Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register

You gotta be kidding me. Electricians won't add a Tesla wall connector on the backup side of ESS

This site may earn commission on affiliate links.
Someone needs to tweet Elon for Tesla to make smart thermostats that talk to the Gateway 2 so they can auto-load-shed AC units if the grid goes down. That hokey 24v relay wire on the Gateway 2 for load shedding doesn't work.

@jjrandorin , Did Tesla really install a "2040" load center that had only 20 regular spots but could hold 40 circuits? I feel like that's a lot of tandems and cheaters...
 
For anyone looking at the labeling in my panel and wondering if tesla did that (the p-touch labels), that was me. For full disclosure, my main service panel I had labeled like that, as I wanted to know what was on every circuit. When the tesla 2 man team of electricians came to do my powerwalls, they saw my main service panel labeling, gave me some props for it, and said:

"we are re routing all the loads in this panel except the EV one to the panel we are putting into the garage. Since you have it labeled like this, and the loads will move around, we will give you the information on which breaker in your main panel becomes which breaker in the backup panel.".

All the loads moved around, but they gave me a paper that said :

Main panel. Backup Panel
breaker 1 Breaker 5

As most know, it is code that the breakers be labeled, but they normally just write "garage" next to it or something. Anyway, they gave me that paper, and I re printed out my labels and re labeled them,

I thought it was very nice of them to give me that chart, as I was going to simply figure it all out again after they left, but they took the time to give me this information. I was really happy with my tesla install team, for this and other reasons.
 
Someone needs to tweet Elon for Tesla to make smart thermostats that talk to the Gateway 2 so they can auto-load-shed AC units if the grid goes down. That hokey 24v relay wire on the Gateway 2 for load shedding doesn't work.

@jjrandorin , Did Tesla really install a "2040" load center that had only 20 regular spots but could hold 40 circuits? I feel like that's a lot of tandems and cheaters...

I dont know what a 2040 load center is... but I took the front panel off this to look at it for something else, and the cabling behind those breakers is very neat. I can share a picture of it if anyone is interested.
 
Each Powerwall 2 can deliver a max of 5 kW continuous and has a capacity of 13.5 kWh. I have 2 and they start and run my A/C. I don't know how long they will last because I only tested it for a few minutes. If we were in a power outage I would likely not use the A/C.
We also have 2 PWs and an A/C backed up. Ours draws somewhat around 2.5 kW when running (which it will do constantly when hot enough.) So, the math says we can probably run our A/C over 8 hours on battery, assuming limited other home loads. For us, that is fine, because even in a worst-case where power fails the moment we go to sleep and our A/C has to run all night (which is highly unlikely) we should still make it to morning. And then we would manage the A/C based on solar availability.

Someone needs to tweet Elon for Tesla to make smart thermostats that talk to the Gateway 2 so they can auto-load-shed AC units if the grid goes down. That hokey 24v relay wire on the Gateway 2 for load shedding doesn't work.

I do wish this was available - and really if Tesla just had official, supported APIs, you could do it through existing smart home solutions. (As it is, you should be able to, but - as we just saw with Tesla changing the authentication - it is potentially less reliable and certainly less user-friendly.) Both because we have gas heat and because we generate less solar in the winter, it doesn't help then, but it would definitely be useful during a summer outage.
 
We also have 2 PWs and an A/C backed up. Ours draws somewhat around 2.5 kW when running (which it will do constantly when hot enough.) So, the math says we can probably run our A/C over 8 hours on battery, assuming limited other home loads. For us, that is fine, because even in a worst-case where power fails the moment we go to sleep and our A/C has to run all night (which is highly unlikely) we should still make it to morning. And then we would manage the A/C based on solar availability.



I do wish this was available - and really if Tesla just had official, supported APIs, you could do it through existing smart home solutions. (As it is, you should be able to, but - as we just saw with Tesla changing the authentication - it is potentially less reliable and certainly less user-friendly.) Both because we have gas heat and because we generate less solar in the winter, it doesn't help then, but it would definitely be useful during a summer outage.
Luckily we tend to cool down some in the summer, so I am thinking of turning off my mini splits, opening up my windows (worst case morning), and turn on my whole house fan. Makes no sense to run AC when outside air is cooler.
 
  • Like
Reactions: jboy210
Luckily we tend to cool down some in the summer, so I am thinking of turning off my mini splits, opening up my windows (worst case morning), and turn on my whole house fan. Makes no sense to run AC when outside air is cooler.

We have similar patterns into July and usually keep the house at 78 in the summer with just cracking a few windows after dark. I have thought about a whole house fan and may add one, but we usually get some breeze since we are at the base of a hill.
 
Luckily we tend to cool down some in the summer, so I am thinking of turning off my mini splits, opening up my windows (worst case morning), and turn on my whole house fan. Makes no sense to run AC when outside air is cooler.
This past summer we had a 50-day period where the temperature never got below 70 degrees. So, while we would certainly be compromising on comfort in the event of an outage out of necessity, even opening windows for the night is not a good option with the way things have been going. If not for our solar install, this summer would have set records for us for electric bills.
 
This past summer we had a 50-day period where the temperature never got below 70 degrees. So, while we would certainly be compromising on comfort in the event of an outage out of necessity, even opening windows for the night is not a good option with the way things have been going. If not for our solar install, this summer would have set records for us for electric bills.
wow, now that is warm
 
A whole house fan is worth every penny!!!!

I put one in last may (2020) and because I have hot days but normally cooler nights (but generally without a breeze) the fan pulling in that cool air in the evening reduced my A/C usage during the summer like 70-80%. It was worth it for me, its one of these home energy things that, in my case did exactly what was advertised.

You have to be ok with pulling all that air inside from outside (dust, etc), but it was certainly worth it to me. I would buy it again in a heartbeat.
 
We have whole house on 2 PWs. This includes 2 mini-split outdoor condensers with 5 indoor heads. We're up north, so running A/C in summer we're typically around 1kWh. Heating in winter is where we have to shed load as we're around 3-4kWh; turning off the mini-splits is done automatically by Raspberry Pis connected to each head when there is an outage longer than 10 minutes. We didn't want the mini-splits on a separate panel as then we'd not be able to run A/C in summer.
 
AC specifically has such a variable amount of load and requirements to start, they cant plan for "future A/C" unless there is a specific make / model that you are in process of installing. 2 powerwalls might work for some A/C, and not for many others. I understand the desire to have A/C on the backup side, but if your home does not have A/C now, you obviously live in a location where A/C is not "a requirement".

You also likely dont know how fast AC would drain your powerwalls. You would likely not use them for very long if you were in a power outage. With that being said, yes I understand wanting A/C backed up so you have the choice. You will need to install it before your tesla install if you want it on the backup side, they will likely not install it later. Other electricians are likely not going to install it on the backup side later either.

See a picture of my backup loads panel below, which includes every load in my home except my EV charger, and that was excluded by my choice because the load balancing feature didnt exist then and I didnt want any chance of car charging draining powerwalls. Red sticker added by tesla for permitting, it as not an option:


View attachment 637547




I actually have (2) A/C condensers connected to my "backup loads" panel, which as I said above, includes every single load in my house except for the tesla wall connector, by my choice. I live somewhere hot, where A/C is "required" (in every home, and apartment), so wanted the A/C backed up. If a home is over 3000 square feet in this area, it has to have 2 A/C units. Mine came with the home and one is for upstairs and one for downstairs. This home is not nearly the size you mentioned yours is, but is 3200 square feet, give or take, so its not "small" either.

View attachment 637545

Since these are the AC units that came with the home, built in 2005, they are "builder grade" ones that are not very efficient at all. They are 3 ton units but as the picture below will show, they are both on the backup loads panel. How long I could run them is another thing. Because each of these takes close to 4kWh of power, thats roughly 8kWh of power used every hour. That means if I had them both on, with the rest of my home, it would be 2 1/4 to 2 1/2 hours from full powerwalls to empty.

We almost never run both units at the same time, even during normal operation. In a power outage, they would only be used in 10-15 minute increments to keep the home from being "unbearable" inside.

In a power outage, if it happened in the middle of the summer, having them backed up means I could use the A/C to "increase my load" so the PV doesnt shut off, and I dont even need to try to put that energy into my vehicle (which I current cant because my charger is on the non backed up loads side).

So, I get wanting to have them on there, even if you wouldnt use them much, but @Notadog is going to have to get A/C installed first, or not have it on the backup loads side. I dont think there is an option for "pre plan for my A/C, when there isnt at least a purchase of the AC unit in progress.

If @Notadog checks these boards, they will find many instances of people being promised an A/C unit would work with a backup (specifically with 2 powerwalls) then people finding out that soft start units dont work with their specific A/C, or that it doesnt work properly. There would be no guarantee that it would work "later". If its a "must have" then it likely needs to be done before the powerwall install.

@jjrandorin Thank you for the details post.

I have a 2000 sq ft, single floor house. The AC contractor suggested a single-stage, 4-ton unit. What questions should I ask either my Tesla advisor or my AC contractor in order for me to select a unit that I know will be efficient enough to be supported by 2 powerwalls? Then I can do a price comparison between adding a third powerwall vs. spending more on a more efficient AC.

Thanks again.
 
The lack of solid load management options from the power wall keeps me from ordering one plus an additional 8kW of solar. It is bad enough that there is no API for managing car charging current from the wall connector, but the Powerwall situation seems worse.
 
I have a 2000 sq ft, single floor house. The AC contractor suggested a single-stage, 4-ton unit. What questions should I ask either my Tesla advisor or my AC contractor in order for me to select a unit that I know will be efficient enough to be supported by 2 powerwalls? Then I can do a price comparison between adding a third powerwall vs. spending more on a more efficient AC.
OK, a few points:

- Consider spending some money on air sealing and insulating to allow for a smaller A/C unit.

- Consider a heat pump to provide heating as well.

- Only use a contractor who will do a Manual J heat loss (gain) calculation for sizing your unit. If they say "houses of your size in this area usually need a 4 ton unit, so we'll go with that," they fail. 4 tons sounds too big to me, but the calculation will tell you.

- There's two issues for an A/C unit on Powerwalls: starting and run time. If you have enough Powerwall inverter power to start your unit, then how long you can run without grid power, or rather how much heat you can move with the energy in the batteries, is proportional to capacity * efficiency. Getting a more efficient unit, or adding more Powerwalls, will increase run time. I think the range of efficiencies available is no more than a factor of two.

- But starting is often the limiting factor, motors require a big current surge to start, and it can be more than 1 or 2 Powerwalls can handle. I.e. you could be in a situation where if the power goes out while the A/C is running, the Powerwalls can switch on fast enough and provide enough power to keep it running, but if it ever turns off (thermostat is satisfied), you can't start it again (it tries to start, the Powrewalls can't handle it, the Powerwalls shut down everything to protect themselves). So if you want to avoid this problem, get an inverter driven compressor. The difference in starting current required is much more than a factor of 2.

- For some reason in conventional central systems, inverter driven compressors are a big price jump. While in mini-splits they are (more or less ?) standard. So be aware of that option (and the line between the two product lines is blurring, as you can get a conventional air handler for a mini split).

Cheers, Wayne
 
@jjrandorin Thank you for the details post.

I have a 2000 sq ft, single floor house. The AC contractor suggested a single-stage, 4-ton unit. What questions should I ask either my Tesla advisor or my AC contractor in order for me to select a unit that I know will be efficient enough to be supported by 2 powerwalls? Then I can do a price comparison between adding a third powerwall vs. spending more on a more efficient AC.

Thanks again.

I am not an expert on this topic of HVAC purchases, as I have not bought one of my own yet. With that being said, I believe the number that is an issue is the HVAC units "LRA". The issue with A/C and a powerwall (or other system) being able to start them when there is no grid, is that the amount of power required to START them is usually quite a bit more than it takes to RUN them.

"Starting" the motor turning requires a larger inrush of power than keeping it turning, which is how I understand it, in laymans terms (which are the only terms I can couch this in, since I dont know the full technical details). I believe LRA is locked rotor amps, or a measure of what is required to start the motor. The higher that number, the more power needed to start it (someone please correct me if I am giving incorrect information here).

Anyway, you can ask the HVAC person what the LRA is of the unit you are thinking about buying, but that is not going to get tesla to "design for it in mind" I dont think. I dont see the choice as "add a A/C or add a third powerwall". The choice is "Add an A/C now to get the A/C unit on the backup loads side (and add a third powerwall or not), or, Add an A/C later and know that you will not be able to put it on the backup side, basically period, end of sentence.


EDIT:: I was posting this the same time @wwhitney was, so sorry for covering some of the same ground.
 
I am not an expert on this topic of HVAC purchases, as I have not bought one of my own yet. With that being said, I believe the number that is an issue is the HVAC units "LRA". The issue with A/C and a powerwall (or other system) being able to start them when there is no grid, is that the amount of power required to START them is usually quite a bit more than it takes to RUN them.

"Starting" the motor turning requires a larger inrush of power than keeping it turning, which is how I understand it, in laymans terms (which are the only terms I can couch this in, since I dont know the full technical details). I believe LRA is locked rotor amps, or a measure of what is required to start the motor. The higher that number, the more power needed to start it (someone please correct me if I am giving incorrect information here).

Anyway, you can ask the HVAC person what the LRA is of the unit you are thinking about buying, but that is not going to get tesla to "design for it in mind" I dont think. I dont see the choice as "add a A/C or add a third powerwall". The choice is "Add an A/C now to get the A/C unit on the backup loads side (and add a third powerwall or not), or, Add an A/C later and know that you will not be able to put it on the backup side, basically period, end of sentence.


EDIT:: I was posting this the same time @wwhitney was, so sorry for covering some of the same ground.
I have 3 mini split systems which with inverter technology I believe is the most friendly to powerwalls? I have 5 heads on 1 compressor, 4 on a second compressor, and 1 on its own compressor. These are all in one 200 amp sub panel in my garage. I am planning of putting 3 powerwalls just on this subpanel, separate from the house.
 
I believe LRA is locked rotor amps, or a measure of what is required to start the motor.
No exactly, but it's a reasonable proxy. I believe LRA is literally what the current would be if the driven load suddenly locks up and the motor can no longer turn the shaft. For the brief steady state that will occur before something overheats.

Starting current is more complex, particularly during the first AC half-cycle. Starting is a situation where the shaft isn't turning and the motor wants to turn it, so that's like LRA. But it also includes inrush current to magnetize the various coils. And probably other stuff I don't understand.

If I recall Tesla's guidance on the matter, within a given design of A/C units, LRA is a good proxy for how many Powerwalls are required to start. But different designs of A/C units will have different starting characteristics, so it's not a good comparison across designs.

Cheers, Wayne
 
@jjrandorin Thank you for the details post.

I have a 2000 sq ft, single floor house. The AC contractor suggested a single-stage, 4-ton unit. What questions should I ask either my Tesla advisor or my AC contractor in order for me to select a unit that I know will be efficient enough to be supported by 2 powerwalls? Then I can do a price comparison between adding a third powerwall vs. spending more on a more efficient AC.

Thanks again.

Absent the details on exactly where you are, 4-tons seems large. I second the comments of @wwhitney. In this day and age, upping the insulation, plugging the leaks in your ducts, and sealing your house are investments that pay dividends year in and year out. Speaking from experience, California homes are generally not well designed from an insulation and sealing perspective, and a small amount of duct sealing, caulking, and insulation goes a long way to reducing your heating and cooling energy needs. We are in the inland side of the California coastal climate, and often a little insulation and an attic fan can eliminate AC needs most years. At least it does for us. We went for R-60 or so in our attic. It took me an afternoon to put in, and made a huge difference winter and summer, not just in costs, but also comfort as there are fewer cold or hot surfaces in the living areas, so it feels more comfortable.

Heat pumps, inverter AC units, and mini splits are all great choices for Powerwalls because they all, to varying degrees, start up gently and don't put enormous starting loads on your electrical system. To make best use of the limited energy in your Powerwalls, you want units with high SEER ratings (more heat moved for the same kWh), and that is also where sealing the house and ducts up and insulating the house well helps reduce the amount of heat that you need to move. (I.e. the Powerwalls will keep your house cooler for longer.)

So, I would insulate and seal things first, (test for air tightness!) and then do your heating and cooling calculations. You will probably find that you need less capacity than you think.

Good luck,

BG
 
People also underestimate the benefits and value of solar barriers. Its 4'x200' rolls of aluminum foil (Home Depot), about $150 per roll, with perforations in it. Staple to underside of roof. I did it over a weekend by my lonesome. Took two days. But reduced the temp in the attic by 20 degrees immediately and the 2nd floor by 15 degrees all the time.