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  • #16
    Originally posted by JSchnee21 View Post
    switching to a Bolt would only net me a ~$1500-2000 per year savings (after subtracting the cost of electric from the cost of gas -- I drive ~30+K miles/yr). And I'd have to buy a new $35K Bolt to do it.
    If you are looking for a new car - you can't exclude the cost of the alternative. Is it worth it? If the goal is to save money - then probably not - buy something used.

    I personally prefer driving an EV over an ICE for normal commute driving and I am willing to pay more for that. Going to gas stations/oil change shop is an inconvenience (nightmare!) to me.

    Utility rates in the California IOUs are complicated whether you have an EV or not though - so whatever nightmare it may sound like isn't because of the EV - the EV just gives you more choices of rate plans.

    Comment


    • #17
      Originally posted by jgd108 View Post
      Wow J.P.M. that was an awesome detailed reply!
      I had to re-read it a few times but it contains great info.

      Will ask my follow-up questions inline to make sure I understood:



      I feel PV sizing was easier before but I forgot about the tiered pricing, although you would think most would fall into Tier 1 right due to their net kWh being close to zero?
      SDG&E's EV-TOU-X rates are not tiered luckily since that's the main reason I moved away from DR rates which penalizes EV charging.

      Just to make sure I got it correct, say I produced for $2000 worth of electricity, and consumed $1700 worth of electricity (using the TOU schedule).
      My understanding is I won't get a $300 check at "true up" but rather a wholesale rate of those extra kWh correct?
      If so what is exactly that wholesale rate? I hear "2-3 cents / kWh" is that even true? Where to find?

      Basically I would mostly produce at off peak (and a little at peak), and on weekends/holidays mostly at super off peak (and off peak).
      And a big chunk of my use would be overnight at super off peak for EV charging.



      Agreed, big spreadsheet for sure! Not sure how to sum up all the hours together easily.
      Also this is using data for a city nearby and historical weather data, performance, etc. so many variables that will change year over year!!




      Miramar data, nice. I used to live in Scripps Ranch and biked to the lake many times.

      And Porsche E, that's a beast. Hopefully they make it soon :P

      Changing rates further complicate calculations for the first few years, let alone many years..

      So my system with the rates increasing might actually generate more credits over time hopefully.. ha!



      You made an excellent point about getting less money on weekends / holidays when going to EV-TOU-5!
      I did output the PVwatts and looked at a few days in June, measured the number of watts made before 2pm for the super off peak on holidays and weekends, and came to about $140 more credit with EV-TOU-2 than EV-TOU-5. The way I see EV-TOU-5 winning is if I charge a lot more, but on the flip side if I travel for a month or only fly to clients I pay a $16 flat fee and get less credits on my generation.
      Wow, again this makes it nearly impossible to predict! ​ I doubt I will be able to educate my neighbor going solar too now !

      Thanks.
      You're welcome. Just be careful to question, in your own mind, everything I write (or anyone else's mental spoor for that matter) until it either makes sense to you or you can be pretty sure it's incorrect in some sense or circumstance(s) and explain why.

      One other thing: All this applies to new using current billing and billing schedules, that is, those not grandfathered under some prior AB 327 mandated tariff schemes, or those not choosing to be grandfathered for old schedule rules or times for some reason(s).

      On tiered vs. TOU schedules: There are some TOU schedules with SDG & E and others that are not completely true TOU by virtue of such TOU schedules (SDG & E's schedule TR - TOU for non solar users for example) having what the POCO calls a "Baseline adjustment credit" that is applied to every kWh from the POCO that's over 130 % of a billing period's baseline usage. Those schedules have high off peak and super off peak rates that are closer to peak rates compared to other TOU schedules that do not use or have the "Baseline adjustment credit" scheme.

      In effect, what happens is that the lower usage portions under such schedules, that is, those TOU schedules that take into account 130% of baseline usage for a billing period, the users get the good effects of TOU pricing for off peak times for those lower usage levels (<130 % of baseline ) in a billing period, but after that 130% of baseline is hit, the off peak and super off peak baseline adjustment credit goes away with the bottom line result that for all additional use in a billing period, higher peak and super off peak rates that get a lot closer to the peak rate will apply. See schedule DR-TOU for details.

      At this time, all SDG & E schedules that apply to solar and/or NEM users do NOT use the "Baseline adjustment credit" scheme. (but stay tuned, things can always change).

      As for your question about credits on a bill: You are correct, you will not see a $300 check. Any accumulated surplus kWh generation over the course of a year at true up will be compensated at the average wholesale rate. Currently, for SDG & E, that rate is ~ $0.0295/kWh. Root around on the SDG & E website for current wholesale rates and the logic and reasons of how/why that rate changes.

      The credits that you see on your bill are only useful and meaningful against billing for what you use.

      That's also the sense I use when I write that an installed STC kW of PV facing south at a 20 deg. tilt in north county San Diego will offset ~ $453/yr. in SDG & E billing. using DR-SES tariff and current rates.

      As for spreadsheets and using them to help figure out the interplay between PV sizing/prices/bill savings, etc. and only for FWIW, I've found it to be not as daunting a task as it looks, mostly because it's a cut/paste/copy deal once schedules and the details of time, season, weekday/weekend/holiday are done and checked.

      Basically, it's a 168 hr. copy job (1 week' s hours = 24 * 7) separately for ~ 7 months of summer and ~ 5 months of winter with March & April super off peak midday adjustments, and holidays adjusted to super off peak times.

      The trick I found that works best for me is to first, last and foremost, read, study and thoroughly understand how the POCO (in this case SDG & E) tariffs and schedules work. This was and continues to be, for me anyway, the biggest PITA. The task is not made easier by the less than helpful and usually quite cryptic ways SDG & E doesn't seem to feel the need to be forthcoming about how things work, but then, I'd not expect them to be. It helps me to remember that nothing can replace persistence. That and a call to the POCO 1X/a while.

      My observation is that most folks who do spreadsheets to help figure out billing don't take the time to fully understand the ins/outs/pitfalls of how a POCO's billing works and usually wind up screwing themselves as a result. A trick I use: Do a spreadsheet and construct it in such a way so as to be able to change the rates and times back to prior rates and times, then use old bills and be able to back into the old $$ amounts. I learned a lot after I did that, and learned that the devil really is in the details. Suit yourself.

      However, once that's dealt with, an 8,760 row spreadsheet, or tasks such as combining POCO supplied historical usage data from 15 minute to 1 hour increments, for example is pretty simple, and the data is useful and some things become easier to make sense of .

      Example: If I have a 4 STC kW system that under current TOU - EV - 5 will generate, say, ~ $453 * 4 = $1,812/yr. in billing credits, it becomes apparent, after a little thought, that, once generated, I can spend that credit by using electricity at any time and at any rate of my choosing. So, at one unlikely extreme, if I use every kWh at super off peak times, I can use, very approx. (not accounting for NBC or monthly minimums for now to keep it simple) $1,812/$0.09375 = 19,328 kWh/yr. and not have much of an electric bill !!

      If, on the other hand, and at the other and in an equally unlikely scenario, I choose to use electricity only during the summer at peak times (and at a rate of $0.53019/kWh), I'll use up all $1,812 of billing credit the system generates after ($1,812/$0.53019) = 3,418 kWh of use.

      The reality is likely somewhere between those two usage figures. Point is, once the mental hurdle of separating generation from usage is mastered, it's easier to understand that users can and do have a lot of control over how much they pay to provide electrical service to their homes both by controlling (lowering) their use and also by being mindful about when that lowered usage is used. Or, that using less and using at mostly off peak times can make a PV system more cost effective. A lot of choice is up to the user.

      As for your comment about weather data, dirty little secret that's hiding in plain sight is that most all the irradiance data, and a lot of the rest of the weather variables including the data for ~ > 90% of the U.S. sites is synthetic and is based largely on extrapolations, and some eyeball observations of 26 historical sites around the U.S. that have, or had, functional pyranometers to record solar irradiance. Most sites that the TMY databases cover (~ 1,300 sites) do not currently, and never had, pyranometric data. It's mostly or entirely synthetic. The observable fact that PVWatts, and other models seem to be decent models for use in system design is probably due in part to the validity of the extrapolation algorithms, but mostly due to the idea that weather is what you get, and so the models are probably no better than +/- 10 % or so over long periods of several years or more. Fortunately, that's usually close enough. This business of PV system design is far from an exact science.

      On the Porsche: The idea is nice, but mostly a fantasy as it fits neither my self image or the public persona of a retired old fart wearing 3-4 days of beard, a wife beater, jeans with holes in the knees, and a 10 yr. old baseball cap with the middle digit emblazoned on it over hair that hasn't seen a barber since retirement. Life is good.

      As for your neighbor, their understanding, and why they're probably late to the PV net metering party, point them in the direction of this thread. Further homework on their part may lead them to the conclusion that the only thing left of the PV smorgasbord is the equivalent of bug juice and crap sandwiches and we're about to run out of bread.

      Comment


      • #18
        I remember in the late 90's, my company signed up for the "save the grid, idle a mfg plant" plan. The end of the power peak was at 4pm, as industry started shutting down for the day. Then in the early 2000's, the Flex Alert plans came out, moved to about 5pm, because Industry was on "Flex-Time" for employees to shift out of gridlock traffic. Now the peak is back to 9pm. Seems fishy to me, that it's moved past sunset.
        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

        solar: http://tinyurl.com/LMR-Solar
        gen: http://tinyurl.com/LMR-Lister

        Comment


        • #19
          Well, of course it depends on where you live, but I took a couple snapshots from California grid, that shows not just demand but also, a second curve w/ Solar and Wind removed.

          What I'd say the 9pm for non-solar and wind to be a pretty reasonable within peak. What I'd be afraid of is if they went and dropped the sun production hours to a super-off-peak on EVs. That would screw everything up. I remember someone showing Hawaii rates that were really low during middle of day from all the solar production on their grid.

          NetDemand.JPGNetDemand2.JPG

          Comment


          • #20
            Originally posted by Mike90250 View Post
            I remember in the late 90's, my company signed up for the "save the grid, idle a mfg plant" plan. The end of the power peak was at 4pm, as industry started shutting down for the day. Then in the early 2000's, the Flex Alert plans came out, moved to about 5pm, because Industry was on "Flex-Time" for employees to shift out of gridlock traffic. Now the peak is back to 9pm. Seems fishy to me, that it's moved past sunset.
            Being a pretty firm believer that companies, including POCOs, will do what they believe maximizes profit (but with less of a view to long term strategies with a more usual knee jerk response to short term band aids), if more use takes place later in the day, for whatever reason, and the POCO believes it will increase their bottom line to set rates in such a way as to tend to, in the POCP's view take advantage of the situation, they'd do it. As for system load and daylight, I remember back in Buffalo, when there was a bimodal peak during most weekdays, one peak in the A.M. around breakfast +/- some and one peak in the P.M., around dinner, pretty much irrespective of the length of the day.

            Today, and in CA, I'd not be surprised if midday distributed and other PV generation is part of the shifting of system demand to later in the day, not so much asf(total load, but lrather relative load and PV generators offset less of the system load later in the day. Kind of what the duck curve is all about, but more for the max to min difference magnitude than when the usage actually occurs. I'd guess distributed PV doesn't reduce system loading as much as it may delay increases in grid loading both over the short (daily/hourly) as well as long term (like months/years).

            Comment


            • #21
              Originally posted by J.P.M. View Post

              You're welcome. Just be careful to question, in your own mind, everything I write (or anyone else's mental spoor for that matter) until it either makes sense to you or you can be pretty sure it's incorrect in some sense or circumstance(s) and explain why.

              One other thing: All this applies to new using current billing and billing schedules, that is, those not grandfathered under some prior AB 327 mandated tariff schemes, or those not choosing to be grandfathered for old schedule rules or times for some reason(s).

              On tiered vs. TOU schedules: There are some TOU schedules with SDG & E and others that are not completely true TOU by virtue of such TOU schedules (SDG & E's schedule TR - TOU for non solar users for example) having what the POCO calls a "Baseline adjustment credit" that is applied to every kWh from the POCO that's over 130 % of a billing period's baseline usage. Those schedules have high off peak and super off peak rates that are closer to peak rates compared to other TOU schedules that do not use or have the "Baseline adjustment credit" scheme.

              In effect, what happens is that the lower usage portions under such schedules, that is, those TOU schedules that take into account 130% of baseline usage for a billing period, the users get the good effects of TOU pricing for off peak times for those lower usage levels (<130 % of baseline ) in a billing period, but after that 130% of baseline is hit, the off peak and super off peak baseline adjustment credit goes away with the bottom line result that for all additional use in a billing period, higher peak and super off peak rates that get a lot closer to the peak rate will apply. See schedule DR-TOU for details.

              At this time, all SDG & E schedules that apply to solar and/or NEM users do NOT use the "Baseline adjustment credit" scheme. (but stay tuned, things can always change).

              As for your question about credits on a bill: You are correct, you will not see a $300 check. Any accumulated surplus kWh generation over the course of a year at true up will be compensated at the average wholesale rate. Currently, for SDG & E, that rate is ~ $0.0295/kWh. Root around on the SDG & E website for current wholesale rates and the logic and reasons of how/why that rate changes.

              The credits that you see on your bill are only useful and meaningful against billing for what you use.

              That's also the sense I use when I write that an installed STC kW of PV facing south at a 20 deg. tilt in north county San Diego will offset ~ $453/yr. in SDG & E billing. using DR-SES tariff and current rates.

              As for spreadsheets and using them to help figure out the interplay between PV sizing/prices/bill savings, etc. and only for FWIW, I've found it to be not as daunting a task as it looks, mostly because it's a cut/paste/copy deal once schedules and the details of time, season, weekday/weekend/holiday are done and checked.

              Basically, it's a 168 hr. copy job (1 week' s hours = 24 * 7) separately for ~ 7 months of summer and ~ 5 months of winter with March & April super off peak midday adjustments, and holidays adjusted to super off peak times.

              The trick I found that works best for me is to first, last and foremost, read, study and thoroughly understand how the POCO (in this case SDG & E) tariffs and schedules work. This was and continues to be, for me anyway, the biggest PITA. The task is not made easier by the less than helpful and usually quite cryptic ways SDG & E doesn't seem to feel the need to be forthcoming about how things work, but then, I'd not expect them to be. It helps me to remember that nothing can replace persistence. That and a call to the POCO 1X/a while.

              My observation is that most folks who do spreadsheets to help figure out billing don't take the time to fully understand the ins/outs/pitfalls of how a POCO's billing works and usually wind up screwing themselves as a result. A trick I use: Do a spreadsheet and construct it in such a way so as to be able to change the rates and times back to prior rates and times, then use old bills and be able to back into the old $$ amounts. I learned a lot after I did that, and learned that the devil really is in the details. Suit yourself.

              However, once that's dealt with, an 8,760 row spreadsheet, or tasks such as combining POCO supplied historical usage data from 15 minute to 1 hour increments, for example is pretty simple, and the data is useful and some things become easier to make sense of .

              Example: If I have a 4 STC kW system that under current TOU - EV - 5 will generate, say, ~ $453 * 4 = $1,812/yr. in billing credits, it becomes apparent, after a little thought, that, once generated, I can spend that credit by using electricity at any time and at any rate of my choosing. So, at one unlikely extreme, if I use every kWh at super off peak times, I can use, very approx. (not accounting for NBC or monthly minimums for now to keep it simple) $1,812/$0.09375 = 19,328 kWh/yr. and not have much of an electric bill !!

              If, on the other hand, and at the other and in an equally unlikely scenario, I choose to use electricity only during the summer at peak times (and at a rate of $0.53019/kWh), I'll use up all $1,812 of billing credit the system generates after ($1,812/$0.53019) = 3,418 kWh of use.

              The reality is likely somewhere between those two usage figures. Point is, once the mental hurdle of separating generation from usage is mastered, it's easier to understand that users can and do have a lot of control over how much they pay to provide electrical service to their homes both by controlling (lowering) their use and also by being mindful about when that lowered usage is used. Or, that using less and using at mostly off peak times can make a PV system more cost effective. A lot of choice is up to the user.

              As for your comment about weather data, dirty little secret that's hiding in plain sight is that most all the irradiance data, and a lot of the rest of the weather variables including the data for ~ > 90% of the U.S. sites is synthetic and is based largely on extrapolations, and some eyeball observations of 26 historical sites around the U.S. that have, or had, functional pyranometers to record solar irradiance. Most sites that the TMY databases cover (~ 1,300 sites) do not currently, and never had, pyranometric data. It's mostly or entirely synthetic. The observable fact that PVWatts, and other models seem to be decent models for use in system design is probably due in part to the validity of the extrapolation algorithms, but mostly due to the idea that weather is what you get, and so the models are probably no better than +/- 10 % or so over long periods of several years or more. Fortunately, that's usually close enough. This business of PV system design is far from an exact science.

              On the Porsche: The idea is nice, but mostly a fantasy as it fits neither my self image or the public persona of a retired old fart wearing 3-4 days of beard, a wife beater, jeans with holes in the knees, and a 10 yr. old baseball cap with the middle digit emblazoned on it over hair that hasn't seen a barber since retirement. Life is good.

              As for your neighbor, their understanding, and why they're probably late to the PV net metering party, point them in the direction of this thread. Further homework on their part may lead them to the conclusion that the only thing left of the PV smorgasbord is the equivalent of bug juice and crap sandwiches and we're about to run out of bread.
              Again appreciate the detailed reply to all my questions J.P.M., very logical and well laid out with examples.

              I think I've reached a point where I will just have to jump right in and see how it pans out! Otherwise analysis-paralysis..

              Produce high and buy low will hopefully work based on my last month data and projections with EV charging.
              One vendor showed with using my data and his software supposedly using PVWatts in the background that I would generate $750 of credits and use $680 for charging the car super off peak night time.
              The rest of the credits would offset the NEM 2.0 NBC (unless that cannot be offset with credits?).

              And maybe in a few years when batteries make sense use them to offset peak hours and eventually go off grid and not have to do all those calculations and worry about their rate increase and TOU periods (if allowed in CA?). I believe getting a Tesla Powerwall is first nearly impossible due to demand and second the SGIP credits are mostly all gone for SDG&E territory. And those Enphase 1.2kw batteries are ridiculous.

              Does anybody know with SDG&E if when you turn on your solar system you are able to switch to a new plan even if I just got into one (EV-TOU-2) which has a one year commitment?

              That's my only hope for EV-TOU-5 at this point

              Comment


              • #22
                Originally posted by Mike90250 View Post
                I remember in the late 90's, my company signed up for the "save the grid, idle a mfg plant" plan. The end of the power peak was at 4pm, as industry started shutting down for the day. Then in the early 2000's, the Flex Alert plans came out, moved to about 5pm, because Industry was on "Flex-Time" for employees to shift out of gridlock traffic. Now the peak is back to 9pm. Seems fishy to me, that it's moved past sunset.
                That's mainly due to solar. At 4pm solar is still generating. In the summer, even at 5pm you are getting significant generation. But around 6pm it drops off steeply - and that's when the 'new' peak for conventional generation starts.

                Which of course is good and bad. Good that from 4-6 you need less generation. Bad in that the ramp rate is now higher (solar going offline AND demand going up due to people getting home.) Given how much nat. gas storage we lost when Aliso Canyon went offline, the reduction in total generation demand (megawatt hours) was a good thing.

                Comment


                • #23
                  Originally posted by jgd108 View Post


                  Produce high and buy low will hopefully work based on my last month data and projections with EV charging.
                  One vendor showed with using my data and his software supposedly using PVWatts in the background that I would generate $750 of credits and use $680 for charging the car super off peak night time.
                  The rest of the credits would offset the NEM 2.0 NBC (unless that cannot be offset with credits?).
                  Without data to look at I can't comment other than to suggest rereading the 1st paragraph of my 10:24 A.M. post.

                  Someone with skin in the game is telling you something that will probably result in financial gain for them. That about right ?

                  If so, and respectfully, Caveat Emptor.


                  Comment


                  • #24
                    Thanks to TAZ427 sending me his spreadsheets, and "closing the loop" on this post I was able to use the output from PVWatts and calculate with SDG&E EV TOU 2 rates how much my system would generate during a year.

                    I also ran the numbers with EV TOU 5 and as expected the generation payout was less by $213.84 ( $2,071.00 versus $1,857.16 )

                    But with my projected usage cost (conservative estimate) is landing me at $1,749.82 for EV TOU 2 and $1,349.67 for EV TOU 5.

                    So with EV TOU 5 from June 2019 I will be having $500 of buffer in my use versus $322 the first year..

                    I guess I can get a second EV and run AC more often even in peak hours!!

                    The cool thing is even if the rates increases EV TOU 5 has such low super off peak rates that solar will just create more revenue.

                    Thanks all, can't wait to get my solar system installed, HOA is reviewing tonight and SDG&E is coming out next week for meter spot.. fingers crossed!

                    Comment


                    • #25
                      Originally posted by jgd108 View Post
                      I just got notified in the Tesla forums about the new SDG&E EV-TOU-5 plan.

                      I recently (last month) switched to EV-TOU-2 since I got the EV and am in the process of getting a PV system installed.

                      https://www.sdge.com/residential/pri...-vehicle-plans

                      It looks like this plan is new as of this month, and it is a really great deal for super-off-peak at about 9cents/KW versus 22cents, if you pay $16 monthly fee.

                      I've ran the numbers in my spreadsheet with the EV-TOU-5 plan and with 250KW charging monthly for the EV in super off peak (and not considering other use could fall in super-off-peak esp. on weekends and holidays):

                      DR summer: $206.05
                      DR winter: $175.08

                      EV-TOU-2 summer: $175.70
                      EV-TOU-2 winter: $137.71

                      EV-TOU-5 summer: $155.44
                      EV-TOU-5 winter: $117.45

                      Since summer is 5 months long, the net rebates over DR rate for a year is:
                      EV-TOU-2 : $413.32
                      EV-TOU-5 : $656.43

                      That's quite a saving, and also I just got the EV climate credit approved for $500 (!) instead of the usual $200.

                      I have yet to call SDG&E (tomorrow) but if I somehow am able to change to EV-TOU-5 and I've got $500 credit (assuming it is going on till 2020), my yearly for next 3 years would be $1600-$500 = $1100

                      That really pushes my PV ROI from 4.5 years to under 7.5 years (OK I know the rates are going to increase, and the EV credit might phase out anytime), but the bottom line it has made me pause and reconsider doing solar next year before 2019 30% credit starts phasing out..

                      Thoughts? Anything I'm missing? Happy to share my spreadsheet in case anyone think it would be useful..

                      And one side question if I do go solar now, how does the $500 EV climate credit works? Do they write me a check at the true up or that $500 will keep getting rolled until I do get a positive bill?
                      My numbers are a bit different than yours. Maybe I don't understand what you are writing.

                      My assumptions:

                      1.) 250 kWh/mo. --->>>> added usage = 3,000 kWh/yr/365 = 8.21918 kWh/day. Summer = 153 days, winter = 212 days.

                      2.) --->>> Summer EV use = 1257.5 kWh, Winter EV use = 1742.5 kWh.

                      3.) For DR rate schedule and yearly EV adder calc. for electricity used I'm assuming you already use 130% of baseline rate, so all added EV charging will be at the over 130% to < 400% tier rate applicable to summer or winter.

                      4.) adding 250 kWh/mo. will not kick you over 400% of baseline usage for any month.

                      5.) All TOU charging is done at super off peak times and rates as applicable.

                      Approximate $$ adders to an annual residential bill for adding 3,000 kWh/yr. for each tariff schedule using assumptions as described above:

                      For DR adder: Summer rate = $0.47504/kWh --->>> 1,257.5 hrs. * $0.47504 = $597.36
                      Winter rate = $0.46504/kWh --->>> 1,742.5 hrs.* $0.40361 = $703.29
                      Total adder = $1,300.65/yr.

                      For EV - TOU - 2 adder: Summer rate = $0.22793/kWh --->>> 1,257.5 hrs. * $0.22793 = $266.62
                      Winter rate = $0.22879/kWh --->>> 1,742.5 hrs. * $0.22879 = $398.67
                      Total adder = $ 665.29/yr.

                      For EV - TOU - 5 adder: Summer rate = $0.09317/kWh * 1257.5 hrs. = $117.16 + ($16/mo. * 5 mo.) = $197.16
                      Winter rate = $0.09403/kWh * 1742.5 hrs. = $163.85 + ($16/mo. * 7 mo.) = $275.85
                      Total adder = $473.01/yr.

                      So, if my assumptions are correct, get an EV in SDG & E territory, and any TOU schedule over DR tiered rate schedule is a no brainer, and at 3,000 kWh/yr. EV-TOU-5 looks like the best deal at this time.

                      TOU-EV-5 is, at this time anyway, a better deal than EV-TOU-2 until the annual super off peak charging gets below ~~($16/mo.*12 mo.)/($0.2284-$0.0935) ~ = 1,423 kWh/yr., or maybe something like 5,000 miles driven/yr. or so. Less than that and EV-TOU-2 might be a better deal, at least under current rates and times.

                      As more of an academic question, I wonder what will happen to super off peak or TOU times and rates in general if the semi absurd happens and EV's REALLY take off, they become ubiquitous and strain the system with night (or other off peak charging times).

                      If my logic, calcs assumptions and numbers are correct, your ROI improvement might just be a bit better than you calc'd.

                      On your question of vehicle rebates : Since I don't (yet) have an EV, I'm not up to speed on utility rebates for EV's.(but that Porsche EV is looking pretty sweet.)



                      Comment


                      • #26
                        Originally posted by J.P.M. View Post

                        My numbers are a bit different than yours. Maybe I don't understand what you are writing.

                        My assumptions:

                        1.) 250 kWh/mo. --->>>> added usage = 3,000 kWh/yr/365 = 8.21918 kWh/day. Summer = 153 days, winter = 212 days.

                        2.) --->>> Summer EV use = 1257.5 kWh, Winter EV use = 1742.5 kWh.

                        3.) For DR rate schedule and yearly EV adder calc. for electricity used I'm assuming you already use 130% of baseline rate, so all added EV charging will be at the over 130% to < 400% tier rate applicable to summer or winter.

                        4.) adding 250 kWh/mo. will not kick you over 400% of baseline usage for any month.

                        5.) All TOU charging is done at super off peak times and rates as applicable.

                        Approximate $$ adders to an annual residential bill for adding 3,000 kWh/yr. for each tariff schedule using assumptions as described above:

                        For DR adder: Summer rate = $0.47504/kWh --->>> 1,257.5 hrs. * $0.47504 = $597.36
                        Winter rate = $0.46504/kWh --->>> 1,742.5 hrs.* $0.40361 = $703.29
                        Total adder = $1,300.65/yr.

                        For EV - TOU - 2 adder: Summer rate = $0.22793/kWh --->>> 1,257.5 hrs. * $0.22793 = $266.62
                        Winter rate = $0.22879/kWh --->>> 1,742.5 hrs. * $0.22879 = $398.67
                        Total adder = $ 665.29/yr.

                        For EV - TOU - 5 adder: Summer rate = $0.09317/kWh * 1257.5 hrs. = $117.16 + ($16/mo. * 5 mo.) = $197.16
                        Winter rate = $0.09403/kWh * 1742.5 hrs. = $163.85 + ($16/mo. * 7 mo.) = $275.85
                        Total adder = $473.01/yr.

                        So, if my assumptions are correct, get an EV in SDG & E territory, and any TOU schedule over DR tiered rate schedule is a no brainer, and at 3,000 kWh/yr. EV-TOU-5 looks like the best deal at this time.

                        TOU-EV-5 is, at this time anyway, a better deal than EV-TOU-2 until the annual super off peak charging gets below ~~($16/mo.*12 mo.)/($0.2284-$0.0935) ~ = 1,423 kWh/yr., or maybe something like 5,000 miles driven/yr. or so. Less than that and EV-TOU-2 might be a better deal, at least under current rates and times.

                        As more of an academic question, I wonder what will happen to super off peak or TOU times and rates in general if the semi absurd happens and EV's REALLY take off, they become ubiquitous and strain the system with night (or other off peak charging times).

                        If my logic, calcs assumptions and numbers are correct, your ROI improvement might just be a bit better than you calc'd.

                        On your question of vehicle rebates : Since I don't (yet) have an EV, I'm not up to speed on utility rebates for EV's.(but that Porsche EV is looking pretty sweet.)


                        Apologies J.P.M. for not updating you on the latest numbers..
                        I have slightly adjusted them based on my recent use on TOU schedule (amazing how dynamic pricing makes you change your habits!).
                        And the projected usage might keep changing obviously.
                        Happy to share my math, in case I have made mistakes (probably!).
                        It is not letting me attach XLS files, can send privately.
                        Last edited by jgd108; 07-19-2018, 02:49 PM.

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                        • #27
                          J.P.M. since there's no PM how can I send you something privately? Thx!

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                          • #28
                            Originally posted by jgd108 View Post
                            J.P.M. since there's no PM how can I send you something privately? Thx!
                            I'd rather not have that happen.

                            No offense, but looking at life as a set of probabilities as I do, I've found it best in these days of seemingly ubiquitous physical and mental sloth, and what's become the usual dichotomous all or nothing outlook on life that the lack or loss of critical thinking skills has produced in most folks, I've found it best to keep mostly to myself. Most contact just isn't worth the aggravation, at least to me, and from the responses I seem to evoke from most folks I do engage with, the feeling seems mutual.

                            I've been rather busy as of late and will respond to your posting probably later today. Briefly, I'm having trouble understanding your spreadsheets.

                            No hard feelings.
                            Last edited by J.P.M.; 07-19-2018, 04:23 PM.

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                            • #29
                              jgd:

                              For non tiered TOU rates for SDG & E there's a method that may be helpful.

                              The trick is to understand that as long as a net metered array does not produce > 100% of annual consumption, PV generation and user/owner consumption can be treated as separate form one another.

                              If a system is operating at a point in time and generates less that consumption at that point, the generation can be considered an off set against what would be a charge for usage at that time. If generation exceeds consumption at that instant (really a 15 minute interval), the excess is credited at the hourly rate and that $ credit can be used against future usage. Either way, the generation can be considered revenue to offset a bill, and that offset is irrespective of annual use, provided that by trueup, consumption is greater than generation.

                              All that means is that a model like PVWatts or SAM or some other model that has hourly output can be used with a non tiered TOU rate schedule, and combining those two will allow a user to estimate annual REVENUE for a system that can be used to offset a bill (but NOT generate excess compensation revenue at the same rate as usage offset revenue), independent of the size of that bill, provided consumption is < generation. That revenue can then be used to size a system to offset as much of a bill as the user wants creates by consumption.

                              An example: Using PVWatts and TMY3 data for Miramar MCAS, and the latest SDG & E rate sheets, a south facing array tilted at 20 deg. will generate about 1,720 kWh/yr. per STC kW of array. Now, any hour's PVWatts output can be multiplied by the corresponding SDG & E hourly rate for that hour. Doing that, and using PVWatts output, and current DR-SES tariff schedule, each STC kW of that south facing 20 deg. tilt array will offset about $453 of annual billing under schedule DR-SES. So, if I currently use 6,572 kWh/yr. and my bill is, say, $1,900/yr. (at a blended rate of $1,900/6,572 kWh = $0.28911/kWh), to offset all but $120/yr. min. charge, I'll need a system size of ~ ($1,900-120)/($453/STC kW) = 3.93 kW --->>> ~~ a 4 kW system.

                              A little thought will show the value of time shifting use to off peak times, or at least away from peak summer times. As an highly unlikely but possible example, if I'm on DR-SES with that 4 kW system, and if I can shift ALL use to off peak at a current rate of ~ $0.22838/kWh ave. summer/winter, I can use (($453*4)+120)/.22838 = 8,459 kWh and eliminate all but $120/ yr. + some NBC's (I'm guessing ~ $60/yr. or so on, say, 3,000 kWh/yr. of non bypassable usage).

                              The more likely reality is that the more I can shift away from peak usage, particularly in the summer, the more electricity I can use with a given system installed and still avoid most of a bill.

                              That example uses DR-SES because I don't have an EV (yet). But it is from a spreadsheet I've done to get optimum orientation for arrays in N. County San Diego, and/or the effect on system revenue as array orientation is shifted from the optimum orientation for systems that are operating under DR-SES (which max. bill offset orientation is, if you're curious, ~ a 200 - 205 deg. az. and about a 30 deg. tilt for a bill offset of ~ $462/yr. per installed STC kW). As I wrote, the method will work for any TOU schedule that doesn't have a tier structure laid over it as DR-TOU and other schedules have. Easy to do your own spreadsheet. Just get an 8,760 row spreadsheet, plug in the hourly output from some model for a 1 kW array, multiply that for each of the 8,760 hours by the appropriate hourly rate and then by the array size you have in mind in STC kW and Voila'- that's about how much you can spend on electricity + min. billing etc.

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

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                              • #30
                                Thanks all for your extensive knowledge sharing and valuable posts.

                                I am new on this forum and want to clarify if my understanding is correct on the SDG&E true-up. Are you saying that, for NEM 2.0 DR-SES, true-up is effectively on net "revenue", not on net generation "kWH"? My question is prompted because everywhere I read in SDGE, it generally says something along the line of... if you generated more "energy" than you use, the excess is credited at wholesale rate; it doesn't say, if the credits for energy sent to grid is more than the cost for energy taken from the grid.

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