Panel/backup question-SolarRoofInMass

[MASS-sunshine]

I'm in the scheduling phase (finally) after a 2-year wait for my Massachusetts Solar Roof install w/ 4 powerwalls. I have 400A service to the house, served by 2x200A basement panels. My advisor just told me that because I'm part of the SMART program in MA, that they can only backup 1 panel and now I need to choose which of the 2 I want to backup. Of course, this drove me nuts. If I'm paying for 4 powerwalls for a 20kwh system, I'd like to be able to backup everything - and then during any grid outage, I'll simply turn off the stuff that I deem to be non-critical during that event. (criticality can change in other words from event to event - in summer, I don't need my garage heater, but in winter I might want it, etc). But from a setup standpoint, I'd want EVERYTHING backed up, no? Then he told me that 'maybe we can use 2 gateways then' - I said maybe? Apparently the SMART program is only good for about 2500 USD over 10 years, so if I have to just opt out of that program it's not the end of the world.

So I guess what I'm asking is - is there a technical limitation that only 1x200A panel can be backed up? And if so, who would handle moving a bunch of breakers over to the panel that I would have to designate as "backed up panel"? Would my own electrician be expected to do that prior, or would Tesla do that as part of the install? This is important because with a roof that's about to crumble off the house, I need these guys to stop delaying and just get started replacing my roof. Lastly, is there such a thing as having 2 gateways? And does that allow you to back up both of the 200A panels? If that's a real solution, and all I have to do is opt out of the SMART program in MA, maybe I'll just do that and not have to change a single breaker.

 

[RBrogen]

If I remember correctly, the restriction is because to be a part of the SMART program you can't be more than a 10kW system, unless that has changed. I have 40 panels and 1 powerwall and was told and read in my SMART contract that it is limited to a 10kW system. So, even though my system has the ability to produce more than 10kW if I upgraded the inverter, my system would no longer be eligible for the SMART program. Based on that, I am going into year 4 of the 10yr contract and after that, I will be upgrading to larger inverter and adding additional Power Walls.

 

[RBrogen]

FWIW, the SMART program payments have been over $1,000 a year for us with a .11/kWh rate, that combined with the Fed/State tax incentives and net metering, we are looking at a 7 yr ROI for the system.

 

[h2ofun]

I'm in the scheduling phase (finally) after a 2-year wait for my Massachusetts Solar Roof install w/ 4 powerwalls. I have 400A service to the house, served by 2x200A basement panels. My advisor just told me that because I'm part of the SMART program in MA, that they can only backup 1 panel and now I need to choose which of the 2 I want to backup. Of course, this drove me nuts. If I'm paying for 4 powerwalls for a 20kwh system, I'd like to be able to backup everything - and then during any grid outage, I'll simply turn off the stuff that I deem to be non-critical during that event. (criticality can change in other words from event to event - in summer, I don't need my garage heater, but in winter I might want it, etc). But from a setup standpoint, I'd want EVERYTHING backed up, no? Then he told me that 'maybe we can use 2 gateways then' - I said maybe? Apparently the SMART program is only good for about 2500 USD over 10 years, so if I have to just opt out of that program it's not the end of the world.

So I guess what I'm asking is - is there a technical limitation that only 1x200A panel can be backed up? And if so, who would handle moving a bunch of breakers over to the panel that I would have to designate as "backed up panel"? Would my own electrician be expected to do that prior, or would Tesla do that as part of the install? This is important because with a roof that's about to crumble off the house, I need these guys to stop delaying and just get started replacing my roof. Lastly, is there such a thing as having 2 gateways? And does that allow you to back up both of the 200A panels? If that's a real solution, and all I have to do is opt out of the SMART program in MA, maybe I'll just do that and not have to change a single breaker.

I have a 400 amp service and 2 200 amp subpanels. I have 2 gateways, one for each panel. each gateway has about 15kw of solar. One gw has 3 PW's, the other 4 PW's. I have a 22kw generator that connects to both subpanels.

BUT, if I were going to do it again, there is a way to combine all this stuff, but not cheap. I could install like a 600 amp panel, and run everything into this under one gateways, since my main loads do not exceed 200 amps. Vines is the expert on this, I just missed knowing him well enough when I did mine,
and I cannot get V3 electric interested to change mine for any amount of money. They are not interested in learning technically how this can be done. Maybe one of the days, right Vines?

 

[jjrandorin]

So I guess what I'm asking is - is there a technical limitation that only 1x200A panel can be backed up?

A Tesla Gateway (which is the device which controls the power flow from / to powerwalls and house), only works with up to 200amp panel. So one "system" on a 200 amp panel. If you wanted both panels backed up, they would be 2 systems, and your 4 powerwalls would become 2 systems with 2 powerwalls each, not one system with 4 powerwalls.

If you did that, its "likely" Your 20kW system and 4 powerwalls would turn into (2) 10kW systems with 2 powerwalls each from a technical perspective. Meaning the 2 powerwalls on one system (gateway) would not backup, see, or interact with in any way the devices on the other "system".

So, yes, there is a technical limitation of 200 amp service per system.

And if so, who would handle moving a bunch of breakers over to the panel that I would have to designate as "backed up panel"?

Your solar installer, whomever that is, per the designed plan that is drawn up.

 

[h2ofun]

A Tesla Gateway (which is the device which controls the power flow from / to powerwalls and house), only works with up to 200amp panel. So one "system" on a 200 amp panel. If you wanted both panels backed up, they would be 2 systems, and your 4 powerwalls would become 2 systems with 2 powerwalls each, not one system with 4 powerwalls.

If you did that, its "likely" Your 20kW system and 4 powerwalls would turn into (2) 10kW systems with 2 powerwalls each from a technical perspective. Meaning the 2 powerwalls on one system (gateway) would not backup, see, or interact with in any way the devices on the other "system".

So, yes, there is a technical limitation of 200 amp service per system.

Your solar installer, whomever that is, per the designed plan that is drawn up.

But my guess is most, like me, could combine the 2 200 amp panels, batteries, solar, into one 600 amp panel controller by one gateway, as vines has figured out how to do. Not cheap, but I went through my cals for my house, and it would work. Would much rather have all my solar and PWs together, which I still am hoping V3 Electric will change their minds and work with me. Hard to believe they are leaving money on the table, but will see.

 

[MASS-sunshine]

A Tesla Gateway (which is the device which controls the power flow from / to powerwalls and house), only works with up to 200amp panel. So one "system" on a 200 amp panel. If you wanted both panels backed up, they would be 2 systems, and your 4 powerwalls would become 2 systems with 2 powerwalls each, not one system with 4 powerwalls.

If you did that, its "likely" Your 20kW system and 4 powerwalls would turn into (2) 10kW systems with 2 powerwalls each from a technical perspective. Meaning the 2 powerwalls on one system (gateway) would not backup, see, or interact with in any way the devices on the other "system".

So, yes, there is a technical limitation of 200 amp service per system.

Your solar installer, whomever that is, per the designed plan that is drawn up.

Very helpful, thank you! I am not interested in having 2 separate systems (split brain syndrome I'd term it, which only leads to problems later). I'd rather make the tough choices now then, and determine what loads should be moved to the 'BackUp panel' - as long as the Tesla assigned electrician does this based on my choices, we should be fine and not delay starting the project any further. As a secondary positive side effect, i will not have to change my SMART program participation, for whatever that ends up being worth. It all counts in the end. Thank you very much, i will definitely be talking to the advisor tomorrow about this to keep things moving forward.

 

[jjrandorin]

You will want to ensure that, if there is a backup loads panel, you make sure you detail what should be in it. The on site installers are going to do whats on the plan, not what you tell them in person, as it relates to what loads go in there or not. Its likely not a big deal if you want a specific 120 "lights" circuit moved, but expecting to just tell them on site "both those AC units go in the backup loads panel" or something is not going to work if thats not whats on the plans.

Tell whomever your assigned rep is, what you expect in the backup loads panel (make a list) and ensure you get information about the plan... before install day I mean.

It looks like you are planning to talk to your advisor, so thats great, I would just ask to be sent the plan before install day. I think its a 1 page diagram, with part numbers and where loads go, etc.

 

[MASS-sunshine]

Excellent advice, thanks again - I am going to document the BackupLoad panel today (and by elimination, the non-backed up panel also)...because of some recent electrical work, nothing is labelled on the panel, though I have mapped about 70% of it so far. Follow up questions if you don't mind - I have a whole panel surge protector that I had installed by the electrician about 2 years ago, when I only had 1 panel. It occupies 2 slots on the panel - obviously that's optional and I could easily remove it to free up space. (Yes I know it's mostly about amperage but I also need the space, not at risk of going over amperage on either panel). So my quesiton is 'does this surge protector breaker serve any purpose post-Tesla PW/gateway deployment?' if not, and even if it does, I think i'm gonna ditch it. Also, I have a Sense device, that monitors my electrical usage, and my legacy solar (that is being removed by Tesla before install of new solar roof). Is there any purpose in me having the Sense device taking up 2 slots also on the panel, in a post-Tesla PW/gateway world? It does tell me what devices are using how much power, so if I can keep it and still get vitals from it, that would be ideal. Knowing my dryer is using 800watts, knowing the hot water tank just kicked in, etc, is helpful knowledge - but if I get something similar from the PW/gateway setup, then obviously it's redundant.

Thanks again for the advice, I'm going to documnet my panel today and would love to free up at least 1 or 2 slots, it's gonna be tight on the 'backed up panel'.

 

[BGbreeder]

Excellent advice, thanks again - I am going to document the BackupLoad panel today (and by elimination, the non-backed up panel also)...because of some recent electrical work, nothing is labelled on the panel, though I have mapped about 70% of it so far. Follow up questions if you don't mind - I have a whole panel surge protector that I had installed by the electrician about 2 years ago, when I only had 1 panel. It occupies 2 slots on the panel - obviously that's optional and I could easily remove it to free up space. (Yes I know it's mostly about amperage but I also need the space, not at risk of going over amperage on either panel). So my quesiton is 'does this surge protector breaker serve any purpose post-Tesla PW/gateway deployment?' if not, and even if it does, I think i'm gonna ditch it. Also, I have a Sense device, that monitors my electrical usage, and my legacy solar (that is being removed by Tesla before install of new solar roof). Is there any purpose in me having the Sense device taking up 2 slots also on the panel, in a post-Tesla PW/gateway world? It does tell me what devices are using how much power, so if I can keep it and still get vitals from it, that would be ideal. Knowing my dryer is using 800watts, knowing the hot water tank just kicked in, etc, is helpful knowledge - but if I get something similar from the PW/gateway setup, then obviously it's redundant.

Thanks again for the advice, I'm going to documnet my panel today and would love to free up at least 1 or 2 slots, it's gonna be tight on the 'backed up panel'.

The surge protector should occupy a very special place in your panel(s). The breaker for it should be the the closest breaker to wherever your meter feed is, and the wires connecting to the breaker should be as short as possible. Protection is measured at the speed of light and nanoseconds.

Personal opinion: With solar and energy storage systems, I think that you need the whole house surge protector even more, as they are pricey electronics. Solar and energy storage equipment are a) expensive, and b) quite sensitive (in the grand scheme of things) to power surges. I think that a high quality surge protector is a required item for any house with solar or energy storage equipment.

I am not a Sense fan, but what it does is a little different than what a gateway will tell you. A gateway will tell you that the house is using 0.9kW, and that is it, whereas the Sense device will, in theory, tell you that your dryer is using 0.8kW, and other stuff is using 0.1kW.

My $0.02 is that when you make up your essential loads list that you also make up a non-essential loads list to up the chances that you get what you want. By extension, I would finish identifying all of your circuits now.

Good luck, and I hope that you get a good crew.

All the best,

BG

 

[MASS-sunshine]

BG, thanks a ton! Couple thoughts...

1. One of my biggest concerns believe it or not, is whether say 4-6 of the existing pinned up romex lines can even be moved/stretched to reach the 2nd panel - I am unclear if there is some way that electricians "stretch" the line to be able to reach a slightly further distance to the other panel. do they splice in another cable or what do they do to, let's say, move 4-6 breakers from the old panel to the newer, non-backed up panel. Right now, the cables are all nice and neatly pinned up on the joists above and there doesn't appear to be any slack available to 'stretch' things another say 2 feet.

2.. Given the high value you place on that panel surge protector, now that I have a 2nd panel would you recommend I place one in there as well, subject to the same guidelines you laid out about placement? I wanna say the Siemens surge protector was about 250 bucks at the time, years ago, does that sound about right for a 2nd one for panel 2? I've also been reminded from my electrician several times that the device is a '1 and done' device, in other words, once it does it's job and prevents a direct strike, it has to be replaced, as it will never take a hit again and be useful. Still, well worth it to protect for that outlier event to save tens of thousands of dollars worth of gear.

3. I like the Sense, been using it for 3 years now - it's definitely not perfect, but it's quite good if you spend time 'training it' - certainly I won't need the Solar version of it anymore (the PWs and GW will report on solar gen i'm sure), but the load awareness per 'device' or 'appliance' is helpful and gives me some satisfaction that I am isolating certain loads and learning how to reduce my electrical spend where possible as I make changes in technology or systems. Question is, how do I re-architect the Sense hookups to accommodate not only the new 2nd panel I now have, as well as a sub-panel that is out in the shed, with a 30A outdoor line homed to it. If I keep the Sense, it needs to be able to report on anything/everything, rather than just what's in panel 1 for instance. This is likely a question for Sense themselves, I can always reach out to them for advice, or even if this will be a setup they can accommodate.

Thanks again for all the support!

 

[Matt-FL]

I had a sense for a few years also, but it became so unreliant after solar that I took it out. I replaced it with a pair of Emporia Energy Vues to monitor 32 individual circuits. I've found it far more useful than Sense overall, as now there is no 'guesswork' or 're-learning' the same device multiple times .

What was unreliable on the Sense? After the solar was installed, Sense was just giving one value for all wattage like it was brand new. It would think it was finding different appliances, but a few days later it would say it found another of the same type. I would test and sure enough, it found my dryer a second time and now the old 'dryer' was never used again. My list of devices was exponentially growing . Then, since I had the solar clamps, I had to move it out of my panel and near the gateway. I was able to find solid connections for house usage, but solar leads would flip, stop working, then start working out of the blue.

I have a surge protector breaker in my system, however I've been watching voltage closely for brownouts. Since the system was installed, I've never seen a brownout during grid outages. The gateway has been handling power switching between grid, solar and powerwalls just as well as my house UPSs. I've seen a maximum of 125v, minimum 121v.

I did have an issue with a grid outage in the middle of the day when my powerwalls were full, where the gateway increases the AC frequency to 65Hz which made my UPSs remain supplying power until they ran out. I put in a ticket with Tesla and they adjusted to accommodate and I've not had that issue since.

I'd venture to say that my Tesla gateway, solar and powerwalls operate every bit as effective as a UPS system, protecting all of my sensitive equipment. I'd say my most volatile equipment is the gateway which is directly connected to the grid, but there isn't (as far as I know) any way to protect that.

 

[BGbreeder]

BG, thanks a ton! Couple thoughts...

1. One of my biggest concerns believe it or not, is whether say 4-6 of the existing pinned up romex lines can even be moved/stretched to reach the 2nd panel - I am unclear if there is some way that electricians "stretch" the line to be able to reach a slightly further distance to the other panel. do they splice in another cable or what do they do to, let's say, move 4-6 breakers from the old panel to the newer, non-backed up panel. Right now, the cables are all nice and neatly pinned up on the joists above and there doesn't appear to be any slack available to 'stretch' things another say 2 feet.

2.. Given the high value you place on that panel surge protector, now that I have a 2nd panel would you recommend I place one in there as well, subject to the same guidelines you laid out about placement? I wanna say the Siemens surge protector was about 250 bucks at the time, years ago, does that sound about right for a 2nd one for panel 2? I've also been reminded from my electrician several times that the device is a '1 and done' device, in other words, once it does it's job and prevents a direct strike, it has to be replaced, as it will never take a hit again and be useful. Still, well worth it to protect for that outlier event to save tens of thousands of dollars worth of gear.

3. I like the Sense, been using it for 3 years now - it's definitely not perfect, but it's quite good if you spend time 'training it' - certainly I won't need the Solar version of it anymore (the PWs and GW will report on solar gen i'm sure), but the load awareness per 'device' or 'appliance' is helpful and gives me some satisfaction that I am isolating certain loads and learning how to reduce my electrical spend where possible as I make changes in technology or systems. Question is, how do I re-architect the Sense hookups to accommodate not only the new 2nd panel I now have, as well as a sub-panel that is out in the shed, with a 30A outdoor line homed to it. If I keep the Sense, it needs to be able to report on anything/everything, rather than just what's in panel 1 for instance. This is likely a question for Sense themselves, I can always reach out to them for advice, or even if this will be a setup they can accommodate.

Thanks again for all the support!

1. Trust your electricians. They will find a way to get the wires moved over. It should be no big deal.
2. This depends a bit on how things will be wired; if the future wiring is that it goes meter splitting to feed two panels, then, yes, having one surge protector in each panel would be optimal. If it is to go meter, panel#1, feeding panel #2, then putting the surge protector into #1 should be sufficient. Surge protectors are a bit like belts and suspenders. One is good, two adds extra help. BTW: The voltage cutoff (clamping voltage) for whole house surge protectors is higher than the usual surge protector outlet strips, so the outlet strips have additional benefit as they clamp closer to the line voltage. Surge protectors are a wear item; they can only absorb so many kJ of energy before they are worn out. One big, close, surge might do it, but a couple hundred small ones will too. My $0.02 is either replace it when the light turns red, or replace it when the warranty for the surge protector is up.
3. I would talk to Sense and see what they have to say. I would comment that, in my view, Sense is trying to do a non-trivial bit of work. Monitoring the line load/voltage, and trying to fingerprint each load is easy when you have one or two loads. As the number of different loads increase, it becomes harder and harder to distinguish one load from another, e.g. refrigerator #1, starting up cold, vs refrigerator #1 starting up while filling the ice maker tray, etc. I didn't think that Sense would work well when the product was announced, and as you and others (e.g. @Matt-FL above) have found, Sense has issues. The Tesla Gateway will give you insights to large loads (think hundred plus watts/load) on a tens of minutes scale, but if you want fine, granular, data on everything, the Tesla Gateway certainly isn't the answer. There are more than a few home monitoring products on the market, none of which I have used personally, but I haven't seen one that to me a) seems to work and b) I would want to have in my electrical panel(s), or scattered around my house. Everyone has a different tolerance for risk and different desires for monitoring. I think that you could probably learn a lot from a Kill-a-Watt type device, and perhaps a clamp on ammeter, but if you want to login to a dashboard to find out where every watt is going in your house at this exact moment, that's not going to cut it, either.

All the best,

BG

 

[MASS-sunshine]

If I remember correctly, the restriction is because to be a part of the SMART program you can't be more than a 10kW system, unless that has changed. I have 40 panels and 1 powerwall and was told and read in my SMART contract that it is limited to a 10kW system. So, even though my system has the ability to produce more than 10kW if I upgraded the inverter, my system would no longer be eligible for the SMART program. Based on that, I am going into year 4 of the 10yr contract and after that, I will be upgrading to larger inverter and adding additional Power Walls.

Mine is spec'd as a 20.6 kW system, so if what you're saying is true, SMART wouldn't be an option for me anyway - to complicate things further, my home has been on SMART for 10 years this year, because of a legacy 6kW panel system. My SREC payments just went from about 350 per quarter, down to 10% of that at the 10 year mark, so roughly 35 USD per quarter. Obviously, that is small pittance, and if that's going to continue to be the rate when I remove the old system and Tesla installs the solar roof, then I don't care very much about the 140 per year that I'd be giving up. If however, the 10-year clock gets restarted to ZERO because of the new install, then I'd be more apt to want to stay in the program of course. Anybody know if the 10-year is per residence, versus per "solar PV system"?

 

[MASS-sunshine]

But my guess is most, like me, could combine the 2 200 amp panels, batteries, solar, into one 600 amp panel controller by one gateway, as vines has figured out how to do. Not cheap, but I went through my cals for my house, and it would work. Would much rather have all my solar and PWs together, which I still am hoping V3 Electric will change their minds and work with me. Hard to believe they are leaving money on the table, but will see.

Interesting. I'm waffling a bit I know, but after reviewing my panels closely tonight, I really will not be able to get all critical loads into 1 panel - it's just not feasible. I think I may be back to the idea of going with 2 gateways, and designating 2 Powerwalls for each gateway/panel. 2 totally separate systems, and maybe as long as they can both be seen in the App on the phone, I guess it doesn't have too many negatives to it. Are there any other gotchas I should be keeping in mind for a 2-gateway system that you can think of?

 

[h2ofun]

Interesting. I'm waffling a bit I know, but after reviewing my panels closely tonight, I really will not be able to get all critical loads into 1 panel - it's just not feasible. I think I may be back to the idea of going with 2 gateways, and designating 2 Powerwalls for each gateway/panel. 2 totally separate systems, and maybe as long as they can both be seen in the App on the phone, I guess it doesn't have too many negatives to it. Are there any other gotchas I should be keeping in mind for a 2-gateway system that you can think of?

Mine works fine with 2 gateways. Seen in app no issue. Just spread assets evenly. If the solar as some better than other for production think about this. I have better panels for the winter, so I tried to make sure they were on my GW with my heat pumps which suck suds in the winter.

 

[BGbreeder]

Interesting. I'm waffling a bit I know, but after reviewing my panels closely tonight, I really will not be able to get all critical loads into 1 panel - it's just not feasible. I think I may be back to the idea of going with 2 gateways, and designating 2 Powerwalls for each gateway/panel. 2 totally separate systems, and maybe as long as they can both be seen in the App on the phone, I guess it doesn't have too many negatives to it. Are there any other gotchas I should be keeping in mind for a 2-gateway system that you can think of?

If you do split things, you might want to think about putting your lower demand loads, like lighting in one panel, and heavy loads in the other and then split the powerwalls 1:3, and the solar at least 1:3. Once built, it won't be trivial to move excess solar energy from one to the other. Having three powerwalls together will better handle any startup surges or multiple heavy loads. Just my $0.02...

All the best,

BG

 

[GregBallantyne]

If you do split things, you might want to think about putting your lower demand loads, like lighting in one panel, and heavy loads in the other and then split the powerwalls 1:3, and the solar at least 1:3. Once built, it won't be trivial to move excess solar energy from one to the other. Having three powerwalls together will better handle any startup surges or multiple heavy loads. Just my $0.02...

All the best,

BG

I'm not the most knowledgeable on this, but from an operation standpoint I would agree. I'd also add that perhaps adding one more Powerwall here would be something to really consider.
Once you start operating this system, your goals may evolve - meaning that you may see a pathway to mostly self powering. When you're self powering, your operation is no different than grid outage operation. You are routinely operating as though there is no grid. That means you'll want to "backup" everything, all the time. With a 3 and 1 split system, one 200A panel will only be getting 30A of run power from one PW. The other 90A. Might make better sense to backup one with 2 PW and the other with 3, or even split your loads to make sense of a 4 and 1 split, if you've got 2 heat pumps perhaps, that sort of thing.
My point is try looking at the system as though it's your main power supply and the grid is your backup. My brain has gone quickly to that perspective in less than 3 months of operation, and I'm ordering another PW to put myself more squarely into that space. But I've just got the one 200A load center.

 

[CrazyRabbit]

Interesting. I'm waffling a bit I know, but after reviewing my panels closely tonight, I really will not be able to get all critical loads into 1 panel - it's just not feasible. I think I may be back to the idea of going with 2 gateways, and designating 2 Powerwalls for each gateway/panel. 2 totally separate systems, and maybe as long as they can both be seen in the App on the phone, I guess it doesn't have too many negatives to it. Are there any other gotchas I should be keeping in mind for a 2-gateway system that you can think of?

I have GE panels, originally two 40 circuit panels, and replaced my backup loads panel with a 80 circuit GE panel so I could fit all my loads into it. If you go this route ask Tesla to install 3/0 wire, it can handle 200 amps where 2/0 can only handle 180 amps. I installed the 80 circuit panel prior to powerwall install and relocated circuits. Tesla installed two service disconnects….
I refused to install two gateways and have my batteries and solar divided up.

 

[MASS-sunshine]

Need some quick help if possible - my electrician is separating circuits today on the 2 panels so that we have 1 panel for backup loads and 1 panel for non-backed up loads - the question is a simple one - do we need to leave any open circuit slots on the "backup panel" for any of the Tesla equipment to use that, or can we load up literally 100% of the space, subject to normal amperage concerns which we are obviously undertaking. My point is, I need every inch of real estate on that backup panel to do what i want to do from a backed up loads perspective, we just don't know if we have to leave a slot or 2 for Tesla's stuff when they come. My Tesla electrician hasn't responded yet (i'm sure they're busy). Thanks a TON guys!