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PowerWall tips for when grid is out!

PowerWall tips for when grid is out!

Hi,

I have 3 PW2 being installed this week and I should be online tomorrow. :)

In my installation, I opted for wholehouse protection and the PWs should be more than enough for 12 hrs+ without any compromise on my appliances and heatpump.

Question: For scenarios where the cars are plugged in and utility power goes out, is the Tesla App smart to trigger a command to the cars to stop the charging process? I certainly could do it manually, but thinking on scenarios when there is no one home.

If answer is no, I have sketched a little system already to solve for this (a sensor + app on raspberry pi that will trigger a stop charge command to the cars)... but I really would like to avoid geeking out on this one. :)

Thanks.

markbraukman | 09. juli 2019

I don't think so. I've not had a power outage when my MS is charging. When I have lost utility power, the PWs kick in. I would think that if my MS was charging at that time, it would drain the PWs and then all would go dark.

Tesla-David | 09. juli 2019

The Tesla app allows us to stop or initiate charging on our MS and M3 easily to manage our 2 PW2’s integrated with our 13.2 kWh solar PV system. We operate in self powered mode with our backup set at 25 percent, and have been sel sufficient since mid February with our setup, not utilizing any grid energy. We try to time our Tesla charging when we have full solar so as not to drain the batteries, and usually stagger charging of our MS and M3.

Tesla-David | 11. juli 2019

I meant to add in response to OP's question, the Tesla app will not stop your EV charging when the power goes off, but you can do so easily from the Tesla app. Obviously if the power goes off you want to turn off as many energy draining applications as possible to preserve the PW2's for essential stuff. I summarized above how we stagger our Tesla charging when the sun is out to maximize the efficiency of the PW2's.

mrburke | 13. juli 2019

Question from someone who does not have the system configured yet. (Waiting for Tesla to get back to me.)

While two PWs are enough to handle my houses total electrical load, it likely that charging my car are 40 amps could overload the 60amps that I believe the two PW can produce when I factor in other household loads.

While, I am happy to manage my loads manually, will I be required to put the charging circuit on a separate panel that is not backed up from the PWs ?

Thanks in advance.

gregbrew | 16. juli 2019

When the grid goes out, flip the Main breaker in your electrical panel, to isolate your system from the grid. Grids are notoriously "dirty" in outages, and can drive the TEG bonkers. It happened to mine.

Once you're sure the grid is back up (and clean), restore the main breaker.

Tesla-David | 17. juli 2019

@mrburke responding to your question about whether 2 PW2’s will be able to handle your home loads and Tesla charging. For us the answer is yes, but we limit the charging to 25 Amps to keep the batteries from draining down, and stagger our charging for both Tesla’s. This has worked for us over the past 13 months. See my summary above. We could manage a higher charge rate, but that would trigger grid draws, which we are trying to avoid.

r_p_rocha | 06. august 2019

Thanks Tesla-David and team. The tips above certainly work well when we are in the house and can notice that power is out and stop changing of our cars through the app. What I would like to do is to automate the process, in case it all happens in the middle of the night while we sleep. The scenario is that cars are charging and then Utility power goes out. The PWs will either pick it up and be drained really fast or their breakers will open the circuit and I will lose battery power into the house (defeating the whole purpose of having PWs to start with). I could and should have installed the car chargers in a separate circuit (not covered by the PWs), but that's water under the bridge now.

PSE (where I live) does send a notification to the phone in case of power outage and it also sends an e-mail... I can write an app to trigger a STOP CHARGE command to the cars as soon as I get the notification... but my main concern is to know how long it takes for PSE to find out about the outage...

Anyway, Tesla could easily solve this with... so here is a feature request to them.

brutschy | 06. august 2019

Tesla-David -- How do you limit the charging to 25 Amps? My Model 3 is set to charge at 48 Amps, and I can find no way to change that.

Tesla-David | 07. august 2019

@brutschy, In your M3 you can easily specify your charging amperage. For our MS, with our 100A HPWC and a second onboard charger, I used to charge up to 80A, but limit it to 25A now as I mentioned, because of the PW2's. Yes the default for charging in the M3 is 48A, but you can easily specify whatever charging Amperage you want to charge at as well as the time you want to charge from your car.

@r_p_rocha, with our setup, we clearly specify the time to charge our two Tesla's so that they do not charge during the middle of the night and thereby drain down our 2-PW2's. I currently stager both cars charging, charging our MS at 9:30 a.m. and our M3 at 10:30 a.m. This has worked well for us.

Sjohnson1975 | 14. august 2019

It would be great if Tesla could make a feature that automatically stops the car from charging when the powerwalls turn on.

I have 3 powerwalls and if my car is charging and the grid goes down I would like it to just stop until the grid is restored.

Hopefully they are working on this.

DermMD | 17. august 2019

In the short-term, an easy solution Tesla could implement very quickly is to get a notification through the App when GRID goes down. I'm glad to experience that the Tesla powerwall take over when the grid goes out is so rapid that it is mostly imperceptible to me and I suspect most other people. Particularly when one is going on about life and not paying attention to the mundane.

Sjohnson1975 | 18. august 2019

I sometimes get a notification from the Tesla app when the grid is down and the powerwalls are running. But, it seems to take quite awhile for it to arrive. One time I got the text message from the power company that the power was out but the Tesla app never sent the notification.

sashton | 21. august 2019

To stop a car charge draining the PWs when the grid goes out I am afraid I do something slightly geeky. I check the GW every thirty seconds for its backup state. If the grid goes down I issue a command to the car charges to stop and scheduled charges and set a mode where the cars only charge when the batteries go over 80% SoC (from PV gain) and stop when they drop below 70%. (via their server API - Myenergi Zappi).

gregbrew | 21. august 2019

I recently found that Powerwalls will refuse to properly take over if the grid goes down while EVs are plugged in. My house lights pulsed as the two PWs tried to take over, saw an excessive current draw and shut down, only to try again over and over. According to the Tesla phone support tech, my PWs reported an instantaneous draw of 104A as they transitioned. Even though both EVs were full, they drew a bunch of current for a few minutes to top themselves off. (I've got three refrigerators trying to come back at the same time as two EVs.)

What "fixed" it was to unplug the EVs, switch off the PWs, and then switch them back on. In the future, while away from home, I'll leave both of my EV(s) plugged in with 1KW EVSEs instead of 3.3kW and 7kW EVSEs.

BTW, my experience with Tesla Energy phone support was as good as it gets. Short hold time, and a knowledgeable first-line tech that was able to access my PWs and tell me exactly what they did, and why. After reading all the negatives about Tesla Support here, I thought I'd throw them a little well-deserved love...

r_p_rocha | 21. august 2019

I believe the peak amperage of 1 PW is 29Amps (7kW) and the sustained amperage is 20 Amps (5kW). Given I have 3 PWs I could draw ~60 Amps for a continuous time, but if my 2 cars are charging (J1772) in the middle of the night and any extra load that kicks in (e.g. heatpumps) it could take the whole system down.

Tesla could easily solve this through automation, sending a stop charge command to the cars. For now I will pursue @sashton's solution above, with a small code running on Azure Functions and polling the PWs to find out status. If in back up state, then issue command to stop charging the car.

@tesla - this should be super easy for you to solve... !

r_p_rocha | 21. august 2019

I believe the peak amperage of 1 PW is 29Amps (7kW) and the sustained amperage is 20 Amps (5kW). Given I have 3 PWs I could draw ~60 Amps for a continuous time, but if my 2 cars are charging (J1772) in the middle of the night and any extra load that kicks in (e.g. heatpumps) it could take the whole system down.

Tesla could easily solve this through automation, sending a stop charge command to the cars. For now I will pursue @sashton's solution above, with a small code running on Azure Functions and polling the PWs to find out status. If in back up state, then issue command to stop charging the car.

@tesla - this should be super easy for you to solve... !

gregbrew | 22. august 2019

You do realize that there are many other EV makers out there? Tesla sending a "stop command" to the cars isn't going to work for a Bolt, a Volt or a Leaf.

sashton | 22. august 2019

@gregbrew I think he's suggesting Tesla can kill a charging for a Tesla charger in the event of a power cut.

Of course, for other cars or chargers one would have to roll ones own solution.

The trigger would be to check /api/system_status/grid_status and any response onther than {"grid_status":"SystemGridConnected"} would indicate a backup situation

I use Myenergi Zappi EVSE and the method to stop all scheduled charge sessions and ensure any manual charges cease is to submit:

https://myenergi.net/cgi-zappi-mode-Zxxxxxxxx-3-0-0-0000
To only permit charging when there is export (which will not happen while islanded) and:-

https://myenergi.net/cgi-zappi-mode-Zxxxxxxxx-0-2-0-0000
To stop any timed charge sessions

where xxxxxxxx is the serial# of the EVSE in question

sashton | 22. august 2019

BTW I am not espousing the use of the Myenergi EVSE with Tesla cars.
The M3 has only recently arrived in the UK and currently there are compatibility issues with these models which appear to stem from the car.
There are no issues with any other EVs: Chevrolet, Jaguar (recent firmware), Hyundai, VW, BMW etc. (as far as I am aware).

mikemillar | 27. august 2019

If you have the new Gateway 2 backup gateway the answer is to have the car charger wired in on the non-backup side as mine is. Then in the event of a power outage the car charger doesn't charge and suck all the juice out of the Powerwall, which only powers the backup side, normally the home loads. Unless, of course , you have a multiple Powerwall installation with enough capacity to charge the car as well as provide the home loads in the middle of the night.

gregbrew | 31. august 2019

Mike, Your technique won't work if the PWs back up the entire house, and the charger is on a sub-panel, as mine is.