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TBC and EV Charging

Discussion in 'Tesla Energy' started by eml2, Aug 1, 2018.

  1. eml2

    eml2 Member

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    I just got TBC yesterday, but I don't have TOU rate.

    Also, I have a MX and usually charge it overnight, say from 1 am to 4 am.

    I do not want to charge my MX using PW since it makes no sense to move energy from a battery to another due to efficiency loss. Since my house load is pretty low during those hours (1 am - 4 am), I don't mind to shut off PW so that both MX charging and house load are coming from the grid.

    For those who has experience with PW's TBC, is it possible I can set it up so that PW will be off between 1 - 4 am, and the rest hours operates as self-consumption?

    Thanks.
     
  2. miimura

    miimura Active Member

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    You should try it. Start with the Balanced mode and set the schedule to Off-Peak when you want the Powerwall to go into Standby and don't use the Peak period setting. I'm not sure this will do exactly what you want because I've never tried it this way.
     
  3. Shygar

    Shygar Member

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    Sounds like it should work in theory. It won't drain the battery during offpeak even if it's at 100%.
     
  4. wwhitney

    wwhitney Member

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    Another option would be have a second CT that measures just the EVSE current, and subtracts it from the total household current so that the Powerwall doesn't see the EVSE usage.

    Cheers, Wayne
     
  5. Neil_dsb

    Neil_dsb Member

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    I have the same question, I have had my PW2 for a year and use TOU cost saving mode, planning to buy a MX within a few months/early next year....any feedback would be appreciated, cheers Neil
     
  6. cwied

    cwied Member

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    Frankly, I don't know if it really makes sense to think of it this way. If the Powerwall discharges it doesn't matter what load it's feeding. You're going to pay the inefficiency cost either way. The electricity that comes from the Powerwall still made a round-trip through a battery, even if you're using it in your house. You're also going to lose a certain amount of the electricity from the grid when charging your car. Going directly from Powerwall to car doesn't add any losses. you just incur it at the same time.

    If you want to limit how much power leaves the Powerwall, the easiest way to do it is using the backup reserve. Just set the reserve so you discharge the desired daily amount.
     
  7. eml2

    eml2 Member

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    I agree that the inefficiency cost is going to incur either way, but I am also trying to minimize the PW cycles. Say without EV charging, I will normally have ~30% left before the sun comes up to recharge it to 100%. Now with EV charging, the PW will be complete drained before the sun recharges it to 100%.

    Ideally, the best way to do it is as @wwhitney suggested, to remove just the EVSE usage. However, I am hoping to leverage TBC functionality without adding any hardware.

    I also agree that backup reserve will do the trick too, but I have no control on when PW will hit my reserve %. On the other hand, I can schedule the car when to start charging.
     
  8. cwied

    cwied Member

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    I guess my question is why would it matter? If you set your reserve at 30%, you will always be at 30% in the morning. There is no difference between pulling from the grid for the EV and using the Powerwall to power your house and charging your EV from the Powerwall and pulling from the grid to power your house unless you end up at a different SoC at the end. Your self-consumption percentage is the same either way. Even if you remove the EVSE from the measured power, all you're doing is changing what the app reports, not your impact on the grid.

    The issue with TBC is that it doesn't do the same net-zero discharging that self-consumption does. The two modes you can get for sure are standby and offsetting the full house load (and exporting all the solar). To do what you want, you'd need one of the homebrew TOU systems that use the local Powerwall API to switch modes.
     
    • Like x 1
  9. miimura

    miimura Active Member

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    For me, it's not about the round trip efficiency loss or extra cycles on the battery. I don't want to discharge the batteries at all during the Off-Peak rate period because my solar was generated during the Part-Peak period. There is no way I want my batteries drained of 26 cent power when I can buy it from the utility at 13 cents. By keeping the solar power in the batteries, I preserve that value. If the batteries get full during the next Part-Peak period, then the solar will be exported and I will be credited at the 26 cent rate.

    Anyway, for the OP, without TOU rates, but with Net Metering, then it's much less critical. I would just try the TBC Balanced the way I said in the second post. It should do what you want and you won't have to worry about babysitting the Reserve setting like I did before TBC was available.
     

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