Rapid Shutdown for Ground mount with inverter in garage

[ggunn]

Oh come on. Yes necessarily, especially since it's a DC coupled ESS, meaning both the PV and ESS power the same inverter. Backup means that if power from the grid is lost then the system will keep running from whichever is available, that's the whole point.

Oh you come on.

I have seen partial home battery backup systems that keep PV running, systems that don't, systems that only keep part of it running, and systems that don't even have PV.

As I said, I don't know much about DC coupled backup systems. I used to play around with Sunny Island stuff, but that was many years ago. But the point is likely moot, as the AHJs I dealt with when I was doing resi systems all required an external bladed lockable PV AC disconnect, so there's the RSD initiator.

 

[SteveO NE]

The 2020 NEC clarifies that inverter output circuits are only covered within the array boundary.

It seems like a distinction without a difference when the service disconnect is the intiation device.

Yeah certainly seemed logical before they made the distinction but I'm sure there were a few too many pissing matches between installers and AHJ's because it wasn't specifically written in the code.

Just make sure to not have the extra 25% figured in for voltage drop purposes. Anyway I have always found it more cost effective to run AC. We don't have to compromise on string quantity and would typically use all 9 (on a 3 7.7 system). Typically we are about 3 volts drop, and again, if you are getting up high enough to trip the inverters, I'll bet you have other problems and would have them even with a perfect conductor. Yes conduit is extremely expensive right now so that is a factor of course. My AC conductors are USE so I often use lesser cost protection methods such as 4" SDR 35 pipe (if I need something big) which is the same cost as 2" PVC. Anyway we apparently both have our system and have it dialed in and for me I find running AC to be simpler and more cost effective.

This is usually how my numbers come out too, factor in the inefficiencies of the system itself when messing with unequal string resistance and current sinking, and it isn't worth it, just terminate it and bring back a combined circuit. That said, I am not usually dealing with smaller arrays where just the coordination alone isn't worth the headache even if it did save a few bucks.

...but with the inverter configured for battery backup it seems that killing the connection to the grid will not cause the inverter to shut down the array since it will try to grid form and keep the optimizers producing...

Seems everyone is caught up on the wrong question. Your question has little to do with the RSD, and more to do with the ESSD. Read up on 706.15. If you otherwise meet the needs of rapid shutdown on the grid side, you need not worry about the rapid shutdown requirements there anymore - your PV system is either capable of rapid shutdown or not and that has to do with how quickly it can disconnect and discharge residual voltage. With an AC coupled or multimode DC coupled system, you need to kill the battery feed and for a residential system you need to have an external means to do so (could be remote) and that should be appropriately placarded near the utility meter with a directory of disconnects for stand-alone or ESS.

 

[SteveO NE]

It's basically all the same. As you know, with Powerwalls and microinverters in backup setup, the service disconnect cannot be the rapid shutdown switch.

Yeah you really cannot follow the letter of the code "For a single PV system...any single initiation device..." unless you have a device that say shunts out the ESS disconnect and the service disconnect at the same time, or if a multimode inverter trips the inverter offline into an RSD mode.

 

[jaggedben]

Oh you come on.

I have seen partial home battery backup systems that keep PV running, systems that don't, systems that only keep part of it running, and systems that don't even have PV.
...

I remain pretty skeptical that you saw a BESS on the same site as PV that didn't keep any of the PV running. Those must be extremely few and far between. I'm going to continue to assume that if someone mentions PV, BESS and backup on the same site that at least part of the PV is going to run with the backup.

But the point is likely moot, as the AHJs I dealt with when I was doing resi systems all required an external bladed lockable PV AC disconnect, so there's the RSD initiator.

A utility disconnect can not be an RSD initiator when a battery ESS can keep the PV system running.

 

[jaggedben]

...



Seems everyone is caught up on the wrong question. Your question has little to do with the RSD, and more to do with the ESSD. Read up on 706.15. If you otherwise meet the needs of rapid shutdown on the grid side, you need not worry about the rapid shutdown requirements there anymore - your PV system is either capable of rapid shutdown or not and that has to do with how quickly it can disconnect and discharge residual voltage. With an AC coupled or multimode DC coupled system, you need to kill the battery feed and for a residential system you need to have an external means to do so (could be remote) and that should be appropriately placarded near the utility meter with a directory of disconnects for stand-alone or ESS.

Actually he's on the 2017 code (he said so on the OP) and in that code there is no requirement for an outside disconnect for the BESS. It's possible for him to have an inside disconnect for the BESS and be all compliant with all his requirements for ESS and disconnects for multiple sources, but not rapid shutdown. Therefore, it's a pertinent question whether his DC conductors from a groundmount trigger any 690.12 rapid shutdown requirement, and how much and how far they have to be on or inside a building to do so. The BESS may affect what he must do to comply with the RSD requirement once triggered, but has nothing to do with whether the PV conductors trigger the requirement in the first place.

 

[ggunn]

I remain pretty skeptical that you saw a BESS on the same site as PV that didn't keep any of the PV running. Those must be extremely few and far between. I'm going to continue to assume that if someone mentions PV, BESS and backup on the same site that at least part of the PV is going to run with the backup.

Do or do not believe; there is no try.

As a matter of fact, in one jurisdiction near me, that is the only way to have both PV and and an ESS. All PV systems must be interconnected outside the customer's meter on its own meter. Weird but true.

A utility disconnect can not be an RSD initiator when a battery ESS can keep the PV system running.

Of course. I'm not talking about a utility disco; I am speaking of a PV AC disconnect. Any PV system where they meter PV separately requires it, and some that do not still get one per the AHJ. Thinking about it, I realize that there are systems where PV and ESS are combined before the disco; I'm not sure how they handle RS. I'll ask our resi guys about it. Like I said, I haven't done any resi systems in quite a while.

 

[pv_n00b]

Yeah it's kinda weird to me. It's almost like the industry expects some fancy system monitor sitting on the dining room table or an app on your phone, and that people will need/want it. I haven't even add any clients that give a hoot. We just tell them to check the inverters periodically for an error code.

Even in larger C&I projects that are several years old I have found that people don't use the monitoring system. A lot of the time the facilities person does not know that it even exists when I ask about it. When the system was installed one person was given the information for the website to go to and monitor the system. That person leaves and it's not documented or they never pass the information to the person at the company who should be monitoring the system. Once in a while I will find someone who is really into it. Leased systems will have someone monitoring them because that's money.
I still see a few Fat Spaniel systems out there and they are dead. Once an old monitoring company goes under all the monitoring goes with it.
As for residential systems, I have talked to quite a few people with PV on their homes and many of them whip out their phones to show me the app that monitors the system. Some even remember how to log into it.

 

[electrofelon]

Even in larger C&I projects that are several years old I have found that people don't use the monitoring system. A lot of the time the facilities person does not know that it even exists when I ask about it. When the system was installed one person was given the information for the website to go to and monitor the system. That person leaves and it's not documented or they never pass the information to the person at the company who should be monitoring the system. Once in a while I will find someone who is really into it. Leased systems will have someone monitoring them because that's money.
I still see a few Fat Spaniel systems out there and they are dead. Once an old monitoring company goes under all the monitoring goes with it.
As for residential systems, I have talked to quite a few people with PV on their homes and many of them whip out their phones to show me the app that monitors the system. Some even remember how to log into it.

I got my monitoring app set up after years of having the system. It was cool for a few days, then I didn't care anymore. As long as my electric bill keeps coming in at $17.43, or whatever the monthly meter fee is, I'm happy

 

[jaggedben]

My impression is that attention to monitoring drops off heavily after a year. That is, once people see the seasonal variation start to repeat itself.

 

[pv_n00b]

The value in monitoring is to set up triggers that send an email to the homeowner saying something needs to be looked at. Expecting a homeowner to check the app once a week to find a low-performing module, or even a dead inverter, will not happen. There are still a lot of people who hit their annual true-up only to find out their inverter died 9 months ago. I would say the same goes for most C&I.

 

[jaggedben]

The value in monitoring is to set up triggers that send an email to the homeowner saying something needs to be looked at. Expecting a homeowner to check the app once a week to find a low-performing module, or even a dead inverter, will not happen. There are still a lot of people who hit their annual true-up only to find out their inverter died 9 months ago. I would say the same goes for most C&I.

<thread drift alert>

Yeah, it's actually kind of ridiculous how many companies that provide monitoring miss the point of this and have terrible or even non-existent implementation and support of alerts.

 

[solarken]

Just my two cents, but I am skeptical of the weather swings argument.

Regarding the length/efficiency, my niche is actually ground mount arrays that are quite far from the house. We have done several that are 700-800 ft away. I have ran the numbers multiple times trying to get it to work, but never found it cost-effective to run DC back versus AC. Even tried it with fronius inverters which do 1000 volt strings, and it just doesn't pan out. The main factors are:

1. For DC you would typically be dealing with CU conductors (although aluminum PV wire is available), vs AL for AC.

2. You probably won't be able to get the DC voltage as high as you think unless you get lucky with the way the panel string up and/or make compromises such as skimping on your available mppts.

3. It's somewhat of a hassle pulling seven conductors versus one plexed aluminum set.

The voltage drop/rise issue certainly favors the DC run, but you're really only looking at about a three volt difference and if you are up that high where that 3-volts breaks the camel's back, you've probably got other issues, like a bad utility voltage regulator.

There are other issues with putting inverter at the array. SolarEdge Energy Hub inverters are just as they are named, a Hub to which everything connects. The inverter has terminals for a high voltage DC battery, a Solaredge EV charger direct connection, CT inputs for monitoring import/export, and an ethernet port for monitoring (yes it also has built-in cellular but that is only guaranteed to work for 5 years).

Also, I don't know why you are skeptical that a complicated power electronic device will last longer in a conditioned environment rather than outside where the weather swings from in a range -10 degF to +100 defF year after year. Inverters will fail less with less environmental variability.

And SolarEdge inverters run at a pretty consistent 400 to 420V, depending on model, no luck involved. They are not subject to string and temperature variation like inverters without optimizers. So there will be less voltage drop in DC lines and there will be no risk of voltage rise cutting off production as there could be with long runs in inverter output AC circuit.

It's fine if you prefer putting the inverter at the array, I am just clarifying some advantages to not doing that especially for SolarEdge systems.

 

[solarken]

Going back to the OP, I think it's clear now that under the 2017 NEC rapid shutdown is required as soon as the DC conductors reach the outside of the building?

In that 690.12(B)(1)'s "or" is inclusive, and the conductors are clearly outside the array boundary. So once the DC conductors reach the outside of the building, they fall under the scope of 690.12 ("PV system circuits installed on . . . buildings").

Cheers, Wayne

I think an argument can be made that a dc run from a ground mount array that comes out of a trench up 1.5 feet or so thru an expansion fitting and turns 90 degrees via an LB thru the Rim board into the home, is not "On" the building. It penetrates into the building, but is not on it, like a length of conduit running along the building. Since the code permits forgiveness of 3 feet of conductor that penetrates the building from having to be controlled, it seems to me that that scenario could be viewed as having no controlled conductor requirement as long as the DC conductors terminate in the inverter within 3 feet of penetration. Realistically, no one would get hurt if that tiny length of conductor were still energized from the inverter to the point the conduit entered the trench. But alas, the code is vague, and there are many interpretations.

 

[solarken]

Oh come on. Yes necessarily, especially since it's a DC coupled ESS, meaning both the PV and ESS power the same inverter. Backup means that if power from the grid is lost then the system will keep running from whichever is available, that's the whole point.

Beyond that, he said it was Solaredge, and we know generally how that works. I just don't know what exact equipment he is using and how Solaredge supports an RS switch these days, I haven't kept up.


It's basically all the same. As you know, with Powerwalls and microinverters in backup setup, the service disconnect cannot be the rapid shutdown switch.

I don't think it is necessary, but having an issue with this AHJ right now just submitting the permit app, since he wants PE stamped dwgs, which is way overkill for this residential system. So I am adding the RSD pushbutton to eliminate any doubt. Since there is a backup interface, it has the terminals for the PB switch, so wiring it there. I am an EIT but not PE, but after this delay, I decided to get my PE, hopefully by August.

Thanks everyone for the discussion points on this thread.

 

[wwhitney]

I think an argument can be made that a dc run from a ground mount array that comes out of a trench up 1.5 feet or so thru an expansion fitting and turns 90 degrees via an LB thru the Rim board into the home, is not "On" the building.

That would certainly be "on" the building in my opinion. Whether or not that is true, once the conduit penetrates the building, the circuit is "in" the building and subject to 690.12.

Since the code permits forgiveness of 3 feet of conductor that penetrates the building from having to be controlled,

That is not correct with regards to 2017 NEC 690.12.

The conductor is in the building, so it meets the scope of 690.12. The conductor is outside the array boundary per 690.12(B). So 690.12(B)(1) applies and the voltage is limited to 30V at 30 seconds after rapid shutdown initiation. The "or" in 690.12(B)(1) is inclusive.

Even if you say that 690.12(B)(2)(2) applies (which the 2020 NEC cleared up that it doesn't), that would be in addition to 690.12(B)(1).

Upshot: there is no 3 foot forgiveness of conductor penetrating the building. There is only a stricter standard for conductors that are within the array boundary but also more than 3 feet within the building. I.e. for a roof mounted array, a conductor that penetrates the roof and run underneath the roof sheathing for more than 3 feet, while never less than 1 foot from the array.

Cheers, Wayne

 

[ggunn]

That would certainly be "on" the building in my opinion. Whether or not that is true, once the conduit penetrates the building, the circuit is "in" the building and subject to 690.12.


That is not correct with regards to 2017 NEC 690.12.

The conductor is in the building, so it meets the scope of 690.12. The conductor is outside the array boundary per 690.12(B). So 690.12(B)(1) applies and the voltage is limited to 30V at 30 seconds after rapid shutdown initiation. The "or" in 690.12(B)(1) is inclusive.

Even if you say that 690.12(B)(2)(2) applies (which the 2020 NEC cleared up that it doesn't), that would be in addition to 690.12(B)(1).

Upshot: there is no 3 foot forgiveness of conductor penetrating the building. There is only a stricter standard for conductors that are within the array boundary but also more than 3 feet within the building. I.e. for a roof mounted array, a conductor that penetrates the roof and run underneath the roof sheathing for more than 3 feet, while never less than 1 foot from the array.

Cheers, Wayne

It seems to me that another way to deal with this might be to build a free standing rack for the inverter(s) just outside the building and only run AC conductors into the building.

 

[wwhitney]

It seems to me that another way to deal with this might be to build a free standing rack for the inverter(s) just outside the building and only run AC conductors into the building.

Yes, that would keep the 690.12 conductors out of the main building. The OP specifies a DC coupled ESS, but the ESS DC conductors could travel from the building to the rack. You could even put a little roof on the rack, which would make it a structure and thus building (as it no longer consists of just equipment), and 690.12 has an exception for ground mount arrays and buildings "of which the sole purpose is to house PV system equipment."

Cheers, Wayne

 

[mddorogi]

We've installed a lot of residential single phase SolarEdge systems with DC coupled LG Chem batteries. The local utility does an anti-islanding test at our PV disconnect where they throw the switch and expect the AC voltage at the AC disconnect to drop to zero. And the local inspectors expect that, when the switch is thrown, everything is off, the rooftop PV, and the battery. The SolarEdge inverter has a remote RSD initiation capability. We install a 3-pole disconnect rather than the usual 2-pole and use the third pole for control wires to initiate the RSD at the inverter. Works fine, always passes anti-islanding, and inspectors are fine with it.