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Grid down, cold, and can't charge PWs?

KY-Lonewolf

Supporting Member
Oct 6, 2019
50
46
Kentucky
Over in the Tesla company forum there is a recent thread that is saying if the powerwall temperature falls below 50 degrees and the grid is down, you will not be able to charge your PWs from your PV system.
The thread comments are very recent. (11/02/19)
I cannot find anything here on TMC.
The thread is not talking about a cold weather start, but recharging the PWs with grid down and temps below 50 degrees F.
It's odd that it's on that forum and no mention here because TMC is much larger with a lot of folks with experience.
Has anybody experienced this??
Thanks in advance for your comments.
 

MorrisonHiker

S 100D 2021.4.15
Mar 8, 2015
9,437
8,588
Colorado
Hmm. This is the first I've heard of it and not what we've experienced personally. We just did a 200+ hour outage test without any problem and much of that was below freezing, sometimes even in the single digits (6F). We even had 8.5" of snow one day and received three Storm Watch notices due to winter weather during the week. We were off the grid and the Powerwalls charged from solar without problems.


We did have an issue last year when our Powerwalls were down to 5% during the middle of a 45 hour outage. In that case, the Powerwalls and solar inverters were in a cycle where the Powerwalls were sending out a high frequency and would shut off the solar temporarily. See this thread: PowerWall Cold Start without Grid Power Tesla updated the firmware on out inverters and have modified the Powerwall settings for some owners to prevent the frequency from going too high.
 

KY-Lonewolf

Supporting Member
Oct 6, 2019
50
46
Kentucky
@MorrisonHiker - Thanks for the great video! Beautiful RED signed powerwalls!
Only one question ............. It looks like you powerwalls are inside so they would not have their inside temperature drop below 50 degrees. The experiences on the other forum state when powerwalls temps drop below 50 degrees, not the outside temperature. Am I assuming correctly from the video that your powerwalls stay warm?
thanks
 

MorrisonHiker

S 100D 2021.4.15
Mar 8, 2015
9,437
8,588
Colorado
@MorrisonHiker - Thanks for the great video! Beautiful RED signed powerwalls!
Only one question ............. It looks like you powerwalls are inside so they would not have their inside temperature drop below 50 degrees. The experiences on the other forum state when powerwalls temps drop below 50 degrees, not the outside temperature. Am I assuming correctly from the video that your powerwalls stay warm?
thanks
Yes, they are inside our insulated garage. When it was 6F outside, it was still above freezing in our garage. Before we insulated it, snow would fall off the car but stay frozen on the garage floor. Now that it is insulated, the snow falls off and melts. Doh!

It was in the 40s in the garage when that video was filmed, hence the puffy Tesla jackets. I'll have to do some temperature checks on really cold days to see how cold the garage gets but it's definitely below 50F on some days. I'll see if we can use a temperature probe inside the Powerwalls as well.

According to the Tesla specs for the Powerwall, it should still work down to -4F but its recommended to keep it above freezing:
ENVIRONMENTAL SPECIFICATIONS
Operating Temperature –20°C to 50°C (–4°F to 122°F)
Recommended Temperature 0°C to 30°C (32°F to 86°F)

A tech did tell us that the problem we had in March was because the Powerwalls were trying to keep warm by increasing the frequency. I haven't heard of that anywhere else. Maybe another test is in order...to try them when they are cold soaked!
 
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jeep1979

Member
Apr 6, 2017
93
154
Crestline
I had this problem a couple of weeks ago and called support. They told me when it is cold out and grid power is down, in my case under 40, that the batteries cannot accept a high charge. At the time my batteries were. At the time my batteries were at 70% and correctly discharging. However Tesla after reviewing the data, said due to the cold, the batteries could only accept a charge of up to 900W. At the time my solar would have produced around 4Kw. With the grid down, there would be no place to send the excess energy so the system output the higher frequency to keep the solar offline.
 
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KY-Lonewolf

Supporting Member
Oct 6, 2019
50
46
Kentucky
@jeep1979 - That's good information to known! 900W max under those conditions ..... how many Powerwalls do you have, and can you take a guess how cold your PWs were at the time?
thanks
 

MorrisonHiker

S 100D 2021.4.15
Mar 8, 2015
9,437
8,588
Colorado
I had this problem a couple of weeks ago and called support. They told me when it is cold out and grid power is down, in my case under 40, that the batteries cannot accept a high charge. At the time my batteries were. At the time my batteries were at 70% and correctly discharging. However Tesla after reviewing the data, said due to the cold, the batteries could only accept a charge of up to 900W. At the time my solar would have produced around 4Kw. With the grid down, there would be no place to send the excess energy so the system output the higher frequency to keep the solar offline.
That sounds similar to what we saw last March. There was an issue with the Powerwalls and our inverters on the 2nd day of a 45 hour outage and the batteries got down to 5%. They kept signaling the solar to turn on and off throughout the day. They didn't give us the details but it sounds like our solar might've been sending too much to the batteries so they would shut down. We should definitely do another test at low SoC. This test, the lowest we got was 14% over the 200+ hours.
 

miimura

Well-Known Member
Aug 21, 2013
6,094
5,695
Los Altos, CA
If you find yourself in this situation - the solar is being shut down by high frequency from the Powerwalls - and you have multiple solar inverters or solar circuits, it would probably be beneficial to turn off one or more of them to reduce the solar output so you don't exceed the charging capacity of the Powerwalls.
 

MorrisonHiker

S 100D 2021.4.15
Mar 8, 2015
9,437
8,588
Colorado
If you find yourself in this situation - the solar is being shut down by high frequency from the Powerwalls - and you have multiple solar inverters or solar circuits, it would probably be beneficial to turn off one or more of them to reduce the solar output so you don't exceed the charging capacity of the Powerwalls.
We only had the problem once we got down to 5% or so on the Powerwalls. We have three inverters and I finally figured out late in the day that I could get the solar to run longer if I only turned on one of the smaller inverters. It was a long day and I was posting on TMC (in the thread mentioned above) and got several good tips. Hopefully there won't be a "next time" but if there is I'll know how to handle it better. If we are ever in that situation again and the panels are covered with snow, I'll only clear off a few of the solar panels instead of the 60% of the panels that I can reach. That would help limit the solar production, hopefully to a level that the Powerwalls could handle. Then once the Powerwalls are charging faster, I can try try clearing off additional panels.
 

charlesj

Active Member
Oct 22, 2019
1,064
218
Monterey, CA
MorrisonHiker:
Was your 200 hour test with the main breaker off simulating grid down?
Perhaps when that software update, battery behaved differently.
Is there a number for that update to make sure mine will have it when installed
even though I may never see below 50 deg in garage.;)
 

MorrisonHiker

S 100D 2021.4.15
Mar 8, 2015
9,437
8,588
Colorado
MorrisonHiker:
Was your 200 hour test with the main breaker off simulating grid down?
Perhaps when that software update, battery behaved differently.
Is there a number for that update to make sure mine will have it when installed
even though I may never see below 50 deg in garage.;)
Yes, for the 200 hour test, we switched off the main breaker. We're actually on the same firmware since May (1.37.1) so I don't know if if any changes have been made. We used to get firmware updates regularly but have been stuck on 1.37.1 for about 6 months now. Things have been working well so we haven't bothered asking for an update since I've seen a few reports of issues on some of the newer firmware versions.

For the 200 hour test, the Powerwalls got as low at 14% on the final day and could've easily charged to capacity most days during the week. We did see the Powerwalls stopped charging at a lower SoC throughout the week. The first day, I think they got to 95% and then each day after that it was slightly lower but they would still charge to at least 84% before they would start throttling the solar production. Since we still had some really sunny days, I would start charging a car or two or do laundry to take advantage of the solar production on days I was home.

I almost wanted to take the Powerwalls down to 5% again to see if the issue had been solved. However, we were under the third Storm Watch of the week and were expecting 3 days of snow in a row so we decided to end the test at 201 hours.
 
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Ulmo

Active Member
Jan 19, 2016
4,324
4,428
Vienna Woods, Aptos, California
Over in the Tesla company forum there is a recent thread that is saying if the powerwall temperature falls below 50 degrees and the grid is down, you will not be able to charge your PWs from your PV system.
The thread comments are very recent. (11/02/19)
I cannot find anything here on TMC.
The thread is not talking about a cold weather start, but recharging the PWs with grid down and temps below 50 degrees F.
It's odd that it's on that forum and no mention here because TMC is much larger with a lot of folks with experience.
Has anybody experienced this??
Thanks in advance for your comments.
Interesting.

The PowerWalls use quite a bit of energy staying warm with their built in heater. Supposedly, the PowerWalls shouldn't get too cold. Maybe they could get too cold if they were turned off by the user? Are we starting to get users turning PowerWalls off and on and expecting them to work right? I wouldn't do that; I always left mine on except when I was first testing their performance.

Just because stupid regulators require a user-accessible OFF switch doesn't mean it's a good idea to turn them off for anything but service reasons (i.e., I don't see a reason for a user to turn them off, unless instructed by the manufacturer).
 

Ulmo

Active Member
Jan 19, 2016
4,324
4,428
Vienna Woods, Aptos, California
A tech did tell us that the problem we had in March was because the Powerwalls were trying to keep warm by increasing the frequency. I haven't heard of that anywhere else. Maybe another test is in order...to try them when they are cold soaked!
I wonder if I have anything like that system in my older ones (2017 version). Where I live, it only freezes a handful of days per year, so it might not make much difference. Mine are outside, though, so get 50º's weather almost daily.
 

jeep1979

Member
Apr 6, 2017
93
154
Crestline
@jeep1979 - That's good information to known! 900W max under those conditions ..... how many Powerwalls do you have, and can you take a guess how cold your PWs were at the time?
thanks

I have 2 Powerwalls setup for whole house backup. I don't know the temperature of the Powerwalls at the time. The overnight temperatures dropped down into the 20s and only got up to about 50 during the day. However, it seemed the batteries warmed up slower than the outside temperatures. In addition, they are mounted on the outside back of my house and are always in the shade.

The support person I talked to could see the temperatures of the batteries and told me they were slowly warming up, but at the time I called they would only accept about 900W, up from a low of 800W. My system is a 6.2KW system, so it pretty much kept my solar off all day. I had planned for the outage by setting my system up for backup mode only the day before, so when the power was turned off, my batteries were at 100%.

It would be nice if Tesla were to publish this information, so we could better understand what is happening with our systems instead of us panicking and calling support.
 
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Odiemac

Member
Apr 19, 2016
110
189
Hayward
This seems strange, Tesla makes a point of emphasizing their cold weather performance. Is the battery heater only programmed to operate on grid power I wonder?

Additional Powerwall Modes | Tesla

When temperatures are low, all batteries have a reduced ability to charge. To help Powerwall counteract this, Powerwall uses Preconditioning. When temperatures are below freezing, Preconditioning turns on and heats your Powerwall to improve operation and charging performance.

To heat itself, Powerwall draws a small amount of energy, which then allows high-power charging. During a cold night, your Powerwall automatically preheats before sunrise so that maximum solar energy can be captured during the day.

You cannot customize this mode because Powerwall can best detect its internal temperature and knows when to enable Preconditioning.

During Preconditioning, the Power Flow screen may show energy flowing to your Powerwall from solar or the grid. This is normal behavior, and the energy is only being used to heat, not to charge.

During winter months, a small amount of your Powerwall capacity is reserved to improve performance in cold weather. This may change your visible total capacity in the Tesla app. Rest assured, your total capacity has not changed – this small reserve is just set aside to improve performance.

Preconditioning, in combination with Tesla’s unique liquid thermal management system, allows your Powerwall to operate at lower temperatures than any other home battery.
 

KY-Lonewolf

Supporting Member
Oct 6, 2019
50
46
Kentucky
Odiemac makes a interesting point with a possibility that the PWs can only heat themselves when the grid is up?
That's the same comments made on the Tesla company forum thread.
The longest power outages we experience here in Kentucky are during cold weather. Ice storms tear the heck out of the infrastructure so power can be out multiple days .......... guess what? It's cold when that happens!
My garage is insulated, and based on this thread, I've ordered a portable propane heater to to use if I need to keep the temperature up in the garage. (45,000 BTU)
 

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Ulmo

Active Member
Jan 19, 2016
4,324
4,428
Vienna Woods, Aptos, California
I have 2 Powerwalls setup for whole house backup. I don't know the temperature of the Powerwalls at the time. The overnight temperatures dropped down into the 20s and only got up to about 50 during the day. However, it seemed the batteries warmed up slower than the outside temperatures. In addition, they are mounted on the outside back of my house and are always in the shade.

The support person I talked to could see the temperatures of the batteries and told me they were slowly warming up, but at the time I called they would only accept about 900W, up from a low of 800W. My system is a 6.2KW system, so it pretty much kept my solar off all day. I had planned for the outage by setting my system up for backup mode only the day before, so when the power was turned off, my batteries were at 100%.

It would be nice if Tesla were to publish this information, so we could better understand what is happening with our systems instead of us panicking and calling support.
You could build an insulating shed around those. Some walls, RockWool inside the walls, and enough waterproofing to keep the RockWool from rotting. Or you could put burnable insulation around the shed, but I'd be afraid of that catching fire. Regardless of whether your PowerWalls are failing or mis-designed, it could help keep them warm enough to function properly. The PowerWalls keep themselves warm, and would cause the shed to stay somewhat warm. You would have to figure out how to vent it during summer and whenever it gets too hot in the shed.
 

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