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Powerwall and AC unit

Discussion in 'Tesla Energy' started by Chancellor32, Jun 14, 2019.

  1. Chancellor32

    Chancellor32 Member

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    So I am hearing mixed things from Tesla and hoping y’all can help. Is it possible for my AC unit to be powered by my PW while the grid is still active? I know during an outage it’s necessary to have 2 in order for full home backup but I thought 1PW was enough to run an ac unit while grid is active.
     
  2. gpez

    gpez Member

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    My home is set up in this exact way, but perhaps you have a time of use consideration which I don't.

    I have an 8.6kw solar array, one Powerwall, and a handful of high wattage appliances including the AC. Since the AC, dryer, and oven draw too many amps and would overload a single Powerwall the solution was to split those circuits off of the panel backed up by the Powerwall and on to a non-critical loads panel (or shed-load panel). During the time the grid is up the Powerwall does not provide any power to the home and all of the draw comes from solar + grid. During a grid outage the non-critical loads are not powered.
     
  3. gpez

    gpez Member

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    I have some diagrams! :)

    There are actually 4 circuits on the non-critical loads panel for me: AC, oven, dryer, and the 240v EV outlet.

    Net of it is that while the grid is up those 4 work. Grid is down, they're offline.
     

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  4. Chancellor32

    Chancellor32 Member

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    So your PW doesn’t provide any power to your home at all? Basically what I am wanting to do is from 6-8pm run my AC unit off of my PW instead of grid in order to avoid demand charges. Trying to figure out if that is possible because if not then the PW is pointless.
     
  5. SoundDaTrumpet

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    I have 2 PWs.
    1. Oven backed up. Need two PW for this. It is a non-motor load, so two PW can handle it. It will be costlier to segregate this single circuit and relocate and the oven is often located in a subpanel downstream. It's most convenient for the electricians.
    2. A/C is not backed up but monitored by the gateway. With the grid up, the PW can offset A/C usage. There's no guarantee your A/C can be backup up because it is old, the basic model, or incompatible with amperage reducing devices. The folks who do have it running in this forum with no modifications have some really high end units 2-3X the cost of mine. You are in Arizona, so likely your unit is higher spec than mine. My 10 SEER really drained quickly during this past weeks heat wave. The PW reacts slowly to stop discharging. Reserve set to 20% and PW stopped at 16%, not enough to get thru a night of power outage. In an outage, the HVAC system will still kick on the blower, and I will still have power to keep the gas furnace going in the winter. 3~4 PW is more appropriate to backup A/C.
    3. EVs ought to be not backup unless you have multiple PW. I have one EV charger isolated from PW, and one unused EV charger that is on the backup circuit for peace of mind.
     
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  6. gpez

    gpez Member

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    It's purely for back up. I live in a place that does not have a time of use charge so all of my high wattage appliances draw from the grid + solar. Figured you were asking about that instead :)

    If your AC draw exceeds the single PW inverter limit I believe multiple PWs are your best option as my understanding is that if it configured for ToU it's all or nothing (can't draw from both the utility and the PW to prevent the PW inverter from being overloaded).
     
  7. cwied

    cwied Member

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    Actually it's fine to draw from both the grid and the PW when the grid is up. It's when the grid is down (during a power outage) that overload is an issue. I've tested with two Powerwalls and a 14 kW load and it worked fine. 10 kW came from the Powerwalls and 4 kW from the grid.
     
  8. diverbelow72

    diverbelow72 New Member

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    What type of AC unit are we talking about? A whole AC unit for the house (central air) or window/portable AC units?

    If it is for central air - Tesla requires min 2 PW's with a SureStart on the central air
    If it is for window/portable AC units - 1 PW is fine.

    I had 2 PW's installed in March 2018 and the whole house is backed up including my central air (3 or 3.5 ton) and EV charger. Tesla installers put a Sure Start on my central air but wired it wrong, come to find out. Good thing a friend of mine is an HVAC person and wired it correctly. So when in use, central air uses 4.5kWh.
     
  9. gpez

    gpez Member

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    That's cool, happy to learn something new about the PW feature set. Is that documented somewhere?
     
  10. NuShrike

    NuShrike Member

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    #10 NuShrike, Jun 17, 2019
    Last edited: Jun 17, 2019
    YES it can, as long as the grid is connected.

    What is your normal power draw for your A/C? There's a LRA (startup current), and a RLA/FLA for (runtime current). If you can find the RLA/FLA off the labeling on your A/C, or you've already been monitoring your power-draw, you can do the math.

    For example, I have a Seer-10 rated A/C which draws ~4 kW. One PW can offset that, but will need 1 kW from the grid. It will not work without the grid.
     
  11. Chancellor32

    Chancellor32 Member

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    See that’s what I was expecting but Tesla is saying not possible. My ac draws at max 3kw to run.
     
  12. cwied

    cwied Member

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    I think they've probably confused themselves. When the grid is connected, the Powerwalls are just offsetting the house load. They can offset up to their maximum capacity and any excess will be provided by the grid. Since everything is electrically connected, you can't really tell which power is coming from the grid and which from the Powerwalls. As long as the total load is less than the Powerwalls' capacity, there won't be any grid import. If more power is needed than the Powerwalls can deliver, it'll just come from the grid.
     
  13. NuShrike

    NuShrike Member

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    Is this context where your A/C breaker is in your backed-up panel?

    You cannot back-up the A/C if the startup/LRA is too close to 5 kW/per PW max.
     

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