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A PowerWall on wheels?

Discussion in 'Model 3' started by longshadows, Nov 14, 2017.

  1. longshadows

    longshadows Member

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    I’m an M3 res holder. The other day, following a major power outage in our state, my neighbor, an engineer, told me that when I get the Tesla, it can "power the house" during outages. Is this true? Is a Tesla a PowerWall on wheels? I’m sure it’s not that simple. Has anyone used an EV to power their house in emergencies? Can a Tesla handle it? Fascinating (and exciting) possibility living in Maine
     
  2. Runt8

    Runt8 Member

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    Tesla doesn't support this capability. Nissan allows it with the Leaf.
     
  3. CmdrThor

    CmdrThor Active Member

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    Any damage resulting from using the vehicle as a stationary power source will not be covered by warranty.
     
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  4. Tam

    Tam Active Member

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    Nissan can do it so Tesla can too but if Tesla allows that, it will be an option for you to opt out of PowerWall purchase.
     
  5. HankLloydRight

    HankLloydRight Fluxing

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    More to the point, they don't want people filling up at a Supercharger (for most existing cars, for free) and then going home and powering their home.

    There is at least one person working on a third-party solution to provide this functionality, though.
     
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  6. Zaphod

    Zaphod Galaxy President (former)

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    Best you can do is use a power inverter to plug into the 12V DC power outlet and convert to AC power. You cannot power your whole house, but would be able to charge your phone, use a TV or other small appliance. No official off-grid power capabilities.
     
  7. DFibRL8R

    DFibRL8R Member

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    But for model 3, there is a fee for supercharging. Other than the issue of excess fast DC charging causing battery degradation, why would it matter if I filled up the car at the neighbor's house, some other EV charger or a supercharger as long as the electricity has been paid for? Tesla is supposedly unable to produce enough batteries to keep up with demand. So why force a customer to buy another battery (Powerwall) just so they can have an emergency backup power supply? To me, this is a feature that would provide a real benefit to the Tesla customer and could sell more Tesla cars (not that they're having a problem with low demand for their cars). Still, I don't like Nissan having a feature like this that is unavailable on a Tesla without some complicated aftermarket electrical hacking.
     
  8. Tam

    Tam Active Member

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    If you live in CA, the maximum Tesla Supercharger fee is $0.20 per kWh while PG&E peak electric rate is $0.39.

    In theory, that's a profit of $0.19 if you pay less at Tesla Supercharger and use that cheap electricity at home.
     
  9. DFibRL8R

    DFibRL8R Member

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    Interesting. In Virginia, the rate Tesla charges is $0.13, right at the retail electricity cost. There must be a reason Tesla is charging below market rates for supercharging in CA but regardless, Tesla could easily make it cost neutral if they chose to. I think the cost argument against using the Tesla vehicle battery as emergency power is a poor argument against it. Heck, I just read about some guy using his Tesla to heat his garage while he was working in it.
    Model S can heat my chilly garage! I hope he didn't steal electricity from a supercharger to do that!:eek:
     
  10. Tam

    Tam Active Member

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    #10 Tam, Nov 14, 2017
    Last edited: Nov 14, 2017
    It's about understanding why Tesla doesn't like Vehicle-to-Grid when it has the brain to allow it:

    1) Powerwall sales might be affected
    2) Supercharger to Vehicle to Grid arbtrage
    3) Wears and Tears.

    You need to give Tesla a reason how it will be beneficial for its investors to use its technology to do those 3 above things.

    An average US household electricity usage is about 897 kWh per month or 30 kWh per day.

    Your long range Model 3 battery pack is about 75 kWh which is more than double an average household can use per day.

    Your warranty is 8 years or 120,000 miles.

    Your rated range for your battery is 310 miles.

    120,000 / 310 miles = 387 complete cycles.

    So if Tesla allows Vehicle to Grid option, the worse scenario for Tesla is: you would almost use up all 387 complete cycles in a year that has 365 days. And it's not even 8 years yet and what if you only drive a few hundred miles a year, so it's no where near 120,000 miles to run out of your warranty yet!

    That's the wear and tear part that Tesla is not willing to finance you!
     
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  11. gregd

    gregd Active Member

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    The charge / discharge cycles when a battery is used in a UPS are rather different than for a car, so the battery chemistry and construction of the cells are somewhat different for a PowerWall vs a Model S/X/3. Using the car to run the house will degrade the battery faster than using it as intended, hence the issue with the warranty. I don't think the effect is massive, but it's enough that the two product lines are kept distinct.

    In an outage, one would certainly look longingly at the KWH sitting in the garage (I know I have), but the car just isn't designed to provide that service. The Japanese version of the Leaf (and I believe the iMEV, too) have that emergency capability as a result of the recent earthquake and tsunami. I haven't read that the capability is available outside of Japan, however.

    Best bet is to use a small 12v inverter to keep a few LED lights on and run the Internet router and a laptop, though even there, I have read reports that some inverters can cause trouble (not related to the battery, however). Get a fire going in the fireplace for some heat. At least burning dead trees is usually carbon-neutral.
     
  12. Zaphod

    Zaphod Galaxy President (former)

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    Batteries for stationary products, i.e. powerwalls, are entirely different chemistry compared to the cells for the vehicles.
     
  13. DFibRL8R

    DFibRL8R Member

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    #13 DFibRL8R, Nov 14, 2017
    Last edited: Nov 14, 2017
    The OP was asking about use of the energy stored in the Vehicle's battery for an emergency outage situation not vehicle to grid. This essentially replaces the need to buy an expensive gas/propane powered generator for the few times a year the grid goes down. I don't see this causing major wear and tear on the vehicle battery or impacting PowerWall sales (most of these residential PowerWall sales are going to places where electricity rates are high with high peak demand charges). And again, Tesla currently has more demand for their batteries than they can supply. I don't think trying to sell every customer two giant battery storage systems (Vehicle plus PowerWall) instead of one is really a good strategic business plan at this time and runs counter to their mission of sustainability and environmental responsibility (it's a waste for someone who just wants an occasional emergency power back up to keep their ice cream from melting in an outage or whatever).
     
  14. HankLloydRight

    HankLloydRight Fluxing

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    Just a loosely related side note. A friend of mine, also a Tesla owner, won a Powerwall or two in the referral program. He also built an electric powered Delorean years ago using lead-acid batteries. We're thinking of salvaging the Powerwall batteries and replacing the lead-acid batteries in the Delorean for about double the range (60 miles, estimated). So really, it will be a "Powerwall on wheels". :)
     
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  15. brkaus

    brkaus Active Member

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    #15 brkaus, Nov 14, 2017
    Last edited: Nov 14, 2017
    - Battery chemistry - not designed for this duty cycle.

    - There is no high power DC->AC inverter currently on the car.

    - When you supercharge, it is putting DC directly into the battery bypassing the AC->DC Convertor. So, that implies a path is possible from the battery to the port and add an external inverter.

    So, it appears like would be possible to create an external device to convert DC->AC and somehow program the car to open the right set of contacts and bridge the battery to the port. But this would also be putting full 400V and full amps to the port (and external device) so it would need to be designed carefully.

    Sure, Tesla probably has all the parts lying around to do it. But it is a big step to actually make a workable, supportable product.

    Edit to add - If this was intended as a backup power supply, I would guess that they would need a foolproof utility disconnect built into the system, so it would have to be preinstalled.
     
  16. DFibRL8R

    DFibRL8R Member

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    Nevermind, I don't need Tesla to produce a simple, elegant solution for emergency back up power using the energy stored in the vehicle's battery, I can just by a PTO generator and use the kinetic energy from the Tesla's wheels to drive a generator instead. pto-generator-500x500.jpeg
     
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  17. Shygar

    Shygar Member

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    Not to mention the powerwall warranty is 10 years.
     
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  18. Big Earl

    Big Earl Member

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    I agree that the chemistry is different between the two products. The car's battery is designed to accept and supply much higher electrical loads in much more challenging weather conditions. I would argue that the car's battery pack is more than sufficient in design to supply a 10 kW load to a house (typically much less) for several hours. The problem is, of course, that there is no DC-AC converter from the factory. You could install your own AC inverter on the 12 volt system as long as it isn't more powerful than the vehicle's DC-DC converter that charges the 12 volt system. In my Fiat 500e, that DC-DC converter is in the neighborhood of 3 kW, so I think it'd be fine with a 2 kW inverter for emergency situations.
     
  19. swaltner

    swaltner Member

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    I think Tesla is just keeping things as simple as possible. It's much easier to guess that their average cost per kWh in California is going to be 20 cents and charge that as a flat rate. They'll profit on someone that is charging during the time window that the electricity is cheapest, but lose a little money on the mid-day peak time charging. So much simpler to have the flat rate than implement time-of-use rates and answer questions related to that.

    In Kansas, there are summer and winter rates. Here again, they don't try to price it exactly, just make it close. Every state probably has multiple rates throughout the day or year and they just sort of wash over all of those variations to make it easier to understand.
     
  20. gregd

    gregd Active Member

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    Minus whatever the car consumes... I doubt they installed a 3kw inverter if they only need a fraction of that. Also, be careful that the power you're tapping into has access to all of what you are trying to suck out of it. There's a BMS (charger) between the DC-DC and the battery, for example, and some electrical switching (not necessarily relays and heavy wiring) to the "Accessory" outlets. Each has their limits. On my car, the Accessory outlet is fused to 8 A, even though there's supposedly over 10x that elsewhere in the system, and some folks have reported damaging the car's 12v DC switching circuitry when running a simple tire inflation pump from it.

    Remember, 2kw is something like 166 Amps. This isn't alligator clips stuff.
     

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