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Powerwall 2 - is it for me?

Discussion in 'Tesla Energy' started by drees, Jul 9, 2017.

  1. drees

    drees Active Member

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    #1 drees, Jul 9, 2017
    Last edited: Jul 9, 2017
    Thinking about a Powerwall 2 - help me make a decision!

    First off, I have a 3.24 kW DC Enphase system (typically around 2.5 kW AC peak in the summer, but occasionally up to 3.2 kW very briefly). Also live in SDG&E territory and currently using the EV-TOU2 (whole house) rate which has off-peak rates around 20c/kWh and on-peak summer rates around 50c/kWh (currently May 1-Oct 31 from 12PM-6PM). Winter rates are only about 15% different between on/off peak, so probably doesn't make much if any financial sense to load shift then once you account for the efficiency of the Powerwall.

    With the SGIP rebate at either step 2 or 3 and 6 months of time/load shifting, it seems that one might be able to get around $450/year assuming ~10 kWh/day and 30c/kWh a simple break-even period around 10 years, or the warranty period of the Powerwall.

    And that's at current rates - it appears that modifications to TOU rates will move TOU time periods later in the day where storage will almost certainly be required if you want to use your solar power at peak utility rates.

    None of that takes into account other non-monetary benefits of load shifting or solar self-consumption, either, or the ability to use the Powerwall for backup power (though admittedly that very rarely happens in my area).
     
  2. doubleohwhat

    doubleohwhat Supporting Member

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    what's your house load like during your peak solar production window? Basically, how much (kWh) are you producing but not using (sending to the grid, etc) each day?
     
  3. drees

    drees Active Member

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    #3 drees, Jul 9, 2017
    Last edited: Jul 9, 2017
    House load is pretty light during the bulk of the peak solar production window. Most of my solar power is typically exported, unless doing laundry and the dryer is running (which we avoid during peak periods). Overall probably net-export around 5-10 kWh from 12PM-6PM utility peak rate. Also have AC, but don't need to run that very often. As the sun goes down, though, load typically starts creeping up and I go from net-exporter to net-importer. Solar system typically generates around 5000 kWh / year. Hopefully would charge Powerwall using solar before peak period allowing for maximum solar export during peak periods and avoiding grid import during peak periods.

    Biggest flaw I can see in my assumptions is that my PV system is probably not big enough to completely fill up the Powerwall during off-peak before 12PM. Might only have 5-7 kWh of solar energy before 12PM on average...
     
  4. RobertF

    RobertF Member

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    I am not familiar with SDG&E rate structure. I live in Huntington Beach's SCE area. I heard that SDG&E had a special something for EV owners. I get a much lower rate at night than you. Check your alternatives. My point is it may be cheaper to add low cost electricity to your over production, making the powerwall economical. Good luck, they don't make it simple. I actually got good info from SCE's EV department.
     
  5. liuping

    liuping Active Member

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    During the summer you can also charge off peek after 6pm.

    However, I've heard the Powerwall2 software is not set up to put out more power than you are using during peek hours, so you might not be able to push the off peek saved power onto the grid during peek hours.

    Realistically, you'd probably get a better return adding a more panels.
     
  6. drees

    drees Active Member

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    Already do 99% of my charging during the lowest rate period from 12AM-5AM using the EV-TOU2 rate.

    Do you have any reference for this and what types of operating modes the Powerwall supports? It does seem that when combined with solar and to claim the SGIP, you do need to charge the Powerwall with renewable power, which means on-site PV.

    Oh, without a doubt that's almost certainly true, though it would force me into NEM 2.0 with any decent sized upgrade from what I understand. I would also want to replace my roof at this point in time with any future rooftop work, so I am looking to push off a solar upgrade for a couple more years. Though if I did end up with under NEM 2.0, there is additional incentive to maximize self-generation since there are non-bypassable charges for each kWh you import from the grid.
     
  7. SoundDaTrumpet

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    You only need to charge with renewable power to qualify for the 30% Federal Incentive Tax Credit for the first 5 years. California's SGIP has no such requirement.

    It's sad not many installers would entertain installing less than 1kW of solar to keep one on California's legacy NEM 1.0.
     
  8. montreid

    montreid Member

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    @drees, same boat as me. SDGE with same layout and 2 EVs. on NEM1.0.

    I've given up hope for someone to do a V2H solution and I decided last month to dive into this with the math of SGIP 3 about 7 years for us and protects against the shift that we've seen already happen to the north on the TOU times.

    I agree the arbitrage is going hard with the current setup programming (see discussion on other PW2 thread on the current programming for discharge) very kludge at the moment. Why can't Tesla simply add a button -- purge battery to 10% and dump to grid discharge?

    To that, why don't they add a port at the end of the battery to connect to Tesla EV for extended battery support in emergencies (and proverbial v2h support)
     
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  9. drees

    drees Active Member

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    Sounds like your calcs are in the same ballpark as mine. What math did you use?

    I have to suspect that the "dump to grid" option will eventually come, at the very least for those "Reduce your Use" late afternoons / early evenings in the summer.

    I also wonder if the utilities will want to use them to do any sort of frequency support as well?
     

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