimura is correct here:

If your true-up has a Net Energy Charge that is higher than the NBCs, then you will be billed for the Net Energy charge and not the NBCs and you will get credit for the MDCs already paid.

Example
This is from my Feb detailed bill, just the off-peak portion of the rate application. As you can see at the bottom (labled GEN), Imports were 541 kWh, Exports -98 kWh, so the net was 443 kWh. You can see that the four underlined NBC components charged for the Exports, while the others were charged for the net.

 

[swedge]

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

Thanks! Do you still use allow the powerwall to discharge during on peak in the winter on E-TOU-C? The price differential is just 1-2 percentages more than the ~10% roundtrip efficiency. I'm thinking of switching from EV2-A back to E-TOU-C as it looks like I am a net exporter either way, and...

teslamotorsclub.com

YRide,

Even when you do get your first monthly detail, it won't say much about what happens in the eventual true-up. If you'd like to look at an example, send me your email in a private message and I'll send a .pdf of my recent NEM2 true-up.

p.s. again this was a response to a posting in a different thread, more appropriate here I think.

 

[Redhill_qik]

I assume we are talking about PG&E NEM here. I understand that other utilities do this differently.

Looking several detailed bills, mine and friends', all of the NBC's are included in the Energy Charges. (example below) If you look at the Rate Application in the monthly bill, you will see that the NBC components are charged on the imported kWh, but are not credited on the exported kWh. The total of those NBC components is logged in the monthly summary and included in the Cumulative NBCs.

So, in the case of the energy charges being larger than the NBCs and the MDC, because the Cumulative Energy Charges already include all of the NBCs, no NBCs are added to the true-up adjustment. The true up adjustment will be the Cumulative Energy Charges minus the MDCs which have already been paid.

I believe that miimura is correct here:

After looking over some other examples, I think that I am wrong on this and that the Energy Charges are inclusive of the accumulated NBCs. I wish I could go back and amend prior posts, but this will have to do.

 

[YRide]

Here is another trick to try. Turn of grid charging one evening, and turn it back on after the solar has mostly recharged the PW, but in time for the gird to bring it up to 100%. Maybe 1 or 2 pm.

If that makes it behave the way you want, and you don't find a simpler fix, it might be possible to automate it. Do you speak Python by any chance? There may be third party apps or services to fine tune PW behavior.

The Tesla App talks to Tesla's servers, not the PW (gateway to be precise) directly. PW then gets it settings from Tesla's servers over your home network. But the software interface between PW and the servers has been at least partially documented, and so third parties and owner's own software can communicate with the server to make changes and read PW status.

Before spelunking that labyrinth though, I still suggest you first figure out why your PW thinks it needs to grid change so much before sun up. There may be a more practical solution once you understand what your PW is thinking.

For example, if you turn off Export Everything, does it still grid charge so much? Or, if you don't car charge for a few days? Or both? You have plenty of solar and PW to cover the house, I think. So maybe all you need is a way to hide the car charging from the PWs, which may be easier than rewiring them. On the other hand, if it is all the Exporting that is confusing it, yet a different strategy might work.

My sense is that it grid charges to the extent it thinks it won't have enough solar to fill up. And it tries to do this during low price times. But it has to decide before the rate change, so it has to estimate your upcoming use and your solar production. Mine appears to even take weather forecasts into consideration, by the way. So even a bad zip code in the configuration could be a culprit, who knows?

My point is that there are many possible solution paths, and the sane approach is to experiment with what is easy to control to see if you can understand why it does what it does.

I found screen shots (all views) of the graphs very helpful, but they don't show what the settings are, so you have to take notes, or screen shots of those as well. Science 1A, keep a lab book.

I did what you are trying. I doubled my annual consumption by adding an EV. I estimated that with EE and GC I needed only ~60% more solar to nearly cover the doubled total, so that is what I added. It meant loosing my NEM1 grandfathering, sigh, but I estimated that trade-off to be advantageous. My $67 true-up is the proof it worked. But I am wishing I had got 2 PW's when I had the chance, and am jonesing for heat pumps and still more solar to run those. Budgets have me dead stopped, though, sigh.

Once you get your inverter fixed and this weird grid charging issue under control, I think you'll have done all you can with what you've got. And the solar is what saves the big bucks. All this other fine tuning is icing on the cake. Like h2ofun says, if you have enough solar, all this other stuff doesn't matter.

First experiment underway…

I’ve set the buy rates in summer part-peak == peak, but left the sell rates as they were (reduced by NBC + 10% RT loss), favoring peak sell.

This seems to have worked *mostly* as expected.

The PW’s did not dump full charge to 5% reserve at 4p. Rather, had a moderate export and somehow anticipated the AC on all night until hitting reserve right at 12a. It was a big jagged export, normally it’s 11.9kW flat, increasing PW as PV declines.

I think technically speaking I lost value, in that some of my export was at part peak. But it required less import then. But it behaved per the table of prices I provided it. Though it should stop know selling in peak is 10c/kWh better, I would have thought it would dump more because buy back rates were technically the same.

However, this still had only minor material impact on GC at midnight. Still went to 86% SoC right away. A bit weird, but in the AM the timed departure pulled from the PW, not from grid, so SoC actually dropped. Then through a combo of GC + PV went to 100% SoC before noon. Worth noting, it was oddly cloudy today I’m Bay Area (craziest sunset last night too with abnormal clouds).

Also, it’s back to sustained 11.9kW export starting at 4p. Let’s see how this plans for the 3p-12a window with new settings.

Anyways, final (3rd) EV just got CoS feature today…so gonna see how those all play with the system. Will let PW algorithm try to stay in this setup for a week or so yo see if it adapts.

Hopefully Tesla will fix the inverter on 8/31. Unfortunately my past experiences with services calls are it’s always the wrong person, doesn’t have the right part, some kinda follow up, etc. I wish the would call before visit and pre-op it, but let’s see.