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Question: difference in to/from Powerwall stats

Discussion in 'Tesla Energy' started by rjdunn, Jul 14, 2018.

  1. rjdunn

    rjdunn Member

    Joined:
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    Location:
    Emerald Isle, NC
    I’ve had my Powerwall running just over a week now, and I’ve noticed that each day, the amount to the Powerwall is higher than the amount from the Powerwall. Maybe a half kW or so, sometimes a bit moreif I store/retrieve more power. Is this:

    • AC-DC-AC round trip loss
    • Power used by the Powerwall itself
    • Something else?
    Thx in advance for the insights of the hive mind ;-)

    The Powerwall seems to be working perfectly, as expected...

    -Joel
     
  2. rjdunn

    rjdunn Member

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    The more I think about it, I believe I’m just noting the 89% rated round trip efficiency, though the numbers work more like 80% on weekly basis for this first week...what are others seeing?
     
  3. cwied

    cwied Member

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    San Mateo, CA
    The powerwalls lose energy over time too. I don't know if that's real leakage or just rounding errors due to the small in- and outflows as they try to maintain a 0 energy flow. The loss seems to work out to about 1% per day. You can see this if you switch to backup-only for a day or two.
     
  4. ewoodrick

    ewoodrick Active Member

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    Batteries are not 100% efficient.
    Inverters are not 100% efficient

    Do you feel any heat anywhere on the Powerwall?
    That's your efficiency
     
  5. Siggy101

    Siggy101 Member

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    Where is your Powerwall situated? Is it outside in full sun or a cold place? If so, it could be the heating/cooling system.
    Otherwise, I would imagine what you are seeing is just the normal losses from AC/DC conversion, component losses etc.
     
  6. rjdunn

    rjdunn Member

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    It’s in a shaded place, mild coastal climate. Yep, I think it’s just normal, but being a newbie, I’m trying to get a baseline normal ;-)

    Thx!

    -Joel
     
  7. Siggy101

    Siggy101 Member

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    Yep, it sounds like that's about normal then.
    Congrats on the nice new Powerwall. I hope it serves you well for many years to come!
     
  8. ons_

    ons_ Member

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    I was just about to ask if anyone else was seeing about .5 kwh loss to/from the powerwall too. Mine is also installed outside in a shaded area. Perhaps it is the norm for colder months. Now I'm wondering what it will look like when things warm up.
     
  9. JohnRatsey

    JohnRatsey Member

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    If it's any use, the Tesla app reports, for my battery, for the last month: From Powerwall 200 kWh, To Powerwall 228 kWh, which indicates about 88% efficiency. The battery is in my garage with, I estimate, a temperature of around 10C / 50F. In addition to the losses noted above, there is also the energy used by the equipment in the battery which will consume some power even of the battery is on standby. Software update 1.28 included "Reduced energy consumption when idle" which should have reduced this.
     
  10. Siggy101

    Siggy101 Member

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    You're quite right that the powerwall will use some energy for temperature management.
    There is also the inevitable ~10% loss when you convert from ac to dc (charging) and then same again when you discharge. If you see 88% efficiency then Tesla are doing an excellent job in the ac/dc/ac conversions.
     
  11. nyprepper

    nyprepper Member

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    Location:
    NE US
    i have 2 PW's and keep them set as backup only. Just sitting in backup mode, they expend approximately 1.5% of their power every 24 hours. When they drop below 97% they will recharge from the solar. Interestingly, they have never displayed as 100% full on the app......they only reach 99%, then they stop charging.

    In terms of charging from Solar, there is a definitely a noticeable loss in terms efficiency. I have not determined exactly what that loss is....but to charge my two PW's from 97% to 99%, in theory, it should take .54 kWh. From what I have observed, it takes almost twice that. I wish the data available in the app was more granular and accessible.
     
  12. MorrisonHiker

    MorrisonHiker S 90D 2018.48.12.1

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    Looks like mine are running at about 85.5% efficiency since September. They are in the garage and used in TBC-Balanced mode.
     
  13. Siggy101

    Siggy101 Member

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    Anything over 80% for both charge and discharge seems perfectly normal to me.
     
  14. miimura

    miimura Active Member

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    Location:
    Los Altos, CA
    My solar output is super weak this time of year, so I'm just bouncing off the Reserve level. For example, today 3.5kWh went into the Powerwalls and 2.4kWh came out. It's not all overhead, for some reason there are small random discharges below the Reserve level.

    Yesterday and Today.

    Chart 2019-01-03 PW only.jpg Chart 2019-01-04 PW only.jpg
     

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