Understanding sdge excess generation

[ekay]

I am about to purchase a solar system, and I am trying to calculate the ROI based on my usage. I have got hourly data from PVWatts as well as from sdge on my usage. Maybe I am overthinking this. I just don’t trust the numbers the retailers are giving me in terms of saving.

anyways, I do not under how the true-up works given the url below. August and July below are negative??? Does that mean they will charge me for having excess???

https://www.sdge.com/residential/savings-center/solar-power-renewable-energy/net-energy-metering/billing-information/excess-generation

[J.P.M.]

You will not be charged for excess generation, but you won't get the anywhere near full retail rate for an annual excess of generation.

If you're on or will be on T.O.U., any single billing period excess generation your system generates will be carried forward and credited at the hourly rate when the excess was generated. It will then be used over future billing periods. At the end of your account year - 12 billing periods - any remaining excess will carry a per kWh value that's the wholesale rate for excess generation in effect for the billing period(s) when such excess was generated. Or, if your net usage for the year exceeds your generation, you'll be billed for that usage at rates in effect at the time when the energy was used.

There's also a bunch of NBC to figure out if you're estimating bills and PV cost effectiveness.

Suggestion: Get very familiar with how SDG & E billing works. Start at the beginning with understand ing billing schedules and which one of the 20 billing schedules you're on, how many days there are in each billing period for each billing schedule, and know that the # of days/billing period changes every year. Then find what climate zone of 4 you're in and whether or not you're considered "all electric" or not. After all that, go to the published rate schedules, find your tariff and get your daily allowance from the published rate sheets. Multiply that daily allowance by each billing period's # of days (the days seldom match the calendar months, and your billing period closure date will rarely fall on the 1st of the month), multiply that by 1.3 and you'll have your per period tier one allowance which may/may not be important to you depending on which tariff you're planning on using. Then figure out NBC charges which are a relatively small additional per kWh charge for EVERY kWh that comes from SDG & E over any/every 15 minute period, regardless of your excess generation situation.

If all this sounds like a PITA, know that it is and it's meant to be. But doing so will self instruct you on how to get reasonably accurate estimates of per period and annual bills. It'll also point out the need for such detail when you discover how much seemingly small omissions or approximations can throw your numbers off. I found that out the hard way. You want to do it right, know that GIGO applies in spades.

The good part is once done correctly, it only needs a cursory view/review to update schedules and rates and policy changes - which rates BTW, change ~ 4+ times /yr. or so.

Once you get your methodology designed and running running, I found a good way to check/debug mine was to see if it matches existing bills. I did that for several years prior to my PV. Doing so helped me REALLY understand just how involved SDG & E residential billing is. Not conceptually difficult, just involved and convoluted.

A couple of other folks here have done methods somewhat similar to my stuff for SDG & E billing and policy. Maybe they can offer comment or opinion.

Take what you want of the above. Scrap the rest.

Welcome to the neighborhood.

[RichardCullip]

Interesting that the last two months the SDG&E true-up price has gone negative. Not sure what that means other than I'm glad my true-up date wasn't in July or August of this year. The true-up payment for excess generation comes at the end of your 12 month period. If, at the end of 12 months, you have excess generation you will be compensated by the posted true-up price for the month your true-up period ends. As an example, my 12 month true-up bill came due in April of this year and I was compensated at the $0.02838 rate posted for April in the true-up table you linked to.

Hope this helps clarify it for you.

[J.P.M.]

Interesting that the last two months the SDG&E true-up price has gone negative. Not sure what that means other than I'm glad my true-up date wasn't in July or August of this year. The true-up payment for excess generation comes at the end of your 12 month period. If, at the end of 12 months, you have excess generation you will be compensated by the posted true-up price for the month your true-up period ends. As an example, my 12 month true-up bill came due in April of this year and I was compensated at the $0.02838 rate posted for April in the true-up table you linked to.

Hope this helps clarify it for you.

Further to the excess generation reimbursement table from SDG & E showing negative values for 7/2020 and 8/2020:

I just got off a rather lengthy conversation w/what seems to be one of the more knowledgeable folks at SDG & E.

The negative excess reimbursement rates shown in SDG & E's excess generation table MAY be either a typo, or a screw up in communication.
The screw up MAY be that someone (or some thing/policy) changed the way excess generation is handled, and that caused the negative to appear, and someone didn't consider consequences down the line.
The person I spoke with said that recent customer excess generation trueups she's seen for Aug. were all for positive $$ values, but she understands my confusion about the published negative compensation rates.
She claims that she will send an e-mail to the powers that be and get a clarification about any changes that might make negative generation rates possible, or if what was a screwup, or something else.
I was given a timeline of 2-3 days for her response to me.

I'll advise as events develop.

Add: While not a smoking gun or proof of anything, I'd also note that the other 2 CA IOU's both have positive values for excess compensation rates for 0/2020 and 8/2020.

[RichardCullip]

That's going above and beyond J.P.M. I hope @ekay appreciates the effort.

[J.P.M.]

That's going above and beyond J.P.M. I hope @ekay appreciates the effort.

N.B.D. but thank you for the comment.

After all the interactions I've had with them over the years, they seem to know me when I call. I don't have them on speed dial but the number is real familiar.

I only hope ekay gets enough information here and elsewhere to do a thorough enough job on the economics of PV sizing to get what he wants and also find out how how quickly oversizing a system can kill it's cost effectiveness.

[ekay]

I just got off a rather lengthy conversation w/what seems to be one of the more knowledgeable folks at SDG & E.

thank you! Yah it clearly does not make sense for the number to be negative. it definitely looks like the number is trending down though.

I’m on ev-tou5, but per your suggestion I need to evaluate some of the other tous, especially if there is a tiered structure.

I was able to update my calculations with the nbcs, and nem 2.0 rules. It’s definitely eye opening on how complicated solar billing is. I charge my ev at night, but the super off peak periods in the spring help cover that. The real kicker is that i would get a huge off peak credit (worth almost nothing), and incur huge charges during on peak.

I have a southwest and a southeast facing roof. It makes very little sense (and cents) to have easterly facing panels with nem2.0 and on peak times.

[J.P.M.]

thank you! Yah it clearly does not make sense for the number to be negative. it definitely looks like the number is trending down though.

I’m on ev-tou5, but per your suggestion I need to evaluate some of the other tous, especially if there is a tiered structure.

I was able to update my calculations with the nbcs, and nem 2.0 rules. It’s definitely eye opening on how complicated solar billing is. I charge my ev at night, but the super off peak periods in the spring help cover that. The real kicker is that i would get a huge off peak credit (worth almost nothing), and incur huge charges during on peak.

I have a southwest and a southeast facing roof. It makes very little sense (and cents) to have easterly facing panels with nem2.0 and on peak times.

For T.O.U. tariffs and using the PVWatts modeled hourly output option, I figured out that treating the PV system generation and converting that to "revenue" by (output/STC kW)*(hourly rate) = hourly "revenue /installed STC kW could be a helpful tool for siting/orienting and also some help for sizing a system. It's also helpful for seeing the penalties for oversizing as revenue doesn't in crease much as system offsets get > 100 % but system costs go up somewhat proportional to system size.

I'm on tiered rates, but for my neighbors on T.O.U. rates and schedule DR-SES, using current rates, for system sizes that generate < annual usage, for zip 92026, every installed and unshaded STC kW of PV on a roof with orientation of 180 azimuth and a 20 deg. tilt will "generate " (or offset) ~ $480/yr. in "revenue" to offset an electric bill. So, for an unshaded system, a, say, 5 kW system will offset ~ 5*$480 ~ = $2,400/yr. of a T.O.U. generated bill pretty much regardless of annual usage and times of use - again provided annual generation < annual use.

Other example estimates:
A 90 deg. azimuth and 20 deg. tilt will offset ~ $402/yr. per installed STC kW.
A 270 deg. azimuth and a 20 deg. tilt will generate ~ $433/yr. per installed STC kW.
And, FWIW, the array orientation that maximizes revenue per installed STC kW for 92026 and current DR-SES tariff is an azimuth of ~ 200 - 210 deg. and a tilt of ~ 30 deg. for ~ $490/yr per installed STC kW of PV.

The rates for on peak and off peak are about the same for DR-SES as for EV-TOU-5, but the super off peak is lower for EV-TOU-5. That super off peak rate will hurt system "revenue" in the March and April for midday super off peak rates and so annual offset revenue will be less, particularly for more southerly azimuths.

You can easily duplicate my stuff If you're reasonably fluent with spreadsheets and understand/incorporate the minutia of SDG & E billing. It's looks like a PITA, but because of duplication it's a relatively easy task.

I've got all DR-SES "revenues"/STC kW for my zip for azimuths 90 to 270 and 20,30 and 40 deg. tilts.

Take what you want of the above. Scrap the rest.

[DrChaos]

thank you! Yah it clearly does not make sense for the number to be negative. it definitely looks like the number is trending down though.

I’m on ev-tou5, but per your suggestion I need to evaluate some of the other tous, especially if there is a tiered structure.

I was able to update my calculations with the nbcs, and nem 2.0 rules. It’s definitely eye opening on how complicated solar billing is. I charge my ev at night, but the super off peak periods in the spring help cover that. The real kicker is that i would get a huge off peak credit (worth almost nothing), and incur huge charges during on peak.

I'm not sure what you're thinking but you may be too pessimistic about understanding the NEM rules. By your mention of "super off peak periods in the spring help cover that", it sounds like you are under the impression that credits from one TOU period cannot be applied to consumption in other TOU periods. That's not true. We accumulate credit, denominated in $ (but not true actual cash money) regardless of the TOU period which can be used for consumption in any TOU period in the one year period, can be banked and applied in future months, and at the end of the true-up period, will be retroactively applied to consumption that could use it in earlier months.

(pardon if I have misinterpreted you, and excuse the didactic lecture to follow)


I am on EV-TOU2, and also have majority of consumption during super off peak for the EV, at least in non covid years. The super-off-peak periods in the spring from 10am-2pm (used to be 12pm) during prime solar generation hours mean only that we get credited for generation at a lower rate than otherwise during those times. So it's not a benefit to us---it only reflects that the state has a surplus of inexpensive electricity relative to demand during those times on average.

The way to think about it is that there are two different $$ accounts. (I am assuming NEM2.0 the current tariff rules). One is the hard-money true billing account, and two is the NEM credit account, which is funny money, up until the true up period.

You have to pay real hard money fees for minimum charges, non-bypassable charges (these count towards minimum on EVTOU2), taxes, and any monthly base metering fees like that on EV-TOU5. You are credited for CA state programs like the climate credit, and EV credits if any (2 years ago there was a final hurrah of $1000, and now it's gone with SDGE).

Everything else is in the funny money account, where you can get credits, in $, for electricity you generate, at the tariff rates (maybe excluding the NBC part of the rate, I'm not sure) which can be applied during the current bill, and either withdrawn or accumulated for the next month's bill. The bill will tell the balance in the account.

At true up date, the remaining credit, if you have one, will be applied to any previous energy charge (not the hard money charges) during earlier months where you might not have had enough credit to offset. This may not happen either (doesn't happen to me as my yearly date is in late March so I start out by generating at a surplus for months). If you have any credits in this fake money account leftover after that, they disappear entirely into SDGE's virtual pocket. If you have a debit left over, then that flips over to the hard-money billing account once per year and you owe them cash.

Completely separately, there is the kWh-based excess generation credit, if you generated more kWh than you consumed during the year (independent of time of day or season), then you get hard-money credited, but at a minuscule price, like 2-3 cents per kWh. Often financially immaterial.

Because of the big difference in TOU rates, it's possible to have debit or credit on the NEM (funny money account) opposite of the kWh net account.

By the way, the EV-TOU2 rate was recently changed upon direction by the CPUC to have a notably lower super-off-peak price than before, i.e. a higher gap between off-peak & peak vs super-off-peak, and there is a gap in the winter too, which used to be only 1 or 2 cents and now is more like 10. This may change your calculation about EV-TOU5 vs EV-TOU2. Because the $16 (?) a month base fee in EV-TOU5 cannot be offset by any solar generation, and I think you would have to add NBC's on top of that. So for me it would be $16 + maybe $10 more in NBC's per month hard money min plus taxes, whereas EVTOU2 minimum is more like $12. I will generally end up with no more than minimum fees + taxes per month minus climate credit in hard money---I want to minimize hard money outlay first.

But if you drive more, have lower efficiency EV's or multiple household EV's, or are a significant net consumer over the year, EVTOU5 might be right for you.

Yes, the on-peak rates in the summer are punishing, but also remember that they're only 5 hours a day for 5 months a year, and there's significant off-peak generation all years, and the rate gap between off-peak and super-off-peak (EV consumption) is high by design in the EV-TOUx rates.

I'm sure SDGE would love to prohibit solar customers from using them if they had their way. (and deep in their black heart they'd like to kneecap solar and have us buy natural gas electricity from parent Sempra)


PS: the link to the official SDGE rate schedules. I would bookmark this.

https://www.sdge.com/total-electric-rates

[J.P.M.]

I'm not sure what you're thinking but you may be too pessimistic about understanding the NEM rules. By your mention of "super off peak periods in the spring help cover that", it sounds like you are under the impression that credits from one TOU period cannot be applied to consumption in other TOU periods.

PS: the link to the official SDGE rate schedules. I would bookmark this.

https://www.sdge.com/total-electric-rates

I was under the impression that the spring super off peak rates ekay was referring to are the 10 A.M to 2 P.M. periods for March and April. Maybe I'm wrong. Also, per my conversations w/ SDG & E, with respect to T.O.U. tariffs, the rates are for consumption and excess generation.

Also, my understanding of what's the official SDG & E rate schedules can be found on the SDG & E website in the current tariff book for SDG & Ender "Current and Effective Tariffs, Electric Tariff Book".
What you reference is correct as far as it goes but is incomplete if the goal is to accurately estimate the cost of SDG & E electricity.
What you reference does not give all the information necessary to correctly calculate or understand what components go into generating a bill, including:
- NBC charges/kWh amounts.
- Info for the 20 different billing cycles including dates and number of days/billing cycle.
- Billing period daily kWh baseline allowances per climate zone.

The last two are necessary to find a billing period's baseline allowance.

All those items and how they interact/interplay are necessary information to accurately calc or estimate a bill.

I'd suggest going to the source - the tariff book - and working from there.

Ekay: Google: "SDG & E + Current and Effective Tariffs".

[ekay]

DrChaos, very astute of you. I did initially assume the credits were only for the TOU periods. I did eventually figure out that credits come in the form of $$$ every month. I might keep 1 or 2 months of EV-TOU5 to see how the tariff's play out. It takes a PHD to decipher tariff sheet that J.P.M. pointed out. But thanks for those sheets. They are much more informative than the consumer ones linked from the main SDGE website.

Also of note, I noticed that SDGE fixed their excess generation webpage. Thanks J.P.M. for getting them to fix it!

[J.P.M.]

It takes a PHD to decipher tariff sheet that J.P.M. pointed out. But thanks for those sheets. They are much more informative than the consumer ones linked from the main SDGE website.

Also of note, I noticed that SDGE fixed their excess generation webpage. Thanks J.P.M. for getting them to fix it!

Doesn't take a PhD, just common sense, persistence and a few minutes rooting around on their website. As I wrote, not conceptually difficult, just involved and convoluted. Best and perhaps most accurate method I found is to first get the methodology/algorithm down and then use it to back into a few prior bills for different times of the year. Once you get to the $0.01, you'll have an accurate method and more importantly, you'll know a lot more about the ins/outs of POCO residential billing policies than you ever thought possible.

If I got SDG & E to fix anything, at least recently, I was probably only one of several folks who called them. My guess is they would have found it anyway. My observation is they don't make many mistakes when it comes to $$, and when they do, it gets caught and fixed beaucoup pronto.

Back in the day, some of the ladies answering the phones there knew me by voice. I do take some credit for being one of many who harangued them into putting all, or at least some of the old tariff sheets on line when I was looking for historical rate patterns, but that was several years ago and the only thing I can prove I had anything to do with it is coincidence of the timing.