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Help requested: To Powerwall not to powerwall w/ solar PV

Discussion in 'Tesla Energy' started by yauname0, Aug 24, 2017.

  1. yauname0

    yauname0 New Member

    Joined:
    Aug 24, 2017
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    Fremont
    I am in the final phases of decision around installing PV panels. Someone suggested adding powerwall and confused me. I dont particularly care for backup power capability. I don't have an EV. Location: Northern California. Solar System Capacity: 4.9 kW DC. Considering one powerwall. Cost without powerwall: $17000; w/ powerwall: plus 8000. (This is before tax credits and SGIP rebates). Based on my last two years bill (PGnE), annually, i use about 3000 kwH during peak hours (3-8 pm), and 6000 kwH during off peak hours. Does it make financial sense to have powerwall? I read that it can be charged only from solar (not the grid). Does that offer enough on-peak/off-peak arbitrage opportunity? Sorry if my questions sound dumb. Trying to educate myself quickly before signing the contract. Thanks for your help!!!
     
  2. Musterion

    Musterion 18h 03m 37s −24° 23′ 12″

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    I know it takes time but I would highly recommend reading through this thread: Powerwall 2 "waiting list"

    It is where all the powerwall pioneers are.

    Folks have posted real install costs and feedback for pretty much every scenario including close to yours, and many in Bay Area. I am shopping for PW2 install and got feedback on my own situation by posting there, but still some unanswered questions (mainly due to how new this is).

    Brief feedback on your questions:

    0) Can you tell me who is your installer and is the solar roof mount? That helps gauge pricing better.

    1) Your solar price is $3.5/W. Below average for recent costs, but you could do better. I got mine below $3/W and that was 3 years ago and ground mount, which is typically more cost. My solar details posted in thread linked above. You should try to beat your county and state using detailed data here: CaliforniaDGStats. (adjust the selections to residential and then drill down).

    2) Your Powerwall price seems high. Based on pricing in linked thread, after deducting cost of powerwall and gateway, they are quoting $1800 for everything else which is install (and possibly taxes) which is on the high end just for a battery, and very high since this is combined with a larger solar project which already has permitting and panel changes, etc.

    3) For whether powerwall is going to help you, you don't have best rate for it (EV rate) so I would say it is questionable if you don't care about backup ability. See the linked thread above for folks who have similar <=5kW solar arrays. Note that to get additional Federal ITC your battery needs to be charged at least 70% of time from solar array, and the credit is pro-rated from 0% to 30% as your charging percentage from solar rises to 100%. (So you only get full federal credit if you never charge battery from the grid). Note that state SGIP has other requirements which you can read about there.

    Good luck.
     
  3. ecarfan

    ecarfan Well-Known Member

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    I charge my Powerwall V1 from the grid or my panels.

    I agree with @Musterion, read the thread he linked to.
     
    • Like x 1
  4. yauname0

    yauname0 New Member

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    Thanks for your detailed response. Appreciate it. The quote I listed above is from SolarCity. It is roofmount. I got lower quotes from third party installers (close to $3 per Watt) but I am concerned if they will be around 20 years from now. Hopefully Tesla will be. My per watt cost from them w/o the battery is $3.45. The CaliforniaDGStats link that you provided me shows higher average costs than that.

    I am still debating whether to go for higher solar capacity systems versus instaling a powerwall. Are there models I can use to figure out cost savings w/ the battery. With the solar panels, my payback is 7 years. I am not trying to buy EV.
     
  5. Musterion

    Musterion 18h 03m 37s −24° 23′ 12″

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    The folks in the other thread have made some cost analyses and even spreadsheets on battery payback.

    Regarding the California stats: that is a new page they are transitioning to and it only seems to show average values. You are correct that people are paying more by this average. But the older page had more data and showed the spread, so you could see min and max and standard deviation. That was much more useful but I can't seem to replicate it in the new site. Maybe you can figure it out and post here. Thanks.
     
  6. yauname0

    yauname0 New Member

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    Thanks Musterion. I did not find any min/max data yet. The paper below suggests powerwall 2 breaks within 10 years along with savings of 1k to 2k. At least in California. Plus there is federal and SGIP credits. So it appears to be a decent deal

    The Economics of the Tesla Powerwall 2
     
  7. SoundDaTrumpet

    Joined:
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    Bay Area, California
    #7 SoundDaTrumpet, Aug 28, 2017
    Last edited: Aug 28, 2017
    Your article uses assumptions that do not match your use case:
    1. Rates differ. Fremont-->PG&E, Solar in CA-->NEM 2.0-->mandatory time-of-use, no EV-->ETOU-A. Per kWh, $0.39 vs. $0.31 peak vs. off-peak in summer. $0.27 vs. $0.26 peak vs. off-peak in winter. Rate arbitrage unfavorable. Discharging powerwall costs $0.10 per kWh over warranties life of system.
    2. Non-self consumption-->FedTaxCredit not eligible
    3. Cost estimate is 20% low. Article doesn't include gateway & sales tax.

    Not having an EV is the greatest impact. Factoring tax credits and rebates is a separate discussion. I hope this helps.
     
  8. JSkrehot

    JSkrehot Member

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    Martinez, Ca
    I did a 6.12 kW self install system that I bought from gogreensolar.com. I am not super handy, but friend helped me with the manual labor of mounting the array and getting the panels on the roof. Probably spent about a week doing it because it was insanely hot in August when doing it and we did not spend all day each day. Besides his help with just "manual labor," my uncle is retired electrician so he helped with just bending all of my conduit so I would not mess it up and have to buy more. My system plus permits and conduit, fittings, and wiring was about 14k. I got the 30% federal rebate, so it cost me $9,800. That is $1.15/W. Gogreensolar estimated my system to produce 9.2 MWh/year. My system is completely south facing and with 43 days remaining last week, I had already produced 9.2 MWh. My year is up Oct 5. So far I am just under 2,000 kWh of excess power generation. My situation is a little different where I can get a total of 8 hours of free charging at 30 miles/hour each day I work, which is three 12 hour shifts per week. This 2,000 extra kWh's, estimated to be about 2,300 extra on Oct 5, will allow me to charge my upcoming Model 3 during any time of day, not just at night. In California, which I am, in the Bay Area, I do not see how a PowerWall will gain anything financially since we have Net Metering. If you want to go green and are really really wealthy and just don't care about money, sure. If you have to go off grid, sure. Otherwise, it doesn't make sense financially. It's a lot more financially sound to get a system that will cover 100% of your electricity costs. I am running my air ALL THE TIME too. My house is COMFORTABLE. Getting a single PowerWall, you can't power your home after sunset and charge up your car, just can't. You would have to have multiple PowerWalls and that is nuts. That extra 2,300 kWh will cover between 7,000 and 7,500 miles of my yearly driving.
     
    • Like x 1
  9. yauname0

    yauname0 New Member

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    Thanks SoundDaTrumpet. If the price differential between the offpeak and onpeak hours is small then the whole savings goes down the tube. Where did you get the tarrifs for Fremont? Are they the same for Northern California? I couldn't find them on pgnE site. Could you share the link.
    SolarCity tells me so long as I charge the powerwall from the panels (clean energy) I am eligible for fed credits.
     
  10. miimura

    miimura Active Member

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    PG&E Tariffs are here: Tariffs
    E-TOU Tariff PDF
    EV Tariff PDF
     
  11. SoundDaTrumpet

    Joined:
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    miimura thanks for posting the link.

    You are correct about the fed credits. The article appears to be charging with grid power.
     

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