Advice on whether this installation is possible

[holeydonut]

First time poster here - I'm trying to get new PV and Powerwall partial backup installed in my home in Northern California. If you have a partial backup system, can you help me understand if my goal is possible?


My goals for the PV + partial backup:

1) When the Utility is working fine, I want the energy generated from my solar and stored in my Powerwalls to help power the ENTIRE house. If these two clean sources aren't enough, then I expect the utility to supplement power.

2) When the Utility goes offline, I want high-amperage items to go offline. Only the 20A and below "backup loads" would get power from my PV or batteries. So, my air conditioning and other high amp appliances would not work.


I've come up with the attached flowchart to describe my situation.

Sunrun says my idea of "load shifting" on the partial backup solution is dangerous to the Powerwall. They agree that if I do a partial backup, then the items upstream of the gateway will benefit from PV or solar power when the utility is working fine. However, they say even if the utility were working fine, the air conditioners would damage the 2x Powerwalls (even though the ACs are upstream of the gateway). So they won't do the installation since Lennox won't let me get soft starts on my AC condensers.

When I spoke to a Tesla sales rep a few months ago, but all they wanted to do a whole house backup with 3x Powerwalls. Unfortunately that option exceeds my budget.

Thanks so much for your help! I'm at wits end with this partial backup option.

 

[Vines]

Your diagram is not how i would design it, but what you want is totally possible.

Sunrun is incorrect that the AC in this diagram will damage the Powerwalls.

3 Powerwalls with SGIP is close to same cost as 2 without it. Many companies are not quoting anything except 3 and more PW due to demand issues, and the cost when you factor in SGIP. Maybe some installers have money left in the 1-2 PW category but many have run out.

 

[holeydonut]

Thanks Vines! If you could design it, what change would you make? Do you have an installer you can recommend me? I'm just a few miles away from you in East Bay.

I think the problem with SGIP is that is tied with PG&E and nobody's getting the SGIP money now-a-days. Plus California is at a massive budget deficit. So no installer is willing to consider the benefit of that rebate in the quoted net cost after all rebates.

 

[wwhitney]

Your goals are the way any partially backed up home normally works. And I agree, Sunrun is wrong.

The basic efficient one-line diagram for a partially backed up system is the following:

Service Disconnect ------------ Non-Backed Up Panel
                        |
                        |
                  Backup Gateway
                        |
                        |
Backed Up Panel ---------------- Generation Panel

This layout typically requires each panel to have a main breaker in it.

Cheers, Wayne

 

[Vines]

SGIP is slowly running out of money but we are on step 3 or 4 right now. Its not gone! You should at least price quote 3 of them vs 2 of them.

See attached image of general edits, and this assumes a lot about your MSP.

If what you have is a 125-200A panel with room for 2 main breakers only then this diagram is good. I do not know how you intend this "Junction" to go.

Pictures of the MSP, with the lid off and the sticker is worth a thousand words.

 

[Vines]

My edits to your image there aren't complete, but its close enough for a concept.

The GW2 has 2 internal sets of lugs on the backup side and 1 on the non backup side.

I'd have the internal panelboard of the GW2 connected to one side of the backup lugs and the PV and PW breakers on that internal subpanel. On the other side of the backup lugs, go to your existing garage subpanel, assuming it can take a 100A Main breaker, or one the bus.

Then the added 100A sub with 100A main would have the (4) 2P 50A breakers that are metered but not backed up.

Alternately, depending on equipment locations the internal GW2 sub could be the non backup loads, but you'd have to use 50/50 tied quad breakers and backfeed the bus with a 100A main.

Honestly though with 3 Powerwalls more of your loads can be backed up than shown.

 

[holeydonut]

My edits to your image there aren't complete, but its close enough for a concept.

The GW2 has 2 internal sets of lugs on the backup side and 1 on the non backup side.... /QUOTE]

Thanks wwhitney and Vines! Much appreciated.

Vines...

For real... how can I just pay you to do this installation instead of Sunrun? Like can I just have Sunrun do the PV and materials sourcing, but you do the Tesla install? You literally know more than any Tesla sales rep or tech support rep I've spoken to.

I've modified my sketch a bit... I think I understand what you mean about the Gateway 2? You are correct, my MSP has two breakers. I was told the only way to get the CT clamps to read the entire house properly was to place the CT somewhere between these two MSP breakers and the PG&E meter. It sounded like they would need to add a JBox with a single master breaker to pull this off.

I'd like to send this revised pic to Sunrun and see if they can assess and try to do it. Does this represent what you mocked up?

 

[holeydonut]

Whoops, sorry I typed my reply into the quote box in my previous post...



Thanks wwhitney and Vines! Much appreciated.

Vines...

For real... how can I just pay you to do this installation instead of Sunrun? Like can I just have Sunrun do the PV and materials sourcing, but you do the Tesla install? You literally know more than any Tesla sales rep or tech support rep I've spoken to.

I've modified my sketch a bit... I think I understand what you mean about the Gateway 2? You are correct, my MSP has two breakers. I was told the only way to get the CT clamps to read the entire house properly was to place the CT somewhere between these two MSP breakers and the PG&E meter. It sounded like they would need to add a JBox with a single master breaker to pull this off.

I'd like to send this revised pic to Sunrun and see if they can assess and try to do it. Does this represent what you mocked up?

 

[wwhitney]

You can edit your earlier post and just move the [/QUOTE] tag.

Cheers, Wayne

 

[holeydonut]

You can edit your earlier post and just move the

tag.

Cheers, Wayne[/QUOTE]


I think my account is too new to do edits - sorry I only see the option to Quote, Reply, Permalink, and Report a post.

 

[Vines]

Here's the edits I'd have you do.

We will expand on other systems as long as the equipment and install are quality. PM me if you want to talk more about that. Current backlog is getting into October for new signups. For now you have gotten some well qualified advice

 

[holeydonut]

Here's the edits I'd have you do.

We will expand on other systems as long as the equipment and install are quality. PM me if you want to talk more about that. Current backlog is getting into October for new signups. For now you have gotten some well qualified advice

Thanks Vines. I really appreciate your guidance and advice on the flow!

 

[miimura]

@holeydonut My system is exactly like what you want. My system was installed with SGIP Step 1 funds in 2018.

The Grid CTs are placed between my main breaker and my main panel. My Gateway is fed with a 125A breaker in the main panel that used to feed a sub-panel. The new Generation Panel and the original sub-panel are fed by the backup side of the Gateway. All my big 240V loads remain in my main panel and are not backed up. A couple important 120V loads were relocated from the main panel to the Generation panel.

 

[holeydonut]

@holeydonut My system is exactly like what you want. My system was installed with SGIP Step 1 funds in 2018.

The Grid CTs are placed between my main breaker and my main panel. My Gateway is fed with a 125A breaker in the main panel that used to feed a sub-panel. The new Generation Panel and the original sub-panel are fed by the backup side of the Gateway. All my big 240V loads remain in my main panel and are not backed up. A couple important 120V loads were relocated from the main panel to the Generation panel.

Thanks Miimura! Does your Tesla app show that your non backup heavy loads still benefit from the Powerwall when you have it in the "self powered" mode and the utility is operational? I heard that mildly cycling the battery each day degrades the overall life of the battery; hope things are holding up well for you.

 

[jjrandorin]

Thanks Miimura! Does your Tesla app show that your non backup heavy loads still benefit from the Powerwall when you have it in the "self powered" mode and the utility is operational? I heard that mildly cycling the battery each day degrades the overall life of the battery; hope things are holding up well for you.

Using any battery "degrades" it some, so does leaving it at max charge, or leaving it empty. Its the nature of batteries. With that being said, tesla has built in some safeguards) like not accessing either the top, or the bottom, of the battery for example.

To answer your question, if the CTs are placed correctly, non backed up loads can pull from the powerwall when the grid is up. I have all loads in my home except one backed up. That "1" is my Tesla wall connector (what many refer to as the "car charger" even though it isnt actually a charger). So, my HPWC is not backed up, and it definitely will use powerwall power if I plug in my car, if the grid is up. It also definitely does not operate at all if the grid is down.

I think its pretty much the standard way tesla installers hook it up, so I am a bit confused at you saying that they didnt understand.... however the CT placement seems to be an installer job, so maybe the phone support people dont know.

Everyone goes about things differently, but, for "me" specifically, I am not the type to try to engage a professional to do a job and then try to sketch out exactly how it should be done. What I mean is, i would not hire someone to install this equipment in my house, then start giving them diagrams on what to do. If I have enough knowledge to sketch out the diagram, I would likely consider doing it myself, and if I dont have enough knowledge to do it myself, thats why I would hire someone to do it.

I educate myself so I know what is going on, but my focus when I hire someone to do work for me is ensuring that we are a good fit personality wise (impossible with tesla to do this) and trying to ensure that they both know what they are doing, and motivated to do a great job for me.

Maybe this comes because I work in IT and troubleshoot / fix things for a living. The "customers" I dislike the most are the ones who try to tell me exactly what to do to fix whatever problem they have brought me there to fix, and try to watch over my shoulder while I am typing away, or otherwise determining what I need to do. I dont have any problem with people who want to know whats wrong, what I found, what I need to do to fix it (I actually love explaining that), and I dont have problems with a discussion over some things like placement, etc.

What bugs me is people who try to tell you click for click what to do... because in my mind if they have that much knowledge, then why am I there in the first place (lol). Anyway, thats likely why I wont do it with others.

To be clear, I will repeat that:

1. Everyone is different and free to do business however is best for them, and
2. I educate myself specifically so I know what is going on, and
3. I try to develop a rapport with the people doing the actual work, so they are motivated to do "their best" for me

It normally works out like I want it to.

Back to topic. What you want OP is pretty standard (non backed up loads being able to use powerwall power when grid is up), so hopefully you dont have to share diagrams with anyone to make that happen. The risk of "sharing a diagram" is that, if technologically possible, they might do exactly what you lay out, even if its not what "should" happen for best use... because "this is what the customer asked for, so I cant get in trouble doing what they laid out as long as it meets code".

 

[miimura]

Thanks Miimura! Does your Tesla app show that your non backup heavy loads still benefit from the Powerwall when you have it in the "self powered" mode and the utility is operational? I heard that mildly cycling the battery each day degrades the overall life of the battery; hope things are holding up well for you.

The previous poster answered very well. However, I will repeat the answer to your question.

Yes, with the Grid CT's placed so that they measure ALL grid consumption, the Powerwalls can offset ALL consumption, even if they are not backed up. This means that if I was running in Self Powered Mode, my EV charging would discharge my Powerwalls. This is one of the reasons that I use Time Based Control - Balanced Mode. As long as I set the cars to charge during Off-Peak, they will charge straight from the grid at my lowest utility rate. That preserves my battery power to offset usage during the Part-Peak and Peak hours.

I don't worry about the Powerwall battery degradation. As far as I can tell, things are holding up very well and the system operates as I expect.

 

[CrazyRabbit]

I would put your cooking appliances on whole home pack up, just know you would have to limit the use. I would want to use microwave and stove.
Also note your blowers will run if your AC turns on... which will waste energy.

 

[jboy210]

...
Maybe this comes because I work in IT and troubleshoot / fix things for a living. The "customers" I dislike the most are the ones who try to tell me exactly what to do to fix whatever problem they have brought me there to fix, and try to watch over my shoulder while I am typing away, or otherwise determining what I need to do. I dont have any problem with people who want to know whats wrong, what I found, what I need to do to fix it (I actually love explaining that), and I dont have problems with a discussion over some things like placement, etc.

What bugs me is people who try to tell you click for click what to do... because in my mind if they have that much knowledge, then why am I there in the first place (lol). Anyway, thats likely why I wont do it with others.
..

One reason I would never work in IT ops.

I am/was a developer. Always hated doing support. People see just their viewpoint of the world and not the fact that the same piece of software supports millions of other users.

 

[jjrandorin]

One reason I would never work in IT ops.

I am/was a developer. Always hated doing support. People see just their viewpoint of the world and not the fact that the same piece of software supports millions of other users.

Lol yeah. I am not a help desk technician ( I dont know many of those who would be able to get powerwalls, lol) but I started there a loooooooong time ago and have been in IT operations in one form or another my entire career.

 

[holeydonut]

Lol thanks for the detailed response jjrandorin!

I guess the thing that is obvious to you has been the worst part of this process for me so far. I'm in NorCal, and I have had 5 different PV + Powerwall installers completely disagree with the statement that "What you want OP is pretty standard (non backed up loads being able to use Powerwall power when grid is up)".

There was a 6th PV + Powerwall installer that agreed about how great the Powerwall was; but this company was Tesla itself. And their PV installers said they couldn't install solar on my home because of the type of roof tiles that I have.

Across the board, the non-Tesla combo installers insist that the only way Powerwall energy will make it to a circuit (regardless if the normal energy utility is up or not) is if the circuit were on the backup loads side of the Gateway. Most absolutely refused to buy into the concept of "back feeding" to a non-backup load when the power utility were online.

They insisted they were the experts on the topic and that I didn't know what I was talking about and they told me to look elsewhere. My suspicion is that Generac and LG Chem do not do partial home backups the way the Powerwall 2 and Gateway 2 are able to do them. So the old school folks only know of the method to back up the whole house or just isolate 5 circuits and create a closed loop for them.

But, as indicated by Vines and yourself, Tesla designed the Powerwall to do great things to spread out clean energy when the power utility was online. So I appreciate everyone's comments here about what is possible since I need this information to finally find an installer to do this work. I was able to convince one installer to come on board and actually install solar on a concrete tile roof while also doing a Tesla Powerwall 2 + Gateway 2 partial home backup that could take advantage of clean energy throughout the home when the energy utility was online.


PS... I wish I could agree with you that letting the experts do their expert thing usually works out. But from what I've experienced, some experts take advantage of the situation to the customer's detriment. For example, I had 2 full HVAC systems replaced in my home a few months ago before COVID. I thought the installer was going to do "the right thing" for me and I let them do what they did best. But it turns out they under-sized both evaporator coils (they matched 2 ton coils to 3 ton systems). And they did not set up my hardware to activate all the features available in the equipment that I purchased.

The smaller evaporator coils reduce each system energy efficiency by 13%, and their failure to enable dual-stage cooling and the variable speed blower fan controls means my total $30k systems have the feature-set of systems half the price. I was told that even though I had bought equipment with the potential of greatness due to advanced features; I did not expressly tell the installer I wanted those features to work. This expert had over 2 thousand positive reviews on Yelp and was the premier installer in the region.

They told me that "the average customer really only cares if the HVAC turns on and off" ... I was later informed by the equipment manufacturer that a lot of the comfort features and advanced energy saving stuff sound cool to get customers excited to pay more, but are just marketing fluff. Very Lame.