Solar/Battery/Grid system based on EG4 18KPV Powerpro

[mciholas]

The purpose of the disconnect on the outside of the house is so fire fighters can shut off all the power going to a house in case of fire.

But it doesn't actually do that. Pulling the inverter grid disconnect leaves the critical panel running off the inverter batteries, leaves the batteries energized, leaves the PV array attached an operating. As far as the inverter is concerned, it looks like a grid failure, nothing more, so it takes over powering the critical panel. Removal of the meter shuts down AC back feed, so the disconnect doesn't need to do that, either. It feels like some sort of residual requirement that doesn't actually do the job intended here.

The 18KPV manual makes it clear the RSD shuts off AC power generation by the inverter, shuts down the batteries, and makes the PV array voltage under 30 volts.

On that last note, how does it make the PV array voltage under 30 volts? The only thing I think it could do it short across the leads. Is that what it does? But then, if someone uses the disconnect for the PV DC leads, the arrays are now back to their open circuit voltage. Or does the PV DC disconnect also short the leads?

 

[BKY2003]

When I got inspected by the power company, the first thing they looked for was that disconnect.

 

[mciholas]

Can you explain the wiring of the critical loads breaker. (70A). Will the critical load panel have access to the grid power at all times? If not when the solar and battery are not available the critical loads want have any power.

The critical panel can be powered in two ways. The main breaker in the critical panel (say it is 100 amps) runs to a breaker in the main panel. If both those are on, the panel is powered exclusively from the grid. Additionally, there is a back feed breaker in the critical panel that goes to the 18KPV load terminals. If that breaker is on, the critical panel is powered through the 18KPV which can be inverter generated power or grid power per the configuration of the 18KPV. An interlock device prevents both the critical panel main breaker and the inverter back feed breaker from being on at the same time.

In normal use, the critical panel main breaker will be off, the inverter back feed breaker will be on, and the 18KPV controls the critical panel power, be it inverter or grid output.

If the interlock device is problematic for code compliance (it does seem to be widely used for generator setups), then I can remove the back feed breaker and have the 18KPV power the main breaker of the critical panel. This leaves me without a bypass option in case the 18KPV has a fault, but if that is what it takes to get the system approved, then that is what I will do. This would match diagram 4.1 in the 18KPV manual.

 

[Mr onetwo]

Then you definitely want the 18Kpv. The interactive disconnect may be built in from looking at the manual.

 

[mciholas]

When I got inspected by the power company, the first thing they looked for was that disconnect.

It is easy enough to provide, simply run the inverter grid connection to a disconnect switch on the outside of the building. I just find it misleading to suggest pulling that disconnect actually makes anything safer than pulling the meter. It doesn't.

From what I can tell, to depower the house, they will do FOUR things:

1. Pull the meter (like a house without PV). This will shutdown the main panel and stop inverter grid back feed. The critical panel will remain powered, batteries hot, PV hot.

2. Pull the inverter grid feed. This results in no change in power state in the house, none at all. It feels like a useless thing just to check a box on the inspection.

3. Hit the rapid shutdown button. This stops the inverter AC output, shuts off the batteries, reduces PV array to safe voltages.

4. Pull the PV DC disconnect. Not sure what this does. If it open circuits the PV leads, they are back to hot voltages if there is sunlight.

Does that capture the event?

Feels like #2 is useless, and #4 might actually make things worse.

Exactly how does RSD make the PV array voltages low?

 

[BKY2003]

Where are you putting the CT then. Mine feeds and draws from the grid port.

 

[mciholas]

NEC code 690.12 deals with the RSD requirements.

What code section deals with the inverter disconnect?

 

[mciholas]

Where are you putting the CT then. Mine feeds and draws from the grid port.

CT be on the main panel feed from the meter. Physically, they would be clamped onto the wires in the main panel just before the main panel 200 amp breaker.

This location means a zero export setting would still power heavy loads in the main panel to the extent the inverter has power to do so.

I don't think CT location affects the safety/disconnect question, but I could be wrong.

 

[Mr onetwo]

get the "pulling the meter" thing out of your head.Not going to happen....that is why a disconnect between grid and main panel is required.The RSD switch is also reqired outside. Shutdown is thru the electronics in the inverter,batteries and TIGO's.

 

[mciholas]

Then you definitely want the 18Kpv. The interactive disconnect may be built in from looking at the manual.

It kind of looked like the RSD did everything the code wanted. It shut down the inverter AC generation, it shut off the batteries, it made the PV leads safe. What else is there to do?

 

[Mr onetwo]

https://support.tigoenergy.com/hc/en-us/articles/360034793973-Design-Essentials-for-Rapid-Shutdown-using-TS4-A-F-and-TS4-A-2F

 

[mciholas]

get the "pulling the meter" thing out of your head.Not going to happen....that is why a disconnect between grid and main panel is required.

The house as it stands now doesn't have a disconnect between meter and main panel. All the houses are that way in this development.

Diagram 4.1 in the 18KPV manual doesn't show any disconnect between meter and main panel.

My understanding is that the standard first responder action is a meter pull since that did a disconnect.

Are all these existing houses not code compliant? Seems odd if true.

 

[mciholas]

https://support.tigoenergy.com/hc/en-us/articles/360034793973-Design-Essentials-for-Rapid-Shutdown-using-TS4-A-F-and-TS4-A-2F

Very helpful.

There is another device on the panels that stays energized when receiving a signal. RSD stops that signal, a timeout occurs, the connection is opened at the array. The array wiring is still hot, but not the feed from it to the inverter.

I was previously unaware of this architecture. Does this replace the manual PV DC disconnect or does that need to exist as well?

This doesn't seem to be mentioned in the 18KPV manual.

 

[Mr onetwo]

The manual disconnect remains I believe. I am not fully up to speed on the 18Kpv since I own a 6000XP.There is a transmitter involved with the TIGO system. https://diysolarforum.com/threads/rapid-shutdown-rsd-on-the-eg4-18kpv.67031/

 

[mciholas]

The manual disconnect remains I believe. I am not fully up to speed on the 18Kpv since I own a 6000XP.There is a transmitter involved with the TIGO system. https://diysolarforum.com/threads/rapid-shutdown-rsd-on-the-eg4-18kpv.67031/

Do I need this Tigo system? The 18KPV has its own MPPT units, so I don't need PV optimizers. It looks like added complexity and parts for what could be a simple disconnect.

If the PV feed lines are okay to be energized from panel to manual PV DC disconnect, then the manual disconnect is good enough.

If the PV line have to be disconnected at the panel array boundary, then a low voltage contactor energized by the RSD button should be sufficient, it just drops when RSD is pressed. I hate to waste the power of the contactor relay, but that is the simplest way to do it. The contactor would be at the array boundary and be 3 pole (3 strings of PV panels).

How about a pull chain that manually moves a disconnect on the roof? Pull it to shut off the array. You go back on the roof (or use a pole) to turn it back on again. That involves no relay.

The edge of the array is about 2 ft from the roof edge where the supply conduit goes to the wall where the disconnect would be. It would be less than 10 ft from array edge to disconnect by wire run. Close enough? 2014 code seems to allow for 10 ft, 2017 code changed this to 1 ft. For me, this change matters since the array is so close to the disconnect I can meet the 10 ft requirement, but not the 1 ft requirement with a wall mount manual disconnect.

2017 NEC 690.12 Rapid Shutdown – Important Changes

Learn more about the important changes to the 2017 NEC 690.12 Rapid Shutdown code.

www.purepower.com

I'll need to see what AHJ in my area is using. How would I find out that for Sarasota, FL?

 

[Mr onetwo]

Call your town office

 

[Mr onetwo]

https://www.nfpa.org/news-blogs-and-articles/blogs/2022/01/06/considerations-for-single-family-residential-electrical-services-based-on-the-2020-nec?l=98

 

[BKY2003]

I am trying to learn, so this might be a stupid question. I thought these two situations contradicted each other? 1. "I do want net metering capability. Or more precisely, I do want to export power if there is excess." 2."zero export setting" its one or the other is it not?

 

[Mr onetwo]

I think so

 

[DIYrich]

I am trying to learn, so this might be a stupid question. I thought these two situations contradicted each other? 1. "I do want net metering capability. Or more precisely, I do want to export power if there is excess." 2."zero export setting" its one or the other is it not?

It is more "net metering doesn't do you any good if you are zero exporting."