Powerwall 101

[jacobp]

Thanks to everyone who took the time (and patience) to provide useful information to me for my upcoming install. Installation of two PWs is scheduled for July 14. As of now, I'm planning to have my two Tesla EV chargers both on backup and powering up from the PW. Is that a bad idea?

 

[SSonnentag]

Thanks to everyone who took the time (and patience) to provide useful information to me for my upcoming install. Installation of two PWs is scheduled for July 14. As of now, I'm planning to have my two Tesla EV chargers both on backup and powering up from the PW. Is that a bad idea?

If you have the new WiFi-enabled Tesla HPWCs, it shouldn't be a problem. You'll be able to program the charging to not occur during power outages, or only at low rates, etc. If you have the original HPWCs, like I do, or other "dumb" chargers, you may want to do as I did and not back up the charging outlets.

 

[BrettS]

If you have the new WiFi-enabled Tesla HPWCs, it shouldn't be a problem. You'll be able to program the charging to not occur during power outages, or only at low rates, etc. If you have the original HPWCs, like I do, or other "dumb" chargers, you may want to do as I did and not back up the charging outlets.

Are you sure about that? I don’t believe that the WiFi wall chargers do communicate with the powerwalls. The new feature that allows the powerwall to control car charging works because the powerwall communicates directly with the car, so that will happen when the car is plugged into any charger. However, right now that’s only supported on model 3 and Y. Apparently support for model S and X is ‘coming soon’.

It certainly makes sense for the powerwall and the charger to communicate and I wouldn’t be surprised if that happens eventually, but I don’t think that’s available right now.

 

[SSonnentag]

Are you sure about that? I don’t believe that the WiFi wall chargers do communicate with the powerwalls. The new feature that allows the powerwall to control car charging works because the powerwall communicates directly with the car, so that will happen when the car is plugged into any charger. However, right now that’s only supported on model 3 and Y. Apparently support for model S and X is ‘coming soon’.

It certainly makes sense for the powerwall and the charger to communicate and I wouldn’t be surprised if that happens eventually, but I don’t think that’s available right now.

I'm not sure at all. I was only basing this on the new HPWC released by Tesla and their followup post about the powerwalls being able to control car charging. I may have jumped to the wrong conclusion as to why/how the new feature works. I hope your idea is right as it would mean I could someday connect my HPWCs up to my PW panel. Hopefully someone can give a definitive answer to this.

 

[jjrandorin]

I'm not sure at all. I was only basing this on the new HPWC released by Tesla and their followup post about the powerwalls being able to control car charging. I may have jumped to the wrong conclusion as to why/how the new feature works. I hope your idea is right as it would mean I could someday connect my HPWCs up to my PW panel. Hopefully someone can give a definitive answer to this.

The feature is not HPWC connected as I have a Version 2 HPWC (non wifi, purchased in 2018) and a model 3, and I have the option in my tesla account that is talked about to limit charging to a percentage of powerwall.

Thanks to everyone who took the time (and patience) to provide useful information to me for my upcoming install. Installation of two PWs is scheduled for July 14. As of now, I'm planning to have my two Tesla EV chargers both on backup and powering up from the PW. Is that a bad idea?

The "issue / concern" with backing up HPWCs with powerwalls is, if there is a power outage during the middle of the night, and you have your car(s) set to charge during the middle of the night, the cars will drain the batteries almost immediately. Charging a tesla vehicle with powerwalls is like trying to fill up 2 D batteries using 2 AA batteries.

While tesla has released a new feature to limit how much the cars drain the batteries in the above scenario, its not released to all tesla vehicles, and we have no idea if it will ever be released to older tesla vehicles. Its much "safer" to not backup those loads but have them monitored, so that when you have grid power, the car can be charged from solar + batteries + grid if you wish, but if there is no grid, the car will not charge. Some of us have had a 14-50 or smaller outlet put on the "backup loads" side so that you "could" charge the car if you want to, during an outage, by plugging in there, but you would not have to worry about the (admittedly rare) chance your car could drain your powerwalls as above.

If I was in a protracted outage, I would only want to use enough powerwall power to charge my car enough to drive to a supercharger or something, personally.

The other concern is the size of the load for those chargers. I would personally not consider putting 2 car chargers on the backup load side (I would ask them to specifically exclude them) but would ask for a 14-50 outlet on the backup side so I could plug in "if I wanted to" during an outage. They are still monitored so as I mentioned during regular use, you can still use part (or all if you want to, for some reason) of your powerwall power to make a small dent in your car charging.

 

[SSonnentag]

@jjrandorin makes great points. Having a separate, rarely-used 14-50 on the Powerwall backup panel sounds like the best solution as it doesn't rely on often-faulty/buggy software and functional wireless communications to prevent tripping your Powerwall overload breakers. I like it!

 

[jacobp]

The feature is not HPWC connected as I have a Version 2 HPWC (non wifi, purchased in 2018) and a model 3, and I have the option in my tesla account that is talked about to limit charging to a percentage of powerwall.



The "issue / concern" with backing up HPWCs with powerwalls is, if there is a power outage during the middle of the night, and you have your car(s) set to charge during the middle of the night, the cars will drain the batteries almost immediately. Charging a tesla vehicle with powerwalls is like trying to fill up 2 D batteries using 2 AA batteries.

While tesla has released a new feature to limit how much the cars drain the batteries in the above scenario, its not released to all tesla vehicles, and we have no idea if it will ever be released to older tesla vehicles. Its much "safer" to not backup those loads but have them monitored, so that when you have grid power, the car can be charged from solar + batteries + grid if you wish, but if there is no grid, the car will not charge. Some of us have had a 14-50 or smaller outlet put on the "backup loads" side so that you "could" charge the car if you want to, during an outage, by plugging in there, but you would not have to worry about the (admittedly rare) chance your car could drain your powerwalls as above.

If I was in a protracted outage, I would only want to use enough powerwall power to charge my car enough to drive to a supercharger or something, personally.

The other concern is the size of the load for those chargers. I would personally not consider putting 2 car chargers on the backup load side (I would ask them to specifically exclude them) but would ask for a 14-50 outlet on the backup side so I could plug in "if I wanted to" during an outage. They are still monitored so as I mentioned during regular use, you can still use part (or all if you want to, for some reason) of your powerwall power to make a small dent in your car charging.

My two EV chargers are plugged into two 14-50 outlets. Are you suggesting that, even in that case, I should not back up the two 14-50s. I suppose one could always simply charge off a backed up 110v outlet until you have enough juice to get to a supercharger. Is that the recommendation?

 

[jacobp]

Its much "safer" to not backup those loads but have them monitored, so that when you have grid power, the car can be charged from solar + batteries + grid if you wish, but if there is no grid, the car will not charge.

How do I make sure that the EV charging loads are "monitored" but not backed up. Is this something i have to tell the installers?

 

[BrettS]

My two EV chargers are plugged into two 14-50 outlets. Are you suggesting that, even in that case, I should not back up the two 14-50s. I suppose one could always simply charge off a backed up 110v outlet until you have enough juice to get to a supercharger. Is that the recommendation?

The concern is that if the power fails while your car is charging and you aren’t aware that it fails (maybe it happens at night while you are sleeping) then your car would continue to charge and it could drain your powerwalls and you would have no power left to power your house. It’s a reasonably small risk because if the power fails while your car is not charging then there’s no problem or if the power fails while your car is charging, but you are aware that it failed and you can go and stop your car from charging and then there is no problem.

Additionally Tesla has promised the ability for the powerwalls to communicate with the car so that when the grid is down it can automatically stop your car from charging when the powerwall drops below a certain percent, however, right now that feature only works for the Model 3 and Y. They say that it will be available for the Model S and X, but don’t say when, other than to say that it’s “coming soon”

So, all that said, it’s up to you. By not backing up your car chargers then you know that there’s no chance that the car might accidentally drain the powerwall, but the risk of that happening is also fairly low.

 

[jjrandorin]

How do I make sure that the EV charging loads are "monitored" but not backed up. Is this something i have to tell the installers?

They (installers) should have a schematic of what will be backed up and what wont. Look and see where your 14-50 outlets are. If they are in a non backed up load panel, but the installers place the CTs a certain way, they are "monitored" in that when the grid is up, they are a part of the regular system, powerwalls can be used to provide power to them, etc.

I believe this is the "normal state" of non backed up loads but I am not an installer. I didnt have to ask anything special for my wall connector. Its not backed up, but I can see when my car is charging by amount of power draw, and the powerwalls will provide power to the wall connector, as long as the grid is up.

I believe its normally set up this way if possible, but each house has different electrical system so it might depend on sub panels, etc. I didnt have any sub panels at my home prior to powerwall install, and now have a main panel that has 1 non backed up load (my HPWC) and my "critical loads" panel which includes every other load in my home.

 

[jacobp]

Thanks again to everyone. My understanding is that the PW design for my home will back up everything. I'll have to think about how I want to deal with the EV chargers. It seems to me, given our car usage habits, that it would be a very, very rare occurrence for our cars to need a significant charge on the night the power goes out. And given that the PW/Car communication may someday come to fruition, it seems that including the chargers in the backup would not pose a significant risk to depleting the battery overnight during an outage. And, if the sun is shining the next day, the battery will be replenished anyway (assuming the daily draw is less than the solar panels produce). On the other hand, if the EV chargers are not backed up, we could always use 110v outlets to charge the cars sufficiently to get to a supercharger. Tough call.