Powerwall 2: Technical

[fresnoboy]

The PowerWall is inherently not good at working with a generator. What you really need is a separate AC input to the system for the generator that is free running and not synchronized to the battery inverter output. This is what Hybrid inverters do - they basically have a separate battery charger running off the generator input. I believe someone said that Tesla is doing a trial with a handful of customers that have generators to see if their preliminary solution works as expected. I assume they are nesting the Tesla gateway inside the generator's transfer switch so that the Powerwall can synchronize to either the grid or the generator. The only question is how they are controlling when the generator starts. Most would automatically start after a few seconds of grid outage. You wouldn't want that to happen with a PowerWall.

Indeed. When they had a DC only version, it lent it self to integration with the hybrid inverters (not like there are a lot of choices there). But AC Powerwalls don't work with those and require a complex control system to avoid nasty things from happening. I am in the process of building a house, so if Tesla disclosed this approach, I could at least design that in to the electrical system, so I could add powerwalls when the software and hardware were ready.

But as of now, I can't do anything, and because of the closed architecture of their system, other companies that do inverters can't really incorporate them into designs either. I am puzzled by what they are trying to optimize for.

 

[miimura]

Indeed. When they had a DC only version, it lent it self to integration with the hybrid inverters (not like there are a lot of choices there). But AC Powerwalls don't work with those and require a complex control system to avoid nasty things from happening. I am in the process of building a house, so if Tesla disclosed this approach, I could at least design that in to the electrical system, so I could add powerwalls when the software and hardware were ready.

But as of now, I can't do anything, and because of the closed architecture of their system, other companies that do inverters can't really incorporate them into designs either. I am puzzled by what they are trying to optimize for.

So far, they have optimized for grid connected self-consumption. If that's what you want it works really well. In the USA, they also provide a UPS-like backup mode that automatically cuts the grid connection when it fails. As long as you have enough solar generation or manage your loads to remain within your solar capacity at the time of the outage, it works well too. Off-grid and additional generator contribution, not so much.

 

[ohmman]

I really think Tesla needs to update the app to support push notifications for power outages. Last night we were surrounded by sudden wildfires, and I realized this morning that our power wouldn't have gone out last night if the fires approached. I'm not suggesting that a power outage is the only way one should (or would) know that there is some local danger, but it would be a useful data point to at least be notified that the grid is down.

 

[fresnoboy]

I think most of the homeowners who suffer from really unreliable power where the Powerwall that really make a difference probably already have generators of some kind. This is esp true since the Powerwall software doesn't support real TOU shifting yet.

That's why I don't understand why gensets are not their sweetspot.

Also, someone told me their "gateway" has a transfer switch that maxes out at 200A. Is that true? If you have a Tesla, you almost have 100A of the house feed for that, much less everything else. Most large homes now are putting in 400A feeds because of electric cars. So it would be sad if they could not use a powerwall 2.

Again, all this could work with other vendors transfer switches and inverters etc... if they made the control interfaces open.

 

[miimura]

I think most of the homeowners who suffer from really unreliable power where the Powerwall that really make a difference probably already have generators of some kind. This is esp true since the Powerwall software doesn't support real TOU shifting yet.

That's why I don't understand why gensets are not their sweetspot.

Also, someone told me their "gateway" has a transfer switch that maxes out at 200A. Is that true? If you have a Tesla, you almost have 100A of the house feed for that, much less everything else. Most large homes now are putting in 400A feeds because of electric cars. So it would be sad if they could not use a powerwall 2.

Again, all this could work with other vendors transfer switches and inverters etc... if they made the control interfaces open.

I think Tesla's not really going after the backup market. If they were, they would have generator connections figured out better.

As for the 200A transfer switch - my house (completed in Oct 2012) has a 400A panel, 320A service conductors, and a 200A main breaker. Most of my household loads are on a 125A sub-panel. If the PowerWall was installed and only backed up the existing sub-panel, I would be happy. They would just install a new panel inside the transfer switch (gateway) and move my solar (2 x 20A 240V breakers), the sub-panel feed (125A 240V), and the PowerWalls (2 x 30A 240V) there. My EV charging would not be backed up, but I'm fine with that. I could charge on 120V in an emergency.

 

[mongo]

I think most of the homeowners who suffer from really unreliable power where the Powerwall that really make a difference probably already have generators of some kind. This is esp true since the Powerwall software doesn't support real TOU shifting yet.

That's why I don't understand why gensets are not their sweetspot.

Also, someone told me their "gateway" has a transfer switch that maxes out at 200A. Is that true? If you have a Tesla, you almost have 100A of the house feed for that, much less everything else. Most large homes now are putting in 400A feeds because of electric cars. So it would be sad if they could not use a powerwall 2.

Again, all this could work with other vendors transfer switches and inverters etc... if they made the control interfaces open.

Alternative is to use a dual lug 400A meter base and feed two 200A panels from it. One can have the Powerwall gateway and backed up loads. The other can have vehicle charging, A/C and other large loads.

Edit: swapped an and for a comma. No Oxford today.

 

[Dexion11]

Well heck after two months got a call from someone at solar city to say they wont install my powerwall in my laundry room because its living space. Thats where my breaker box is and it was sized right for the powerwall right bellow it but they say its against policy to put it there. So they are two for two with me first they wouldnt sell me the model s i ordered because i wanted 40kwh and didnt want to pay 10k more for 60 then a few weeks later they said they would limit the 60s to 40 i find out from a post online but i had already bought a leaf then they wont do a powerwall for policy reasons because i must live in my laundry room. My garage isnt attached and it gets to be about 145 in the summer. Ah well good luck with your installs.

 

[mongo]

Well heck after two months got a call from someone at solar city to say they wont install my powerwall in my laundry room because its living space. Thats where my breaker box is and it was sized right for the powerwall right bellow it but they say its against policy to put it there. So they are two for two with me first they wouldnt sell me the model s i ordered because i wanted 40kwh and didnt want to pay 10k more for 60 then a few weeks later they said they would limit the 60s to 40 i find out from a post online but i had already bought a leaf then they wont do a powerwall for policy reasons because i must live in my laundry room. My garage isnt attached and it gets to be about 145 in the summer. Ah well good luck with your installs.

Is the breaker box on an outside wall? If so they may be able to mount it outside and run conduit through the wall.

 

[Dexion11]

Oh sure there could be places it would work. Two issues with that, they didnt ever come out and look just said no we wont put it there and have to cancel and i want it to last so putting it outside and having it hit 150F plus when the sun in phoenix hits it is outside operating specs. When i tried to suggest something else she just read back what the rejection of that location said. Anyway, It really needs to be inside to last. I cant park the car in the garage in summer as it gets to be 145 in there or more so i park it under covered parking at work which keeps it a cool 120.

 

[mongo]

Oh sure there could be places it would work. Two issues with that, they didnt ever come out and look just said no we wont put it there and have to cancel and i want it to last so putting it outside and having it hit 150F plus when the sun in phoenix hits it is outside operating specs. When i tried to suggest something else she just read back what the rejection of that location said. Anyway, It really needs to be inside to last. I cant park the car in the garage in summer as it gets to be 145 in there or more so i park it under covered parking at work which keeps it a cool 120.

That sounds frustrating. If I can be of help brain storming options, I'd like to assist. I haven't done a Powerwall, but I did replace my 400 amp service, main panels, and installed a new feeder to a garage I'm (slowly) building.

 

[nativewolf]

Oh sure there could be places it would work. Two issues with that, they didnt ever come out and look just said no we wont put it there and have to cancel and i want it to last so putting it outside and having it hit 150F plus when the sun in phoenix hits it is outside operating specs. When i tried to suggest something else she just read back what the rejection of that location said. Anyway, It really needs to be inside to last. I cant park the car in the garage in summer as it gets to be 145 in there or more so i park it under covered parking at work which keeps it a cool 120.

Whenever I read about someone in Phoenix having heat issues I think about the comedian, forget his name-dead now, who was famous for screaming. One of his skits was about not living in the f'ing desert because you know there is no water and it is hot.

So, in that vein of levity....might I suggest an alternative solution for your PW needs, Delaplane VA. Move to Virginia. Or alternatively, send your PW to my home . I promise to put in a nice cool location, then the PW will be cool even if you are doing a living impression of slow cooked bbq. On another note...140 is almost my temp goal for BBQ on a slow smoke. A fund raising idea comes to mind. Just park the car in the sun with some pork in spices, and at night roll down the windows and become a food car.

 

[NOLA_Mike]

Whenever I read about someone in Phoenix having heat issues I think about the comedian, forget his name-dead now, who was famous for screaming. One of his skits was about not living in the f'ing desert because you know there is no water and it is hot.

 

[commasign]

Technical question: What happens when the grid is out and the solar PV system is generating more energy than the house can use, and the Powerwall is already fully charged. Does the Powerwall turn off the solar inverter? At what point does it turn the solar inverter back on? Does it turn the solar inverter off and on throughout the day to drain the battery a bit and then top it off? Or is there some mechanism to throttle the production somehow (where does the excess energy go)?

 

[miimura]

Technical question: What happens when the grid is out and the solar PV system is generating more energy than the house can use, and the Powerwall is already fully charged. Does the Powerwall turn off the solar inverter? At what point does it turn the solar inverter back on? Does it turn the solar inverter off and on throughout the day to drain the battery a bit and then top it off? Or is there some mechanism to throttle the production somehow (where does the excess energy go)?

@Ulmo showed that the PowerWall gradually increases the frequency to try to curtail the solar. His SolarEDGE inverter did not curtail gracefully and shut down when the frequency went "out of range" causing a solar inverter fault and shut down. When the PowerWall SOC dropped, it returned the frequency back to 60.0Hz and eventually the solar inverter checked the frequency again and restarted. He was disappointed that the Tesla and SolarEDGE stuff did not work together better given their prior cooperation on the DC PowerWall 1.0. His posts about this start around Page 5 of this thread.

 

[commasign]

@Ulmo showed that the PowerWall gradually increases the frequency to try to curtail the solar. His SolarEDGE inverter did not curtail gracefully and shut down when the frequency went "out of range" causing a solar inverter fault and shut down. When the PowerWall SOC dropped, it returned the frequency back to 60.0Hz and eventually the solar inverter checked the frequency again and restarted. He was disappointed that the Tesla and SolarEDGE stuff did not work together better given their prior cooperation on the DC PowerWall 1.0. His posts about this start around Page 5 of this thread.

Thanks. That's helpful. I have a pair of Sunpower-branded SMA Sunnyboy inverters (SB6000M and SB8000M). Anyone know if these behave similarly?

 

[miimura]

Thanks. That's helpful. I have a pair of Sunpower-branded SMA Sunnyboy inverters (SB6000M and SB8000M). Anyone know if these behave similarly?

In theory, SunnyBoy should behave better because they're known to work that way with the SMA SunnyIsland battery inverters. However, I've never seen any operational information about them at the level of detail @Ulmo presented in this thread.

 

[commasign]

In theory, SunnyBoy should behave better because they're known to work that way with the SMA SunnyIsland battery inverters. However, I've never seen any operational information about them at the level of detail @Ulmo presented in this thread.

Got it. Will try to run some tests next time I have a day off.

 

[dlieu]

I recall the engineer was "Mariana" , Yes it was surestart and the issue was resolved . I have tested it and its working fine. The power draw was 3.0KW and Initial current draw was 4amp.

Yeah ok they retrofited mine too, now seems to start fine on backup. haven't run a_lot_ of tests. I am not sure what AC capacity i have (came with the house), but it can't be too large. Where i live on the bay, homes were not even built with conditioners in the beginning (not that hot enough), everything installed I think is post-construction. I will probably experiment more once the air is better with all the fires and all.

 

[Ulmo]

OT: There's a huge swath of the middle of California that is just sand. I want to fill it with solar panels, since I see no other use for it. Homes would just sink in it. Trees can't grow: they'd fall over. But I could find ways to stick the solar panels in there and auto-rotate toward the sun; whenever the anchor moves, the panels would just keep moving to fix. Maybe walk around.

 

[Ulmo]

Version 1.6.0 of the firmware seems to have quite a few bugs compared to prior versions. I haven't been testing the PowerWalls lately, but tonight I ran into a lot of problems:

• Today, when I set the battery reserve high to use grid during high grid solar energy production when rates were low while drying clothes, it took two tries in the app to set the level, since it gave up once (typical iPhone crappy app programming that just gives random errors, wanting the human to correct computer errors).
• At 3PM, when there was no programmatic way to tell the PowerWalls to start up again, and the rates go sky high, I did what I've done dozens of times before, turn off the PG&E link. For the second time ever and the first time when use was under 2kW, it dropped the power of the house for a fraction of a second, rather than having continuous power, like it did during all of my other experiments. This caused all the electronics of the house to reset.
  
• When I set the battery reserve very low so that it would use the battery and turned PG&E back on, it only used the battery until it got down to my previous high reserve setting. In other words, the reserve setting didn't even work when it thought it had worked.
• When I forced use of the battery by turning PG&E off again, despite less than 2kW of use, it once again dropped the electricity for a fraction of a second. This caused a third of the electronics of the house to reset.

I used to say the PowerWalls are great UPS's, but now, I'm seeing all sorts of failures. What changed? I never changed any of the PowerWall configurations (physically or in the software configuration); the only thing I've done is set things via the Tesla iPhone App.

I haven't had these problems in prior versions of the Gateway firmware, which is what leads me to believe that something changed in the way Tesla is doing things programmatically, and for the worse.