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Switching between Powerwall and power company

Discussion in 'Tesla Energy' started by Alketi, May 6, 2016.

  1. Alketi

    Alketi Member

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    Maybe this is obvious, but will a Powerwall power the house while it has a charge, and then automatically switch out to allow the house to be powered by the power company otherwise? Then switch back in when it has a charge again, etc.?

    I'm asking because I have solar panels, but my local power company charges me more for my usage than it pays for my generation. Thus, I have two meters, not a net meter. So, it's advantageous for me to cut down my power company usage but still keep the power company connection, as going off-grid is not feasible.
     
  2. Ampster

    Ampster Member

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    That is question for the SolarEdge inverters, since you most likely will have to buy one to work with the Powerwall. Presumably it will have a setting that minimizes grid use. My hybrid inverter has a setting like that.
     
  3. Alketi

    Alketi Member

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    Ah, does it only work with the SolarEdge? I've actually got microinverters, so I'm generating AC essentially at the panels. Sounds like it wouldn't work then...
     
  4. Rockster

    Rockster Active Member

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    It's my understanding that only the SolarEdge SE7600A-USS inverter works natively with the PowerWall at this time.
     
    • Informative x 1
  5. Alketi

    Alketi Member

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    Actually, now that I think about it some more -- is an inverter actually needed?

    I remember at one point Tesla was pitching the cost savings of charging the Powerwall from the grid at night (when rates are cheaper) and using the energy during the day? Is that use-model not possible with the production Powerwall?
     
  6. Ampster

    Ampster Member

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    I also have micro inverters but I am on a time of use rate and net metering. Mine is an AC coupled system. I think you would have to abandon your micro inverters and rewire your panels to work with a SolarEdge inverter. Essentially you could abandon your existing arrangement with your utility (separate meter) and only run the SolarEdge inverter behind the remaining meter. You will have to do the math to see if that will give you a good payback. Fortunately you have good historical data for production and consumption.
     
  7. ecarfan

    ecarfan Well-Known Member

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    That is what I have been told also by my Tesla Energy contact. That inverter is required to be used with the Powerwall.

    I am going to be buying that inverter and a Powerwall directly from Tesla Energy within 4 weeks, they have told me.
     
  8. Rockster

    Rockster Active Member

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    I'm anxiously awaiting my system design documents from Solar City. They assure me that they're designing a system that's ready for a PowerWall. I'm wondering: if I get a PowerWall later is it subject to the 30% tax credit or must it be purchased as part of the solar system to be eligible?
     
  9. Ampster

    Ampster Member

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    It is best to check with a tax professional, however I believe that the Powerwall can be added later even in a different tax year. I installed solar in 2014 and added a battery storage in 2015 and my tax accountant didn't flinch.
     
  10. Xminus6

    Xminus6 Member

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    That's what I'm wondering. I don't really care to have a Powerwall tied into my PV system because I would never charge it with solar energy. It wouldn't make sense to charge a Powerwall with energy I can sell at $.44/kWh to replace energy I can buy at $.11/kWh. I'd only want to charge at off-peak to offset my on-peak usage and allow my PV system to sell all of its generation during Peak and Partial Peak without having to supply the house with power.

    The benefit is I wouldn't have to change out my inverters for my PV system and I get a better payback. It looks like two PW would payback about $5/day in time-shifted energy usage. So $1500/year roughly. That would make them a reasonably good purchase decision.
     
  11. ecarfan

    ecarfan Well-Known Member

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    You need an inverter to convert the Powerwall DC output to AC.

    As far as I know, you can charge the Powerwall at times when your kW cost is low and then use it during the day.
     
  12. Alketi

    Alketi Member

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    Oh -- the inverter is on the OUTPUT! Of course! So it's AC input / DC output. And, as of now, there's only one inverter that works with the Powerwall -- the SolarEdge?
     
  13. electracity

    electracity Active Member

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    Enphase is starting to release its battery product in Australia. If you have enphase inverter you will want to track their release schedule. That battery will simply connect to your main panel.
     
  14. Utahken

    Utahken Member

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  15. ecarfan

    ecarfan Well-Known Member

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    The inverter is DC in/AC out.

    Powerwall takes DC in from solar panels and stores it. Inverter pulls DC from Powerwall or solar panels and sends it to your house circuits (AC) or back to the grid.

    Tesla Energy has told me that only the SolarEdge 7600 series inverter can be used with the Powerwall.
     
  16. Alketi

    Alketi Member

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    Sorry to belabor the point, but based on Musk's original statements I was under the impression that the Powerwall would work even for folks who DON'T have solar panels because they could charge it at night (AC-in from the grid) and use it during the day.

    If it's DC-in, then that previous statement is not the case. Can you clarify? Did the behavior of the Powerwall change, or is what I wrote above a misunderstanding?

    Cheers.
     
  17. Ampster

    Ampster Member

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    #17 Ampster, May 12, 2016
    Last edited: May 12, 2016
    I will try. There are several ways. The first being solar panels and solar edge optimizers. The second being with a DC power supply or charger running off your house AC and providing approximately 350 volts DC. You would have to figure out how to control that charger. Either a voltage programmable relay or some signal from the built in DC to DC converter. Presumably it would be timed to go on during your super off peak rate.
    In the other side the Powerwall would connect to the SolarEdge inverter which would power your critical loads panel. That would let all of your solar output be sold to the grid. The unknown is how you would program the SolarEdge inverter to come on and switch to the critical loads panel. My inverter has a programmable setting that sets when the critical loads panel will be powered by the inverter. Did that answer your question?
     
  18. Aussie

    Aussie Member

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    Well, the statement is kind of true. You don't technically need solar panels. But you still need an inverter and the rest of the SolarEdge gear for the AC/DC and voltage conversion. But then the system would work just with the grid. But most probably there are better systems out there to achieve this goal.
     
  19. bryand

    bryand Member

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    When my PowerWall was installed, it was made clear to me that the power utility would disconnect me if they found I was charging the PowerWall at cheap rate and selling the energy back to the grid at prime rate. So the issue may be with the power company, not the PowerWall. As a result, I believe UK installations cannot charge the PowerWall from the grid, only from PV. In any case, the gains are greatest when you are storing your own solar-generated energy rather than simply time-shifting your grid consumption. The SolarEdge inverter can be set up to disable the battery at certain times of day, so my setup doesn't use the battery during off-peak hours, when I am charging my car on cheap overnight electricity. (A typical car charge for me is 28 kWh so the PowerWall's 6.4 kWh wouldn't make much impression on that).
     
  20. ecarfan

    ecarfan Well-Known Member

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