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Need some help sizing my system and questions on how SCE netmetering works

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  • Need some help sizing my system and questions on how SCE netmetering works

    New user in Southern California Edison territory here.

    Just starting on the process for looking at solar this year - we got bids back in 2010, but it was too expensive for our needs then, so we decided not to proceed. Fast forward to today and we now own TWO long range electric vehicles that both have about an 80 mile round trip commute. That works out to a LOT of energy and now we want to take another look at solar.


    We got one EV in December, (replacing a plug in hybrid) and the 2nd just last month, so I have had to do some projections for our annual usage based on how much our super off-peak usage will increase since I don't have the actual data. Here is what I am currently projecting:

    (These are monthly kWh totals. Projected means I tried to apply a factor to account for charging both cars and actual was what our meter read during the actual period last year )
    • August: 2487 (this is the only month we have actuals for both cars.)
    • July: 2342 actual
    • June: 2372 projected (2032 actual)
    • May: 1755 projected (1467 actual)
    • April: 1690 projected (1399 actual)
    • March: 2083 projected (1708 actual)
    • February: 1826 projected (1493 actual)
    • January: 1937 projected (1594 actual)
    • December: 1676 projected (1087 actual)
    • November: 1461projected (1077 actual)
    • October: 1346 projected (964 actual)
    • September: 1535 projected (1143 actual)

    Total projected annual kWh usage: 22512 kWh . So, LOTS.

    We are living in a house built in 2010 with good insulation, double paned windows, radiant barrier in the attic, all LED lights, etc. The only efficiency improvements we haven't done are a smart thermostat, switching to a gas dryer vs electric and installing a swamp cooler. For various reasons we probably won't be making those changes (I do have a programmable thermostat, its just not wifi connected, etc). Really before the electric cars, we weren't solar candidates based on our usage.

    My roof surfaces I have to work with are a large area at a 90 degree east-facing azimuth and a smaller roof (maybe only 10 panels) at 180 degree. Living in the high desert, so no shading issues. Initial numbers coming in from companies via energy sage are looking at anywhere from 30 to 41 panels across both surfaces and systems sized from 10-13 kW. Initial prices coming in from 2.99/watt to 4.27/watt.

    Since we are looking at a very large system, I am wondering how netmetering might play into choosing a system size for us. We could go for a system that is sized for 100% of our usage, but I wonder if it wouldn't make more sense to get a smaller system that takes advantage of the netmetering on a TOU plan.

    My impression from reading the (mostly indecipherable) language from my POCO, SCE, was that my account would be credited for generation at the retail rate on a monthly basis. My interpretation of that was on a daily basis I would be credited for the peak and off peak rate while I was generating during the day (for excess production), then at night I would get to use those credits up at my super-off peak rate. So if I am sending kWh back to the grid during the .45/kWh rate, I then get to use that up at the .13/kWh rate at night. So I could generate 1kWh at peak rates and use that for 3kWh at night during super-off peak for example.

    But the first company we had out (Tesla Energy - I know, I know), the rep stated that it doesn't work that way. He stated I would be credited only by kWh vs the value of those kWh. So it would be one for one. If I generated 1kWh during the peak times, I only got to use that for 1kWh at night period.


    So I wanted to see if other SCE netmetering customers might could chime in on how that actually works. If its 1 for 1, then I need to size my system for my actual usage. If its done on a $$ credit amount instead, I can size my system smaller to take advantage of the TOU rates.





  • #2
    Originally posted by Az_Rael View Post

    So I wanted to see if other SCE netmetering customers might could chime in on how that actually works. If its 1 for 1, then I need to size my system for my actual usage. If its done on a $$ credit amount instead, I can size my system smaller to take advantage of the TOU rates.
    It is a $ credit. If off peak price was 0.20 / kWh, and peak price was 0.40 / kWh, for every 1 kWh you export during peak times you can import 2 kWh during the overnight off-peak.
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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    • #3
      Originally posted by sensij View Post

      It is a $ credit. If off peak price was 0.20 / kWh, and peak price was 0.40 / kWh, for every 1 kWh you export during peak times you can import 2 kWh during the overnight off-peak.
      Awesome, thanks! I did some Excel-Fu with some PV Watts runs and I think a 10.8-11kW system will work for me then.

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      • #4
        Originally posted by Az_Rael View Post

        Awesome, thanks! I did some Excel-Fu with some PV Watts runs and I think a 10.8-11kW system will work for me then.
        Just keep in mind that any spreadsheet numbers you use need to account for 2 changes that will make PV less cost effective:
        1.) NBC's. that are actually the lesser of the two in terms of $$ impact
        2.) The T.O.U. time periods are shifting, with peak times changing to later in the day. If you have spreadsheets using the old times, make sure those times are current with what may be in the offing. Vendors seem to be keeping pretty quiet about all the changes. Looks like SCE has already instituted most of the time changes, but it's probably worth double checking.
        Last edited by J.P.M.; 09-10-2017, 09:48 PM.

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        • #5
          Originally posted by J.P.M. View Post

          Just keep in mind that any spreadsheet numbers you use need to account for 2 changes that will make PV less cost effective:
          1.) NBC's. that are actually the lesser of the two in terms of $$ impact
          2.) The T.O.U. time periods are shifting, with peak times changing to later in the day. If you have spreadsheets using the old times, make sure those times are current with what may be in the offing. Vendors seem to be keeping pretty quiet about all the changes. Looks like SCE has already instituted most of the time changes, but it's probably worth double checking.
          I did put a guess in for the NBCs. I did .05/kWh on net electricity I use from the grid on a monthly basis. I THINK that is how they will be calculated.

          I am using the latest TOU times, thanks. It looks like generation during Peak hours is much reduced now. I keep on top of those since I need to know when to charge my cars during super off peak.

          It seems like the farther into the evening they push peak times, the more they will anger non-solar customers as well as solar customers. Maybe that will limit some of those changes in the future. Maybe.
          Last edited by Az_Rael; 09-10-2017, 11:56 PM.

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          • #6
            Originally posted by Az_Rael View Post

            I did put a guess in for the NBCs. I did .05/kWh on net electricity I use from the grid on a monthly basis. I THINK that is how they will be calculated.

            I am using the latest TOU times, thanks. It looks like generation during Peak hours is much reduced now. I keep on top of those since I need to know when to charge my cars during super off peak.

            It seems like the farther into the evening they push peak times, the more they will anger non-solar customers as well as solar customers. Maybe that will limit some of those changes in the future. Maybe.
            You're mostly on the right path. The NBC is probably closer to ~~ $0.02/incoming kWh or so. That rate is a published number but it's probably hiding out of plain sight.

            While the POCOs don't like net metering one bit, I don't think their primary purpose in how they are manifesting rate reform is motivated by any emotional need to screw PV owners. It's mostly about the bottom line and load management. If PV owners wind up as cannon fodder as a result, I don't think the POCOs are losing sleep over, but I'm just as sure that result, at least to the extent it may be occurring, is/was not the primary motivation for their actions. Like Michael Corleone said: "It's just business."

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            • #7
              May not make a big difference, but it looks like you are projecting a pretty even power increase month to month for the second EV. FWIW, from my experience, I use a bit more power in the winter months to heat the cabin, driving in rain, etc. - not sure if you have accounted for that - especially when/if the EV uses resistance heat. On top of that, super off peak where I am is more expensive in the winter than summer (SDG&E).
              5.7 kW DC enphase M250 + SW285 solar patio cover

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              • #8
                Originally posted by philips View Post
                May not make a big difference, but it looks like you are projecting a pretty even power increase month to month for the second EV. FWIW, from my experience, I use a bit more power in the winter months to heat the cabin, driving in rain, etc. - not sure if you have accounted for that - especially when/if the EV uses resistance heat. On top of that, super off peak where I am is more expensive in the winter than summer (SDG&E).
                Good point. I don't know how much of that I will be able to project though. The winter use is captured for the one EV, but without the year over year data it's hard to guess.

                Luckily super off peak is the same year round in SCE country so that helps.

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