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  • Leveraging SDGE TOU rates with an EV?

    I've seen Ampster refer to the ability to leverage TOU rates with an EV to reduce electric bills to near minimum while consuming more electricity than solar produces on an annual basis. I'd send a PM for the details on how to accomplish this, but, alas, this forum software preclude that. So the next best thing, is to ask about this is a new (at least new to me) topic. I would love to get a general outline of how to leverage TOU rates to minimize the final POCO bill come True-up time.

  • #2
    I'm on the road so initially this will be brief. Essentially it is buy low and sell high. With summer differentials between Peak and Off Peak of at least$0.30 per KWhr for every hour you store on the grid at $0.50/kWh you can almost drawn down 4kWhrs at $0.15. I would be happy to discuss in more detail later.
    9 kW solar. Driving EVs since 2012

    Comment


    • #3
      Originally posted by Ampster View Post
      I'm on the road so initially this will be brief. Essentially it is buy low and sell high. With summer differentials between Peak and Off Peak of at least$0.30 per KWhr for every hour you store on the grid at $0.50/kWh you can almost drawn down 4kWhrs at $0.15. I would be happy to discuss in more detail later.
      Thanks for the quick overview. This will give me enough to work on for now. I'll just have to brush up on my Excel modeling skills and review various SDG&E rates options.

      Comment


      • #4
        For SDG & E on the NEM T.O.U. rate for PV users which is DR-SES, it amounts to shifting as much use to super off peak rate times as possible and then off peak for as much of the rest as possible, and avoiding as much peak time usage as possible.

        Under the old T.O.U. rates it was realistically possible to have a PV system that generated less than was used and still wind up with a bill that was <0.

        While that's still possible under the new raates and times, a min. bill while using more than generating is a lot harder to pull off, mostly because the hours of peak charges have shifted to times away from hours when high solar generation is likely.

        Long and short of it is to minimize all usage and then stay away from use during peak pricing as much as possible. Then, and if possible, have an array orientation that produces the highest annual bill offset per installed STC kWh. That 2d part is mostly not possible for fixed roof orientations.

        For you, your optimum array orientation in Poway is about 200 - 215 deg. az and about a 30 deg. tilt. At current DR-SES rates an array at your house and at that ~~ orientation will produce about $470/yr. in "revenue" per installed STC kW of capacity. You can then "spend" that revenue on your electric bill. So, a 5 kW system will produce ~ $470/yr. * 5 kW =`$2,350/yr.

        More info if you want it.

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        • #5
          Originally posted by J.P.M. View Post
          For SDG & E on the NEM T.O.U. rate for PV users which is DR-SES, it amounts to shifting as much use to super off peak rate times as possible and then off peak for as much of the rest as possible, and avoiding as much peak time usage as possible.

          Under the old T.O.U. rates it was realistically possible to have a PV system that generated less than was used and still wind up with a bill that was <0.

          While that's still possible under the new raates and times, a min. bill while using more than generating is a lot harder to pull off, mostly because the hours of peak charges have shifted to times away from hours when high solar generation is likely.

          Long and short of it is to minimize all usage and then stay away from use during peak pricing as much as possible. Then, and if possible, have an array orientation that produces the highest annual bill offset per installed STC kWh. That 2d part is mostly not possible for fixed roof orientations.

          For you, your optimum array orientation in Poway is about 200 - 215 deg. az and about a 30 deg. tilt. At current DR-SES rates an array at your house and at that ~~ orientation will produce about $470/yr. in "revenue" per installed STC kW of capacity. You can then "spend" that revenue on your electric bill. So, a 5 kW system will produce ~ $470/yr. * 5 kW =`$2,350/yr.

          More info if you want it.
          Thanks for your insight. The fixed roof orientation is hard to get around. For me it's 191 deg, az and 23 deg. tilt. As you said, under NEM 2.0 it's much harder to find a rate schedule that makes it possible to pull off. I am in a position where I'm currently paying the minimum ($0.338 per day) and I have room to increase my usage with a PHEV to get more bang for my buck. The EV-TOU-5 rate plan would be great, as there's a big differential btwn on-peak and super-off-peak, but the $16.00/month fee cancels out any savings I could anticipate under any realistic EV charging scenario I can dream up.

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          • #6
            Originally posted by RichardCullip View Post

            Thanks for the quick overview. This will give me enough to work on for now. I'll just have to brush up on my Excel modeling skills and review various SDG&E rates options.
            I have two excel files to do NEM calculation that may be of use

            https://1drv.ms/x/s!At3vMAQjaOZLkRp6...jb4jK?e=EyjbIH

            https://1drv.ms/x/s!At3vMAQjaOZLkSOv...i8r1o?e=2lI4b2


            Mod note - use these files at your own risk. They are not sponsored or endorsed by this forum.
            Last edited by Mike90250; 11-28-2019, 02:57 AM.

            Comment


            • #7
              Originally posted by scrambler View Post

              I have two excel files to do NEW calculation that may be of use.......


              Thanks. I'll take a look at those.
              Last edited by Mike90250; 11-28-2019, 02:58 AM.

              Comment


              • #8
                Originally posted by RichardCullip View Post

                Thanks for your insight. The fixed roof orientation is hard to get around. For me it's 191 deg, az and 23 deg. tilt. As you said, under NEM 2.0 it's much harder to find a rate schedule that makes it possible to pull off. I am in a position where I'm currently paying the minimum ($0.338 per day) and I have room to increase my usage with a PHEV to get more bang for my buck. The EV-TOU-5 rate plan would be great, as there's a big differential btwn on-peak and super-off-peak, but the $16.00/month fee cancels out any savings I could anticipate under any realistic EV charging scenario I can dream up.
                You're welcome. I believe I found similar to what you found with respect to the EVTOU rates.

                I appreciate the roof/fixed orientation bind/limitations.

                FWIW, a 191 deg. az., 23 deg. tilt yields ~ $465/yr. per STC kW in bill offset under DR-SES in/around N. County San Diego. So, for example, if you only used power at super off peak rates of ~ $0.24558/kWh blended summer/winter, you could use ~ ($465/yr.-STC kW)/($0.24558/kWh) = 1,894 kWh/yr per STC kW and avoid most of your bill. At the other rate extreme of summer on-peak pricing of $0.53571/kWh you could use ~ $465/$0.53571/kWh = 862 kWh/yr. per STC kW and avoid most of a bill.

                Your usage and times will result in a blended average price per kWh. But, if you assume the PVWatts model as a reasonable dart throw of irradiance and generation patterns and quantities, then the amount of "revenue" a system produces (and that can only be used to offset regular billing charges) will be as fixed and representative of what's likely to happen as the PVWatts model's generation. Generation used internally and not exported to the grid will have the same revenue value as if it was exported to the grid.

                The method also provides a means to help game the system as Ampster is writing about. You start out with what is an approximately fixed $$ amount per year or billing period that is the $$ value of the electricity an array generates. Then you get to look at how to spend those $$'s at various times and in various amounts, or see the effects of time shifting of loads has on a residual bill.

                The method works for DR-SES but will work for most any T.O.U. tariff, including those that have a tiered rate system laid over them. In such cases, a billing schedule needs to be inserted into the spreadsheet to account for when to stop applying the tier one billing credit per kWh. That also means all the variables that affect the basic monthly allowance need to be accounted for, as will which actual billing schedule is being used by the account. PITA details but not hard to understand, and need be done only once per account/residence.

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                • #9
                  FWIW, the TOU tariffs I have chosen over the past 8 years have never had a tiered overlay. I have always had two EVs during that time and tiered rates are something I avoided because of the diminishing returns as kWhr usage goes up.
                  9 kW solar. Driving EVs since 2012

                  Comment


                  • #10
                    Originally posted by Ampster View Post
                    FWIW, the TOU tariffs I have chosen over the past 8 years have never had a tiered overlay. I have always had two EVs during that time and tiered rates are something I avoided because of the diminishing returns as kWhr usage goes up.
                    More FWIW: I didn't see T.O.U. rates with a tiered overly - at least in CA - until a couple/3 years ago. I believe SCE and PG & E started them ~ the same time. SDG & E didn't have one until ~ 18 months ago. The SDG & E T.O.U tariff for residential PV users does not use/overlay a tiered rate, at least not at this time. Other SDG & E T.O.U. tariffs do.

                    It took me a while to get the spreadsheets for tiered rate T.O.U. tariffs right, mostly because of how the basic daily allocation and thus billing period allocations for determining tier one sizes and so credits are determined. Not conceptually difficult as that's needed for the old, straight tier tariffs, but more details than necessary for straight T.O.U. only tariffs if accuracy is wanted.

                    Some (most ?) residential customers of SDG & E and probably the other 2 CA I.O.U.'s will probably be on a tiered T.O.U. tariff either by ignorant default or by informed choice/design at some future point.

                    Comment


                    • #11
                      Originally posted by J.P.M. View Post
                      ....
                      Some (most ?) residential customers of SDG & E and probably the other 2 CA I.O.U.'s will probably be on a tiered T.O.U. tariff either by ignorant default or by informed choice/design at some future point.
                      Is that based on some policy directive from the CEC? The change in rates that I see more clearly is the transition to a more fixed component of the rates. As noted above by @RichardCullip one of the SDG & E EV rates has $16 fixed component.
                      9 kW solar. Driving EVs since 2012

                      Comment


                      • #12
                        Originally posted by Ampster View Post

                        Is that based on some policy directive from the CEC? The change in rates that I see more clearly is the transition to a more fixed component of the rates. As noted above by @RichardCullip one of the SDG & E EV rates has $16 fixed component.
                        Well, since we're talking about a tariff, and since the CEC does not have the authority with respect to rates or tariffs for the CA IOU's, the answer to your question is "I don't believe so".

                        The way I understand it, the CEC is the state's primary energy policy and planning agency.

                        The CPUC on the other hand and through its oversight, regulates the I.O.U.s with respect to rates, and for this conversation, tariffs.

                        There is a difference.

                        BTW, with respect to the change in rates that you see more clearly as the transition to a more fixed component of the rates: Is that based on some policy directive from the CEC or other CA gov. agency ?

                        Since my crystal ball is still in the shop, what I wrote is based on my opinion only, as is most or at least a lot of what gets written around here.

                        More opinion here: Your insightful question might have been more helpful if you had shown the rest of my post and not, in effect, taken what I did post more than a little out of the context of tiered TO.U. rates being a rather recent development. If you had quoted or at least understood the context of my post, it might have been clear to you that my opinion was based on prior events with respect to new or revised tariffs as I saw them, and the direction I see them headed, not unlike what seems to me to be your opinion that rate changes are more clearly a transition to a more fixed component of the rates.

                        As you write, and like you (I'm inferring your opinion here and not some factoid based on policy), I'm reasonably confident the POCO's would like to see a more fixed form of revenue and a larger fixed fee component of rate structures such as SDG & E's proposed 400 % hike in min. billing period charges, some .

                        On the other hand, tiered T.O.U tariffs look, to me anyway, as an up and coming way for the POCOs, IMO only, to game the system by making the already murky (for what seems to me to be most consumers anyway) rate schemes more muddy.

                        It's all opinion, but that's just my $0.02.

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

                        Comment


                        • #13
                          This is probably old news, but in case you missed it, SDG&E has a proposed rate change in front of the CPUC. It includes a $10 fixed monthly charge and a monthly bill minimum of $38. The $10 fixed charge is not included in the monthly bill minimum. If approved by the CPUC this rate change will go into effect in 2021. The main driving motivation behind this change is that low electrical users, such as those of us with solar, aren't paying our fair share of the fixed costs for maintaining/improving the grid. Ouch

                          https://sdgenews.com/article/fixed-c...ll-whats-story

                          Comment


                          • #14
                            Originally posted by RichardCullip View Post
                            This is probably old news, but in case you missed it, SDG&E has a proposed rate change in front of the CPUC. It includes a $10 fixed monthly charge and a monthly bill minimum of $38. The $10 fixed charge is not included in the monthly bill minimum. If approved by the CPUC this rate change will go into effect in 2021. The main driving motivation behind this change is that low electrical users, such as those of us with solar, aren't paying our fair share of the fixed costs for maintaining/improving the grid. Ouch

                            https://sdgenews.com/article/fixed-c...ll-whats-story
                            Yea. Don't know how that will wring out as it winds it's way through the lobbies and cloakrooms of the CPUC.

                            If it does become reality in some form (?), and depending on how it's structured, and similar to the ways NEM rate/T.O.U. time restructuring lowered array cost effectiveness by ~ 22 - 25% or so, such a charge may wind up as another example of some of the risks of oversizing an array based on assumptions of increasing array cost effectiveness from rates that are assumed to only go up, and that such an assumption is not a always a slam dunk or the only thing that affects an electric bill.

                            If that $38 min. charge/billing period is against usage, and again, depending on how it's structured, for this oversimplified example only, that could reduce the value of an array's first $ 38 worth of generation per billing period to zero. That is, the $38 charge might well be there regardless of the amount of any PV generation.

                            To greatly oversimplify: Say I use 1,000 kWh over a billing period and I generate 1,000 kWh over the same period, and I pay $0.38/kWh flat rate to the POCO.

                            Without the $38 min. charge, my bill is $0.

                            If the $38 charge is in place, and if it's against usage, even though my POCO usage = zero, my bill is still $38.

                            So, for this very oversimplified example, my array's ability to offset $38 of my bill per billing period just disappeared, making the investment in the (now oversized) PV less cost effective, probably by something like 10% or so for this oversimplified example.

                            Or, looked at another way, since there's no way array capacity can make up that $38 by more generation (except by the almost as cost ineffective method of getting ~ $0.03 to $0.05/kWh for excess generation at trueup), the array just became oversized by about 10 % or so. I'll have something like 1,200 kWh/yr. of excess generation that is worth $0.03- $0.05 or so at trueup. If I'm already oversized, things just got worse.

                            Now, I sure didn't know that was going to happen when I sized the array any more than I knew rate restructuring would make my array less cost effective. I'm just saying that there are a lot of uncertainties about array sizing, and some of them can run counter to the usual logic that oversizing will always be a safe bet with respect to getting the most bang for my buck.

                            If that min. charge does become reality in some form, my guess is it'll have the effect of reducing array sizes for informed potential future PV owners but have little to no effect on the thinking (or lack of thinking) by most potential PV owners.

                            Guess we'll all have to wait and see what flushes out of the pipe.

                            A bit off topic, but for my situation, NEM, 1.0, tiered rates, with an additional min. charge in place my bill will increase by 12* $38 = $456/yr. A very simplified analysis: The array size I require for a 100% offset of my current usage is 3,924 STC W. The array size that offsets all but $456 of that usage is 3,150 STC W. I'm not complaining, and unlike most it seems, I didn't get an array with any hope of cost effectiveness as a design goal, and I knew things are subject to a future full of unknowns, but if I was doing the same thing with a $38/billing period min. charge in place, I'd have probably taken that into account.

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                            • #15
                              Originally posted by J.P.M. View Post

                              More FWIW: I didn't see T.O.U. rates with a tiered overly - at least in CA - until a couple/3 years ago. I believe SCE and PG & E started them ~ the same time. SDG & E didn't have one until ~ 18 months ago. The SDG & E T.O.U tariff for residential PV users does not use/overlay a tiered rate, at least not at this time. Other SDG & E T.O.U. tariffs do.

                              It took me a while to get the spreadsheets for tiered rate T.O.U. tariffs right, mostly because of how the basic daily allocation and thus billing period allocations for determining tier one sizes and so credits are determined. Not conceptually difficult as that's needed for the old, straight tier tariffs, but more details than necessary for straight T.O.U. only tariffs if accuracy is wanted.

                              Some (most ?) residential customers of SDG & E and probably the other 2 CA I.O.U.'s will probably be on a tiered T.O.U. tariff either by ignorant default or by informed choice/design at some future point.
                              Back to the original question: I am in SDG&E with solar and an EV. My solar generation, over a year, is about net even with my consumption including an EV. I don't yet have air conditioning.

                              I chose the TOU-DR-P rate. I think it is optimal for my condition. More specifically: in summer months there is a 10c difference between "off-peak" (when most generation happens) and super-off-peak (when I would charge the EV and consume the most), so I can accumulate credit faster than energy use. Additionally, there is only a 1c increment for the on-peak, when I may use electricity and solar generation is low to zero. I like not having to stress too much about the on-peak hours.

                              The issue though is that there is a large penalty rate for the Reduce Your Use days, which are called occasionally on very hot summer weekdays (no guarantee but nearly always true)---a $1.16 increment to rate between 2 to 6pm on those days. Summer 2019 there were none, Summer 2018 there were four. But as they were 2-6pm, as I planned to totally minimize consumption on those times they ended up being a very good generating bonus as I had net generation during those hours, maybe $15 in credit per RYU day!

                              SDG&E rates here: (bookmark this page!): https://www.sdge.com/total-electric-rates

                              If I were to be a heavier consumer, e.g. with significant AC use, then the EV-TOU-5 rate would be optimal---as there is a huge gap between generation hours rates and super-off-peak (EV charge time) rates, and this gap is present year round. At the cost of $16 per month of hard money that can't be offset with generation, plus the non-bypassable charges, so maybe $25 per month? The upside would be that I would earn large generation credit from rate arbitrage that could be used for AC or other consumption.

                              For TOU-DR-P the combination of minimum bill and NBC's + taxes results in a net minimum hard money bill of about $12 per month.

                              I think the best rate plans for EV+Solar users in SDG&E are TOU-DR-P and EV-TOU-5.

                              Note there is also TOU-DR rate (not really advertised) that is like the other TOU rate that SDG&E is pushing, but with a lesser gap from on-peak to off-peak. But the gap from off-peak to super-off-peak is more like 6c vs 10c, similar to EV-TOU-2 and DR-SES (which are almost the same).

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