Powerwall 2: Technical

[Dexion11]

I am currently waiting an install of a single powerwall. I have a small condo in phoenix. In the last 300 days my demand peaked over 5kw 6 times so it seems to be a good fit for a pw2. I have a couple of questions that ive seen conflicting answers to and a few i can't find answers for. If anyone knows thanks in advance.

1. I have a 3ton central ac. It uses about 2600 watts to run. Can a single powerwall start that ac? I saw a post that is im assuming going to be moved here about someone with 2 3 ton acs and two powerwalls and he couldnt start them even one at a time. Until tou becomes a reality (i have no solar just terrible on peak rates so i can break even in 8.5 years assuming install is under 1k) i plan to flip the breaker at 3 until 8pm. No good answer from tesla. Without ac which is 75% of my use its a non-starter.

2. Will i be allowed to just do whole house even though my panel is 22kw rated? Ive seen evadence both ways.

3. Inverter is rated at 5kw and 8 peak for 10 seconds. What about 6000 watts how long ?

4. No one may know this yet but with tou can i peak shave 5000 watts from demand and then excess need comes from the grid?

Thanks

 

[Parzival]

I am currently waiting an install of a single powerwall. I have a small condo in phoenix. In the last 300 days my demand peaked over 5kw 6 times so it seems to be a good fit for a pw2. I have a couple of questions that ive seen conflicting answers to and a few i can't find answers for. If anyone knows thanks in advance.

1. I have a 3ton central ac. It uses about 2600 watts to run. Can a single powerwall start that ac? I saw a post that is im assuming going to be moved here about someone with 2 3 ton acs and two powerwalls and he couldnt start them even one at a time. Until tou becomes a reality (i have no solar just terrible on peak rates so i can break even in 8.5 years assuming install is under 1k) i plan to flip the breaker at 3 until 8pm. No good answer from tesla. Without ac which is 75% of my use its a non-starter.

I have three Powerwall 2's and a 2-stage A/C which consumes about 2kW and 4kW depending on first and second stage. The blower motor uses another 200W. My stack of three PW2's cannot start this particular A/C unit. When they installed the Powerwalls, they checked the inrush current of the A/C with a clamp ammeter. I would not expect to run an A/C of that size with one Powerwall at all. I am trying to get Tesla to come out and install a soft start unit on my compressor, which should reduce the inrush current from over 150 amps to something reasonable like 60 amps.

At the moment, when the A/C starts up, the Powerwalls do not enter a fault state, but my house blacks out for a quarter second (the lights literally go off) and all the electronics reboot.

2. Will i be allowed to just do whole house even though my panel is 22kw rated? Ive seen evadence both ways.

No way. You'll need a sub-panel with critical loads moved into it.

3. Inverter is rated at 5kw and 8 peak for 10 seconds. What about 6000 watts how long ?

I would not count on more than 10 seconds.

4. No one may know this yet but with tou can i peak shave 5000 watts from demand and then excess need comes from the grid?

TOU should be coming, but the current 1.7.0 software does not support it.

 

[Dexion11]

Yeah just checked 50 amp starting inrush. Ok so given that #4 is really important. I do remember reading someone said if the grid is available they can start their ac then it runs on the powerwalls. So this could work as peak shaving with the grid and my ac could start. Im only 1.5 months in to the process i doubt ill see if before 2018 so at that point if tou is up then we will know the answer.

 

[Parzival]

Yeah just checked 50 amp starting inrush. Ok so given that #4 is really important. I do remember reading someone said if the grid is available they can start their ac then it runs on the powerwalls. So this could work as peak shaving with the grid and my ac could start. Im only 1.5 months in to the process i doubt ill see if before 2018 so at that point if tou is up then we will know the answer.

Yes, I have no problems starting my A/C from the PW when the grid is up.

 

[Dexion11]

Thats good to know. So via the app you see the usage that corisponds to the running ac coming from the powerwall?
How is yours wired in whole house or a sub with the ac on the sub panel?

 

[eml2]

I have 2 Powerwalls wired into the whole house main panel. Also have two 3 ton A/C units. When the grid is online, I can see from the app that when the 1st A/C starts, power comes momentarily from grid (in addition to PW), then disconnect from the grid a second later. Same thing happens when the 2nd A/C starts. Once both A/C are running, all the power comes from PWs only. Total from the 2 PWs at that time is around 6.8 kW.

 

[rw99]

Our cabin is limited to electricity only, so we have an aging heat pump for both heating and cooling. Currently waiting on the engineering plans for a Tesla 12.7 kW system with two Powerwall 2s, and I'm wondering if I should swap in a new heat pump that could run off the PWs. Anyone have a recommendation?

Or is AC just too much to ask from a couple Powerwalls?

 

[Parzival]

Thats good to know. So via the app you see the usage that corisponds to the running ac coming from the powerwall?
How is yours wired in whole house or a sub with the ac on the sub panel?

I have three wired into the whole house via the PV backfeed panel.

 

[mongo]

Our cabin is limited to electricity only, so we have an aging heat pump for both heating and cooling. Currently waiting on the engineering plans for a Tesla 12.7 kW system with two Powerwall 2s, and I'm wondering if I should swap in a new heat pump that could run off the PWs. Anyone have a recommendation?

Or is AC just too much to ask from a couple Powerwalls?

There are more solar friendly systems. I'm looking at a Chiltrix unit for the garage I'm building.

 

[fresnoboy]

Many larger tradition systems pull up to 100 amps to start and run at 40 amps which is problematic for many generators. If you have a Mitsubishi VRF style AC system, they start off small, at 5 amps and then spool up to 35 amps, and those systems are much easier to accommodate.

 

[commasign]

Any recommendations to maximize battery longevity and minimize degradation? Is it like the Tesla car battery where we should avoid having the battery at 100% in high heat for extended periods of time?

 

[Parzival]

Any recommendations to maximize battery longevity and minimize degradation? Is it like the Tesla car battery where we should avoid having the battery at 100% in high heat for extended periods of time?

One Tesla rep I spoke to suggested using self consumption mode with a 50% reserve as the most conservative approach. Another said not to worry, that it’s covered by a 70% capacity warranty and self managed. Yet another said there is hidden capacity to preserve lifespan.

I’d love to see a tear down of a Powerwall 2! But I doubt that will happen for years unless someone just decides to donate theirs to science.

It does seem to me that leaving it fully charged or discharged for long might be bad.

 

[sreehyd]

Just wanted to share experience I had with my 2 Powerwalls installed few weeks back (4 weeks). So-far we have good experience.

My setup :

200 Amp panel
No SOLAR
2 powerwalls backup entire home , except Tesla Charger (80Amps).
Firmware 1.6.0​

Following are few issues/observations noted while running exclusively on 2 PW's without Grid Power
1) The system was tripping moment A/C was turned on, We noticed the A/C was trying to consume approx 3.0 KW and plus about 0.3 KW of other house hold loads
2) Single PW is limited to draw below 2.5KW, and 5 KW when combined with both PW's. If the power draw exceeds 2.5 or 5KW respectively the system was tripping.
3) During Soft switch between Battery Power to Grid power , The switch-over is smooth and didn't observe any flicker. But during Hard switch ie., power failure, We notice a small flicker, My UPS & sometimes my Gas Range detects the switch and indicate an interruption on respective panels.
4) Charging rate of each PW is 3.3KW and when teamed up with both PW's , it still limits charging @3.3KW & NOT 6.6 .


Solutions and Feed back from TE.

1) TE engineer was at my property to fix A/C issue, They explained , Initial draw current was in excess of 120Amps which lasts about 200ms . I believe both PW's together were very sensitive and unable to handle the surge. They suggested to install "surestart" device on A/C that would limit initial current draw. After the install we took the reading & surprisingly, Now the current draw was dropped to "4amps" and ofcourse the continuous draw was around 15 to 20amps. no change in that.

2) According to the engineer, The power draw limitation seems to be "Firmware" related, I am still waiting on TE's advise. According to them and from Spec's it should be able to handle 10KW continuous when both PW's are active.

3) Thats just observation & I didnt see that causing any interruption to any of my devices or appliances.

4) TE's said it is normal behaviour and affirmed by saying its hardcoded in firmware to charge @1.6KW per PW and when teamed up as a pair, it should charge @3.3KW. I did some tests in last few days, each PW power draw is 3.3KW, & as a pair is still 3.3KW. Even my PGE records agree that single PW is charging @3.3KW. I have relayed my findings to TE, need to wait and see what they are going to say about it .

Overall I am pleased with TE response & PW powerformance.

-Sk

 

[mongo]

2) Single PW is limited to draw below 2.5KW, and 5 KW when combined with both PW's. If the power draw exceeds 2.5 or 5KW respectively the system was tripping.

Is that 2.5 kW on a single phase (120V)? That would match up to 5kW total (240V load).

 

[eml2]

4) Charging rate of each PW is 3.3KW and when teamed up with both PW's , it still limits charging @3.3KW & NOT 6.6

I also have 2 Powerwalls. From the Tesla app, I can see that my PWs are charged up to 6.7 KW. Note that I have solar. Maybe that is the difference?

 

[dlieu]

Just wanted to share experience I had with my 2 Powerwalls installed few weeks back (4 weeks). So-far we have good experience.

My setup :

200 Amp panel
No SOLAR
2 powerwalls backup entire home , except Tesla Charger (80Amps).
Firmware 1.6.0​

1) The system was tripping moment A/C was turned on, We noticed the A/C was trying to consume approx 3.0 KW and plus about 0.3 KW of other house hold loads
[...]

Solutions and Feed back from TE.

1) TE engineer was at my property to fix A/C issue, They explained , Initial draw current was in excess of 120Amps which lasts about 200ms . I believe both PW's together were very sensitive and unable to handle the surge. They suggested to install "surestart" device on A/C that would limit initial current draw. After the install we took the reading & surprisingly, Now the current draw was dropped to "4amps" and ofcourse the continuous draw was around 15 to 20amps. no change in that.

[...]
-Sk

I have exactly same set up and the same problem. Except i did not get a solution. Did sure start work for you? What did you end up with? can you share who on TE team solved it? because i couldn't get it done so far. Is this the device you ended up using? : Hyper Engineering | Single Phase

still in search of solution -- thank you.

 

[Parzival]

I've seen my three Powerwalls charge at the limit of my solar system's output, around 11.5kW.

The Hyper Engineering product is the one Tesla uses to fix A/C starts. I am expecting them to install one on mine next week.

 

[dlieu]

I just had a funny thought. What if you re-provisioned your system as though you had solar? You may not have enough CTs to do it and you may have to trick the system with some fake CT readings from your charging station, but if you tricked the system into thinking you had solar, at least you could activate the Self Consumption mode. Then the only thing you would have to do is change the mode each night and each morning back and forth from Self Consumption to Backup and back again.

Refer back to earlier posts in this thread about how to re-do the provisioning.

BTW I found one report in exactly this situation when the power wall was provisioned in error to have solar while it had not. In that situtation, the charging from grid apparently was reported as limited to no more than 50%. I wonder if there's some fundamental limitation with current software like that. I see abolutely no reason why Tesla would disable the "self powered" menu and "backup" software switch, unless there were some fundamental issue with that.

 

[sreehyd]

I have exactly same set up and the same problem. Except i did not get a solution. Did sure start work for you? What did you end up with? can you share who on TE team solved it? because i couldn't get it done so far. Is this the device you ended up using? : Hyper Engineering | Single Phase

still in search of solution -- thank you.

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.

 

[sreehyd]

I also have 2 Powerwalls. From the Tesla app, I can see that my PWs are charged up to 6.7 KW. Note that I have solar. Maybe that is the difference?

It appears SOLAR could be playing role here .. Probably they will tweak the logic for installation without SOLAR in future ?