Partial vs. Whole Home Backup?

[Notadog]

Hi, I'm planning on installing a 8.16 kW system along with 2 Powerwalls.

Under the design summary, they listed my backup type as Partial Home. The rep told me that I would need 3 Powerwalls to get a Whole Home backup system. Is that true?

Can I specify that I would like a Whole Home backup configuration instead? I figure this would allow me the flexibility to turn on whatever appliance I want, I would just need to be careful with my total load on the system.

Am I correct? Are there any pros and cons that I'm missing?

Thanks.

 

[Road.Runner]

yes you can specify and reject the design and send it back to the design team.
if you get whole home and dont do your kw math correctly, there is no one else to blame but yourself. They made a recommendation, you choose to second guess them. ( look at the chart, what appliances do you have, do you have a big house, are you a big energy user, etc)
the criteria they look at is the temporal peak and continuous load in kw usage. 1PW is 5-7 kw peak, 2PW is ~12-14kw, 3PW is 19-21kw.
most likely your appliances are pushing you over capacity of what 2PW can output during a backup. the usual offender is A/C.
1) select an AC with a very low LRA, LRA close to RLA, RLA <151. or install a soft start device so when it kicks on there will be a gradual peak energy demand instead of a spike in demand (this may void warranties).
2) or you can look into home automations to limit peaks (to limit running items @ the same time), ie: water heater, range, microwave/air fryer, dishwasher, hvac, washer dryer, in restricted mode during an outage. In outage mode, you can make an home automation to only allow certain things to be allowed only at night when demand is lower.
you can go high tech with smart home automation or low tech ( https://www.walmart.com/ip/GE-24-Ho...-Timer-1-Grounded-Outlet-White-15153/25524763 ).
3) how many days do you need power for. Outages in my area are only a few hours. Hurricane regions may need a couple 1 week even with day time recharging. Bayarea like you may only need to cover 2-3days with daytime recharging.

 

[Notadog]

Thanks for the helpful reply.

I have yet to install an AC but the one that I am going to install has LRA 105.7 and RLA 15.6.
According to this page, it should be compatible with 2 Powerwalls.

So is the only difference between partial and whole home is that the partial home setup is foolproof, whereas for the whole home, I will have to do some kW calculation in order to not overload the Powerwalls? I only have a fridge and chest freezer that constantly draws power, everything else I can turn off.

 

[fragchild]

My plans with 2 PW called for "partial home" because of my AC, and the online team wouldn't budge. The day of install the electrician asked if I wanted a soft start so he could give me "whole home" and I agreed. I haven't had any issues, but I have seen spikes of 11kW if stove, water heater, and AC all kick in. So in the vent of a true outage I would certainly be power frugal.

 

[wjgjr]

The A/C is going to be the biggest factor for a lot of people in whether or not you can do whole-home backup. You will need an LRA number well under 60A (with a soft-start, if your unit supports it.) Each PW will be on a 30A breaker, so that is where the 60A comes from. The "well under" is because the A/C start will be on top of whatever else might be running at the time of an outage. There may be other major draws (like EV chargers) that might also be causing a concern for Tesla.

Even assuming you can get to where it is unlikely you will hit the 60A number, as posters above note, it can be pretty easy to hit the discharge limit for 2 PWs or, even if you don't, to discharge them very quickly in an outage. It is possible to discharge the PWs inside 3 hours without maxing the discharge rate.

All that said, we have whole-home backup with 2 PWs. The sure-start device Tesla installed addressed the A/C startup current (LRA) issue, and with a smaller house (and gas heat for the winter) we should be able to operate for a number of days if needed without too much inconvenience. However, the specifics depend on a number of factors, including the size of your PV array (which will determine how quickly you can re-charge your PWs, and is the limiting factor for multi-day outages), weather/location (which gives you a sense of how likely you are to be able to re-charge and how much you can expect at different times of year), and the specifics of your home load (how large, what is truly critical even in an outage, how willing you are to manage the load, etc.)

 

[jrweiss98020]

Your solution may be to back up all but the AC.

 

[holeydonut]

This is one of the times you may want to look at a different installer.

I originally wanted a partial backup due to my AC’s, but it was better to just add a 3rd powerwall and do a whole home backup. PG&E actually torpedoed the design for partial home backup.

California currently has a large scale incentive program for residents who get 3 or more Powerwalls. Since there are no more funds left for 2 Powerwalls, this effectively makes the 3rd powerwall “free” even if you don’t qualify for the resiliency or low income programs.

The two gotchas are that
1) Tesla won’t help process the large scale rebate
2) The program may be running out of funds

There are some Bay Area installers that are well versed with this program though.

SGIP with Large Scale Energy Storage (3 x PowerWalls) with Tesla or Individual

 

[h2ofun]

Thanks for the helpful reply.

I have yet to install an AC but the one that I am going to install has LRA 105.7 and RLA 15.6.
According to this page, it should be compatible with 2 Powerwalls.

So is the only difference between partial and whole home is that the partial home setup is foolproof, whereas for the whole home, I will have to do some kW calculation in order to not overload the Powerwalls? I only have a fridge and chest freezer that constantly draws power, everything else I can turn off.

foolproof, what does that mean. No matter what you do, there is only so much suds. Use it up, and its gone. Some could do in an hour, some could do in a day. Just depends what you run.

We just had a power outage here from the storm. At 2 am, my generator kicked in, and I ran everything in the house I wanted. But, it was load. Sure wish I had some PW's. But I know when power is out, I need to only run the must stuff. But in my case, if the batteries go dead, I just turn my generator on. I will be all set.

 

[jjrandorin]

Thanks for the helpful reply.

I have yet to install an AC but the one that I am going to install has LRA 105.7 and RLA 15.6.
According to this page, it should be compatible with 2 Powerwalls.

So is the only difference between partial and whole home is that the partial home setup is foolproof, whereas for the whole home, I will have to do some kW calculation in order to not overload the Powerwalls? I only have a fridge and chest freezer that constantly draws power, everything else I can turn off.

I havent read the entire thread (and likely should) but you cant simply "tell tesla I want whole home backup with 2 powerwalls" when their design team told you "you need 3 powerwalls for whole home backup".

What you CAN do, is possibly leave loads you dont care about in the main panel, so the backup panel backs up what you want, but if their calculations say you need 3 powerwalls for "whole home backup" they are not going to do whole home backup with 2, and just "trust you to turn off loads".

Thats not how it works. It doesnt matter if you "can" turn it off, it matters what the load calculations say, and what your home draw is etc. You likely will be able to do everything except for the AC and that is considered partial backup.

I have a "partial home backup" which backs up my entire home except for my tesla wall connector. I dont know if you have a EV etc, but leaving out big loads like an EV charger or an AC is considered "partial home backup" even if everything else is backed up.

 

[h2ofun]

I havent read the entire thread (and likely should) but you cant simply "tell tesla I want whole home backup with 2 powerwalls" when their design team told you "you need 3 powerwalls for whole home backup".

What you CAN do, is possibly leave loads you dont care about in the main panel, so the backup panel backs up what you want, but if their calculations say you need 3 powerwalls for "whole home backup" they are not going to do whole home backup with 2, and just "trust you to turn off loads".

Thats not how it works. It doesnt matter if you "can" turn it off, it matters what the load calculations say, and what your home draw is etc. You likely will be able to do everything except for the AC and that is considered partial backup.

I have a "partial home backup" which backs up my entire home except for my tesla wall connector. I dont know if you have a EV etc, but leaving out big loads like an EV charger or an AC is considered "partial home backup" even if everything else is backed up.

Why is it wrong to not trust I am not stupid enough to run stuff when my power it out, like my over, dryer, etc? That is exactly what I have been telling my contractors when they installed my generator, and even with my battery process.

 

[jjrandorin]

Why is it wrong to not trust I am not stupid enough to run stuff when my power it out, like my over, dryer, etc? That is exactly what I have been telling my contractors when they installed my generator, and even with my battery process.

Its all done by load calculations, etc. As long as the load calculations say its "safe" to install and the equipment can all be used (even if it drains the battery super fast) they would do it. I have both my ACs on the backup side, as they are safe to use with my load calculations.

I wouldnt want to actually use them much in a power outage, because they would drain the battery too fast (in just a few hours) but the load calculations say I can, so they did it for me.

I know you understand this, as well, so I assume this is just another one of those "asking to be asking" situations.

 

[h2ofun]

Its all done by load calculations, etc. As long as the load calculations say its "safe" to install and the equipment can all be used (even if it drains the battery super fast) they would do it. I have both my ACs on the backup side, as they are safe to use with my load calculations.

I wouldnt want to actually use them much in a power outage, because they would drain the battery too fast (in just a few hours) but the load calculations say I can, so they did it for me.

I know you understand this, as well, so I assume this is just another one of those "asking to be asking" situations.

No, not asking it that way. The reasons everything has circuit breakers is if one tries to pull too much, it blows. This does not work? And if not, then yep, why That is how my generator was hooked up. Only has a 100 amp breaker and it is hooked up to both my 200amp panels. If I were to turn my entire house on, pretty sure I would blow the generator breaker.

 

[wjgjr]

I havent read the entire thread (and likely should) but you cant simply "tell tesla I want whole home backup with 2 powerwalls" when their design team told you "you need 3 powerwalls for whole home backup".

I agree, though it occurs to me as I re-read that there potentially is a disconnect between the current information Tesla has and what OP is planning, having mentioned plans to install a new A/C.

So, in this case, it might be worth confirming with Tesla what it is that is causing them to require 3 PWs for whole-home backup in this situation. If it is solely due to the existing A/C, potentially they can adjust for the new one if you provide that information. It also may be a situation like @fragchild had where you will need to talk to the electrician on-site about changing the setup.

As a bit of an aside, I think this is an area where Tesla really should generate some custom (offline/printed) documentation for customers regarding their system, and, in particular, identify where there are potentially large loads that could drain batteries, or, in the extreme, actually cause the system to go offline during an outage. They do have a lot of information online, but it is more generic, and in an outage the information may not be accessible. Additionally, where the users of this forum tend to be more aware of battery runtime, home loads, etc., I am not sure the average customer will be.

 

[jjrandorin]

I agree, though it occurs to me as I re-read that there potentially is a disconnect between the current information Tesla has and what OP is planning, having mentioned plans to install a new A/C.

So, in this case, it might be worth confirming with Tesla what it is that is causing them to require 3 PWs for whole-home backup in this situation. If it is solely due to the existing A/C, potentially they can adjust for the new one if you provide that information. It also may be a situation like @fragchild had where you will need to talk to the electrician on-site about changing the setup.

As a bit of an aside, I think this is an area where Tesla really should generate some custom (offline/printed) documentation for customers regarding their system, and, in particular, identify where there are potentially large loads that could drain batteries, or, in the extreme, actually cause the system to go offline during an outage. They do have a lot of information online, but it is more generic, and in an outage the information may not be accessible. Additionally, where the users of this forum tend to be more aware of battery runtime, home loads, etc., I am not sure the average customer will be.

Yeah I agree with this premise, and maybe I am reading the OPs statements wrong, but OP said "I have yet to install an A/C...." and I read that as "I dont have an AC ...".

In any case, I agree 100% that the OP should find out exactly why they are telling them "whole home backup requires 3 powerwalls". What I was saying, is that a person cant simply say "oh I only want 1 powerwall, but I want whole home backup, so just hook it up and I wont turn some stuff on". Once the calculations show a configuration "works" from a code perspective, then at that point it will be up to the user to manage it.

Like I said with my A/C units. I have both of them on the backup side. When they are on, they consume about 4.5 kWh of power each (from memory). I only have 2 powerwalls, so it doesnt take a lot of math to see that if both are. running during a power outage, at 9kWh they would completely drain my batteries in 3 hours.

So, I would only run them for 10-15 minutes at a time, during an outage, if absolutely necessary, but I do have the choice to, because the "calculations worked" for them to remain in my backed up loads panel.

The calculations did not support having my wall connector at 60 amps also included in my backup loads panel, so it was the one thing left out. I could have asked them to change out the breaker on it, and had it turned down to 30amps, or,do what I did and leave it out. I couldnt just tell them " put it on the backup loads panel and I just wont use it, I dont care what the calculations say".

 

[h2ofun]

Yeah I agree with this premise, and maybe I am reading the OPs statements wrong, but OP said "I have yet to install an A/C...." and I read that as "I dont have an AC ...".

In any case, I agree 100% that the OP should find out exactly why they are telling them "whole home backup requires 3 powerwalls". What I was saying, is that a person cant simply say "oh I only want 1 powerwall, but I want whole home backup, so just hook it up and I wont turn some stuff on". Once the calculations show a configuration "works" from a code perspective, then at that point it will be up to the user to manage it.

Like I said with my A/C units. I have both of them on the backup side. When they are on, they consume about 4.5 kWh of power each (from memory). I only have 2 powerwalls, so it doesnt take a lot of math to see that if both are. running during a power outage, at 9kWh they would completely drain my batteries in 3 hours.

So, I would only run them for 10-15 minutes at a time, during an outage, if absolutely necessary, but I do have the choice to, because the "calculations worked" for them to remain in my backed up loads panel.

The calculations did not support having my wall connector at 60 amps also included in my backup loads panel, so it was the one thing left out. I could have asked them to change out the breaker on it, and had it turned down to 30amps, or,do what I did and leave it out. I couldnt just tell them " put it on the backup loads panel and I just wont use it, I dont care what the calculations say".

do you have the code section you reference that supports our thoughts. I am just trying to get the facts as to where the line is

 

[jjrandorin]

do you have the code section you reference that supports our thoughts. I am just trying to get the facts as to where the line is

No, but thats the system designers job. Its the system designers job to present the customer with "where the line is". If one doesnt trust what they are being told by that person / that company, then they need to hire someone else.

 

[RKCRLR]

OP
If you still don't have an AC unit you should select a different one with lower LRA. It may cost a little more but it will be worth it in the long run if you really want to use AC during a power outage. Without solar generating you won't be able to run it long but if the sun is shining you should be good as long as you can get it started.
I'm currently trying to get Tesla to fix my whole home backup so the AC works during an outage. They apparently didn't get the correct specs for my AC and it turns out a SureStart device isn't compatible with my reverse run AC compressor.

 

[aesculus]

The calculations did not support having my wall connector at 60 amps also included in my backup loads panel, so it was the one thing left out. I could have asked them to change out the breaker on it, and had it turned down to 30amps, or,do what I did and leave it out. I couldnt just tell them " put it on the backup loads panel and I just wont use it, I dont care what the calculations say".

Actually my system is set that way. My heat pumps are three levels deep, cannot be isolated and cannot operate when the PWs support the house. Tesla knows that and told me it is my responsibility to turn them off during a power outage event.

They stated if I failed to turn them off and they came on when being supported by the PWs, the PWs would trip off and go into a wait state (I think 15 minutes?) before trying again. This would go on forever until I manually rectified the issue.

My plans are to come up with an automated solution to this issue that would turn off the heat pumps when there was no grid power but other things have gotten in the way of me doing this for now. And with COVID, I am not going anywhere for awhile so I have extra time to ponder and build the solution.

 

[h2ofun]

Actually my system is set that way. My heat pumps are three levels deep, cannot be isolated and cannot operate when the PWs support the house. Tesla knows that and told me it is my responsibility to turn them off during a power outage event.

They stated if I failed to turn them off and they came on when being supported by the PWs, the PWs would trip off and go into a wait state (I think 15 minutes?) before trying again. This would go on forever until I manually rectified the issue.

My plans are to come up with an automated solution to this issue that would turn off the heat pumps when there was no grid power but other things have gotten in the way of me doing this for now. And with COVID, I am not going anywhere for awhile so I have extra time to ponder and build the solution.

What you stated is what I am assuming I can do!! Whether it is the PW that trips off, or the GW breaker, etc. seems there are all the safeguards needed that nothing is going to burn up and catch on fire?

I know when my generator starts, all my heavy loads are on time delays. So when I lost power this morning, both ATS's engaged, generator started, but it took a while before each compressors timer engaged, all at different times, before my mini splits turned back on again.

I just get confused when some say but because of code or load calcs, etc, it limits what one can do. Then I see a post like yours and scratch my head and trying to understand the differences.

Thanks

 

[aesculus]

I just get confused when some say but because of code or load calcs, etc, it limits what one can do. Then I see a post like yours and scratch my head and trying to understand the differences.

Many of the safeguards are just that. Something to take control for the unforeseen situations where safety is a concern. In my case I am purposefully taking advantage of that feature operationally, which probably was not as designed.

Tesla and I negotiated this up front and had a big discussion about it at a lot of different levels and persons. They may not be so willing to do this today but I do know of a number of other installations that have the same type of issue.