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PowerWall with Model S/X charge cable attached

Discussion in 'Tesla Energy' started by Electric Joe, May 3, 2016.

  1. Electric Joe

    Electric Joe Member

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    I have no solar panels on my roof yet, but am hoping to add some to offset a portion of my electricity use. About half of the electricity I buy each month is consumed by my Model S, so I don't care whether the solar generated power goes into my appliances or my car. It seems to me that it would be a great idea for Tesla to build PowerWalls with charge cables on them (or a component that can be easily connected to a series of PowerWalls) so that a Model S/X/3 owner can avoid the entire concept of power inversion by taking DC from the solar panels, storing it in the PowerWall, then transferring it to the car in the evening as direct current, the same way a supercharger does. The downside would be that the PowerWall wouldn't be able to provide AC power to the house during a power outage, but the upsides are huge: no expensive DC-AC inverter is needed, no complex house/panel/transfer switch wiring is necessary, no DC-AC conversion inefficiencies are introduced. Sure, the 6.4 kWh capacity of one PowerWall is not enough for my daily commute, but 25.6 kWh is (4 PowerWalls).

    Given the option, I'd rather spend my money on panels and PowerWalls to use this simple setup rather than panels, PowerWalls, an inverter, a transfer switch and more electrical wiring/labor.

    Has this been discussed before? Charging a car directly from a series of PowerWalls seems like a pretty obvious idea.
     
  2. ecarfan

    ecarfan Well-Known Member

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    And a very expensive one. Each Powerwall is 7kW (actually slightly less since some is reserved and cannot be accessed). So to charge even an S70 from 20% to near full is going to take over $20K worth of Powerwalls, plus install costs. Does that sound attractive to you?
     
  3. Electric Joe

    Electric Joe Member

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    Obviously that's a dumb idea, and not what I suggested, but charging from 45% to 85% (my 2-hour commute) would be feasible, and could be done with four PowerWalls. That's a reasonable investment when rolled into a solar installation.
     
  4. wang5150

    wang5150 Member

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    I also doubt Tesla would want owners to supercharge up their cars to recharge their Powerwalls for free electricity.
     
  5. electracity

    electracity Active Member

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    You want to charge your car with the least expensive electricity. Within the life of your current car, the lowest cost will never be from a powerwall.
     
  6. Electric Joe

    Electric Joe Member

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    Yeah... again not what I said.
     
    • Helpful x 1
  7. Electric Joe

    Electric Joe Member

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    Do I? I'm sure I'm not the only person who wants to charge his car with the least polluting electricity, which may very well be from a PowerWall.
     
  8. electracity

    electracity Active Member

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    The least polluting will be charging when the sun is shining: Panels at home and a charger at work.
     
  9. int32_t

    int32_t Tesla Spotter

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    That's a neat idea, and might even facilitate faster turn-around from your commute to a weekend trip. Still, I think the sheer quantity of energy storage required to make most commutes feasible would make the cost of the system prohibitive. Homes use so much less energy than a vehicle, so 6.4 kWh is enough for most days and is more practical. Besides, the state of power electronics these days is so good there is minimal loss. Good solar PV inverters operate in the 95-98% efficiency range. Also, if you are grid-tied anyway and simply have a Powerwall for backup, your system could continue to feed electricity to the grid (which you probably get paid for, depending on your region) when the battery is full and the sun is still shining.
     
  10. timk225

    timk225 Member

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    The cheapest charging will be.... anywhere that is not on your electric bill! Superchargers, at work, etc.
     
  11. ecarfan

    ecarfan Well-Known Member

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    My apologies for misunderstanding your proposal. I still think that your idea of using 4 Powerwalls is not anywhere near cost effective compared to charging your car at off peak rates. Maybe you could tell us what you pay for electricity where you live? My off peak rate is k$01.0/kWh. At that rate it costs me a few dollars to charge from 45% to 85%. No Powerwalls required.

    Next month I am buying a Powerwall from Tesla Energy to be part of a new solar system I will have installed. I'm not buying the Powerwall to charge my Teslas, but to reduce my electric bill overall and provide back up power when the grid goes down.
     
  12. Chet

    Chet Member

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    I think you mean "$.10" per kWh.
     
  13. ecarfan

    ecarfan Well-Known Member

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    Yep, typo on my part. My off peak rate is $0.10/kW.
     
  14. montreid

    montreid Member

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    Neat idea, but if MI has netmetering and Time Of Use (TOU) like CA does, you won't be asking about this.

    every kWH I generate and feed to the grid i get 0.48 vs charged only 0.16 for overnight charging. Even with conversion losses, still makes sense to charge at night at lowest rate (one could also argue that charging during the day as a whole is wasteful and that one should DISCHARGE your EV battery during the day via V2G smartgrid concepts as much as possible then recharge at night.
     
  15. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Active Member

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    In CA, you could expect that charging during the day will end up better because it will allow CA to continue to add solar.
     
  16. deonb

    deonb Active Member

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    YES!! Absolutely. 10 powerwalls for $20K? You kidding - that sounds really attractive!

    Where can I haz me some Powerwalls for $2K each?
     
  17. JSkrehot

    JSkrehot Member

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    East Coast, maybe PowerWall makes sense, however, being I live in CA, where your grid is down for at most a couple hours, ever, spending the extra money on a bigger solar system would be much more effective. You can't use enough energy at night to justify the cost of a PowerWall, not yet, WAY WAY TOO EXPENSIVE, currently. I am installing a 6.12 kW system from gogreensolar (with Edge Inverter incase I ever want a PowerWall when MUCH LESS EXPENSIVE), this will offset my yearly usage by 114%, don't have my Tesla yet but as soon as the M3 deliveries hit the West Coast (30 min from factory), I am set with home solar and a 14-50 Nema plug. $13,300 after taxes and permitting and get 30% back in April when taxes filed. Pays for itself in 4.5 years, produces a little over 9,200 kWh per year, upgradeable with more panels depending on how many kWh my Tesla increases my usage. I have 8 free level 2 charge stations at work too.
     
  18. JSkrehot

    JSkrehot Member

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    East Coast, maybe PowerWall makes sense, however, being I live in CA, where your grid is down for at most a couple hours, ever, spending the extra money on a bigger solar system would be much more effective. You can't use enough energy at night to justify the cost of a PowerWall, not yet, WAY WAY TOO EXPENSIVE, currently. I am installing a 6.12 kW system from gogreensolar (with Edge Inverter incase I ever want a PowerWall when MUCH LESS EXPENSIVE), this will offset my yearly usage by 114%, don't have my Tesla yet but as soon as the M3 deliveries hit the West Coast (30 min from factory), I am set with home solar and a 14-50 Nema plug. $13,300 after taxes and permitting and get 30% back in April when taxes filed. Pays for itself in 4.5 years, produces a little over 9,200 kWh per year, upgradeable with more panels depending on how many kWh my Tesla increases my usage. I have 8 free level 2 charge stations at work too.
     

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