PowerWall 2 Best Practice

[q2bruiser]

Hello. I have been lurking and finally joined. Appreciate the vast array of knowledge here.

Having searched, I cannot find a definitive answer to what I hope is a simple question. First my setup.

Am in CO. Have a 9.2kwh system plus 2 PW2s. My electric company does 1 to 1 net metering so from an efficiency standpoint, the most logical choice is to send all my over production to the grid, which I do. My 2 PW2s are set to backup mode 100%.

But, from a longevity standpoint is it best practice to keep the PWs topped off all the time? I understand the onboard controls/systems require power for maintenance so there is minimal cycling in 100% backup mode. Or should I allow the PWs to cycle some small percentage a day? There is no monetary benefit to do so for me, I am only searching for best practice.

I understand many have a set and forget mindset about this. I get it. But, I have made my recent investments to last. I am older and have done, I hope, my last major investments in my home.

Thank you for your help.

 

[jrweiss98020]

The Powerwalls are designed to be "topped off all the time". There is no way to avoid it, unless you repeatedly cycle them, which also causes some wear. I just leave mine in Backup mode as you do, and do a couple off-grid tests each year.

 

[q2bruiser]

The Powerwalls are designed to be "topped off all the time". There is no way to avoid it, unless you repeatedly cycle them, which also causes some wear. I just leave mine in Backup mode as you do, and do a couple off-grid tests each year.

Thank you!

 

[Evans]

I believe powerwall2 uses NMC (nickel-manganese-cobalt) chemistry, which don't like staying close to 100% SOC (state of charge) for long periods. Having said that, it would be interesting to see what behaviour others here have configured and their current battery pack capacity.

I'll start - I have mine set to time of use and on a typical summer day it discharges to around 93% (based on what I see in the tesla app). The battery fully charges by around 9 AM and stays at 100% to roughly 6 PM in summer season and staying around 93% from 9PM till the next sunrise. For winter, I'd say it fully charges around 11 AM and stays at 100% until around 4 PM. It will discharge to around 65% by 9PM and stay that way till the next sunrise.

I've had my 2 powerwalls for about 1.5 years and currently https://teg/api/system_status shows the following for each battery:

nominal_full_pack_energy

14068

nominal_full_pack_energy

14067

A powerwall2 is supposed to have 13.5kw usable capacity, so I'd say there's very little degradation so far.


Update:
I forgot, temperature is also pretty important to lifespan of battery so this information should be included as well.

My powerwalls are kept in the garage and average ambient temperature in summer is around 80F, winter is around 50F.

 

[tfan2018]

I believe powerwall2 uses NMC (nickel-manganese-cobalt) chemistry, which don't like staying close to 100% SOC (state of charge) for long periods. Having said that, it would be interesting to see what behaviour others here have configured and their current battery pack capacity.

I'll start - I have mine set to time of use and on a typical summer day it discharges to around 93% (based on what I see in the tesla app). The battery fully charges by around 9 AM and stays at 100% to roughly 6 PM in summer season and staying around 93% from 9PM till the next sunrise. For winter, I'd say it fully charges around 11 AM and stays at 100% until around 4 PM. It will discharge to around 65% by 9PM and stay that way till the next sunrise.

I've had my 2 powerwalls for about 1.5 years and currently https://teg/api/system_status shows the following for each battery:

nominal_full_pack_energy

14068

nominal_full_pack_energy

14067

A powerwall2 is supposed to have 13.5kw usable capacity, so I'd say there's very little degradation so far.


Update:
I forgot, temperature is also pretty important to lifespan of battery so this information should be included as well.

My powerwalls are kept in the garage and average ambient temperature in summer is around 80F, winter is around 50F.

What's the number supposed to represent and what's the number supposed to be for a new power wall? My PW installed 9 months ago is showing 13928

 

[SaveOurPlanet]

Just curious, what is your goal when you purchased the PWs? I see PWs as consumable meaning I use it as intended and I expect it to diminish in value or capacity. I used to be on self-powered 70% of the time the last 15 months but now on time-based and set peak time from 3pm-12am for house to be powered by the PWs, I have scheduled charging of my car after midnight and only want to charge it from the grid. So far there is little or no degradation of the PWs, but even if there is, Tesla has a 10 years 70% capacity warranty. Even if it dropped to 71% and no replacement from Tesla, PWs would still be good for my need, and if gets worse after that I would have a much bigger problem than buying new ones with my own money. If you buy a boat, do you keep it in dry dock to preserve resale value?

 

[bmah]

I believe powerwall2 uses NMC (nickel-manganese-cobalt) chemistry, which don't like staying close to 100% SOC (state of charge) for long periods. Having said that, it would be interesting to see what behaviour others here have configured and their current battery pack capacity.

They're lithium-ion batteries. Data sheet:

https://www.tesla.com/sites/default/files/pdfs/powerwall/Powerwall_2_AC_Datasheet_EN_NA.pdf

Bruce.

 

[Evans]

What's the number supposed to represent and what's the number supposed to be for a new power wall? My PW installed 9 months ago is showing 13928

The number is the capacity of your battery in Watts, I don't know what the value should be for a new battery but mine has been about 14000 since it was first installed.

They're lithium-ion batteries. Data sheet:

https://www.tesla.com/sites/default/files/pdfs/powerwall/Powerwall_2_AC_Datasheet_EN_NA.pdf

Bruce.

Yes, but lithium-ion is more of a general type of battery which can have varying chemistries. For example, I think iron phosphate chemistry can also be called lithium ion, but might have different characteristics on whether it can better stay at 100% SOC (closer to 95% in actuality since there's around a 5% buffer at the top, so we see 100% but its really 95%). Still I'd say 95% is a little on the high side for NMC chemistry.

 

[Penny24]

So what is the best way to use the PW system? I set my system to self power down to 20% but majority of the morning it would run down to about 50% and recharge to full at about mid-day and send to the grid after. I practically use it like a cell phone, however to preserve longevity is there a different strategy I can use?

 

[Evans]

I'm not sure there's emperical evidence what best practice is, I'm hoping there will be more takers in sharing behavior of their powerwall and their current degradation.

 

[jjrandorin]

I'm not sure there's emperical evidence what best practice is, I'm hoping there will be more takers in sharing behavior of their powerwall and their current degradation.

There are a couple of threads with discussion along that vein here that I am aware of. I believe the largest one is here:

Powerwall 2 Available Energy After 2 Years

First time poster, long time visitor. I'm trying to understand the current energy retention level of my 2 year old Powerwall 2's. They don't seem to be holding the kWh's I expect. I'll share some numbers I've got and would like to hear from others if I'm looking at this the right way. My two...

teslamotorsclub.com

With that being said, I dont think there is a "best way" to use these, because it depends on what someones goal is. There is also no way to stop charging them before 100%, so they are going to get to 100% in the app regardless. 100% in the app isnt actually 100% of the battery capacity though.

What the discussion is, then, is do you leave it at "100%" or use it for TOU arbitrage, or some combination, and that is a fairly personal decision.

 

[sunwarriors]

So what is the best way to use the PW system? I set my system to self power down to 20% but majority of the morning it would run down to about 50% and recharge to full at about mid-day and send to the grid after. I practically use it like a cell phone, however to preserve longevity is there a different strategy I can use?

I used to have my reserve at 40%, but raised it to 60% since I net export anyways and figure 20% less discharge cycles will preserve my battery slightly longer. 60% is generally enough to use the battery during on-peak and I go back to the grid when it's not on-peak anymore (for now).

I'll move it back to 40% probably in the winter/spring assuming no cloudy days in a row since for my use case, the summer months are actually worst since we need the AC during the afternoon/evening and with it on, we actually don't export much anymore. I also don't want it to drain the batteries to a lower % during the summer in case of a power outage (I'm set on self-powered).

In the long run, I don't think it'll matter too much, but that's what I'm doing.

 

[schettj]

What's the number supposed to represent and what's the number supposed to be for a new power wall? My PW installed 9 months ago is showing 13928

PW2s should be ~13.5k, My 10 month old PW is showing 13981, seems legit.