Is Full State of Charge Harmful to PW2

[Mayer]

Two PW2s installed yesterday.
Very exciting time.
I’m just learning how to navigate and understand data provided by App, and reading/learning plenty here too.

I am on east coast and likely won’t draw from PW during off-peak hours because the TOU rate is only 0.062 and super off peak is 0.042.

Two Questions:

1. Does PW2 battery degrade faster if left fully charged 24/7 (used for outages only);

2. Since peak rate for TOU is higher, 0.306, can home/app be set to automatically draw from battery during rainy, snowy, overcast days or is that something users do manually with the App?

 

[jjrandorin]

The tesla powerwall 2 warranty, when charged by solar, is 10 years and unlimited charging cycles, to retain at least 70% of its capacity. There isnt any provision in the warranty for how many charging cycles if charged by solar, nor is there one for leaving it with 100% reserve.

I dont have the answer to this, but would say that follow the warranty a company puts out for product usage expecations.

Since there is no way currently using Tesla app to stop the powerwalls from re filling (like people want to charge their vehicles to 75.2342452% on tuesdays, and 83.2132415135% on thursdays), if you cycle it at all, you will be filling it up to what it calls 100%.

I have not seen an answer to this question from a Technical perspective, and have seen it asked more than once. We have regular members of this subforum who dont cycle their powerwalls, and others who use them for Time of Use settings daily. I dont think it matters in any way that is going to matter.

 

[Mayer]

Yes, I was aware of the warranty terms but like a car (or more than a car), hoping to get >10 years out of PWs so plan is to use them gently rather than daily.
But I had forgotten Tesla doesn’t limit charge cycles for warranty coverage (which is meaningful) and was unaware that App won’t enable reduced charging like on the vehicle batteries.
Thank you @jjrandorin for the reply!

 

[jjrandorin]

I think its relevant that the warranty is 70% capacity at 10 years, not "still working" at 10 years. When this discussion tends to come up, there are a couple of different viewpoints on it. My own viewpoint is, it would be worse to try to "gently use it" and then have calendar aging etc have the capacity be 26% capacity loss at 10 years, than simply just use it like I want to (whatever that is) and if its going to degrade a lot, hopefully it hits 30% before the 10 years time frame.

Thats not a universal thought process though ( far from it) and many people want to try to "gently use" them.

Tesla gets pilloried (and sometimes rightly so many times, at least in my opinion) For having a somewhat "CA centric" stance on things, since it started out as a CA company and presumably was testing things in CA. In CA, because of electricity plans here, these things get used daily by almost everyone that has them (as there isnt any reason not to, and plenty of financial reason TO use them daily), so they would have been tested for daily cycle use.

If I were in your shoes, I would set my reserve to something minimal, like 80-90% or something, just to not have it sit there forever not being used, but again there is no technical science I am putting forth for that, its just what I would do if I was somewhere I did not need to use them.

 

[Redhill_qik]

I think its relevant that the warranty is 70% capacity at 10 years, not "still working" at 10 years. When this discussion tends to come up, there are a couple of different viewpoints on it. My own viewpoint is, it would be worse to try to "gently use it" and then have calendar aging etc have the capacity be 26% capacity loss at 10 years, than simply just use it like I want to (whatever that is) and if its going to degrade a lot, hopefully it hits 30% before the 10 years time frame.

Thats not a universal thought process though ( far from it) and many people want to try to "gently use" them.

Tesla gets pilloried (and sometimes rightly so many times, at least in my opinion) For having a somewhat "CA centric" stance on things, since it started out as a CA company and presumably was testing things in CA. In CA, because of electricity plans here, these things get used daily by almost everyone that has them (as there isnt any reason not to, and plenty of financial reason TO use them daily), so they would have been tested for daily cycle use.

If I were in your shoes, I would set my reserve to something minimal, like 80-90% or something, just to not have it sit there forever not being used, but again there is no technical science I am putting forth for that, its just what I would do if I was somewhere I did not need to use them.

I am in the "gently use it" camp as I don't need to deeply discharge my Powerwalls for Peak/Off-Peak NEM price arbitraging. I have mine set to 85% during the Summer period and 92% during the Winter period. I do this partly to help out the grid during the Peak periods, partly to get some higher NEM credits to ensure a negative annual balance, partly because I think that it is a good idea to exercise the charge/discharge circuitry so that any faults are discovered early and not during an actual outage, but mostly because I want to minimize solar kWh loss recharging the Powerwalls so that I can export more.

@jjrandorin That is a very interesting thought that gently-using-it might result in less overall wear at 10 years ending up on the wrong side of the warranty condition.

My two Powerwalls are reporting (through web REST API) that they have a nominal capacity of 27.455 kWh or 1.6% higher than the specification at the 3 year mark. This has been very steady for the 2.5 years that I have been recording the data. My Powerwalls seem to have a very good set of batteries, but I know that isn't the case for everyone.

 

[shahryaran]

Lithium ion battery degradation: what you need to know

The expansion of lithium-ion batteries from consumer electronics to larger-scale transport and energy storage applications has made understanding the many mechanisms responsible for battery degradation increasingly important. The literature in this complex topic has grown considerably; this...

pubs.rsc.org

 

[brkaus]

And I don’t believe you can fill them from the grid except under storm watch which is determined by Tesla. But that may depend on what federal credits you accepted when installing the system.

 

[jjrandorin]

And I don’t believe you can fill them from the grid except under storm watch which is determined by Tesla. But that may depend on what federal credits you accepted when installing the system.

Sometime in the past couple of years, many of us have had the ability turned on by tesla to charge from the grid whenever we want.

Lithium ion battery degradation: what you need to know

The expansion of lithium-ion batteries from consumer electronics to larger-scale transport and energy storage applications has made understanding the many mechanisms responsible for battery degradation increasingly important. The literature in this complex topic has grown considerably; this...

pubs.rsc.org

I dont find dropping a link to a white paper on the general topic to be helpful at all in this circumstance, unless you also know exactly what battery chemistry is in a powerwall, and how the BMS interacts with it, and how that is impacted by the fact that powerwalls are promised 13.5kWh of storage but ship with 14+kWh of storage, so have some degradation threshhold built in already.

 

[Matt-FL]

I've got four Powerwalls that have been installed and running for over a year. After install, my total capacity was 60.1kWh. After 14 months, I'm at 58.5kWh. Not bad, starting out one year in still above the expected maximum capacity.

In 14 months, I've degraded by 2.66%. From a linear perspective, a 30% loss would be 0.25% per month over 120 months. At the linear rate, I should have lost 3.5%.

My batteries are pretty much fully discharged and recharged on a daily basis. I'm for a zero power bill and maximum ROI, and I plan to put the batteries through their paces. I also expect that in 15 years when I need to probably replace these, there will be newer and better options.

I'm in the boat of 'if I own it, I'm going to use it'. I'm not one to buy something to put it on display. Okay, other than that Star Trek Enterprise Mega Bloks set, but that's me getting off topic

This technology is going to be old in ten years. Like using a laptop from ten years ago to play modern video games. Not going to be your best experience. Why not use the heck out of them while they are still in their prime?

My 2 cents

 

[Mayer]

For all the reasons stated above, I intend to use the PWs on a daily basis, if for no other reason then to clear out all the bugs, so I’m confident it will work when it’s actually needed in a power outage.
Also, I have to take a look at the TOU rates as the peak rate appears to have jumped significantly after opting into the program last month.

 

[shahryaran]

Sometime in the past couple of years, many of us have had the ability turned on by tesla to charge from the grid whenever we want.



I dont find dropping a link to a white paper on the general topic to be helpful at all in this circumstance, unless you also know exactly what battery chemistry is in a powerwall, and how the BMS interacts with it, and how that is impacted by the fact that powerwalls are promised 13.5kWh of storage but ship with 14+kWh of storage, so have some degradation threshhold built in already.

Read the article

 

[jjrandorin]

Read the article

Its not on powerwalls, which is what this discussion is about, so, no thank you.

 

[BGbreeder]

Read the article

I am going to flag this as not a particularly helpful response.

If someone suggests that a link isn't particularly helpful, then please at least have the kindness to address the issue(s), or don't post in the first place. I did read the article, which is OK in my book, but not particularly outstanding, and not directly relevant to Powerwall behavior. If you are one of the authors, my apologies.

What about that particular review article struck you as relevant to the charge / discharge / standby behavior of Powerwalls? Batteries do have differences, even if they are nominally "lithium ion", as do battery management systems, as does charge/discharge/storage temperatures, as well as charge/discharge profiles and rates. Subtle differences in electrolyte, barrier films, anode / cathode treatments, the trace metals composition, construction and construction processes, and in the details of the nanostructures of all of the above, can, and do, have profound effects on battery performance characteristics. (Some of which were touched on in the paper) Again, how do these stack up in aggregate for a Powerwall system to impact the longevity under various charge / discharge settings?

I happen to understand many of the above, and I can say that I haven't a clue about what the bottom line is for a Powerwall. I do find the data from owners who are logging their system status over time interesting, although I guess I do wonder how accurate any particular reported value for pack capacity is at any given point in time. BMS undergo periodic recalibration of their own estimates, so I would be inclined to take any given value with a grain of salt, but the trends are, I suspect, informative and reliable. (I'm not dumping on Tesla here. It is not trivial to accurately measure power flow in/out, due in part to inaccuracies in measurements (ADCs, bit level accuracy, and the vagaries of silicon and all that) and a certain amount of rescaling to cell voltage(s) is inevitable, but each cell has slightly differing voltage/state of charge relations due to the aforementioned effects and others.)

******

Personally, I am happy to have the Powerwall as a backup. Like many things in life at a certain level of examination, I tend to treat it as a black box. There is no way to know many of the inner working details, and for things under software or firmware control, those details could change in the next update. Which leaves me on the page of using them for backup, and a certain amount of charge/discharge to slip past most of our peak usage, though thanks to @Redhill_qik's detailed analyses, I realize that also isn't worth sweating. My plan is if a Powerwall drops below warranty levels at nine and a bit years, I will address it then. Lots of water yet to go under the bridge...

All the best,

BG

 

[Mayer]

I am thrilled with my purchase.
As previously posted, I initially was investigating a propane generator to satiate my family who grew tired of candles and our Vermont Casting wood stove during outages (which worked fine for 15 years).

After pricing out a generator and a supplemental propane tank, I came back around to the idea of a tesla power wall, but first did some due diligence, consulting, local installers, including the local family owned business that installed my Sunpower solar panels for a SunVault.

Eventually, I settled on the PW2, after toying with the idea of waiting for the PW3.

After 48 hours, I am so pleased with the product, particularly Tesla’s energy monitoring App.

Initially, it was our intention to use the PW exclusively for outages but after comments above, and more importantly, after using the app for the past 48 hours, it’s just way too much fun to monitor, adjust and come to understand the flow of energy.

Simply stated, controlling the flow of power is pretty darn cool.

 

[h2ofun]

I am thrilled with my purchase.
As previously posted, I initially was investigating a propane generator to satiate my family who grew tired of candles and our Vermont Casting wood stove during outages (which worked fine for 15 years).

After pricing out a generator and a supplemental propane tank, I came back around to the idea of a tesla power wall, but first did some due diligence, consulting, local installers, including the local family owned business that installed my Sunpower solar panels for a SunVault.

Eventually, I settled on the PW2, after toying with the idea of waiting for the PW3.

After 48 hours, I am so pleased with the product, particularly Tesla’s energy monitoring App.

Initially, it was our intention to use the PW exclusively for outages but after comments above, and more importantly, after using the app for the past 48 hours, it’s just way too much fun to monitor, adjust and come to understand the flow of energy.

Simply stated, controlling the flow of power is pretty darn cool.

Just depends. I have friends who were out of power for 14 days. Was not enough sun to fill pw's for normal living. They ran they generator for 14 days and never skipped a beat.

With my 7 pws, and 22kw generator on a 500 gallon LP tank, I can last forever.

 

[Mayer]

No doubt @h2ofun, you are prepared for the Apocalypse … or extended grid failure, at the very least.

Adding a 22 kw LP generator is certainly still in the mix but will wait until we add the detached garage so the generator/tank can be neatly tucked alongside. Who knows, maybe some additional panels on top with another set of PWs below.

Sure would be a nice spot to park a Tesla Roadster too!

A guy can dream, right?

 

[shahryaran]

I am going to flag this as not a particularly helpful response.

If someone suggests that a link isn't particularly helpful, then please at least have the kindness to address the issue(s), or don't post in the first place. I did read the article, which is OK in my book, but not particularly outstanding, and not directly relevant to Powerwall behavior. If you are one of the authors, my apologies.

What about that particular review article struck you as relevant to the charge / discharge / standby behavior of Powerwalls? Batteries do have differences, even if they are nominally "lithium ion", as do battery management systems, as does charge/discharge/storage temperatures, as well as charge/discharge profiles and rates. Subtle differences in electrolyte, barrier films, anode / cathode treatments, the trace metals composition, construction and construction processes, and in the details of the nanostructures of all of the above, can, and do, have profound effects on battery performance characteristics. (Some of which were touched on in the paper) Again, how do these stack up in aggregate for a Powerwall system to impact the longevity under various charge / discharge settings?

I happen to understand many of the above, and I can say that I haven't a clue about what the bottom line is for a Powerwall. I do find the data from owners who are logging their system status over time interesting, although I guess I do wonder how accurate any particular reported value for pack capacity is at any given point in time. BMS undergo periodic recalibration of their own estimates, so I would be inclined to take any given value with a grain of salt, but the trends are, I suspect, informative and reliable. (I'm not dumping on Tesla here. It is not trivial to accurately measure power flow in/out, due in part to inaccuracies in measurements (ADCs, bit level accuracy, and the vagaries of silicon and all that) and a certain amount of rescaling to cell voltage(s) is inevitable, but each cell has slightly differing voltage/state of charge relations due to the aforementioned effects and others.)

******

Personally, I am happy to have the Powerwall as a backup. Like many things in life at a certain level of examination, I tend to treat it as a black box. There is no way to know many of the inner working details, and for things under software or firmware control, those details could change in the next update. Which leaves me on the page of using them for backup, and a certain amount of charge/discharge to slip past most of our peak usage, though thanks to @Redhill_qik's detailed analyses, I realize that also isn't worth sweating. My plan is if a Powerwall drops below warranty levels at nine and a bit years, I will address it then. Lots of water yet to go under the bridge...

All the best,

BG

do as you wish.
They refused to read the article. It would have been helpful if they read the article.

 

[ucmndd]

With that big of a difference between peak and off peak rates, you should at minimum set up time based control and rarely/never draw from the grid during peak.

 

[eml2]

I have my 2 PW2 for more than 5 years. Let them drain to 0% many times during past 5 winters, and charge to 100% many times as well. Note that 0% shown in the Tesla app is not true 0%. I think it is around 5%.

As of today, the owner API live_status endpoint reports it still has 26.859 kwh total_energy_pack.

My Powerwalls are located in the basement. Ambient temp is between 55F - 70F.

 

[Mayer]

With that big of a difference between peak and off peak rates, you should at minimum set up time based control and rarely/never draw from the grid during peak.

Will Time Based Control automatically schedule Powerwall to kick on at dusk (before Peak ends at 6 PM)?

I am predicting it will, but will adjust manually if needed.