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‘Backup Only’ sends to house too

Discussion in 'Tesla Energy' started by copilot&Dj, Jan 8, 2020.

  1. copilot&Dj

    copilot&Dj Member

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    F12271C1-5B45-4802-BF19-BE7B230E0629.png 57E693A1-122A-4AE3-9954-4A6660D1FE39.png F12271C1-5B45-4802-BF19-BE7B230E0629.png F12271C1-5B45-4802-BF19-BE7B230E0629.png Have ‘Backup Only’ selected. However I’m watching the app alternate between sending solar strictly to the powerwall, then a second later also sending to the house too. Why is this? I’ve selected the solar energy just be used for Backup Only.
     
  2. copilot&Dj

    copilot&Dj Member

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    (Sorry, new to this forum and can’t fig out how to remove dupe pics from my post)
     
  3. power.saver

    power.saver Supporting Member

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    As house load shifts, and solar increases/decreases, a small amount is diverted to house or sometime grid until the PW inverters catch up. This is normal behavior.
     
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  4. copilot&Dj

    copilot&Dj Member

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    Thank you for the reply. - The house shows 8kW usage in both the 'solar direct to battery only' instance, and when the solar was splitting between the battery and the house. (Maybe the house load was about to change?)
     
  5. copilot&Dj

    copilot&Dj Member

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    Sorry, I meant .8 kW
    (if anyone knows how a user can delete or edit his posts, please let me know. Thanks)
     
  6. power.saver

    power.saver Supporting Member

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    Possibly, though more likely the solar was changing too. Only Solar, Grid and PW are measured, house is the remainder of the power flow. So if solar increases, but the PW hasn't caught up, the "extra" will default to house.

    You can edit after a certain number of posts, since you're new, not yet.
     
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  7. chrisbailey13

    chrisbailey13 Member

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    Backup Only refers to Powerwall usage, not solar. the house will consume solar energy when the powerwalls are fully charged, or when the solar energy generated is more than the powerwalls can accept at once. it is also possible for the solar to provide energy to the Powerwalls, House and Grid at the same time when the latter two do not consume all the energy being generated.
     
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  8. charlesj

    charlesj Member

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    If you don't see the 'edit' feature in your post, it is too late to delete.
    Don't know how long that feature is in place after posting, a few hours, or a day.
     
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  9. cwied

    cwied Member

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    Remember that electricity flows freely through wires, so there is no way to direct the specific energy from solar directly to the Powerwalls. The only thing under control is how much power the Powerwalls are generating or absorbing. The lines are just a way of making the power flows easier to understand. When the Powerwalls lag a bit in adjusting their charging/discharge rates or there is a rounding error causing a mismatch in values, the end result can be that extra flows are shown for a short amount of time.

    Note that it would be just as correct to describe the situation as .4 kW going from the grid to the Powerwall with the house being supplied by .4 kW from the grid and .4 kW from solar, just not as intuitive or representative of the intent of the schedule.
     
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  10. JayClark

    JayClark Member

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    The other thing I think I've noticed, is that when a new & heavy load comes on line in the home, the Powerwall might take a few moments to "catch-up" in terms of ramping up the battery to cover the new load. When this happens I'll sometimes (not always) see the grid blip on briefly with a flow to the house for a few seconds, or even up to 10-20 seconds. But then also, I'll eventually noticed that the gateway seems to then adjust things so that a roughly "equivalent" amount flows back to the grid to offset (if I'm in TOU/Cost-Saving or Self-powered mode).

    For example, while I might have seen 500 watts flowing form the grid momentarily, say for 10 seconds, it seems the gateway might shoot 1000 wats back for 5 seconds or so - the end result usually for me is I have zero draw during that period on my utility bill, even though I saw things bouncing around. Usually when the house is running a a fairly level state I don't notice much of this happening.

    Also, keep in mind, the Tesla App on the phones can have gaps in receiving updated data. For a while I had switched my gateway from ethernet to wifi, and didn't realize the gateway was dropping the wifi connection usually for 5-10 seconds every minute, and sometimes dropping for many minutes as it tried to bounce between the ethernet and wifi connections - really weird behavior. When this happened the app would show power draw, that I knew wasn't happening. For example, I shut off the car charger at one point, yet the App would show a large draw still occurring for a up to a minute longer than I knew was reality. Eventually I remembered to log into the gateway web server directly, and could see the power load had dropped, even though the app was still showing it as if the car was charging.
     
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  11. Fredneck

    Fredneck Member

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    Devices like these are not all bused together on a single wire with electricity flowing in every direction. The flow of energy is directed and gated by the electronics. So it very much does decide how much energy from the solar cells is directed to which destination, the power wall, the home or the grid.
     
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  12. Ampster

    Ampster Active Member

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    Yes, but isn't it the higher voltage that the inverter puts out that determines to which load it will flow to? The grid presents as a load when its voltage is less than the inverter. A Grid Tie inverter only has one connection to a service panel or sub panel and current will flow to all the panels behind the meter based on their loads before any excess goes to the grid. The panels are bussed together by their breakers on the main panel with other load breakers.

    Perhaps we are saying the same thing.
     
  13. Fredneck

    Fredneck Member

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    I'm not sure. The battery has a power converter that accepts current based on the need to charge the battery or supplies power as needed. The solar panel inverter generates power in phase with the line and controls how much current it puts out based on the power available from the solar cells. The house wiring is dumb and simply draws power from whoever it is connected to.

    I don't know exactly how Tesla or anyone else wires their systems, but if they want the solar power to charge the batteries it can be done by wiring it all together on a single power bus and letting the components talk to one another to draw what is intended for that moment. Any demand that isn't satisfied by the solar would come from the grid. But to use the battery when the grid is down definitely requires a contactor to isolate the grid and requires the solar inverter to operate stand alone. Otherwise you are right, the power can all be bused on a single set of wires.
     
  14. Ampster

    Ampster Active Member

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    The Tesla PowerWall is AC coupled to the Grid Tie solar inverter. I assume that is what you mean when you mention those devices have to have a common power buss in order to work. As I mentioned earlier the main service panel is common to all the breakers and subpanels, except when the grid is down and, as you mention, the transfer switch disconnects everything except the critical loads (or the whole house), the Grid Tie inverter and the PowerWall.
     
  15. cwied

    cwied Member

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    #15 cwied, Jan 9, 2020
    Last edited: Jan 9, 2020
    Remember that the Powerwalls are AC-coupled, not DC-coupled. Each Powerwall unit has an inverter that feeds into the house wiring, same as the solar inverter. The inverters are all grid-tied, so they feed into the grid power. The gateway just has a transfer switch that sits between the grid and the backed-up circuits to disconnect in case of grid failure. It isn't doing any directing of power. In the case of a power outage, the transfer switch opens and the Powerwall inverters take over generation of the power. When the solar comes back, it syncs to the Powerwall power as if it were the grid.

    I'm not sure what system you're used to, but the Powerwall system definitely does connect everything to the same wire. That's part of what makes integration into an existing system so easy.
     
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