Powerwall 2 Available Energy After 2 Years

[KyleDay]

This is certainly interesting. I have 3 powerwall 2s that I’ve had in daily use for 3 years and NetZero is reporting zero degradation. In fact, it’s reporting “full pack energy of 40,818Wh and also says expected full pack is 13,500Wh x 3 =40,500Wh”. In other words, I have negative degredation.

 

[KyleDay]

I should also add that my Powerwalls are kept in a fairly warm Phoenix, AZ garage that regularly gets over 120F in the summer months. Not ideal I guess but no degredation? About two years ago I used the json query to manually ask the gateway what the full pack energy was at that time, and it didn’t report any degradation at that time either.

 

[morbidz]

i'm guessing you mean 40,500. Pretty cool.

My 3 PW2 after 3.5 years in backup only mode are @ 38,942.
One PW2 was replaced proactively by Tesla without me noticing any issues, they just open a ticket and came by to swap .
PW#1(original) 11,970 remaining
PW#2(original) 11,881 remaining
PW#3(3 months old) 15,091 remaining

 

[KyleDay]

Interesting that your third powerwall 2 reports 15kwh. That’s way too much??? Should be in the 13,500wh range.

 

[charlesj]

i'm guessing you mean 40,500. Pretty cool.

My 3 PW2 after 3.5 years in backup only mode are @ 38,942.
One PW2 was replaced proactively by Tesla without me noticing any issues, they just open a ticket and came by to swap .
PW#1(original) 11,970 remaining
PW#2(original) 11,881 remaining
PW#3(3 months old) 15,091 remaining

Good to know Tesla can be proactive, from time to time.

 

[jjrandorin]

This is certainly interesting. I have 3 powerwall 2s that I’ve had in daily use for 3 years and NetZero is reporting zero degradation. In fact, it’s reporting “full pack energy of 40,818Wh and also says expected full pack is 13,500Wh x 3 =40,500Wh”. In other words, I have negative degredation.

Thats probably (almost certainly) because those powerwalls did not start with "13.5kWh" of storage, even though thats what they are rated for. They probably started with 14kWh or more.

 

[offandonagain]

Thats probably (almost certainly) because those powerwalls did not start with "13.5kWh" of storage, even though thats what they are rated for. They probably started with 14kWh or more.

Indeed, the initial capacity of a Powerwall 2 is usually around 14.5kWh or 15kWh (depending on the revision).

This is certainly interesting. I have 3 powerwall 2s that I’ve had in daily use for 3 years and NetZero is reporting zero degradation. In fact, it’s reporting “full pack energy of 40,818Wh and also says expected full pack is 13,500Wh x 3 =40,500Wh”. In other words, I have negative degredation.

With multiple Powerwalls, I'd recommend you connect to the Gateway/Powerwall+ to get the detailed per-battery degradation. The combined stats you get otherwise can hide issues. As an extreme example, you could have two batteries at an initial 15kWh capacity and one battery with 20% degradation, but the combined view would show 0% degradation. (This is unlikely in your case because it sounds like all your batteries were installed around the same time, but there might still be some variation.)

You'll need to use the mobile app to connect to the Gateway, I just added a note about that to the web version.

 

[Matt-FL]

My powerwalls all started at just over 15.2kWh at install. At 19 months, they are each between 14.3 and 14.6, so just over 6% degradation from the original starting kWh, but still 107% of warranted capacity (13.5kWh in US). Mine are set to 20% reserve, but typically drain to about 50% at night unless we have a few consecutive cloudy days, or my wife decides to set the thermostat at arctic levels.

Powerwall dashboard shows between 14.8 and 15.1 max capacity at the time I installed and started logging (about 9 months after install).

If this continues on a linear curve of about .047kWh per month, by August 2032 I'll be at 9.56kWh, just above the 70% mark of 13.5kWh capacity.

That's a pretty close margin (and making a lot of assumptions).

 

[Vostok]

My powerwalls all started at just over 15.2kWh at install.

I wish I knew what mine was at install. If only I knew about the API back then. My earlier post on page 8 - based on linear trending backwards of my data - implies that my Powerwall started on 83% of the initial “usable capacity” of 13.2 kWh, i.e. 11.0 kWh (the warranty document here says the “usable capacity” is 13.2 kWh, not 13.5 kWh).

Which of course makes little sense.

Scenario “A” - it was 13.2 kWh at install (or even higher) then something seriously bad happened to it between install and 30 months to make it lose a lot of capacity in a very short time.

Scenario “B” - it wasn’t 13.2 kWh at install, but only 11 kWh or thereabouts. But presumably that would have been reported and identified during the commissioning process and declared a lemon on arrival.

The only thing I can think of is my Gateway dying at Month 13. It completely carked it for no obvious reason. And when the Gateway dies, the battery stops charging and proceeds to discharge to the house until it is empty. And it sat on empty for 15 days until Tesla repaired the Gateway under warranty.

I did ask Tesla whether having the battery discharged for 2 weeks was going to be a problem but they assured me it would not be, that it would need to be fully discharged for something like 6 months before permanent cell damage might occur .

 

[gsdubs]

I wish I knew what mine was at install. If only I knew about the API back then. My earlier post on page 8 - based on linear trending backwards of my data - implies that my Powerwall started on 83% of the initial “usable capacity” of 13.2 kWh, i.e. 11.0 kWh (the warranty document here says the “usable capacity” is 13.2 kWh, not 13.5 kWh).

Which of course makes little sense.

Scenario “A” - it was 13.2 kWh at install (or even higher) then something seriously bad happened to it between install and 30 months to make it lose a lot of capacity in a very short time.

My hunch is Scenario A, and the PW came with at least 14.5 kWh initial capacity. If that's true you've lost ~1kWh of capacity per year on average over ~ 5 years. That's way too much degradation for a healthy PW. My 1st PW2 (P/N 3012170-05-B) was installed 4/5/21 and it died 1.6 years later. In that time it went from 14800 Wh to 13165 Wh, so I also lost about 1kWh per year of capacity. My 2nd PW2 (3012170-05-E) has 1/4th the annual degradation.

I do see two AUS/NZ warranty docs for PW2 on tesla.com, 2017 which says 13.2 kWh and 2021 which says 13.5kWh for the same P/N. I would ask Tesla to apply the latter criteria; as soon as the battery hits 9450 Wh capacity in the next few months they should replace under warranty.

 

[jjrandorin]

That is worse than mine… manufactured January 2019, 26.9% degradation. It seems odds-on it will degrade more than 30% within the next 12-18 months.

I wonder if PW2’s are a ticking timebomb for Tesla, as more and more trigger the warranty. While many seem to be doing just fine, there’s a bunch that aren’t.

Just throwing something at the wall, with nothing but speculation on my part....

What it feels like to me, is that at least some (probably most?) of the early powerwall 2s (by early I mean through the end of about 2020 or midway through 2021) were probably manufactured with either the rated capacity (13.5kW in the US) or very very slightly more than that capacity.

It seems to me that at some point, Tesla decided to put an extra kW or so in them, and also likely tweaked the charging algorithms so that 100% charge isnt actually 100% of the capacity of the actual physical installed battery.


One could get really annoyed by this (and I wont blame anyone who does) but that type of thing is what the 10 year warranty is to protect against. I have proof myself that Tesla will eventually replace them under warranty (although it took a long time in my case, they had not quite hit the threshhold but had a noise issue Tesla could not resolve).

I believe Tesla also "could" replace these with remanufactured powerwalls, like they do with car batteries (I think their warranty might allow them to do this) but in my case mine were brand new powerwalls, still in the box, with the protective wrap still on (that I got to pull off myself this time, unlike when my original powerwalls were installed).

Its my belief that Tesla is going to end up replacing a larger percentage of the early installed PW2s but again that is just nothing but pure, 100% speculation on my part, with no data to back it up. Nothing more than a hunch.

 

[Vostok]

Whenever I hit the warranty trigger, I will share my experience here . As quick as my degradation has been, the trend still says the warranty trigger is ~2 years away. So we’ll see.

 

[Matt-FL]

This footnote seems to mark a change to PW2 hardware, prior to March 2019. You could be on to something @jjrandorin

Compared with 2017 PW 2 specs:

The newer version is lighter, but most likely a change to internal battery types. It also was slimmed down slightly, 2mm in width and 8 mm thinner.

 

[Jeremy3292]

Just throwing something at the wall, with nothing but speculation on my part....

What it feels like to me, is that at least some (probably most?) of the early powerwall 2s (by early I mean through the end of about 2020 or midway through 2021) were probably manufactured with either the rated capacity (13.5kW in the US) or very very slightly more than that capacity.

It seems to me that at some point, Tesla decided to put an extra kW or so in them, and also likely tweaked the charging algorithms so that 100% charge isnt actually 100% of the capacity of the actual physical installed battery.


One could get really annoyed by this (and I wont blame anyone who does) but that type of thing is what the 10 year warranty is to protect against. I have proof myself that Tesla will eventually replace them under warranty (although it took a long time in my case, they had not quite hit the threshhold but had a noise issue Tesla could not resolve).

This makes sense to me as we all know charging to 100% and/or keeping the state of charge (“SOC”) at 100% is very bad for NMC and NCA cell chemistry longevity. Tesla adding an extra ~1 kWh of “hidden” capacity to give a little more buffer from a true 100% SOC would help a lot with longevity. Some people even have above 15 kWh capacity as shown in this thread upon install.

13.5/14.5 = 93.1% true SOC
13.5/15.0 = 90% true SOC

I am gettin 3 PW’s installed soon, so I will report what my starting capacity is and manufacture date once my install is done.

 

[Vostok]

@jjrandorin or anyone else for that matter - can anyone clarify the 37 MWh throughput limit under the PW2 Warranty when the battery is not used solely for self-consumption?

I don’t participate in a VPP, but I do use the grid to charge my battery overnight if solar production is forecast to be poor the following day. I do that in order to arbitrage grid rates on a ToU plan and save quite a bit of money. By doing that, less than 5% of my grid electricity consumption has been at peak rates.

At first blush, doing that would seem to mean I’m not solely “self consuming” hence not on the “unlimited cycles” branch of the Warranty but the “37 MWh total throughput” branch.

Question is - how is that measured and is that a number than can be discovered via the API (either Tesla Owner API or the Gateway API)?

Also what does this limit mean in practice? That the Warranty is no longer 10 years, but effectively the date when 37 MWh is hit? So if capacity falls below 70% and before throughput reaches 37 MWh, then you are covered. But if capacity falls below 70% after 37 MWh throughput is reached, even if that’s before 10 years is up, you are no longer covered at all?

The way it is written is a bit ambiguous. Thanks.

 

[jjrandorin]

I apologize but I have no idea, myself. The only thing I know is whats printed (the same things it appears you are reading). Maybe someone else has more information on the topic, but I am not sure on that.

 

[offandonagain]

@jjrandorin or anyone else for that matter - can anyone clarify the 37 MWh throughput limit under the PW2 Warranty when the battery is not used solely for self-consumption?

I don’t participate in a VPP, but I do use the grid to charge my battery overnight if solar production is forecast to be poor the following day. I do that in order to arbitrage grid rates on a ToU plan and save quite a bit of money. By doing that, less than 5% of my grid electricity consumption has been at peak rates.

Probably best to check with Powerwall support directly. My version of the warranty (I posted the process to get it and link here) seems to explicitly allow grid charging. Footnote 3 for TBC says:

Storing energy generated by the grid or an onsite solar array, and using that stored energy for time-of-use load
shifting.

I've seen other versions of the warranty that don't have that clause, probably because they predate the grid charging option. Whether Tesla will apply these warranty changes retroactively is anyone's guess.

Question is - how is that measured and is that a number than can be discovered via the API (either Tesla Owner API or the Gateway API)?

If what I've been told by Powerwall support is correct and they only look at discharged energy, you can get that metric from the Gateway API (/system_status, energy_discharged) or the Netzero app. The Tesla app will show lifetime discharge as well, but only the combined value for all batteries; also the app data is less reliable than the data that comes from the battery.

 

[gsdubs]

Just throwing something at the wall, with nothing but speculation on my part....

What it feels like to me, is that at least some (probably most?) of the early powerwall 2s (by early I mean through the end of about 2020 or midway through 2021) were probably manufactured with either the rated capacity (13.5kW in the US) or very very slightly more than that capacity.

It seems to me that at some point, Tesla decided to put an extra kW or so in them, and also likely tweaked the charging algorithms so that 100% charge isnt actually 100% of the capacity of the actual physical installed battery.


One could get really annoyed by this (and I wont blame anyone who does) but that type of thing is what the 10 year warranty is to protect against. I have proof myself that Tesla will eventually replace them under warranty (although it took a long time in my case, they had not quite hit the threshhold but had a noise issue Tesla could not resolve).

I believe Tesla also "could" replace these with remanufactured powerwalls, like they do with car batteries (I think their warranty might allow them to do this) but in my case mine were brand new powerwalls, still in the box, with the protective wrap still on (that I got to pull off myself this time, unlike when my original powerwalls were installed).

Its my belief that Tesla is going to end up replacing a larger percentage of the early installed PW2s but again that is just nothing but pure, 100% speculation on my part, with no data to back it up. Nothing more than a hunch.

I agree that anecdotally I see higher failure rates in the early PW2s. My own experience attests to that. My first PW2 failed 1.6 years after install, but the replacement PW2 has been rock solid.

I thought that Tesla made true reliability improvements for my replacement PW2, but what if they also did the opposite of your speculation, by loosening the spec?

What if early PW2's had a usable 13.5kWh capacity and, due to rates of PW2 degradation in the install base, Tesla had a warranty liability problem on their hands if they didn't do something? So sometime in 2021 they reduce the guardrail and made the usable capacity 15kWh, while keeping the warranty limitations the same? (I read that the physical capacity limit of the PW2 is closer to 17kWh) This would give each PW2 an additional 1 kWh head start against degradation, just enough to safely get the bulk of the install base past the "9.45 kWh capacity after 10 year" (or 37.8MWh, whichever occurs sooner) warranty mark.

Many early PW2 users claim that they only had 13.5kWh capacity accessible. But newer PW2 installs seem to have 15kWh usable today, i.e. 100% = 15kWh. I think you can test this by charging from 0% to 100% on a new PW and confirming it takes a little over 15kWh (the one-way efficiency is only about 97%, which you can determine by calibrating against a nominal_full_pack_energy reading from API/Netzero). Or just charge from 20% to 100% and divide the energy charged by 0.8, calibrate, and compare.

There is a data report from an Australian battery testing center ITP referenced elsewhere in this forum, and they were tracking Energy Discharged per cycle and expected lifetime, running 3 cycles a day for 3 years. Their final report notes that sometime in Nov 2021 after a firmware update their usable capacity jumped up by 1 kWh. Perhaps it's just an anecdote but others can confirm or rebut from their own experience.

 

[gsdubs]

@jjrandorin or anyone else for that matter - can anyone clarify the 37 MWh throughput limit under the PW2 Warranty when the battery is not used solely for self-consumption?

Hi @Vostok see the discussion on what we think are the origins of the 37 MWh throughput limitation here. Practically speaking, the warranty is still 10 years and your PW2 still having a usable capacity of 9.24kWh or 9.45kWh (depending on if you use 13.2 or 13.5 kWh specified original capacity), as it is highly unlikely one can reach 37 MWh in 10 years. Even if you are doing grid-exporting or VPP. Agree with @offandonagain that the ground truth to compare against 37 MWh is your PW's lifetime exported energy.

 

[Vostok]

Footnote 3 for TBC says:

Storing energy generated by the grid or an onsite solar array, and using that stored energy for time-of-use load shifting.

I've seen other versions of the warranty that don't have that clause, probably because they predate the grid charging option. Whether Tesla will apply these warranty changes retroactively is anyone's guess.

The warranty that came with my PW2 says its “effective date” is 9 February 2017 and doesn’t have that clause.

However if I use the App to go to PW2 support documents, the warranty there has an “effective date” of 18 Nov 2021, and it does have that clause. It also states the energy capacity as 13.5 kWh not 13.2 kWh, and says the warranty applies to Part Number “2012170-xx” which is what I have.

So I interpret that as Tesla has updated the warranty that applies to this product, effective from that date, even though the product was installed before that date.

Which would mean grid arbitrage still falls within the “unlimited cycles” branch of the Warranty. But VPP would not.

The change to 13.5 kW usable capacity would also bring forward my warranty trigger by nearly a year, to 6.4 years.