Rapid Shutdown & more for residential off grid system in FL

[mattcony]

By some small miracle I was granted approval for a 2-string solar setup (4+4) on my residential home in Orlando FL with very little input, engineer drew them after telling them what I wanted & an engineer stamped them and permission was granted. The setup is "off grid" specifically using off the shelf all in one Bluetti portable solar generators for emergency and recreationally use. I was fed-up of having panels over the garden and the risk of them getting damaged was high. Now I have the approval I need to get into some of the finer detail before I even turn a bolt and begin. I'm trying to educate myself further, so I do this right first time and pass inspection.

1st item that comes up is a Rapid shutdown solution - from research I have the choice of IMO Fire Raptor or TIGO. As I'm not connected to the grid, I'm assuming I need a manual push button by my main panel outside for EMS BUT how should the power source keeping it live be managed. Should my portable unit power it keeping it 100% isolated or can it be powered by the Grid AC. (Assuming EMS would hit the emergency stop & turn my main supply panel OFF from the outside.

Disconnect / Combiner box’s – This must be external also ? does this have to be outside close to the RSD button or can it be inside my garage where the bluetti will be positioned

I’ll leave it at that for now and work on these 2 key items, thanks for any help !



This is my diagram from the plan set- essentially is this diagram twice over for each string.

 

[x98myers7]

RSD can be powered from grid or directly from inverter. I would power from the bluetti, because if you don't, and the grid goes down... solar goes down. alternative is to consider this as a "critical load" (as I noted below) and set up a transfer switch to allow you to change the keep-alive signal from the bluetti or the grid.

if you go with IMO FireRaptor, the modules need a 24v signal, which you can provide using a 120v-24v transformer (just like the one for your doorbell).

I would suggest you install a 120v AC subpanel and connect the bluetti to it via a TT30R junction box with a 30amp single pole breaker as the input. then, run your critical loads circuits out to a manual transfer switch on your home main panel. you always want to isolate the main panel for grid down so you can never backfeed. I like reliant controls transfer switches. they're easy to wire and instructions are clear.

also, don't forget to install a ground-fault DC breaker as required for residential.

you need to check with your local inspector on their preference for RSD and PV disconnect switches. They have final say.

good luck figuring out an off-grid arc-fault solution. if you do, let me (end everyone here) know.

ask your inspector about what equipment is acceptable for all of the above. "listed" means different things to different inspectors. some will say it all has to be UL. others don't care.

 

[ncsolarelectric]

You said you had an approved, engineer-stamped plan. All that information should be on the plans if it was properly engineered. If they approved the plans without that information on them, then I would talk to the inspector about it and see what he is expecting to see. Is your area still on NEC 2014?

RSD requires a single point of control. It needs to disconnect the PV wires at "both" ends because the Bluetti may still have voltage on those wires for more than 10 seconds. Therefore, the Disconnect Combiner should also control the Tigo/FireRaptor devices so that it disconnects the wires at both ends. Otherwise, it probably won't be compliant.

Honestly, Idk. I've never tested the voltage at the PV terminals of that inverter when operating without solar panels connected, or how long it takes to discharge after the solar panels are removed. Just remember that the wires receive voltage from both ends, not only from the solar panels. This is one of the main issues with putting an off-grid system on the roof. Most of the inverters are not designed to meet NEC requirements even if they meet UL 1741.

 

[kendive]

You have to get permission to setup a bluetti solar generator? LOL never heard of that. I would be just doing it myself and not tell anyone.

 

[ncsolarelectric]

You have to get permission to setup a bluetti solar generator? LOL never heard of that. I would be just doing it myself and not tell anyone.

No, but a permit is required to put solar panels on a building.

 

[mattcony]

You said you had an approved, engineer-stamped plan. All that information should be on the plans if it was properly engineered. If they approved the plans without that information on them, then I would talk to the inspector about it and see what he is expecting to see. Is your area still on NEC 2014?

Honestly, Idk. I've never tested the voltage at the PV terminals of that inverter when operating without solar panels connected, or how long it takes to discharge after the solar panels are removed. Just remember that the wires receive voltage from both ends, not only from the solar panels. This is one of the main issues with putting an off-grid system on the roof. Most of the inverters are not designed to meet NEC requirements even if they meet UL 1741.

Thanks Todd good to hear from a different prospective, Florida is on NEC 2017 to the best of my knowledge. I just setup the Bluetti with a panel to test the PV input remaining high. It was sitting at 40v for 3 seconds after disconnect then dropped to 75mv and continued to fall.

RSD requires a single point of control. It needs to disconnect the PV wires at "both" ends because the Bluetti may still have voltage on those wires for more than 10 seconds. Therefore, the Disconnect Combiner should also control the Tigo/FireRaptor devices so that it disconnects the wires at both ends. Otherwise, it probably won't be compliant.

This would dictate that the combiner / disconnect box is outside for EMS to serve as an "all in one" and a remote button would not be required? But also can be NO more than 10ft from the Bluetti unit either ?

 

[x98myers7]

This would dictate that the combiner / disconnect box is outside for EMS to serve as an "all in one" and a remote button would not be required? But also can be NO more than 10ft from the Bluetti unit either ?

I have the same question on physical location.

so far the only physical location requirements I've found are "readily accessible"

 

[ncsolarelectric]

Thanks Todd good to hear from a different prospective, Florida is on NEC 2017 to the best of my knowledge. I just setup the Bluetti with a panel to test the PV input remaining high. It was sitting at 40v for 3 seconds after disconnect then dropped to 75mv and continued to fall.



This would dictate that the combiner / disconnect box is outside for EMS to serve as an "all in one" and a remote button would not be required? But also can be NO more than 10ft from the Bluetti unit either ?

I'm impressed that the voltage dropped that quickly. Was the AC plugged in? Was it running on battery at the time? That's when those capacitors may be getting filled from other sources and not discharged. It's great if it works as you say!

If the wires discharge to < 30V in 10 seconds without disconnecting from the inverter, you're good. All you need is the Tigo and 24V source.

 

[mattcony]

This project fell behind quite a lot due to my panels on my permit no longer being available so had to go through the permit amendment process but ready to start !


I'm looking for advice on where to add my ground level DC disconnect, is there a preference or stipulation if it should be before the combiner (A) or after the combiner (B). Aware amp rating will change after the combiner and must be still in spec or is it at installed discretion.





Also any suggestions for a DC 2string combiner that will pass inspection please (so many DIY versions). Midnite Solar 15A 2-String Combiner, Fused, MNTPW2.

https://www.greentechrenewables.com/product/midnite-solar-15a-2-string-combiner-fused-mntpw2

Do the WATTS24/7 combiner boxes pass inspection or mostly for DIY, they look well made?

https://watts247.com/product/solar-panel-combiner-box-4-circuits-to-2/


Thanks

 

[ncsolarelectric]

If you only have 2 identical strings, a fused combiner box is not required. Fuses on the strings are not required to combine them. You can use Y-connectors. You can use wire nuts (WAGOs) in the switch box to combine them after the switch. You only need a fused or circuit breaker between the combined strings and the inverter, if there is not one built in.
I'm still not confident that when the Bluetti is plugged in and the panels are plugged in, and you turn it off, that the panels will comply with RSD. You can avoid the need for ArcFault sensors by using metallic conduit inside the building.

 

[mattcony]

If you only have 2 identical strings, a fused combiner box is not required. Fuses on the strings are not required to combine them. You can use Y-connectors. You can use wire nuts (WAGOs) in the switch box to combine them after the switch. You only need a fused or circuit breaker between the combined strings and the inverter, if there is not one built in.
I'm still not confident that when the Bluetti is plugged in and the panels are plugged in, and you turn it off, that the panels will comply with RSD. You can avoid the need for ArcFault sensors by using metallic conduit inside the building.

More Great info thanks ! I'll be sure to continue the EMT inside the building (garage) for all my conduit ! - Is there any part of the code you can point me to for reference on this incase I get challenged?

@x98myers7 - Earlier you mentioned the ground-fault DC breaker and I stumbled on your "build" posts last night which were very informative and opened another rabbit hole for me to go down! I looked at the MNDC-GFP63, MidNite Solar you used in your application, reviewing the wiring this requires a direct connection to the battery DC negative which I don't have as its a the AC200 is a sealed unit. Are there any other setups / options you can suggest may work for my use case?

Also I read in your build that the grounding must be connected via the main breaker panel and not to the ground rod directly - is that still the case?

updated the drawing with a few changes that were mentioned:

​

Thanks All !

 

[mattcony]

I took a 2nd look at the install instructions for the midnight solar GFP63 unit and at the bottom of the page there is a note that says#

For Battery-less DC-GFP installations connect the white wire to PV negative rather than Battery negative

Could this be applied to my situation, would this be OK. It would look something like this;

 

[mattcony]

Thought id come back and close this out - Inspection day today by the City. All passed !

The guy was nice didn’t want talk much until he started asking the questions, he is used to seeing grid tied non battery systems all day long. So once I explained to him a little more he was pretty cool about the whole thing. Had a good look at everything inside and out and once he understood the portable unit concept a little better, he gave me the all OK.

The setup has been fully functioning for around 6 weeks now with no issues, averaging around 5.6kw per day between household consumption and battery recharging. Panels will produce way more that I can bank each day. I originally started out with x2 AC200's but decided to sell one halfway through the build and move to an AC300 & 1 battery pack, this has been pretty awesome so far for what it is and performs very well but I’ve quickly realized I need &want more. Although expandable I think I will part ways with the AC300 and opt for a more permanent setup now like an EG4

Thanks for everyone’s help and comments along the way !

 

[ChrisG]

Brilliant, So now you can simply replace everything behind the PV at will? Never thought about getting a ‘portable system’ approved like that, specifically with rapid shutdown.

 

[MrM1]

Whats code is fl on now, still 2017? did you have to have panel level or array level shut down

 

[mattcony]

Whats code is fl on now, still 2017? did you have to have panel level or array level shut down

2017 - Yes

 

[zanydroid]

Looks awesome!

A little concerned though about others copying this and running afoul of AHJ potentially interpreting arc fault detection code a different way.

Is the array designed to be unambiguously code compliant for arc fault?

EDIT: this thread gets into the complexity and the comma disaster prior to NEC2023

Change in 2023 NEC code around PV arc fault.

I was working on a design and came across an 'interesting' :( change around PV arc fault protection in the 2023 NEC. In the 2020 code, you could have PV circuits going to your house without arc fault protection if the circuits were in metallic raceways (Conduits), In the 2023 code they seem...

diysolarforum.com

 

[SniperX]

Thought id come back and close this out - Inspection day today by the City. All passed !

The guy was nice didn’t want talk much until he started asking the questions, he is used to seeing grid tied non battery systems all day long. So once I explained to him a little more he was pretty cool about the whole thing. Had a good look at everything inside and out and once he understood the portable unit concept a little better, he gave me the all OK.

The setup has been fully functioning for around 6 weeks now with no issues, averaging around 5.6kw per day between household consumption and battery recharging. Panels will produce way more that I can bank each day. I originally started out with x2 AC200's but decided to sell one halfway through the build and move to an AC300 & 1 battery pack, this has been pretty awesome so far for what it is and performs very well but I’ve quickly realized I need &want more. Although expandable I think I will part ways with the AC300 and opt for a more permanent setup now like an EG4

Thanks for everyone’s help and comments along the way !

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Great job! The pictures are great. Glad it worked out for you.