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Help me understand Powerwall2 use case

Discussion in 'Tesla Energy' started by masam, Jun 9, 2017.

  1. bonaire

    bonaire Active Member

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    I would want NMC in Model 3 in the smaller pack size to allow for a longer battery lifespan. NMC allows more cycles than NCA, nominally - if you add the secret sauces that Panasonic does to the NCA, you do get more cycles - but not like NMC cycles. NCA was going to be used in PW 1.0 "Backup Battery" solution, which was cancelled. NMC is/must be used for daily cycling. Now, for cars, not everyone cycles daily and NCA works out (unless you are Uber'ing and driving 200+ miles daily).
     
  2. montreid

    montreid Member

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    Tell me if you think NMC or NCA tech is in Tesla's new battery.

    Audio is kindof crappy, but doable. The presentation does skew towards NCA and doesn't mention anything about Maganese supply chain which would lend me to think NCA is solely being produced for PW2 and Model 3. Tesla afterall is about scale and splitting production into two separate lines will reduce the overall throughput to support the 400K+ Model 3 and the PW2 demand.

    Tesla Battery Director Discusses Evolution From 18650 To 2170 + More - Video
     
  3. bonaire

    bonaire Active Member

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    I think that NMC has to be in PW2. Car most likely continues to be NCA for cost savings. PW2 can be made with existing NMC 18650 size for a while. Since Powerpacks need to daily cycle so NMC is what is needed. I would also design an LTO option for 25,000 cycles so a powerpack could last 20-30 years or more. Selling to grid providers should not require a possible 12-15 year replacement cycle. Go for longevity and a near 30-35 year lifespan. Down the road, we need cars with long lifespans, perhaps 50kWh of LTO offering two way power flow for V2H battery standby options.
     
  4. montreid

    montreid Member

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    @bonaire - true about lasting, but Tesla isn't about lasting -- it's about getting volume and efficiency to get prices down. --- and worry about duration later. The warranties appear to be in line with NCA batteries which makes sense for the short term on rampup. The video states they are specifically using the 2170s for PW2

    I totally agree that it would be nice, but get it if Tesla is doing this for the near term. I'm waiting for them to get back to me to discuss layouts with our PV system -- if DC PW2 would work with our inverter or AC PW2 to KIS (but lose some % in the conversions).

    Would love to have this for straight arbitrage and hope for the day for V2H (or V2-anything outside activity).
     
  5. bonaire

    bonaire Active Member

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    What you describe about "getting volume and prices down and worrying about duration later" can lead to a large dissatisfaction syndrome should things go badly in the near-term out years, such as year 5. I guess by then they could say "well now, we have NMC at the same cost and scale as NCA ... so yeah, that's what we have now..." Thing is - the taste left in the EV industry could sour in that the first buyers would have been deemed Beta-testers and used just to create the "ramp". It's one reason MS 60 cars were only given a 125k mile warranty, for example and the 75+ size batteries might be deemed "they won't recharge enough cycles before the car expires so let's not worry about it". If the cars were given 8 year, "unlimited mile" warranty, then those who actually do reach 250,000 miles in 8 years will be very few and nobody will hit the wall on NCA during the warranty period.

    My money is on blends like LTO and Li-S longer term. Li-S, once the right doping is found, for hopefully 2500 full cycles offering twice the density (thus smaller cars with longer range at cheaper prices). LTO is for grid storage of 25,000-30,000 cycles without a need for being small. When they build a hydro power plant - they do it for 100-200 year lifespans and not 30.
     
  6. montreid

    montreid Member

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    As you said, new tech and life cycles a lot faster and tighter. 10 years ago solar panel were 110W; now the same size has 300W+ for 1/2 the cost. The current panels are still well within 50% of lifespan. So wanted larger array and limited roofspace, it'd have to replace the existing system while still having dutiful lifespan.

    Point - One can spend a lot for the prettiest and coolest battery, but it also is that the NCA based PW2 will get the job done, cheaper, quicker, and efficiently within the 7-10 year warranty limits and that's fine for the early adopters of this today.

    Like BetaMax, NMC maybe better suited, but VHS (NCA) may win the day by sheer numbers and efficiencies of scale to cost lowering.
     
  7. bonaire

    bonaire Active Member

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    NCA is not used in powerwalls and powerpacks, though. You couldn't do 10 years of daily cycling. The pw backup battery was going to be NCA but they cancelled it and went with double capacity pw2. Which some have or may install for backup purposes only. One guy posted here about his recent system in the northwest and they don't have arbitrage programs. He just wanted standby, instant switchover for grid fails.

    Tesla Powerwall 2 Price Disrupting The Market For Real!
     
  8. Ampster

    Ampster Member

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    #48 Ampster, Jun 25, 2017
    Last edited: Jun 25, 2017
    Every vehicle except Teslas would have to be modified to have access to the DC battery buss. The additional equipment to connect it and then to invert it would also be expensive. EVS are already expensive. I tried it briefly on a VW Conversion and it was more convenuent to buy some used Nissan Leaf batteries. I already had the inverter. My manual switch over process took 5-10 minutes.
     
  9. montreid

    montreid Member

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    Not quite sure about that. If you have a central inverter and a DC, should already be ready to do this-- Nissan and Honda have shown CHAdemO is capable, and would believe same would be for the SAE Combo standard. They've demo'd an inverter plug directly to a Leaf to give that.

    With the PW2 can't see why they can't simply have a connector from Tesla to PW2 as a battery extender. ==of course Tesla would much rather sell 2more PW2 instead of leveraging that 60-100kwH battery sitting in the driveway in emergencies, right?
     
  10. bonaire

    bonaire Active Member

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    Well, Nissan Leafs in Japan are supporting V2H. So, it can be done. A home base-load is about 1-2KW, maybe peaking at 3-4KW if you keep much of the HVAC off the circuits. A Volt could handle 5-6 hours or more of 1-2KW. The point is - it's not hard but the industry hasn't matured and the Li-Ion batteries have not proven to last enough cycles to warrant this type of extended use.

    We need it - it will come some day. Then we can find added consumer value in buying an EV for more than transportation. If it keeps you from also buying a $10-12k or more Generac generator installation - you can also run off-grid with a hybrid home solar PV + car scenario. It would also keep you from needing a PowerWall(s). It is the right thing to do. Home owners with two EVs certainly have way more power on board in their cars than a wall full of PowerWalls.

    Link from 2012 supporting Nissan Leaf work on V2H.
    Nissan's LEAF to Home Power Control System V2H PCS - My Nissan Leaf Forum

    Projects like this are the R&D needed to further the design.
    Technology milestone reached
     
  11. WannabeOwner

    WannabeOwner Active Member

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    I haven't done the sums but am curious to know:

    If you, just to take a single example case, cycle your EV battery twice as often (i.e. once day commuting to work and ALSO once a day powering house during peak hours, or "commute + Peak house use" doubles your battery drain) that then will halve the battery life.

    Is the halving-battery-life cheaper / beneficial in other ways compared to having two batteries, each purpose built for the job (one for EV the other for Static storage), which then last twice as long?

    I can see that the finance arrangement, on a single battery, looks more attractive short term :)
     
  12. montreid

    montreid Member

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    I wouldn't call it cycling twice. I charge our battery once every night. Say you have one powerwall and drain it completely daily for support. That's 14kwH ~50 miles equivalent of extra driving.

    We have lots of reports of daily Tesla drivers deep draining 200+ miles daily without battery issues Ave users use even less; so the premise of the additional 14kwH load drain that's spec'd at max 7KwH that PW2 does, I don't see it having any significant consequence on a Tesla Car battery to drain 14kwH more in the evening once it arrives home to support the duckbill effect of my solar system and shift grid usage to super off peak times.

    The car battery will charge overnight again and be ready to repeat the next day at 100% charge.

    I see there's a theoretical advantage on the NMC, the pure financial advantage of having already paid for a 60-100kwH battery that's unused greatly outweighs any moderate life cycle drain on that battery. Tesla simply wants to make more $$$ to fund the Gigafactory buildout and sell as many PW2s. I get that from their perspective and why they don't simply add a DC port on the back of the PW2 to allow Tesla cars to daisy chain in for emergency backup -- that too would be too logical and kill additional PW2 sales.

    I would think state programs like SGIP would mandate this as their whole goal is to bring on grid stabilization for the growing duckbill phenomenon and fastest easiest way is expansion of existing self gen projects with batteries for that smoothing. Mandate (or provide additional rebate funds) for V2H solutions in that program
     
  13. WannabeOwner

    WannabeOwner Active Member

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    The example I picked was 50:50 - seemed an easy ratio to choose to start with, but of course there are people who commute more / less than the distance equivalent to 14kwH and/or would use more home-battery than that, but if you use your House Battery for 14kwH and you drive your can 14kwH a day, then you are using your battery twice as much and shortening its life by half.

    Sure, but you cannot scale that to infinity! Use twice as many kwH and you halve the life of the battery - if the battery has a life of 20 years, and you halve it to 10 years, its still a good long life. But if you had Static storage AND an EV then the battery in each would last 20 years. I am sure I am simplifying, and there is some efficiency and some curves rather than straight line graphs, but you surely cannot say "battery has a life of X years at Y kwH used per day, and the life is STILL X-years at 2 x Y kwH used per day".

    I'm just not sure that using my EV battery to power my home is the best approach. My home battery can be charging from my Solar Panels during the day (when my car is at work). I could put the Solar generated power into the grid (and, in effect, charge my car [at work] with those same electrons .. .and then drive them home), but the Middle-Man is going to help himself to a healthy profit, and I lose the opportunity to Store/Discharge for TOU rates if my EV is not at home, and I have no Home battery. I have days when I know I am going to need my EV and can not afford for it to be discharging into the house (and I either have to micro-manage that, or run the risk that when I want the car it isn't charged).

    I can see the attraction, particularly from the financial standpoint for short term finance rates, I just don't think its necessarily the right solution.
     
  14. montreid

    montreid Member

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    I'm speaking from the California grid-tied : TOU net metered perspective which I would say is more than half of this forum's audience.

    The use-case for battery to to get off peak times using the battery. Solar can charge the battery or dump to the grid on netmetering for the most part for all intents and purposes. The key is to get off the pk TOU times which currently overlays 6pm for many and PGE land 4-8pm already. That will probably increase in the evening hours as TOU shifts further with Solar renewables continuing to increase.

    If one doesn't plug in V2H for the day? sure. rely on the grid -- not a biggie. SGIP actually doesn't expect discharge support all the time from the wall mounted batteries.

    My point is it's cheaper to fully utilize something you have (then replace when due) instead of investing on something MORE and not utilizing existing capacities. V2H accomplishes this more effectively than buying more batteries.
     
  15. bonaire

    bonaire Active Member

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    Even better, SGIP basically buys you a powerwall if you full-discharge 50 times a year. What would be nice is if it was grid signalled, not owner initiated. By signalling, you get trackable data. Now, it is up to the powerwall owner to track it and provide the verification.
     
  16. SoundDaTrumpet

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    My use case is to charge with solar excess during partial peak period from 7AM to ~2PM as best as possible. This is to remain qualified under federal ITC rules to charge with renewables generated onsite. Between 2PM to ~6PM, I am usually sending excess to the grid still at peak rates. If the excess goes into the Powerwall, rate arbitrage drops to $0 and maybe negative since the Powerwall is 90% efficient if I happen to use this stored energy. After 6PM, my solar production drops quickly about the same time household usage jumps, so this is when batteries and rate arbitrage can help offset my undersized solar array as I am still paying at true-up under net metering. After 11PM, weekdays, it makes no sense to for the powerwall to operate. (See note 1 below). I hope Tesla updates their app to avoid using the power wall during off-peak rates.

    (1) California as expecting to pay about ~$0.10-0.12 cents per kWh just to discharge from the Powerwall system. My cost calculation assumes installation costs after both Self Generation Incentive Program (SGIP) rebate and federal incentive tax credit (ITC) divided over the warrantied life of the Powerwall.
     
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  17. SoundDaTrumpet

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    Lloyd, your statement about how California PG&E EV-A rate schedule is not forever is quite sobering. Using rate arbitrate even at $701 dollar per year (thanks miimura) is not guaranteed into the future. I was comparing different rate plans and the differences between the Electric Vehicle plan vs. ALL other rate plans is quite staggering. It's too good, and I know it will be taken away. The EV-A rate plan can't be depended on for ROI calculations to convince the wife. The conversation swings from hybrid investment/nice-to-have to a full-on expense.
     
  18. miimura

    miimura Active Member

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    I am reasonably confident that the EV-A rate plan will remain in place for more than 10 years - long enough to have paid back the PowerWall after SGIP or Federal Tax Credit. The main reason I feel that way is that the rates follow the "Duck Curve" demand profile. The highest rates are 2-9pm, exactly where the head of the duck is. For the foreseeable future, the number of people in the Residential rate class with batteries will be so small as to not matter for the purposes of ratemaking policy. In addition, I fully expect California to implement some demand response programs that Tesla can connect with that will unlock further compensation to accelerate the return on our investment beyond arbitrage and self consumption.
     
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  19. Ampster

    Ampster Member

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    #59 Ampster, Jul 15, 2017
    Last edited: Jul 15, 2017
    Let me weigh in with an alternative view about how I use a battery system. I don't know if this kind of programming is available for a powerwall so my comments might not be useful for this thread. I have a Outback Radians hybrid inverter. I run it in off grid mode from 2pm until 8pm. It is behind the meter and therefore is not permitted to send power to the grid. It powers a critical loads panel that draws an average of 500 Watts per hour. When my solar is generating that means 500 more Watts of solar goes to the grid and earns a credit at the peak rate. As solar production falls off, I save 500 Watts of usage at those same high rates. I charge it from 1AM and it is usually is done by 5AM. A rough calculation is that round trip I loose 15%. I am on NEM 1.0 with SCE.
     
  20. Ampster

    Ampster Member

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    I agree. The only caveat i would make is there is an anomaly in the duck curve in California where large solar has to be cutrailed some days in the morning. There is some talk that rates should be very cheap at that time to encourage load. I don't know if that will affect retail prices or there will be another solution in the wholesale market.
     

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