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Tesla PowerWall without Solar

Discussion in 'Tesla Energy' started by Alexander, May 2, 2015.

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  1. Alexander

    Alexander P# 8,878

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    #1 Alexander, May 2, 2015
    Last edited: May 3, 2015
    Let me start off by saying that the Power Wall combined with Solar is the best solution by far. However, if you're like me and you haven't converted to solar yet, I think investing in a Power Wall without Solar is still a very smart investment. Here's why:

    I have a separate meter for my car that's on a Time of Use plan. That Time of Use plan has worked out very well for me and for the purposes of charging my car. I pay 11 cents per kWh during off peak hours which is an extremely good rate (even when compared to solar). But that's just for my car.

    I've always felt that a Time of Use plan for my home would make sense if I could find a way to store the energy during Super Off Peak hours and use it during peak hours. With the Tesla Power Wall I can do that!

    Right now my home is on a tiered system where I pay 15 cents a kilowatt for Tier 1 and max out at 31 cents a kilowatt for Tier 4. I'm almost always in Tier 3 or 4 by the end of the month.

    But if I switched to a Time of Use plan my cheapest rate would be 11 cents a kilowatt during Super Off-Peak hours and 36 cents during On-Peak hours.

    My plan is to buy one or two of the Power Walls and have them charge up during Super Off-Peak hours and set them to power the house during peak hours. That way I'm always paying 11 cents a kilowatt regardless of the time of day. That and it would get me one step closer to a perfect Solar solution when (not if) I eventually make the switch .


    Note - Please do not email me or try to sell me on Solar. I've done all the math, I've had quotes from every Solar company you can imagine (including Solar City) and I haven't switched yet for reasons that I'm not going to discuss here. Every time I tell someone that I haven't switched to Solar yet I get an ear full. I will invest in Solar sometime in the next year or two, but I'm not doing it yet for reasons that - frankly - I'm tired of explaining. So please do not message me about it, I will not respond. Thank you :)
     
  2. wk057

    wk057 Senior Tinkerer

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    #2 wk057, May 2, 2015
    Last edited: May 2, 2015
    Well, if you haven't seen my thread on this topic, you might want to check it out.

    I've also done up a spreadsheet as an example of grid arbitrage.

    For you, I see a delta of $0.25 for on peak vs off peak. Assuming you shift 7kWh per day per PowerWall from one to the other it comes out to $1.75/day savings. So, assuming no other costs and 100% efficiency, that's about 5 years to break even on the PowerWall. Add in a realistic 93% one way efficiency (PowerWall->Inverter->Loads or Grid->Charger->PowerWall) and you're at even longer than that.

    Keep in mind that the 7kWh PowerWall is the one capable of this task, not the 10kWh one. Also keep in mind that you can only shift the capacity of the PowerWall, not arbitrarily "all peak usage" magically becoming off-peak. You'd need enough PowerWalls to cover *all* peak usage after efficiency losses to do that.

    Then add in that you'll need an inverter/charger capable of actually doing the grid arbitrage, plus installation, and you'd be well beyond a 7 year ROI.

    And this is assuming that grid rates stay in favor of this setup for that long, which seems unlikely.

    Honestly, even with solar, in your situation the PowerWall doesn't make much of a difference, assuming the on-peak rate is when the sun is shining.
     
  3. donv

    donv Member

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    I'm actually interested in one as a backup. I have a house where the power goes off frequently in the winter (at least 4-5 times per year, sometimes for days at a time). There is no natural gas service, so a generator doesn't seem feasible. My big question would be how many powerwalls I'd need to have reasonable coverage.
     
  4. Eclectic

    Eclectic Member

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    Thank you for the very informative analysis, wk057. I have to admit that most things electrical seem like wizardry to me and I don't understand the basic concepts beyond what a kWh is and how many I use. The question I have, and I didn't see it addressed directly in the thread you linked to, is whether a chain of PowerWalls could even run a typical househould during peak times. I live in a hot area in CA and for many months of the year we have the AC going, as well as fridges, other appliances, etc. Do you have any thoughts on whether we'd be able to run the house during summer days from whatever is stored in PowerWalls?
     
  5. wk057

    wk057 Senior Tinkerer

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    Well, each PowerWall outputs 2kW. At the max, 9 of them, that's 18kW.

    A typical central air unit will use 3-5kW, depending on size, so you're looking for at least two units just for central air. Hot water heater will hit 5kW (another 2.5 units), cooking is up to 7kW, etc, etc. So I think it'd be more about the actual demand than capacity in that situation. 2kW from a 7kWh battery seems pretty low IMO, meaning it'll take more to be useful.

    - - - Updated - - -

    Mentioned in my other thread, the cheapest standby generator I found was about $1900 and put out 7kW. That's 3.5 PowerWalls worth of output power. Unless you're running minimal loads during your outages (like one refrigerator and a couple of LED lights) a couple of PowerWalls will not help you in a multi-day outage, IMO.

    If you're trying to maintain typical usage, the 90kWh bank of nine would give you almost three days of average user use (~33kWh/day).
     
  6. eye.surgeon

    eye.surgeon Member

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    The ROI for me and I suspect most residential users is borderline ridiculous. The same is true for my model S, of course, but at least with that I get a lot of fun and enjoyment out of it. For the powerwall, not so much. Frankly, without government subsidies like the cars get, it's a bad investment...even with economies of scale and battery prices coming down, they can't compete on a level playing field with the legacy power grid. Most attempts I have seen completely ignore the cost of installation and inverters, which could double the ROI of the battery alone.
     
  7. SBerg

    SBerg Member

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    Thanks for the analysis - the inverter is what kills this unless you also do solar. We already have solar but I doubt the PowerWall could be linked into our SunnyBoy inverter. It would be great if Tesla did a model with an integrated inverter, a true plug-n-play setup.
     
  8. wk057

    wk057 Senior Tinkerer

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    It probably would work. If you have the SunnyBoy version that lets you run as a backup power source, then the backup version of the PowerWall would probably help you.
     
  9. Alexander

    Alexander P# 8,878

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    #9 Alexander, May 3, 2015
    Last edited: May 3, 2015

    Sorry for the late response. I posted this then took off for a fun filled day with my daughter :D

    So I read your thread and WOW. Very through, and a very worth while read! Thank you and you're right. I ran the numbers for my household and this is what I got:

    - Over the last 12 months I've consumed 9,799 kWh just powering my house (my car is on a separate meter)
    - Over the last 12 months I've paid $2,025.56 for that electricity, which averages to .21 cents a kilowatt
    - Over the last 12 months my highest draw from the gird was 6.40 kWh in 1 hour
    - Over the last 12 months my average hourly draw was 1.12 kWh per hour
    - Over the last 12 months the most energy I consumed in a single day was 72.27 kWh's

    Correct me if I'm wrong, but from what I understand now I...

    - Would of needed a minimum of 4 PowerWall's to of handled my highest draw of 6.40 kWh
    - Would of needed 11 PowerWall's to get me through my most consuming day of 72.27 kWh in one day
    - Would of only saved $979.90 if I had PowerWall's and pulled from the grid exclusively during Super Off-Peak hours (at .11 cents a kWh)
    - Would only realize an ROI after 15.6 years with 4 PowerWalls (which includes $1,500 for installation and $1,800 for an inverter/charger)

    So it doesn't make sense... but costs and ROI's aside. Id still be interested in doing it just to be that much closer to the dream of off grid living. But yes, from a financial perspective it doesn't look very appealing if the sole intent is to save money (which was my original thought). So thank you!


    Here's some of the data I used to get these numbers.

    Month
    Total kWh
    Charges
    May
    615
    $ 111.08
    Jun
    910
    $ 203.67
    Jul
    1287
    $ 306.47
    Aug
    1506
    $ 376.17
    Sep
    974
    $ 210.35
    Oct
    828
    $ 118.16
    Nov
    998
    $ 240.69
    Dec
    542
    $ 101.74
    Jan
    656
    $ 126.45
    Feb
    396
    $ 63.03
    Mar
    529
    $ 96.75
    Apr
    558
    $ 71.00
    9799
    $ 2,025.56
     
  10. SabrToothSqrl

    SabrToothSqrl Active Member

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    31c a kWh?! I'm around 8c and that's too high! No hourly or tier system here...
     
  11. jeffhre

    jeffhre Member

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    That is why California has lower per capita electricity use.
     
  12. RobStark

    RobStark Active Member

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    Gasoline at ~$.05 per gallon in Venezuela and Saudi Arabia is the reason why they use fuel so efficiently there.
     
  13. GreenPenguin

    GreenPenguin Member

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    What's your energy pattern now? Most usage during the day or most at night?

    Was the 6.4 kwh peak during the middle of the day?

    You only care about the peak usage during the TOU peak period as those are what you're offsetting.

    I think if you can shift your usage and use a device like the powerwall to compliment your strategy it could work.

    But if you're saying if you have high usage during the day that can't be modified than the ROI may not be there.

    But what if you just did 1 unit instead of 4, you still save some money (compared to your current tier rate) or the break-even is still too long?

    Also keep in mind there is value of having a back-up. Say natural disaster or even rolling blackouts.
     
  14. Chris TX

    Chris TX Active Member

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    After seeing the presentation on the PowerWall, I quickly realized installing the max of 9 of these things wasn't going to cut it. I do wish they had pricing on the 100kWh PowerPack "for commercial use". Our next house will be covered in solar and I want to capture as much as possible when I'm not feeding the grid.
     
  15. Newb

    Newb Member

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    I read somewhere that the 100kWh Powerpack is $25,000.
     
  16. Alexander

    Alexander P# 8,878

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    I work from home several days out of the week, so the majority of my usage is during the peak day time hours. Especially in the summer when the AC is on.


    It was the hour between 4:00 and 5:00PM on a Thursday in August 2014. It was 101 outside so my AC was probably on full blast. I don't remember what was going on that day, but I was thinking about turning everything on in the house - including the AC - and leave it on for an hour to see what that kind of load looks like.


    The ROI would be worth it if I could get away with using no more than 2 PowerWall's. But to do that I would have to watch my usage throughout the day and try to stay under a 1kW an hour. I could do that in the winter, but in the summer that would be almost impossible. My AC consumes about 2.5kW's an hour, so having just 2 PowerWall's wouldn't work for summer use.

    But I might do it anyway just to be closer to off the grid living.
     
  17. SBerg

    SBerg Member

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    Unfortunately (actually fortunately) our PV system is about 12 years old and the SunnyBoy will not provide power during an outage. We are on TOU metering and this time of year we pump back more juice to the grid during partial-peak and peak hours and charge the MS during off-peak. I would not want to be charging the PowerWall during peak and partial-peak only to have it charging the car during off-peak - seems that would defeat the purpose of TOU metering. Or, am I missing something?

    Is the PowerWall "programmable" like the MS so you can tell it when to charge and discharge?
     
  18. Chris TX

    Chris TX Active Member

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    This is my big question. Right now, my power is free from 9PM to 6AM. If I can charge up the PowerWall/PowerPack during that time, (along with my two cars) I can have it switch to pure battery power at 6AM and run until it gets low. I know the PowerWalls won't be able to run all the time with my current load, but would give a bit of a boost. I might just get a PowerWall to play with, then swap it out for a PowerPack.
     
  19. jaysquyres

    jaysquyres Member

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    I saw Tesla's commercial batteries today at Oncor in Dallas. There are 2 of the 100kWh packs A & B x 3 (3 lines commercial.) They are happy with them. Here are pics:
    20150504_153004.jpg
     

    Attached Files:

  20. jaysquyres

    jaysquyres Member

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    Also, their control room is cool. They have Solar, Diesel Generators, Turbines, and they will be adding Wind "Future Source," for their Micro-Grid. Pics:
    20150504_152625.jpg
    20150504_152228.jpg
     

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