SDG&E's NBC Calculation for NEM-ST

[sensij]

It has been discussed in other threads, but I want to pull this particular topic into its own.

I had sent in inquiry to SDG&E to explain the 3 kWh NBC charge on my last bill. Here is their response:

Thank you for contacting SDG&E. The electricity the customer uses (consumption) and the electricity the customer generates (generation) is collected on an interval level (15-minute intervals). If the amount of consumption for a 15-minute interval exceeds the amount of generation for the same interval, this net consumption is the amount billed for the NBC charge. This is done for each interval during the billing period.

This doesn't obviously jive with what is on my bill, since I have several hundred kWh of 15 min intervals with import in the "off peak" TOU period that seem to be getting netted out against the intervals with export, and not contributing to the NBC calculation.

I'll respond to them with my specific usage, and see if I can make any progress.

[inspron]

Funny, I was trying to understand their calculation methodology as well right now. I called SDGE several times to better understand their consumption netting period (15 minutes, daily, monthly, or annual) but each time I was told monthly. Although, I am not sure if the CS reps really understand the differences.

NBC negatively impacts your bill. Sounds like they are under billing these charges? Sorry if I misunderstand your situation. If so, why raise the issue to SDGE?

[sensij]

Funny, I was trying to understand their calculation methodology as well right now. I called SDGE several times to better understand their consumption netting period (15 minutes, daily, monthly, or annual) but each time I was told monthly. Although, I am not sure if the CS reps really understand the differences.

NBC negatively impacts your bill. Sounds like they are under billing these charges? Sorry if I misunderstand your situation. If so, why raise the issue to SDGE?

If it is being under-billed, I suspect a billing correction will occur at some point. For the sake of planning, and for improving the accuracy of information shared here in the forum, I'd like to understand what is going on. The CPUC is revisiting this topic, but to the extent I understand, it may only to be looking at whether 15 min or 1 hour is the appropriate interval over which to calculate.

[J.P.M.]

Funny, I was trying to understand their calculation methodology as well right now. I called SDGE several times to better understand their consumption netting period (15 minutes, daily, monthly, or annual) but each time I was told monthly. Although, I am not sure if the CS reps really understand the differences.

NBC negatively impacts your bill. Sounds like they are under billing these charges? Sorry if I misunderstand your situation. If so, why raise the issue to SDGE?

Are you on tiered rates or T.O.U. ? That shouldn't make a difference in the NBC calculation, but if you're on tiered rates, they may have become confused about what your question was.

[J.P.M.]

If it is being under-billed, I suspect a billing correction will occur at some point. For the sake of planning, and for improving the accuracy of information shared here in the forum, I'd like to understand what is going on. The CPUC is revisiting this topic, but to the extent I understand, it may only to be looking at whether 15 min or 1 hour is the appropriate interval over which to calculate.

I'll be calling them as well, but since I'm on tiered, I may get another answer still. Like Charley wrote, and from what you and he provided for documentation, I'm pretty well convinced they have an error, but the C.S. folks may not know it. After looking at several websites that deal with all 3 of the I.O.U's that all seem to be saying the same thing as the spiel you got, and seeing your's and Charlie's bills, I gotta' believe something is screwed up or they're not explaining how they handle NBC thoroughly enough, perhaps for reasons they'd not like to talk about.

Have you checked your SDG & E meter for kWh received and kWh transmitted ? If what everyone is saying, including SDG & E it seems, the number that shows "DEL" is what's delivered from SDG & E and ought to be the quantity that NBC is calculated on.

[sensij]

Have you checked your SDG & E meter for kWh received and kWh transmitted ? If what everyone is saying, including SDG & E it seems, the number that shows "DEL" is what's delivered from SDG & E and ought to be the quantity that NBC is calculated on.

I read that value from the meter using the rainforest Eagle and publish it in my PVOutput data, in the extended value fields. Today, for example, summation delivered started at 1668.723 kWh, and as of 5:25 pm, it reads 1697.972.

Summation received started at 1783.200, and is at 1823.957 at 5:25.

"received", in this case, means energy fed into the grid, while "delivered" means energy consumed.

If I look at my last billing period, 6/26 started at 994.002 for summation delivered, and ended on 7/25 at 1412.515. That is 418 kWh, about the same as the 415 kWh that I calculated when looking at the downloaded 15 min data from SDG&E.

https://pvoutput.org/intraday.jsp?id...07&dt=20170803

[J.P.M.]

I read that value from the meter using the rainforest Eagle and publish it in my PVOutput data, in the extended value fields. Today, for example, summation delivered started at 1668.723 kWh, and as of 5:25 pm, it reads 1697.972.

Summation received started at 1783.200, and is at 1823.957 at 5:25.

"received", in this case, means energy fed into the grid, while "delivered" means energy consumed.

If I look at my last billing period, 6/26 started at 994.002 for summation delivered, and ended on 7/25 at 1412.515. That is 418 kWh, about the same as the 415 kWh that I calculated when looking at the downloaded 15 min data from SDG&E.

https://pvoutput.org/intraday.jsp?id...07&dt=20170803

Yea, the definitions of delivered and received need to be seen and used from the POCO's perspective.

I'd also note that 418-415 = 3 kWh. Look like a familiar NBC number from your last bill ?

Side note, and a bit off topic, but FWIW, I used the delivered and received numbers as a backup/confirmation to my method of calibrating what my Sunpower monitor says the array produced. Turns out by my reckoning, the monitor reads ~ 0.51% high.

[sensij]

I'd also note that 418-415 = 3 kWh. Look like a familiar NBC number from your last bill ?

Yeah, you know that the coincidence of that number is going to drive me nuts until I can find some time to work through all the data and explain it. It is a sickness.

[J.P.M.]

Yeah, you know that the coincidence of that number is going to drive me nuts until I can find some time to work through all the data and explain it. It is a sickness.

Maybe part sickness, part need to get to the bottom and get answers, part ?. For all we, or anyone knows, it might be as simple as something like rounding error in from 15 minute summations of data to 1 hr. same as numerical integration estimates improving in accuracy as the increments gets smaller. But who knows at this time.

[sensij]

Maybe part sickness, part need to get to the bottom and get answers, part ?. For all we, or anyone knows, it might be as simple as something like rounding error in from 15 minute summations of data to 1 hr. same as numerical integration estimates improving in accuracy as the increments gets smaller. But who knows at this time.

This is interesting. The 3 kWh difference comes from the fact that by reading every "delivered" value that the meter reports, I see some additional energy that gets netted out when looking at the 15 min interval in the download from SDG&E's site. The delivered value updates at seemingly random intervals... sometimes less than 5 min between updates, sometimes as many as 20, probably related to a minimum amount of consumption that needs to occur to trigger an update, but I haven't figured out the pattern yet.

So, going from a (call it) 7.5 min average interval to a 15 min interval reduced reported delivered energy by 3 kWh over the month.
Going from a 15 min interval to a 1 hour interval reduced reported delivered energy by another 3 kWh over the month.

I really doubt either of these numbers is related to the 3 kWh of NBC's on the bill, but I'll have to wait until next month to test it and see.

[J.P.M.]

This is interesting. The 3 kWh difference comes from the fact that by reading every "delivered" value that the meter reports, I see some additional energy that gets netted out when looking at the 15 min interval in the download from SDG&E's site. The delivered value updates at seemingly random intervals... sometimes less than 5 min between updates, sometimes as many as 20, probably related to a minimum amount of consumption that needs to occur to trigger an update, but I haven't figured out the pattern yet.

So, going from a (call it) 7.5 min average interval to a 15 min interval reduced reported delivered energy by 3 kWh over the month.
Going from a 15 min interval to a 1 hour interval reduced reported delivered energy by another 3 kWh over the month.

I really doubt either of these numbers is related to the 3 kWh of NBC's on the bill, but I'll have to wait until next month to test it and see.

I think you found were most all of the NBC shows up, but I was kind of thinking something the same as you write, That is, maybe the 3 kWh has something to to do with either when data is snagged during a time interval, or what may be a difference between what gets reported in 1, one hour interval, or what get reported as the sum of 4 consecutive, fifteen minute intervals for the same period. That is different time period methods are feeding the billing. Differences might occur if, for example, a large draw, say a clothes dryer, or an A/C cycles in shorter intervals and/or while PV output is galloping up/down under intermittent cloud cover. One or two of those 15 minute intervals could be a utility import period with the others a net export to the grid. If the summing periods are not the same ( 4 ea. 15 minute vs. 1 ea, 60 minute), the reported numbers could be different between them.

I'll keep scratching my head and cogitating over the weekend.

[CharlieEscCA]

Better to scratch your head than scratch your privates.

Weekend humor. Couldn't help myself. Sorry

[J.P.M.]

Better to scratch your head than scratch your privates.

Weekend humor. Couldn't help myself. Sorry

Nothing to be sorry about.

Sounds like you speak from experience.
One good turn deserves another.

That's actually when some of my most productive output occurs. Helps to clear my sinuses too.

Nicely done.

[CharlieEscCA]

Latest bill is just in, latest craziness in terms of trying to understand NBC. Full details later, but my total monthly consumption (my estimate) was close to 1900 kWh over the 29 billing days. Net usage was 540 kWh from the grid, with much more put into the grid to then draw at a different time (i.e. would expect kWh charged NBC would be greater than the 540 net).

All of my 540 net usage from the grid was covered by my credit (it took $136.20 off my credit, leaving me with $236.50 credit balance -- which again makes me feel like I'll make it through the warm days between now and the end of Oct, i.e. the period with great peak credits, in good shape and likely onto a true-up of only minimum bills due).

But this month showed NBC applied to 44 kWh for an amount of $0.76, and then again the NBC sort of got rolled into the minimum monthly fee instead of being in addition (the bill was $0.18 higher than the days X daily minimum fee, then very small taxes of $0.43 added to that).

The confusion as to how and where NBC's are coming from continues unabated.

[J.P.M.]

Latest bill is just in, latest craziness in terms of trying to understand NBC. Full details later, but my total monthly consumption (my estimate) was close to 1900 kWh over the 29 billing days. Net usage was 540 kWh from the grid, with much more put into the grid to then draw at a different time (i.e. would expect kWh charged NBC would be greater than the 540 net).

All of my 540 net usage from the grid was covered by my credit (it took $136.20 off my credit, leaving me with $236.50 credit balance -- which again makes me feel like I'll make it through the warm days between now and the end of Oct, i.e. the period with great peak credits, in good shape and likely onto a true-up of only minimum bills due).

But this month showed NBC applied to 44 kWh for an amount of $0.76, and then again the NBC sort of got rolled into the minimum monthly fee instead of being in addition (the bill was $0.18 higher than the days X daily minimum fee, then very small taxes of $0.43 added to that).

The confusion as to how and where NBC's are coming from continues unabated.

I'm sure it's a PITA to post, but if you wouldn't mind sharing, what does the bill look like ?

Thanx,

J.P.M.