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Graph Of The Day – Powerwall 2 warranty is under 9 years for most households if cycled once per day

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tesla-powerwall-2Tesla has released the warranty for the DC version of the Powerwall 2.  The warranty for the AC version has not yet been released, but I think it is a safe bet to assume it will basically be the same.

The warranty is a large improvement over the one for the original Powerwall.  When cycled once per day the Powerwall 2 has the lowest cost per warrantied kilowatt-hour of any battery system by a large margin.

But for many households, the Powerwall 2 warranty is likely to last for under 9 years rather than the full 10 years I was expecting.

Length Of Powerwall 2 Warranty When Cycled Once Per Day

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The Powerwall 2 warranty has two categories.  The first is for people who only charge it off solar power.  In this case the warranty  lasts for 10 years and has unlimited cycles.  Unlimited cycles sounds wonderful, and it certainly isn’t bad, but only charging off solar means people who are on-grid and have time-of-use tariffs won’t be able to charge it using low cost off-peak grid electricity, while people who are off-grid won’t be able to charge it using a generator.  Because of these limitations, most people are likely to fall into the second warranty category.

The second category allows a Powerwall 2 to be charged off things other than solar, but the warranty is limited to 10 years or a total of 37,800 kilowatt-hours of stored electricity – whichever comes first.

If the battery was cycled once per day and its capacity never deteriorated from when it was new, the warranty would be over in 7 years and 8 months.  Unfortunately, all lithium-ion batteries deteriorate with use and over time even if they’re not used.

The warranty promises they will still have at least 70% of their capacity left by its end, whether it is 10 years or 37,800 kilowatt-hours.  If we assume the average battery will have 75% of its original capacity by the time its warranty is finished and that deterioration happens at a constant rate, then the warranty will last a little over 8 years and 9 months when cycled once per day.

If a Powerwall 2 is cycled at a different rate, the following graph shows how long the warranty can be expected to last.  In the unlikely event it is cycled twice a day it will only last 4 years, while if it is cycled 0.8 times a day it will last a full 10 years.

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Finn Peacock is Founder & CEO at SolarQuotes

   

  • Chris Fraser

    Thank you. These posts are an excellent resource for those considering the next step to energy independence.

  • eveee

    In order to use the PowerWall 2 without solar, it would have to be charged from the grid. Then the electricity could be had at minimum retail, where the time of use premium is the least.

    It has a fairly high energy capacity at 13.5 kwhr. A fairly high energy usage is needed to absorb it, and a solar system larger than 2.5kw. 7 to 8 peak solar hours is fairly high and available in Brisbane. At that rate, even the 2.5 kw solar system does pretty well.
    https://www.livingin-australia.com/sunshine-hours-australia/

    https://www.livingin-australia.com/images/sunshine-hours-brisbane-adelaide.jpg

  • Mike D

    Annoying post. Almost no one will cycle the battery completely twice a day.
    Yes, I will top it up at night, and again when my panels are collecting sunlight during the day. I will discharge during the morning and evening peaks. I may use 6 kWh in the morning, and 10 kWh in the evening.
    If you need to drain the battery all the way twice per day you need more battery.

    • That is why the post gives you 4 scenarios: cycled at 0.8, 1, 1.2 and 2 cycles per day. So you can see how various usage patterns affect the warranty.

      • neroden

        0.8 is the only reasonable scenario in the list. Try some lower scenarios.

        Look, I don’t even cycle my car battery once a day.

        • Reposit power has terabytes of real home battery data. They tell me their customers typically cycle 0.8 to 1.2 with some up to 2.0

          • neroden

            And how big are their batteries? The bigger the battery, the less it gets cycled.

  • Bob Fearn

    “Powerwall 2 warranty is likely to last for under 9 years rather than the full 10 years I was expecting.”
    And how long is the warranty on that car of yours??

  • Tony Wilson

    This “disclosure” smacks of pure tabloidism. Unless there is some important information inexplicably not disclosed by the article, it’s a complete nonsense.

    The Tesla warranty (according to the information provided in the article) does not count power cycles, it counts actual discharge. No-one in their right mind is going to run down a battery all the way fully charged to fully discharged every day. You always want some spare capacity on hand, unutilised, ready for the unexpected. And if you have even the slightest sense of mechanical sympathy, you won’t run anything you own at 100% load as a daily routine. Do you turn the volume on your stero to “10” and leave it there till the
    speakers blow out? Do you drive your car at red-line revs all day,
    every day? If you are using more than about half, or at very most two-thirds of your battery capacity *every day*, then you need to moderate your power use or buy a bigger battery in the first place. 100% usage every day is simply thrashing the poor thing and it serves you right if it fails after “only” 8 years of extreme usage.

    So, in reality, we need to divide that hysterical “8 year” headline by a reasonable usage factor to get an actual warranty life under normal, sensible usage. Even if we assume hard usage (average drain of 66%) rather than normal usage (50%), that “8 year” warranty expiry turrns out to be 12 years. (With normal usage it would be 16.) So, in reality, for any reasonable use case, the warranty is in fact 10 years, regardless of how you charge it. Note that this is a good, sensible policy. Normal use, even hard use, is covered by the ten year warranty, but extreme abuse – which is exactly what subjecting a battery to 100% cycles daily for ten years amounts to – is not.

    Rank tabloid beat-uppery. Renew Economy is better than this.

    (Disclaimer: I am working only from the information contained in the article. If there is some further fact which negatives this simple, obvious logic, it should have been printed in the first place.)

    • Hi Tony. Please feel free to read the detailed blog post linked to from this summary post. If you do you will learn that Tesla warrant 100% DoD. Real world data shows that home batteries in Australia are being cycled between 0.8 and 2 cycles per day. Tesla are offering a headline warranty claiming ‘unlimited cycles’ when the reality is that the warranty is limited for most practical applications. People about to drop $10k+ on a battery may be keen to know that so they can make an informed decision.

      Kind renewable regards, Finn

  • john

    I have used 90% round trip first year with 2% degradation to 70% year ten.
    1 cycle per day and 100% DOD this results in warranty expiry in year 10.
    It would be at 38927 kWh at that time from 35478 year 9.
    So the 10th year would see it exceed the 37,800 kWh warranty.
    Perhaps the Redflow has a case except for the 80% round trip figure.
    They lift that to 90% and build in the inverter they are very much in the picture.