SDG&E EV rates - EV-TOU-5 vs EV-TOU-2?

[DrChaos]

Back in April we got the PTO from SDG&E to start up our newly installed solar panels. It's a 4kW (DC) system with 12 LG335 panels feeding a SolarEdge Inverter. We are very pleased with the first 6 months of operation. The system design was over-sized for our current electric use since I was anticipating adding an EV to our demand early next year. Budget constraints require waiting a bit for the new car.

In the mean time I've been brushing up on my spreadsheet skills (used to build big oil production forecasting spreadsheets for Chevron in my previous life) and am attempting to model the impact to our SDG&E bills once we start charging our new EV. Which, if you are curious, will most likely be a Kia Niro PHEV. I'm now at the stage where I need to proof-check my calculations. I would love t have something to compare my results with to see if I've got something seriously wrong or if I'm in the right neighborhood of the answer. I am wondering if there's a tool available that lets me plug in my anticipated net energy values for On-Peak, Off-Peak, Super-Off Peak periods and NBCs. and then generate what the anticipated SDG&E charges under the EV-TOU-5 and EV-TOU-2 rate schedules might be?

My spreadsheet calculations are currently duplicating our monthly SDG&E bills to within a penny or two so I feel like I can model our electric use and resulting bill under our current TOU-DR rate schedule. It did take me a couple of billing cycles to work out how SDG&E calculates the individual line items in their bill. Not an easy task as those of you that have tried it can probably attest to.

Thanks in advance.

Have you been able to successfully replicate the SDG&E billing on a rate-plan that involves both tiers and time-of-use? I cannot do so for TOU-DR-P. I can't figure out the baseline credit---even knowing the baseline credit per kWh I can't figure out how the # of kWh to base the credit on is computed. I.e. I have X in total consumption kWh per month in super-off peak and peak billing periods and -Y in net generation. I do not get X * the tier kWh tier credit (it's less) or any combination of X and Y that I can figure out.

Back to the EV & solar, this is also my situation. Here's what I think: if you have significant EV and total consumption then EV-TOU-5 is a no-brainer. But there is a minimum hard-money lower limit of $16 plus the non-bypassable charges (depends on usage, but maybe $7-10?) per month that you will owe out of pocket regardless of generation.

EV-TOU-5 has an enormous rate gap between the off-peak (when solar generates) and the super-off peak (when you charge your car), and this gap extends all year (though March & April some prime solar hours are on super-off-peak). You can earn significant $ credit because of time arbitrage even if kWh generation and consumption is balanced. If you don't care about the ecological footprint you could use this to enjoy extra AC in the summer, particularly before 4pm.

If your consumption is lower or production higher then I recommend looking at TOU-DR-P, which is what I'm on, if you can manage the critical "reduce your use" days. There were none in 2019 summer and 3 or 4 in 2018 summer. They will always be very hot weekdays and charge an extortionate rate penalty $1.16/kWh for consumption during these hours, 2 to 6pm. But if you can be out of the house and consume almost nothing, these can give you great credit from solar generation which is feasible at those hours, like $10-$15 a RYU day. Furthermore, in the summer outside those RYU days, the 4-9 pm on-peak is only 1c more than offpeak, so you can feel OK about using a fan or AC at 8pm. EV-TOU-* is a large on-peak vs off-peak differential.



The main advantage otherwise of TOU-DR-P is (a) a good gap of about 10c between off-peak solar generation time and super off peak EV consumption during the 5 summer months. (b) lower real-money monthly charges, there's about $11 in a minimum bill, but unlike EV-TOU-5, the non-by-passable charges count towards that minimum. So excluding the climate credit I see TOU-DR-P at a hard lower limit cost of $125 per year and EV-TOU-5 at about $250-$300 per year, but you'll get lots of credit $$ on EV-TOU-5. All other rate plans I saw (https://www.sdge.com/total-electric-rates) had only about 6c gap of off-peak over super-off peak.

I think these two rate plans are best for solar + EV users. I'm on TOU-DR-P. For you I might start with that with the EV for a year, and if @ the true-up yearly the hard money cost is more than $250 I would switch to EV-TOU-5. How much do you consume now without EV?

[J.P.M.]

Thank you for your detailed explanation. You've given me quite a bit to digest. Some of which I've worked thru already but some new good stuff here. I've been concentrating on figuring out SDG&E billing process and have yet to tackle forecasting solar generation. Thanks for the hint on using PVWatts hourly data. That's a new source of data for me as I've only used monthly data up to now. Hourly data would be a much more accurate way to parse out future solar generation into the TOU of periods.

On a side note, at this point in time I just realized that I don't need an online tool to check the accuracy of my SDG&E billing model. I just need some kind person to share a few values from a recent, preferably in 2019, monthly SDG&E bill using either the EV-TOU-5 or EV-TOU-2 rates. I would need net energy for the On-Peak, Off-Peak and Super-Off Peak period plus the NBC total for the month and the resulting bill total.

For any use my stuff may have, you're most welcome.

Using hourly or more granular data may look like a PITA and lengthy task, and it can be, but not necessarily because of the size of the spreadsheet. Rather, it's the necessary details and stuff that one mostly needs to find mostly on their own with most of the discovery by trial/error rather than instruction from informed and knowledgeable sources.

As I wrote, to figure out the SDG & E billing process, I've found most all of what's required in the sources I mentioned. Download and study them and my bet is you'll be well along the way to reaching your stated goals. Perhaps some helpful soul(s) can provide copies of billing usage.

I'd respectfully suggest you'll need a spreadsheet that accounts for most or all of the details I mentioned to get a match between the spreadsheet and a bill, including the billing schedule and climate zone data as well as whether or not the supplied data is for a std. or an all electric customer. As I wrote, the devil is in the details. What you don't know or don't account for will screw up the results.

[RichardCullip]

Thank you for your detailed explanation. You've given me quite a bit to digest. Some of which I've worked thru already but some new good stuff here. I've been concentrating on figuring out SDG&E billing process and have yet to tackle forecasting solar generation. Thanks for the hint on using PVWatts hourly data. That's a new source of data for me as I've only used monthly data up to now. Hourly data would be a much more accurate way to parse out future solar generation into the TOU of periods.

On a side note, at this point in time I just realized that I don't need an online tool to check the accuracy of my SDG&E billing model. I just need some kind person to share a few values from a recent, preferably in 2019, monthly SDG&E bill using either the EV-TOU-5 or EV-TOU-2 rates. I would need net energy for the On-Peak, Off-Peak and Super-Off Peak period plus the NBC total for the month and the resulting bill total.

[J.P.M.]

One short answer to your question is there may be something similar to what you're looking for but I don't know of one on the open market or in the open literature.

Since I was also looking for what you describe and came up empty, I did it myself. Very broadly and very briefly, the general approach/method I've done/found that works for me is to first find all the information necessary to correctly determine what SDG & E does to get a per kWh price for every kWh they charge me for at any time and in any quantity. Then, I repeat the quest and get a per kWh price they pay me for what I send back to them. Then, I subtract one from the other while keeping in mind things like NBC and such that can be confusing. The devil is in the details.

What's below is a brief description of some on the details of the way oversimplified description given above..
It's lengthy but offered on a take it for what it's worth or ignore it basis.

Still reading ? Take a deep breath.

I've done what sounds a lot of what sounds like you're describing/looking for. I first did it ~ 2006 after I moved into this house for the old and still used DR tiered rates and after some effort, I got to the penny for all the bills I replicated. I then added solar generation from spreadsheets and programming for PV generation that's similar to what you'll get from SAM or other generation models like PVWatts. That spreadsheet for the generation/billing/use under sch. DR was/is ~ 100 MB and generates a bunch of array and economic parameters besides a net bill.

I'm not a spreadsheet guru (which may be a giveaway of how simple the spreadsheet portion of the task is), but that was indeed the easier portion of the task.

To get what I think you're describing/asking about, I used 8,760+ row spreadsheets. That sounds daunting, but for rates, it starts with what's mostly a copy job of 2 different 168 hour weeks - one for summer, one for winter, and the March - April super off peak time period adjustments. Then those weeks are copied a bunch of times.

Note: If/Before you go further, download your SDG & E pre PV green button usage - the stuff in 15 minute increments. You'll need it for total future usage estimates. Using pre PV acquisition usage is easier than using post PV acquisition green button data which needs to have PV generation added to get total usage. Using post PV acquisition green button data is certainly possible but more PITA steps are required to add solar monitor data to post PV PTO usage data (and any or either way, they'll both be estimates of future use. SDG & E 15 minute data only goes back 15 months for reasons I couldn't get a good answer for. The prior PV acquisition usage data is mostly helpful to get a handle on your usage patterns as well as total usage, particularly for any T.O.U. billing estimates.

A bigger PITA for me was how to compress (8,760*4) 15 minute usage data cells to 8,760 hourly usage cells, but as I wrote, I'm not a spreadsheet guru. Note too that combing 4 ea. 15 minute intervals into 1 hr. intervals will cost some accuracy for NBC charge calculations. See below for some details of why. For my data, the error from combining the 15 minute data into 1 hr. data was small, and since I'm on NEM 1.0 and also not going on a tiered rate anytime soon, if ever, I live with that error. See below for some details of NBC.

I'd guess a bigger PITA, and perhaps the biggest source of error for you may be learning all the stuff that SDG & E does that will affect a how a per kWh charge is generated and how a PV generated kWh is valued by the POCO.

All this isn't conceptually difficult. It's just that there are a lot of little hooks with most of those hooks most likely linked to one another in ways not easy to grasp or apparent, mostly because SDG & E - like most POCO's - has nothing to gain by making it user friendly or easy to understand.

But, believe it or not, and fortunately, most of the information that's needed can be gleaned from looking at and studying the effective tariff sheets. Google "SDG & E + effective tariffs". Also, Google "SDG & E biling cycle schedule".

To investigate and estimate what any SDG & E tariff will do to my, or your, electric bill, needed info found on the tariff sheets includes, but is not necessarily limited to:
- Rates, including total rate and rate components of the total (the rate components or some of them, mostly for NBC adjustments).
- Minimum daily charge.
- For T.O.U. tariffs, times of peak, semi, off and super off peak rates.
- For straight tiered rates (sch. DR) and T.O.U. tariffs that have tiered rates laid over them, daily baseline allowances for whichever one the 4 climate zones you live in for summer/winter as well as for homes with gas service or all electric (no gas service).
The daily baseline allowance is where the billing period baseline allowance comes from. Billing period baseline allowance = (daily baseline allowance) * (number of days in a period). The billing period baseline allowance is used for the old tiered schedules and all the tiered T.O.U. schedules. At this time tier one usage for any billing period is 130 % of the billing period baseline allowance.
The min. daily charge is $120/yr/365 days/yr. That's why the min. billing period charge is close to but not equal to $10/billing period but instead ($120/365days/yr.)*(# of billing days/billing cycle).

Study the rate tariff sheets until you're comfortable with all the terms and how and in what ways all the components can and will interact with one another and other things to influence the price of a kWh going in either direction.

You will also need the billing schedule. It has a large influence on a bill. Some things to know about billing schedule(s):

- There are 31 different billing cycles.
- Your billing cycle number is on p.2 of your bill near the top to the right of your meter number.
- Each cycle has 12 billing periods. All billing periods are about 30 days, but the number of days doesn't have any relation to the month lengths they cover or any relation to different schedules. Also, the # of billing days and the read date changes for each schedule every year. Aside: I ran an analysis and the only seasonal or annul pattern I might be able to see was a slightly higher number of summer billing periods that had less than the average # of days (which means lower monthly tier one sizes when rates are higher and so (big surprise) slightly more revenue for the POCO.
- As a practical matter, I picked one year (2006) and used that billing cycle schedule and billing closing dates for all subsequent calcs. Life is not perfect and all this B.S. is nothing if not about estimates. 2006 started on a Sunday, and that made things a bit easier for me for the 168 hour week calcs. You'll understand if/when you get going with all this.

That's for calculating/generating/back calculating a bill without any net metering involved. FWIW, I checked/debugged my billing algorithm for tiered rates by checking the results against my prior to PV bills with the tariff schedules in effect for the checked periods and found that to be the best/fastest way for me to catch errors in my calcing logic.

Another thing to keep in mind: All the tariffs change several times/yr, or more. Stay on top of the rates and keep the old rates for reference if you want accuracy for current bills.

To generate 12 annual bills = an annual cost of electricity from SDG & E for an account that has a NEM 2.0 PV system, I'd suggest you use the PVWatts model for system generation and use the hourly output option for PV generation data.
See the PVWatts model and read all the help info screens for best use of that model.

A simplified overview: What I do/did with a spreadsheet to get an annual bill or a bill for any billing period linked to a PV system: For each hour in a year, subtract [(a system's hourly generation, either actual or modeled) * (the per kWh rate charged for that specific hour as calc'ed)] from [(some actual or calculated or estimated hourly total usage)*(the per kWh rate I calculate for that specified hour.]
Then, I do that 8,760 times, sum the totals for each billing period and for the total year. Note that the credited rate needs to be reduced for NBC. A bit more on that below.

That method will work for DR-SES calc'ed bills. For other T.O.U. rates that have a tier scheme laid over them, the billing periods come into play as additional adjustments to the hourly rates both charged and credited with both reduced for all tier one usage in a billing period.

Big note: SDG & E uses civil time for all data. That is, all the times from them are local and daylight saving time if applicable. Most models, including PVWatts DO NOT account for D.S.T.
I found it easier to adjust the PVWatts or other PV modeling data to D.S.T. when I transferred it to the billing spreadsheet, but other's may find it easier to go the other way. Either way, not doing the DST adjustment will make any results FUBAR.

On NBC: It's charged on every kWh that SDG & E sends to your residence. That's not every NET kWh over a day, billing period or year. It's EVERY kWh as determined in 15 minute increments. So, as a brief example, if, for any one 15 minute time increment, you use, say, 3 kWh and your PV system produces 1 kWh, you will draw 3 -1 = 2 kWh from the POCO. Now, say the next 15 minute increment has you using 1 kWh and your PV system producing 3 kWh for a net total of 3 - 1 = 2 kWh sent to the POCO. The net for the two 15 minute periods is 2 (- 2) = zero net draw from the POCO for the two 15 minute periods, and that's how the billing would be without NBC. However, WITH NBC, you're charged for every net kWh the POCO sends you over every 15 minute period with a reset every 15 minutes. So, for the example, the first 15 minute period you'd be charged NBC for 2 kWh. For the second 15 minute period you'd be charged no NBC because you didn't draw anything from the POCO. But, because the NBC charges are netted out and reset every 15 minutes, over the total 30 minute period, while you'd have a net zero usage, you'd still be charged for 2 kWh of NBC. That's an example of how and why combining four 15 minute periods into one hour as I do can throw off the NBC calculation. For my rate calcs. when using MEM 2.0, I simply reduce the per kWh credit from SDG & E by the NBC amount for every kWh I send back to the POCO. That's not exactly accurate, but I've found the error is small. The alternative is to use 15 minute increments and 8,760 * 4 = 35,040 row spreadsheets.

Take all the above for what it's worth to you. The hope is it'll be of some use in your search to find some canned method to help compare rate plans and find the best one for your needs. Or, if you find similar to what I turned up, maybe an aid to doing your own.

Good luck.

[RichardCullip]

Back in April we got the PTO from SDG&E to start up our newly installed solar panels. It's a 4kW (DC) system with 12 LG335 panels feeding a SolarEdge Inverter. We are very pleased with the first 6 months of operation. The system design was over-sized for our current electric use since I was anticipating adding an EV to our demand early next year. Budget constraints require waiting a bit for the new car.

In the mean time I've been brushing up on my spreadsheet skills (used to build big oil production forecasting spreadsheets for Chevron in my previous life) and am attempting to model the impact to our SDG&E bills once we start charging our new EV. Which, if you are curious, will most likely be a Kia Niro PHEV. I'm now at the stage where I need to proof-check my calculations. I would love t have something to compare my results with to see if I've got something seriously wrong or if I'm in the right neighborhood of the answer. I am wondering if there's a tool available that lets me plug in my anticipated net energy values for On-Peak, Off-Peak, Super-Off Peak periods and NBCs. and then generate what the anticipated SDG&E charges under the EV-TOU-5 and EV-TOU-2 rate schedules might be?

My spreadsheet calculations are currently duplicating our monthly SDG&E bills to within a penny or two so I feel like I can model our electric use and resulting bill under our current TOU-DR rate schedule. It did take me a couple of billing cycles to work out how SDG&E calculates the individual line items in their bill. Not an easy task as those of you that have tried it can probably attest to.

Thanks in advance.