Adding Schneider XW Pro

[fafrd]

I ordered the Tigo RSD and dual (2 panel) boxes to mount on the panels.

I don't think the Midnight has any way to interface with the Tigo RSD and that doesn't appear to be required. I screwed up and ordered parts before getting my permits approved, so I'm rushing to get my permit package together this weekend.

I believe midnight charge controllers include a dry contact relay. There might be settings to open the relay in case of an arc fault or ground fault. I haven't looked into this, but in theory it would work if:
I am remembering correctly and it is a dry contact.
And
If midnight has the option to connect the aux output to an arc fault or ground fault.

If I were to install RSD modules on my DC panels, it would be purely to protect firemen. That’s simple because you just power the heartbeat transmitter with grid power so that if the grid goes down or the main breaker trips, DC panels are disconnected.

If you want backup power, it’s a bit more complicated but not much. You need to power the heartbeat monitor from the UPS output but only through a disconnect switch accessible near the main breaker (for the firemen to disconnect if needed).

What is the failure more you are concerned about and thinking RSDs can protect against?

 

[400bird]

What is the failure more you are concerned about and thinking RSDs can protect against?

Passing inspection. Hence my comments about integrating arc fault and RSD not being required. I'm not sure that is correct, but unless I'm told otherwise I'll find out for the city next week.

 

[fafrd]

Passing inspection. Hence my comments about integrating arc fault and RSD not being required. I'm not sure that is correct, but unless I'm told otherwise I'll find out for the city next week.

Hope you don’t mind my horning into your thread to educate myself.

I assumed my SCC (Epever) and breakers provide all the protection I need against arc faults or ground faults - doesn’t your Midnight Solar SCC detect those fault conditions and enter not a fault mode that must be cleared before drawing power again?

I’d like to understand the fault condition your concerned about and the reasons your AGJ does not believe a Midnight Solar SCC does not provide required protection (in case my Epever SCC suffers from the same deficiency).

 

[fafrd]

Passing inspection. Hence my comments about integrating arc fault and RSD not being required. I'm not sure that is correct, but unless I'm told otherwise I'll find out for the city next week.

Motivated by this discussion, I did a little googling and found this sobering article: https://www.acsolarwarehouse.com/news/solar-fires-dc-arc-faults-on-solar-systems/

From my quick perusal, this claims there are only 2 ways to protect against arc faults:

-low string voltage (<80VDC strings)

-use of Microinverters

They claim that even use of RSDs will not protect against all arc faults but it looks to me as though they are speaking about string-level RSDs rather than module-level RSDs.

My grid-tied array is Microinverter-based and my small DC-coupled array is 1S meaning <50VDC, so appears I’m OK.

But I’ve been mulling about eventually switching to high voltage swings and a high voltage battery, and this has certainly made me realize that not all DC voltages carry equivalent risk…

 

[400bird]

Hope you don’t mind my jumping into your thread to educate myself.

I assumed my SCC (Epever) and breakers provide all the protection I need against arc faults or ground faults -

Highly unlikely. Arc fault detection is limited to very few (typically high end) charge controllers. More have ground fault detection, but it's not a common feature.

You should look it up if you are concerned. There are UL listings related to making the charge controller safe and able to pass inspection.
I doubt that EPever has either ground fault, arc fault, or RSD integrated.

doesn’t your Midnight Solar SCC detect those fault conditions and enter not a fault mode that must be cleared before drawing power again?’ Id like to understand the fault condition your concerned about and the reasons your AGJ does not believe a Midnight Solar SCC does not provide required protection (in case my Epever SCC suffers from the same deficiency).

There are two separate code requirements of concern here for roof mounted PV.

Remote shut down is about fireman safety. There needs to be a switch accessable to the fireman that will get the voltage down to a safe level real quick. This is not something the charge controller does. It can't stop voltage from existing on the roof and between/under the panels.

Arc fault detection. This detects arc, typically due to failed MC4 connections or wiring damage. Arcs cause fires. Series arcs happen when current flows, current flow can be stopped by the charge controller. Hence the built in arc fault detection.

 

[Hedges]

I would seem that Arc Fault tripping RSD would serve to stop parallel fault.
(but inserting RSD boxes gives you ten times as many opportunities to have arc faults due to interspecies mating of connectors.)

 

[fafrd]

Highly unlikely. Arc fault detection is limited to very few (typically high end) charge controllers. More have ground fault detection, but it's not a common feature.

You should look it up if you are concerned. There are UL listings related to making the charge controller safe and able to pass inspection.
I doubt that EPever has either ground fault, arc fault, or RSD integrated.

I'm sure you are correct.

But here is the quote from that article I linked to:

'DC arc faults only occur on string inverter systems that have unprotected DC voltage circuits above approximately 80 volts DC.

DC arc faults do not occur on solar systems that use microinverters and some systems that use DC optimisers that reduce the DC voltage to safe levels in the event of a fault.'

I've got a 1S3P string whose worst-case Voc is under 50V, o this suggests I do not need to be concerned about arc faults on my ow-voltage array - would you agree?

There are two separate code requirements of concern here for roof mounted PV.

Remote shut down is about fireman safety. There needs to be a switch accessable to the fireman that will get the voltage down to a safe level real quick. This is not something the charge controller does. It can't stop voltage from existing on the roof and between/under the panels.

Arc fault detection. This detects arc, typically due to failed MC4 connections or wiring damage. Arcs cause fires. Series arcs happen when current flows, current flow can be stopped by the charge controller. Hence the built in arc fault detection.

RSD for protection of firemen I understand and have no questions about. It's potential safety issue with arc faults and/or ground faults I am concerned about. With a 1S array under 50V and a 24V battery, do you think there are any significant safety concerns with arc faults and/or ground faults that I need to educate myself on?

Thanks.

 

[fafrd]

I would seem that Arc Fault tripping RSD would serve to stop parallel fault.
(but inserting RSD boxes gives you ten times as many opportunities to have arc faults due to interspecies mating of connectors.)

Do you agree with the claim in that article that keeping DC voltages under 80VDC is one way to avoid any concern with arc faults?

 

[400bird]

I'm sure you are correct.

But here is the quote from that article I linked to:

'DC arc faults only occur on string inverter systems that have unprotected DC voltage circuits above approximately 80 volts DC.

DC arc faults do not occur on solar systems that use microinverters and some systems that use DC optimisers that reduce the DC voltage to safe levels in the event of a fault.'

That article feels like equal parts marketing and scare tactics with some repeating of our NEC standards.

I've got a 1S3P string whose worst-case Voc is under 50V, o this suggests I do not need to be concerned about arc faults on my ow-voltage array - would you agree?

RSD for protection of firemen I understand and have no questions about. It's potential safety issue with arc faults and/or ground faults I am concerned about. With a 1S array under 50V and a 24V battery, do you think there are any significant safety concerns with arc faults and/or ground faults that I need to educate myself on?

Thanks.

You could try it and find out. Do like the arc fault videos and see how big of an arc you can build.

 

[400bird]

I would seem that Arc Fault tripping RSD would serve to stop parallel fault.

Yeah, that's my thought of I can make it work the the purchased equipment and no downsides, I'll do it.

(but inserting RSD boxes gives you ten times as many opportunities to have arc faults due to interspecies mating of connectors.)

Right?! It's more than double the number of connections and I end up mating different brands more often. With a string, all the series connections between panels will be the same brand, your only possible brand change happens at each end of the string for the home run.

Now I have a brand change from the home run to the RSD box and from the RSD box to each panel.

In my 2s string. I would have 3 MC4 connectors.
Once the RSD boxes are added I've got 6. It would be 8 if I used individual RSD boxes (not the dual)

 

[Hedges]

Do you agree with the claim in that article that keeping DC voltages under 80VDC is one way to avoid any concern with arc faults?

Never say never, but it should reduce it.

 

[GXMnow]

RSD is for the safety of firemen. I do want to have that functional. I was hoping the Midnite Solar charge controller produced the keep alive signal, but it seems that it does not. If I go the Tigo route, I would power the keep alive transmitter from one of the breakers in my Enphase solar combiner. That way, the one disconnect for the Enphase will also shut off the DC panels. IT would be great to also have an ARC fault trip off the Tigo RSD boxes. I looked at the latest online manual for the Midnite Solar Classic and it does have a function where an array ground fault can trip the aux relay, but no mention of Arc Fault in the aux relay section.

Midnite does offer their Modbus Map, and there is a location 0x00040000 "Arc Fault Occurred If Set". I could have my PLC monitor that and use one of the relay outputs to also cut power to the RSD keep alive transmitter. Location 0x00010000 sets if there is a ground fault. With the length of the address, I think these are bits in a 32 bit register.

Here is the link to the online PDF

https://www.midnitesolar.com/pdfs/classic_register_map_Rev-C5-December-8-2013.pdf

It does appear to be from 2013.

The more normal addresses look like this
4119 Watts
4121 PV input current

I can't find simple PV volts or Battery Volts. IT has peak reach, total KWH per day. The layout is odd.

 

[400bird]

4115 and 4116 look like 1 second average battery and PV voltage to me.
The modbus map was another plus for the Midnight, it should integrate well considering I'm already using modbus.

 

[ChrisG]

I thought the Schneider SCC can detect both arch and ground faults and integrate with the Schneider RSD solution that then is integrated with Tigo. I may be talking nonsense but I believe that is what I read a month ago on the solution.

 

[400bird]

I thought the Schneider SCC can detect both arch and ground faults and integrate with the Schneider RSD solution that then is integrated with Tigo. I may be talking nonsense but I believe that is what I read a month ago on the solution.

The charge controller doesn't have that integration. It's in a separate module, MPPT Disconnect RS. That alone retails in the $700 range.

MPPT Disconnect RS

El MPPT Disconnect RS es un accesorio para los controladores de carga Conext™ MPPT, que proporciona un cumplimiento simplificado del NEC 2017.

solar.se.com

 

[Shimmy]

RSD is for the safety of firemen.

True, but the ability to drop the module voltage is also useful for arc fault protection, hence the value of integrating ground fault and arc fault into the RSD. I just think it is silly that the charge controller can't integrate that functionality for much less than the $700 Schneider charges for the MPPT-RSD.

 

[pvdude]

Preparing and collecting components for Winter 22-23 projects!
Ordered the Conext MPPT 100 600: 6kW Solar PV Charge Controller to run the new PV strings.

Looked at the Q.PEAK DUO XL-G10.3 / BFG 480 watt, but don't have room for them on the shop roof. (87" - too long to fit under the existing)

Plan "B": collecting quotes for 16 of these, as they are 75" long, and thus will overhang the roof edge only 2"
The local Rexel.com has them, a 20 mile drive.

Also replacing the 17 year old AO Smith electric water heater (5kw load) with a
"Heat pump" water heater.
The ancient AO Smith still works perfectly, but "time and technology march on"

 

[mnd]

True, but the ability to drop the module voltage is also useful for arc fault protection, hence the value of integrating ground fault and arc fault into the RSD. I just think it is silly that the charge controller can't integrate that functionality for much less than the $700 Schneider charges for the MPPT-RSD.

I was a bit sticker shocked at the RSD but after installing mine and having a look inside there is a bunch of stuff going on and it would be difficult to duplicate all the functionality and level of integration at the price point.

My only problem with the RSD is that I can't seem to assign a unique Xanbus ID to mine, but both show up just fine in Insight.

 

[ChrisG]

I was a bit sticker shocked at the RSD but after installing mine and having a look inside there is a bunch of stuff going on and it would be difficult to duplicate all the functionality and level of integration at the price point.

My only problem with the RSD is that I can't seem to assign a unique Xanbus ID to mine, but both show up just fine in Insight.

So this is awesome. Confirmation that the RSD actually works well for ground/arch. Quick question, with remote switch/button this will shutdown both the panels and inverter?

 

[mnd]

So this is awesome. Confirmation that the RSD actually works well for ground/arch. Quick question, with remote switch/button this will shutdown both the panels and inverter?

The remote initiator shuts down everything. The local disconnect just breaks connection to the PV.

 

[400bird]

I ran into my first stumble working on the permit last night.
The Tigo RSD modules have a 500 watt limit.
I'll be well under both the voltage and current limits. But they list the 500 watt limit without any clarification (STC, NTC...)
My panels are 480 watt STC, for the front side. With the rear theat pushes them over 500.

I started looking at other options. AP systems does offer RSD but, they are few and far between. I can't find a vendor with both the panel electronics and transmitter in stock and I haven't seen any feedback on their use at all.

I just remembered Arizona Wind and Sun. It appears they list the components,m and make it look like they're in stock.

 

[Hedges]

The actual limit of such a device is likely not watts, rather Volts, Amps, and some complicated equation related to voltage conversion taking place inside it. Possibly the 500 watt limit is valid at a particular Vmp. If it was an optimizer, it would have many more operating points. If just an RSD, it either delivers near-zero volts in shutdown (SolarEdge outputs 1V per panel), or it delivers whatever voltage and current the panel produces.

As far as permits, any review would look at 480W spec.

Here's a 1-channel 700W Tigo:

Tigo TS4-A-F

The TS4-A-F enables cost effective rapid shutdown functionality in a 1 module to 1 TS4 configuration. The TS4-A-F is both IEC and UL certified for global acceptance. The TS4-A-F is UL PV Rapid Shutdown System (PVRSS) certified with hundreds of inverters to comply with NEC 2014, 2017, and 2020...

www.tigoenergy.com

https://assets-global.website-files.com/5fad551d7419c7a0e9e4aba4/631bb8c38d31f53701ce1335_TS4-A-F%20(700W)%20(15A%20and%2025A)%20(Fire%20Safety%20Add-on)%20Datasheet%20EN.pdf

(same current specs as the following?


This one says 2 channel 500W each, but that's at 15A. Allows 700W each with 20A Imp/ 25A Isc.
Unless your panels are high current, probably falls under the 500W limit.

TS4-A-2F, Tigo's newest rapid shutdown solution for commercial rooftops

www.tigoenergy.com

https://assets-global.website-files.com/5fad551d7419c7a0e9e4aba4/631a8861dec2553614e31baf_TS4-A-2F%20(700W)%20(15A%20and%2025A)%20(ire%20Safety%20Add-on%20for%202%20Modules)%20Datasheet%20EN.pdf

500W at 15A Imp = 33.3V Vmp.
700W at 20A Imp = 35V Vmp

Up to 80 Voc allowed.
They seem to be saying more Imp current is allowed, up to 20A, but not more Vmp. Wonder why, since Voc ought to be the limit.
Does it really accept 500W at 7.5A, 66.6V? But not 600W at that voltage?

 

[400bird]

Interesting, my concern was not about the possible failure. After all the 480 watt panel is more likely to produce 400 watts that 500 in actual use.

I am concerned about not passing inspection/getting the permits approved. In my searching I didn't find the 700 watt option. I'll start searching to see if it is commercially available.

 

[Hedges]

For both the models I linked, it was just a different operating point of same RSD box. For higher current PV panel.
Possibly two (smaller) panels paralleled would work for that; not sure the latest RSD rules limit watts just volts.
But your large panels, 2 paralleled, would be way over watts limit of this RSD model.

I think inspection and permits will depend on rated watts of panel. Which is based on front side, not backside.

 

[Shimmy]

They seem to be saying more Imp current is allowed, up to 20A, but not more Vmp. Wonder why, since Voc ought to be the limit.

Aren't they essentially resistors acting as a voltage divider that shunt the panel? That would limit the maximum input voltage to ensure code-compliant output voltage.