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Partial vs. Whole Home Backup?

Vines

Active Member
Jul 20, 2018
1,876
2,205
Silicon Valley, CA
you are required to be able to power "expected" loads for automatic backup power sources. which means any thing that can switch on automatically, like refrigerator, heating/cooling, hot water, well pump... which means if you can't handle it in need to be on a non backup panel.

Correct, you are required to be able to start any of the loads on the backup system, but not required to start them all at once. This where the education comes into play.

Since the AHJ aren't requiring load calculations that prove the ESS can support all the loads its up to the installer to properly educate the customer and lead them to the best solution for the customers expectations.

Taking the power away from the customer is silly. No reason to add a whole extra panel for non backup loads with a customer who understands the limitations and either turns off his HVAC themselves or has a dead battery in 3 hours because there is no sun to recharge it. Instead allow them to put the car charger on the backup system so you have some place to pass all the PV generation once the stationary batteries are full. Leave the HVAC on backup so that when the summer heat is really pumping, perhaps the PV plus PW can run things quite well when irradiance is high, even for several hours depending on the time of year and energy resources compared to other useage.

I prefer to design where you don't "protect the customer from themselves" and instead educate them about the pros and cons of the choices you think are best with what you can provide at a reasonable cost. Just because throwing the car charger, HVAC and oven all on at once could overload a 3 Powerwall system, doesn't mean you can't still design it that way, just educate the customer: don't use everything at once.

Powerwalls are not damaged by overloading them, they have an internal load management system that protects them so there is no safety hazard to putting more on the load side that they could handle at once, as long as any single thing on the load side could be started.
 

h2ofun

Active Member
Aug 11, 2020
2,490
426
auburn, ca
Correct, you are required to be able to start any of the loads on the backup system, but not required to start them all at once. This where the education comes into play.

Since the AHJ aren't requiring load calculations that prove the ESS can support all the loads its up to the installer to properly educate the customer and lead them to the best solution for the customers expectations.

Taking the power away from the customer is silly. No reason to add a whole extra panel for non backup loads with a customer who understands the limitations and either turns off his HVAC themselves or has a dead battery in 3 hours because there is no sun to recharge it. Instead allow them to put the car charger on the backup system so you have some place to pass all the PV generation once the stationary batteries are full. Leave the HVAC on backup so that when the summer heat is really pumping, perhaps the PV plus PW can run things quite well when irradiance is high, even for several hours depending on the time of year and energy resources compared to other useage.

I prefer to design where you don't "protect the customer from themselves" and instead educate them about the pros and cons of the choices you think are best with what you can provide at a reasonable cost. Just because throwing the car charger, HVAC and oven all on at once could overload a 3 Powerwall system, doesn't mean you can't still design it that way, just educate the customer: don't use everything at once.

Powerwalls are not damaged by overloading them, they have an internal load management system that protects them so there is no safety hazard to putting more on the load side that they could handle at once, as long as any single thing on the load side could be started.
yes
 

CSFTN

Member
Aug 24, 2014
925
511
Memphis, TN
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.
Anyone know if most recent tech, inverter controlled AC (Carrier Infinity 20VS) by definition have soft start?
 
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RKCRLR

Member
Apr 13, 2020
407
145
Garden Valley, CA
Keep in mind that many HVAC systems have a circuit that can be controlled by a relay to prevent the unit from running when activated. This is how utility companies used to control your AC when you signed up for the program (don't know if they still offer the program).
My Carrier heat pump has the option and it is over 10 years old.
 

Notadog

Member
Jan 26, 2021
41
4
SF Bay Area
My project advisor has approved a 2 Powerwall, whole house backup install. However, he said that if I were to add an A/C unit or EV in the future, I would be unable to connect them as part of my backed up loads. Is this true? Would there be anything there that would physically prevent my electrician from making the necessary connections?

I just have a standard home setup with no pumps or anything that would draw big power (no sump pumps, well pumps, pool pumps, heat pumps, etc...). I would at least like to have the A/C backed up in the future without installing 3 Powerwalls. Thanks.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
8,910
9,931
Riverside Co. CA
My project advisor has approved a 2 Powerwall, whole house backup install. However, he said that if I were to add an A/C unit or EV in the future, I would be unable to connect them as part of my backed up loads. Is this true? Would there be anything there that would physically prevent my electrician from making the necessary connections?

I just have a standard home setup with no pumps or anything that would draw big power (no sump pumps, well pumps, pool pumps, heat pumps, etc...). I would at least like to have the A/C backed up in the future without installing 3 Powerwalls. Thanks.

my opinion is the same as I had in the thread by @holeydonut when you asked that question:

Is this only a concern because it's Sunrun?

I'm planning a whole home backup and Tesla Solar has approved it. However, I don't have an A/C or Tesla vehicle right now but I do plan on purchasing both next year. Would there be any issues adding both the A/C and Tesla to the backed up loads next year?

Hard to say, because these are construction projects, but my gut feeling is "probably" as the answer to your question of "will there be any issues adding an AC and tesla charger to the backup loads panel after install".

You would be MUCH MUCH MUCH better off with buying those things first, and getting the load calcs / system setup with them there, than trying to add them later. you probably wont have much issue adding them to the home in general, but adding them to the backup side? I believe that would be a [email protected]$## as evidenced by OP here, and many others (like myself) who have stickers on their systems that basically forbid adding anything to the backup side.
 

h2ofun

Active Member
Aug 11, 2020
2,490
426
auburn, ca
my opinion is the same as I had in the thread by @holeydonut when you asked that question:
I never understand why some do not do it right at the beginning. Then some when try to do something are told they cannot and get upset. Or something does not work right and they get upset. Oh well, ... This is why I am putting on two 11.4K inverters. At least the wiring, breakers, etc will be sized if I want to add more capacity, my infrastructure is all set.
 

aswami

Member
Feb 12, 2021
78
69
Phoenix
My project advisor has approved a 2 Powerwall, whole house backup install. However, he said that if I were to add an A/C unit or EV in the future, I would be unable to connect them as part of my backed up loads. Is this true? Would there be anything there that would physically prevent my electrician from making the necessary connections?

I just have a standard home setup with no pumps or anything that would draw big power (no sump pumps, well pumps, pool pumps, heat pumps, etc...). I would at least like to have the A/C backed up in the future without installing 3 Powerwalls. Thanks.

I was told the same thing for my 2 Powerwall installation which is scheduled for next month. They told me my future EV charger could not be added to the Powerwall backup. They could only backup whatever I had connected to my breaker box right now. So, I went ahead and installed a Tesla Wall Charger, although I don't have a Tesla car right now. I have asked them include it in the Powerwall backup, and am waiting for confirmation from them. As per Tesla's website, 2 Powerwalls should support lights, plugs, 120 V small appliances, gas dryer, air conditioner, electric range, well pump and EV charging.

PS: I wanted the full house backup also, but they wanted me to choose any 2 of the oven, cooking range, AC and dryer. I chose the range and the AC.
 

h2ofun

Active Member
Aug 11, 2020
2,490
426
auburn, ca
I was told the same thing for my 2 Powerwall installation which is scheduled for next month. They told me my future EV charger could not be added to the Powerwall backup. They could only backup whatever I had connected to my breaker box right now. So, I went ahead and installed a Tesla Wall Charger, although I don't have a Tesla car right now. I have asked them include it in the Powerwall backup, and am waiting for confirmation from them. As per Tesla's website, 2 Powerwalls should support lights, plugs, 120 V small appliances, gas dryer, air conditioner, electric range, well pump and EV charging.

PS: I wanted the full house backup also, but they wanted me to choose any 2 of the oven, cooking range, AC and dryer. I chose the range and the AC.
Seems they are doing what they should, making sure they do not sell something that the customer would try to use, not work worth beans, and then try to blame them.
 

Dan123

Member
Jun 19, 2018
451
297
Miami
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 suggest trying to get a compressor with a lower LRA rating (variable speed). They are also more energy efficient and better dehimidifiers.

The thing is that they can't count on the homeowner to do load balancing. What if you are not home? What if you sell the house? The system has to work without your intervention. If you have a load that cannot be supported by two Powerwalls, that will cause them to constantly shut down. So they don't want to install something that is not going to work.

You can go with a partial backup, and then move whatever loads into the partial backup panel.
 

holeydonut

Supporting Member
Jun 27, 2020
1,543
903
East Bay NorCal
You can go with a partial backup, and then move whatever loads into the partial backup panel.


I think this is only true if you have the equipment in your house before you install your solar and PV.

My understanding is that if you add a sub-panel outside the gateway (not connected to the non-backup lugs of the Gateway), someone has to run CTs upstream to a point that can sense the load drawn by that new panel. This is the only way your ESS energy could make it upstream to your new sub-panel when the Utility grid were operational. Naturally if the grid goes down, no energy is making it upstream.

If you're adding stuff afterwards, it's unlikely an electrician will be able to run the CTs since they will be unwilling to touch and configure the Tesla Gateway. They will also not add a sub-panel to the non-backup-loads side of the Gateway 2 that is metered since this would involve touching the Gateway as well. I don't see Tesla Energy sending a Power Ranger back to a previously serviced home to work on a new non-energy project.

So adding the heavy loads after the PV and ESS is installed could mean a sub-optimal setup. It's best to get those heavy loads in the house before adding PV and ESS even if those heavy loads aren't backed up when all is completed.
 

holeydonut

Supporting Member
Jun 27, 2020
1,543
903
East Bay NorCal
I never understand why some do not do it right at the beginning. Then some when try to do something are told they cannot and get upset. Or something does not work right and they get upset. Oh well, ... This is why I am putting on two 11.4K inverters. At least the wiring, breakers, etc will be sized if I want to add more capacity, my infrastructure is all set.


IMO, I think the problem is you don't know what you don't know. It's impossible to do things "right" since so many experts out there (I don't mean on TMC) that want to push a solution to get a sale. Unless your job is to literally design these systems for a living where you can master-plan your house, it's unlikely you'll get the right thing at the right time because the people selling the tech don't provide education about the truth/limitations of what is about to happen.

When I first started trying to get my system set up, I had people straight up lying to me.

I remember smallish lies like:
"the only way to rack solar on a tile roof now-a-days is with tile hooks; there are no other options."
"contra costa county has huge setback requirements from skylights"
"one powerwall should be enough for your house"
"you can never backup an AC unit"
"soft starts and hard starts are the same"

But I also remember big lies like:
"there's no way for the Tesla system to see loads outside of the gateway, so your ACs (not backed up) will never see energy from the battery no matter what."
"Tesla never wants you to put your EV on the backup side since your car would drain your batteries"
"you don't need to upgrade your main service panel"


I simply wasn't smart enough to know what was a lie and what was true. It's like being told the ice is freezing windmills causing Texas to be without power. Makes for a cute story...

The pros who often sell this tech love to gaslight customers and peon homeowners because it's easy. I guess most customers just want to pay the least amount possible and just don't care about some of this stuff as well.
 

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