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What will powerwalls charge up to before excess dumped to grid?

sorka

Well-Known Member
Feb 28, 2015
8,165
5,938
Merced, CA
Assuming there are days that I'm gone or using very little energy and the PWs charge high enough that excess solar starts going to the grid, what level is that? I hope it's nowhere near 100%. Is there a way to control maximum SOC without having to resort to tricks such as setting the peak time period to convince the system to dump excess back to the grid earlier than it would normally? i.e. say my PWs get to 85% by 1 PM but I don't want the charge to go any higher, so I move my peak start from 3 pm to 1 pm just to get solar to dump to the grid now.

If the normal max SOC outside of storm watch is say 85%, then I'm ok with that but I wouldn't want daily charges to 90%.
 

sorka

Well-Known Member
Feb 28, 2015
8,165
5,938
Merced, CA
I don't know of any way to stop charging PWs before 100%. Nor do I know why you ant to

My response WAS going to be because you don't want to charge lithium ion batteries to 100% unless it's really necessary but then it occurred to me that I might be assuming incorrectly the battery chemistry, so I'll go research that first before I reply :)

There is one reason at least regardless of chemistry that I would not want my powerwalls to reach more than 97% and that is all my powerline automation will cease to work if my AC is no longer 60 Hz.
 
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BrettS

Active Member
Mar 28, 2017
2,112
2,520
Orlando, FL
The powerwalls are lithium ion, but it is believed that the 100% shown in the app is not actually 100% and the powerwalls don’t allow themselves to be charged to an actual 100% in order to protect the batteries.

Also, keep in mind that the line frequency issue only happens when you are off grid. If you are connected to the grid then the line frequency will stay at 60Hz no matter what the SOC of the powerwalls. The only potential times that you would see the frequency go up would be if the power happened to fail while the powerwalls were fully charged.

Or if the powerwalls got fully charged while the power was out (although in this case it’s not likely that the frequency would get over 60.5Hz because your modern inverters will shut off at 60.5Hz. It’s unlikely that any electronics would have an issue with 60.5Hz)
 

gcsutton

Member
Jun 28, 2020
94
41
Tucson, AZ
My response WAS going to be because you don't want to charge lithium ion batteries to 100% unless it's really necessary but then it occurred to me that I might be assuming incorrectly the battery chemistry, so I'll go research that first before I reply :)

There is one reason at least regardless of chemistry that I would not want my powerwalls to reach more than 97% and that is all my powerline automation will cease to work if my AC is no longer 60 Hz.
I believe I read they're different chemistry than vehicle batteries. Since one of their uses is backup, they may tolerate a high SOC.
 

sorka

Well-Known Member
Feb 28, 2015
8,165
5,938
Merced, CA
The powerwalls are lithium ion, but it is believed that the 100% shown in the app is not actually 100% and the powerwalls don’t allow themselves to be charged to an actual 100% in order to protect the batteries.

Even if it's not a true 100% but 100% is say 90%, charging to 90% every day is still a lot worse on overall lifetime than say charging to 80%.
 

sorka

Well-Known Member
Feb 28, 2015
8,165
5,938
Merced, CA
I believe I read they're different chemistry than vehicle batteries. Since one of their uses is backup, they may tolerate a high SOC.

Lithium nickel manganese cobalt oxide (NMC) with about double the cycle life of regular lithium ion. But depth of charge use is still non linear in how it effects lifetime. i.e. One charge/discharge from 0% to 100% is far worse than 5 charge/discharge cycles from 40% to 60% even though both scenarios cycled through the same kWhs.

Also, I believe I remember reading that storm watch actually exceeds 100% as those that are fully charged from storm watch note that the SOC remains at 100% even after several kWh worth of discharge.
 

BrettS

Active Member
Mar 28, 2017
2,112
2,520
Orlando, FL
Even if it's not a true 100% but 100% is say 90%, charging to 90% every day is still a lot worse on overall lifetime than say charging to 80%.

I’m not sure that’s entirely true. I believe that lifetime is primarily affected by charge/discharge cycles, but I don’t believe that routinely cycling between 90% and 30% would be significantly different than cycling between 80% and 20%.

It has definitely been demonstrated that charging to an actual 100% can affect the battery longevity and it’s possible that going to routinely going to 80% may be somewhat better for the battery than 90%, but I don’t think that that 90% is “a lot worse”. Tesla builds a lot of intelligence into the system to protect the batteries.
 

sorka

Well-Known Member
Feb 28, 2015
8,165
5,938
Merced, CA
It has definitely been demonstrated that charging to an actual 100% can affect the battery longevity and it’s possible that going to routinely going to 80% may be somewhat better for the battery than 90%, but I don’t think that that 90% is “a lot worse”. Tesla builds a lot of intelligence into the system to protect the batteries.

That's true but Tesla still says don't charge past 80% daily unless you need it. If you need it, do it but they are clear that the higher charge, the more it will effect lifetime. And it most certainly has been demonstrated that depth of charge for x number of kwh matters but I'm sure Tesla is balancing between the most optimal perfect use pattern and convenience for the consumer.
 

jboy210

Supporting Member
Dec 2, 2016
5,198
3,234
Northern California
The powerwalls are lithium ion, but it is believed that the 100% shown in the app is not actually 100% and the powerwalls don’t allow themselves to be charged to an actual 100% in order to protect the batteries.

Also, keep in mind that the line frequency issue only happens when you are off grid. If you are connected to the grid then the line frequency will stay at 60Hz no matter what the SOC of the powerwalls. The only potential times that you would see the frequency go up would be if the power happened to fail while the powerwalls were fully charged.

Or if the powerwalls got fully charged while the power was out (although in this case it’s not likely that the frequency would get over 60.5Hz because your modern inverters will shut off at 60.5Hz. It’s unlikely that any electronics would have an issue with 60.5Hz)
Did you get Tesla to set your Gateway to only rise to 60.5 Hz? They lowered mine to 62.5 Hz but did not want to go lower. As I read the specs on my Delta M inverters is shows they provide 59.5 to 60.5 Hz, so I am not sure why Tesla would not go lower. Maybe being conservative with the inverter's exact frequency cut off?
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
9,592
10,833
Riverside Co. CA
Even if it's not a true 100% but 100% is say 90%, charging to 90% every day is still a lot worse on overall lifetime than say charging to 80%.

There is no current way to charge the powerwall like many charge the car. It will charge to 100% in the app if there is enough solar to do so.
That's true but Tesla still says don't charge past 80% daily unless you need it. If you need it, do it but they are clear that the higher charge, the more it will effect lifetime. And it most certainly has been demonstrated that depth of charge for x number of kwh matters but I'm sure Tesla is balancing between the most optimal perfect use pattern and convenience for the consumer.

Since this is not any of the tesla car sections, I am not going to get into the "what tesla says or doesnt say" regarding charging to 80% for the cars. I will just say that there isnt any way that I am aware of to do what you are asking with the powerwall. In fact, tesla has designed the app so that if you put it in backup only the powerwalls float between 97 and 100% for days / months on end, and if you use other modes the powerwalls will charge up to 100% visual in the app when there is power to do so.

TL ; DR, no way to charge to 80% using the tesla controls that I am aware of, although I do believe I remember reading someone here had scripted / automated something for themselves to do something similar to what you are asking for.

I think it was @JayClark (who I am tagging here to see if I am remembering that correctly or not.. sorry if I am mis remembering this)

I personally think charging to 100% for the powerwalls is a non issue, since tesla allows people to put them in backup only mode and run them that way for what would be years, with no change in warranty.
 
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BrettS

Active Member
Mar 28, 2017
2,112
2,520
Orlando, FL
Did you get Tesla to set your Gateway to only rise to 60.5 Hz? They lowered mine to 62.5 Hz but did not want to go lower. As I read the specs on my Delta M inverters is shows they provide 59.5 to 60.5 Hz, so I am not sure why Tesla would not go lower. Maybe being conservative with the inverter's exact frequency cut off?

My max frequency is set to 62.5 as well, but as I’ve posted in other threads the powerwalls will slowly raise the frequency as the SOC gets higher. So if you are operating off grid, as the powerwalls hit about 98% the frequency goes up to 60.1, then 60.2, then it keeps slowly going up until it hits 60.5. At that point the inverters shut off and since the powerwall SOC is no longer going up the frequency doesn’t get higher than 60.5. As the house runs off of the powerwalls and the SOC goes back down the frequency will slowly lower until it gets back to 60Hz.

I have verified this several times while I was off grid by watching the line frequency with my Kill-A-Watt as the powerwalls approached a full charge.

The only time you should see the powerwalls raise the frequency all the way to 62.5 (or whatever the max frequency is) would be if the power fails while the powerwalls are at a 99% or 100% charge level.
 

aesculus

Still Trying to Figure This All Out
May 31, 2015
4,471
2,539
Northern California
I believe I read they're different chemistry than vehicle batteries. Since one of their uses is backup, they may tolerate a high SOC.
With the PW2 they are the exact same batteries made in the same factory the same way. Some go to Powerwalls, some go to Powerpacks and some go to cars (M3/Y).
 

gpez

Member
Apr 25, 2019
689
567
USA
If you are noticing some devices not working even at 62.5hz and your inverters are complaint with a 60.5hz shutoff you should be able to get Tesla to lower the frequency further with some complaining. Mine is set to 62.0hz because my home automation switches and LED lights were still going crazy at 62.5hz. Maybe I just can't see it any more at 62.0hz :)

There is one reason at least regardless of chemistry that I would not want my powerwalls to reach more than 97% and that is all my powerline automation will cease to work if my AC is no longer 60 Hz.

It doesn't quite work like this.

When off grid the Powerwall raises the local frequency to signal your PV to stop producing. Even if you could set a max charge % the system would still need to raise the frequency when that limit is reached. You'd just be moving when the frequency changes relative to the Powerwall charge rather than avoiding the frequency change...
 

jboy210

Supporting Member
Dec 2, 2016
5,198
3,234
Northern California
With the PW2 they are the exact same batteries made in the same factory the same way. Some go to Powerwalls, some go to Powerpacks and some go to cars (M3/Y).
So they are not using the same battery cells that went into older model S or X? If so, this is probably a good thing since those older designs had more limitations.
 

sorka

Well-Known Member
Feb 28, 2015
8,165
5,938
Merced, CA
If you are noticing some devices not working even at 62.5hz and your inverters are complaint with a 60.5hz shutoff you should be able to get Tesla to lower the frequency further with some complaining. Mine is set to 62.0hz because my home automation switches and LED lights were still going crazy at 62.5hz. Maybe I just can't see it any more at 62.0hz :)

I have over 200 Insteon devices in my home so I think I need to ask Tesla to lower my max frequency too :)
 

wjgjr

Active Member
May 11, 2020
1,251
988
Silver Spring, MD
It doesn't quite work like this.

When off grid the Powerwall raises the local frequency to signal your PV to stop producing. Even if you could set a max charge % the system would still need to raise the frequency when that limit is reached. You'd just be moving when the frequency changes relative to the Powerwall charge rather than avoiding the frequency change...
That is easily avoidable with just a little more logic that has "max charge on-grid" and "max charge off-grid". If you rarely lose power, it probably doesn't matter much, but you could set your on-grid limit to 90% or 95% and to 100% off-grid, so that if an outage occurs during a period of daytime overproduction, the system would continue to run while you had some time to adjust loads (like cranking the A/C or charging the EV, if appropriate) to use the excess energy. Having had some time with my system, I realize for me outages are rare, and the lost production would be fairly minimal, but it is not a difficult problem if Tesla wanted to address it.

I still think it is poor that they don't have a true advanced mode where you have direct control over the system (with appropriate restrictions in place to disallow things like grid charge/discharge with PWs, assuming that is not allowed) to directly define charge/discharge rules rather rely on the Tesla modes that can sometimes be unpredictable.
 

BrettS

Active Member
Mar 28, 2017
2,112
2,520
Orlando, FL
I have over 200 Insteon devices in my home so I think I need to ask Tesla to lower my max frequency too :)

It’s probably not a bad idea, but again, it’s not likely a problem that you will run into frequently. The only time you will see the max frequency is if the power fails while the powerwalls are fully charged. Unless you are in backup only mode and have frequent power outages this will only happen very rarely.
 

aesculus

Still Trying to Figure This All Out
May 31, 2015
4,471
2,539
Northern California
I have over 200 Insteon devices in my home so I think I need to ask Tesla to lower my max frequency too :)
You can try. I got them to 62.5 hz too and they were there when I tested the insteon device that would not work. They stated that was as low as they were willing to go even though my inverters trip at 60.5 Hz.
 

Flick75

Member
Aug 11, 2020
25
7
Kailua, HI
So they are not using the same battery cells that went into older model S or X? If so, this is probably a good thing since those older designs had more limitations.

The model 3, model Y and PW2's all use 2170 power cells. And as an extra FYI, the 21 stands for 21mm's wide and the 70 is 70mm's tall. I have one from a model Y on my desk encased in clear epoxy in a jar.
 
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