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Drawing from Powerwalls and sending to grid at the same time?

EVRider-FL

Member
Aug 18, 2015
776
443
South Florida
I've had my solar panel plus Powerwall system operating for about 10 days now, and enjoy monitoring the system using Power Flow in the Tesla app. Today I saw something odd (see photo): it appeared that I was drawing power from the Powerwalls and sending power to the grid at the same time (around 4pm in the chart). I haven't seen this before.

Why would this happen? I would expect energy to go back to the grid only when solar is producing more than the home is using, in which case the Powerwalls should either be charging or doing nothing. I also downloaded the data to see if it was just a UI issue, but the data shows the same thing.

At the moment, I have the Powerwall reserve set to 0% because I'm trying to determine if the Powerwalls can get me through the night without using the grid. I don't have any time-based settings.

DB117814-31DD-4FB7-ACE6-C00FC8A0AE1F_1_101_o.jpeg
 

Will792

Member
Oct 9, 2018
39
22
CT
You can do rough estimate of how much time you have of battery run time by looking at averaged recent electric consumption. Each PW is around 13KWh so 1.3KW consumption will have 10 hours of runtime with reserve set to 0. It is very likely that most of your electric consumption comes from AC which stays very consistent, as long as outside temperature does not change much.
 

EVRider-FL

Member
Aug 18, 2015
776
443
South Florida
Can you also post the image with solar generation displayed?

And what are your settings under the Customize tab?

Here you go. I removed the home usage from this version because it made the graph too busy. I would resize these images to make them smaller, but I can’t seem to do that on an iPad (I posted the last one on my Mac).


702B3DA9-58C3-4680-A7C1-7FD5FD03BCF4.png

E6A6D13F-831A-43AD-8B02-503EE9DF1104.png
 

EVRider-FL

Member
Aug 18, 2015
776
443
South Florida
You can do rough estimate of how much time you have of battery run time by looking at averaged recent electric consumption. Each PW is around 13KWh so 1.3KW consumption will have 10 hours of runtime with reserve set to 0. It is very likely that most of your electric consumption comes from AC which stays very consistent, as long as outside temperature does not change much.
I did some estimates based on my nighttime consumption, and I figured I’d get about 13.3 hours from the Powerwalls, which might be a little less than I would actually need to make it through the night if the grid was down. I figured running the batteries to 0% would confirm (or refute) that.

Related question: if the grid is down, what happens when you generate some power but not enough to meet demand? I’ve never lived in an area where they have brownouts, but is that essentially what happens? If I’m home I can turn off circuits to reduce load, but there’s not much I could do if I’m away.
 

power.saver

Grid Specialist
Supporting Member
Mar 4, 2018
631
666
Arcadia, CA
Related question: if the grid is down, what happens when you generate some power but not enough to meet demand? I’ve never lived in an area where they have brownouts, but is that essentially what happens? If I’m home I can turn off circuits to reduce load, but there’s not much I could do if I’m away.
During a grid outage, if the house load exceeds solar production, then the PW will shut down after they are depleted and you won't have any power.

Once solar production exceeds house load and starts to recharge the PW and supply the house, they should come back on. Also once the grid is restored, they will come back on.
 
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EVRider-FL

Member
Aug 18, 2015
776
443
South Florida
During a grid outage, if the house load exceeds solar production, then the PW will shut down after they are depleted and you won't have any power.

Once solar production exceeds house load and starts to recharge the PW and supply the house, they should come back on. Also once the grid is restored, they will come back on.

What happens to the solar production while it’s less than the house load?
 

power.saver

Grid Specialist
Supporting Member
Mar 4, 2018
631
666
Arcadia, CA
What happens to the solar production while it’s less than the house load?
As long as the PW is not depleted, the PW will make up the difference between the solar production and the house load. At night, the PW will supply the entire house load, as solar production is zero. This is okay until the PW runs down, at which point it will turn off.
 

Flick75

Member
Aug 11, 2020
80
45
Hawaii
This is okay until the PW runs down, at which point it will turn off.

Technically it doesn't turn off it goes in to standby and the green light on the side the PW will be solid. Not trying to be anal, I just don't want the OP to be confused as there is a difference between standby and being turned off.
 

power.saver

Grid Specialist
Supporting Member
Mar 4, 2018
631
666
Arcadia, CA
Technically it doesn't turn off it goes in to standby and the green light on the side the PW will be solid. Not trying to be anal, I just don't want the OP to be confused as there is a difference between standby and being turned off.
I should have said "turn off power to the home" as that was the point I was trying to make.
 

EVRider-FL

Member
Aug 18, 2015
776
443
South Florida
As long as the PW is not depleted, the PW will make up the difference between the solar production and the house load. At night, the PW will supply the entire house load, as solar production is zero. This is okay until the PW runs down, at which point it will turn off.
I meant during an outage, when the Powerwalls are depleted, what happens to the solar production if it isn’t enough to handle the house load? In my system, solar flows directly to the house first, then the Powerwalls, then the grid.
 

jboy210

Supporting Member
Supporting Member
Dec 2, 2016
5,471
3,468
Northern California
I meant during an outage, when the Powerwalls are depleted, what happens to the solar production if it isn’t enough to handle the house load? In my system, solar flows directly to the house first, then the Powerwalls, then the grid.
It is an interesting question. I assume if you don't have enough solar production to meet the house load then the power would flow to the Powerwalls for storage. At some point, the Powerwalls should have enough energy to power the home since the backed-up loads should have been configured with critical loads or whole house based on house consumption and number of Powerwalls.
 

slcasner

Active Member
Supporting Member
Feb 20, 2011
1,350
910
Sunnyvale, CA
I assume if you don't have enough solar production to meet the house load then the power would flow to the Powerwalls for storage.
I believe that's not possible because the house loads, the solar inverter and the Powerwalls are all hardwired together. There are breakers separating them, but no contactor that can open to separate the house loads from the solar inverter and Powerwalls. The only contactor is the one in the Gateway to isolate the whole system from the grid.
 

yblaser

Member
Aug 4, 2018
84
57
South Bay Los Angeles
When you are off grid and the powerwalls are fully depleted if your backed up circuits in your home attempt to pull more power than the solar is producing the whole system will shutdown, go into standby and you will completely lose power. After some amount of time the powerwalls will attempt to restart to charge from the solar but if your load is still greater than what the solar can produce they will shutdown again. At this point you need to manually load shed to reduce your home load so that the powerwalls can restart and charge from solar.
 

jboy210

Supporting Member
Supporting Member
Dec 2, 2016
5,471
3,468
Northern California
When you are off grid and the powerwalls are fully depleted if your backed up circuits in your home attempt to pull more power than the solar is producing the whole system will shutdown, go into standby and you will completely lose power. After some amount of time the powerwalls will attempt to restart to charge from the solar but if your load is still greater than what the solar can produce they will shutdown again. At this point you need to manually load shed to reduce your home load so that the powerwalls can restart and charge from solar.
So we are lose the solar production if we have the home load too high?

That seems a bit of a design flaw since we have these empty powerwall(s) capable of absorbing the solar production. Why is it set up this way? Potentially you could go an entire day without home power and full sun if solar's production was not enough to meet the home load.
 

power.saver

Grid Specialist
Supporting Member
Mar 4, 2018
631
666
Arcadia, CA
So we are lose the solar production if we have the home load too high?

That seems a bit of a design flaw since we have these empty powerwall(s) capable of absorbing the solar production. Why is it set up this way? Potentially you could go an entire day without home power and full sun if solar's production was not enough to meet the home load.
Yes. Because if home load is more than solar, there is no power to recharge with, and more importantly, there isn't even enough power to run the house. If you are in this situation, turn off all your home loads or open breakers in your panel so that only solar and the PW are still on. Then all your solar will go to recharging the PWs.
 

yblaser

Member
Aug 4, 2018
84
57
South Bay Los Angeles
So we are lose the solar production if we have the home load too high?

That seems a bit of a design flaw since we have these empty powerwall(s) capable of absorbing the solar production. Why is it set up this way? Potentially you could go an entire day without home power and full sun if solar's production was not enough to meet the home load.
In a grid out situation you will always need to pay close attention to your home's energy usage and manually shed loads as necessary. Even if the powerwalls are fully charged if you exceed the rated power draw of the powerwalls and whatever solar you are producing they will shutdown.

See: Best Practices During Power Outages | Tesla Support

Running Low on Energy​


If Powerwall has less than 10% energy remaining, it will enter a standby state and stop providing power to your home. If your system is connected to the internet, you'll receive a push notification in the Tesla mobile app when Powerwall enters standby.


When in standby and paired with a solar energy system, Powerwall will automatically attempt to recharge from solar for six minutes every hour between 8 a.m. and 4 p.m. local time. If enough solar is available to charge Powerwall while still powering your home, this automatic charging will continue. Otherwise, it will wait for the next hour to attempt charging again.
 
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ZBB

Emperor
Feb 27, 2013
1,574
294
Scottsdale
Yes. Because if home load is more than solar, there is no power to recharge with, and more importantly, there isn't even enough power to run the house. If you are in this situation, turn off all your home loads or open breakers in your panel so that only solar and the PW are still on. Then all your solar will go to recharging the PWs.
Thanks for posting this -- really good tip that could be very useful during a long grid outage. For those of us with whole-home backup, I believe all that's required is to turn off the master breaker in the panel -- since that's downstream from the gateway and is simpler than flipping each individual breaker off. That would turn off power to the house, but keep the solar and powerwalls connected. Alternately, you could turn off the breakers for things like AC to shed the big draw and still power refrigerators. Having a targeted or partial outage that is controlled would be a good way to charge the Powerwalls back up to ensure overnight power for example...
 

Will792

Member
Oct 9, 2018
39
22
CT
In a grid out situation you will always need to pay close attention to your home's energy usage and manually shed loads as necessary. Even if the powerwalls are fully charged if you exceed the rated power draw of the powerwalls and whatever solar you are producing they will shutdown.

See: Best Practices During Power Outages | Tesla Support

Running Low on Energy​


If Powerwall has less than 10% energy remaining, it will enter a standby state and stop providing power to your home. If your system is connected to the internet, you'll receive a push notification in the Tesla mobile app when Powerwall enters standby.


When in standby and paired with a solar energy system, Powerwall will automatically attempt to recharge from solar for six minutes every hour between 8 a.m. and 4 p.m. local time. If enough solar is available to charge Powerwall while still powering your home, this automatic charging will continue. Otherwise, it will wait for the next hour to attempt charging again.
I think that current limit for consumers, in case of off-grid mode, is a sum of PV production and PW discharge limit. Example: if my solar produces 15KW (60A) and I have 3 PWs (5KW or 20A for each) my house can consume up to 120A.

During blackout I was able to charge Tesla at 40A while using appliances with combined draw around 40A. By default Tesla GW disables car charging, unless PW SOC is higher that 70%.
 

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