Starting system design for EG4 18kpv grid tied w/ net metering + battery setup

[y0bailey]

Forgive my amazing starting drawing, I banged this out in the few minutes before work so it isn't pretty.

I am early into the planning phase of taking my Solar Edge grid tied system into a eg4 18kpv hybrid inverter. Goal being preserve my net metering, but eventually getting a 15-20KWh battery setup to keep my well pump and essentials going when the grid is down. All essential circuits are already on my basement 200A load panel.

Here is my service entrance/meter and two 200A exterior breakers. The right breaker goes into the basement


From that right 200A breaker, a 4/0 x 3, 2/0 G aluminum service entrance cable enters the basement, runs in the basement ceiling, and powers the basement load panel/breaker box. Again, all essential circuits are in this one panel.

I've got the DC/PV stuff calculated and within spec there. I still need to find/purchase a SolarEdge Key to turn off the optimizer protections and make them compatible with my inverter).



But here is when things get hairy. My plan was the cut the original service entrance cable in my basement (after the 200A exterior breaker), run it into a disconnect (please double check the specs on that disconnect to make sure it is safe), then from the disconnect "downsize" the wire to 3/0 copper x3 and 6 AWG copper ground (the maximum size I can fit in the inverter) into the inverter. Out of the inverter I run the same 3/0 x 3 and 6 AWG ground in conduit back up into the basement ceiling, mount a large junction box that can handle these big-wire unions, and then splice it into the remaining original 4/0 x 3 2/0G service cable to finish the run to the basement load breaker box.

I know just enough to be dangerous, and I'm sure I've overlooked 100 issues. I would love any input, or love someone to tell me just to stop and hire a professional (which I won't do and will just cancel the project).

 

[FilterGuy]

The overall structure looks correct.

* Do you know what the service rating is? With 4/0 aluminum, it may have been less than a 200A service. (It depends on the type of insulation on your original 4/0 aluminum wire.) The main breaker is 200A. This breaker should be no larger than your service rating.

* Make sure that any connection to the aluminum wire is rated for aluminum. If it is not rated for aluminum it becomes a significant fire hazard over time. (This includes the splicing union)

* I did not look up the 299A AC disconnect

I am not familiar with the solar edge optimizers. Do they have rapid shutdown capability?

A few things to check for:

WIll you need an outside Rapid Shutdown Initiator?
What are the requirements for accessability of the AC disconnect and the PV disconnect?

 

[y0bailey]

The overall structure looks correct.

* Do you know what the service rating is? With 4/0 aluminum, it may have been less than a 200A service. (It depends on the type of insulation on your original 4/0 aluminum wire.) The main breaker is 200A. This breaker should be no larger than your service rating.

* Make sure that any connection to the aluminum wire is rated for aluminum. If it is not rated for aluminum it becomes a significant fire hazard over time. (This includes the splicing union)

* I did not look up the 299A AC disconnect

I am not familiar with the solar edge optimizers. Do they have rapid shutdown capability?

A few things to check for:

WIll you need an outside Rapid Shutdown Initiator?
What are the requirements for accessability of the AC disconnect and the PV disconnect?

*I will have to dig around to find the service rating on the panel. I will report back in.

*The splices are copper/aluminum rated. I will double check every other other connection point.

*I believe when using the SolarEdge Key to make the Solaredge optimizers compatible with the EG4 inverter I will be removing their built in rapid shutdown capability.


As far as "needing" a rapid shutdown initiator outdoor...I don't know the answer to that. I haven't researched this yet, but seeing as I don't want to burn my family alive and would like to save things in case of fire, I am going to start research here and plan to install one.

I also don't know the requirements for the AC/PV disconnects. I am assuming they are needed outdoors based on the professionally done SolarEdge setup having both. The current plan has the PV disconnect outside, but the AC disconnect will be located in the basement. However, the 200A outdoor panel/utility breaker is "grid side" to the solar setup...so things can be easily cutoff from the exterior of the house. I'm sure there are code requirements here I may not meet...but I am not going to move from this house EVER, so I'm not going to lose a lot of sleep over that aspect. I mostly just care if the choice is UNSAFE for my family.


I hugely appreciate the response. It's nice to know my general plan is sound with a few tweaks here and there required.

 

[y0bailey]

The overall structure looks correct.

* Do you know what the service rating is? With 4/0 aluminum, it may have been less than a 200A service. (It depends on the type of insulation on your original 4/0 aluminum wire.) The main breaker is 200A. This breaker should be no larger than your service rating.

* Make sure that any connection to the aluminum wire is rated for aluminum. If it is not rated for aluminum it becomes a significant fire hazard over time. (This includes the splicing union)

* I did not look up the 299A AC disconnect

I am not familiar with the solar edge optimizers. Do they have rapid shutdown capability?

A few things to check for:

WIll you need an outside Rapid Shutdown Initiator?
What are the requirements for accessability of the AC disconnect and the PV disconnect?

Popped into the basement breaker...it says "this panel rating is the same rating as the main breaker"...so it's 200A, and it's breaker is outside in the picture from my first post.

I don't think that changes anything as far as I can tell!

 

[zanydroid]

Hmm interesting to learn about the Solar Edge key so I googled it

Powering People’s Lives Around the World | SolarEdge

Turn your businesses and homes into a sustainable energy hub with a SolarEdge inverter solution and the SolarEdge energy manager platform.

www.solaredge.com

This implies that RSD is preserved

Presumably if RSD was not required for your original permit they won’t force you to add it now.

RSD is mostly for first responder safety.

I would be concerned about stacking RSD on other MLPE in two ways. One, it may no longer be compatible with the listing. Two, they could block each other from receiving the signal or from getting enough voltage from the panel to operate (WTF will happen if your RSD need 16V from panel to activate but the other device is dropping it to 1V because it thinks it is in charge of RSD). They are most likely never tested in a stacked configuration, since that is super rare and not normal. And it is extremely likely that neither manufacturer will be able to tell you how well it would work

 

[y0bailey]

Hmm interesting to learn about the Solar Edge key so I googled it

Powering People’s Lives Around the World | SolarEdge

Turn your businesses and homes into a sustainable energy hub with a SolarEdge inverter solution and the SolarEdge energy manager platform.

www.solaredge.com

This implies that RSD is preserved

Presumably if RSD was not required for your original permit they won’t force you to add it now.

RSD is mostly for first responder safety.

I would be concerned about stacking RSD on other MLPE in two ways. One, it may no longer be compatible with the listing. Two, they could block each other from receiving the signal or from getting enough voltage from the panel to operate (WTF will happen if your RSD need 16V from panel to activate but the other device is dropping it to 1V because it thinks it is in charge of RSD). They are most likely never tested in a stacked configuration, since that is super rare and not normal. And it is extremely likely that neither manufacturer will be able to tell you how well it would work

So these are more education words for "I don't need a RSD" because my optimizers will have it even if I use the key to unlock them?

 

[zanydroid]

Dunno, a little confused by your phrasing there actually, it doesn't match my mental model of how the optimizers and RSDs work.

MLPE = module level power electronics. Basically any panel level thing you connect to the DC outputs of the solar panels. The way optimizers and RSDs work is, they sit between the solar panel and the string, and can "fully disconnect" the string (more accurately, they drop the voltage down to 1V so that there is some standby power available to bootstrap the system). A solar panel will have something like 30-60VOC, and since the MLPE is direct connected there is no engineering reason it needs to operate at 1V input voltage.

What year did you install your optimizers? What was the NEC in effect? Do you have the original plans / can you request them from installer or city? That often has this type of detail included. (I bet your AHJ is more incentivized to help you, since you pay them tax dollars every year and your installer is probably in a GTFO mode about dealing with an old customer).

You can also short circuit this research by calling someone at SE, they should know the answer given your part number of the SE optimizers and the Key. If you find the right department.

If SE was trying to sell the optimizers after the PANEL LEVEL (key point, there is also ARRAY LEVEL which is one NEC revision earlier IIRC) RSD requirement came in for NEC, then they MUST be compliant with panel level, otherwise they can't sell it in the US (or would be limited to selling to the jurisdictions still on the array level rules, or to people with ground mounts that are exempt. And in the latter case, this would usually be people with bad engineering skills since they should have put the ground mounts away from shade etc that would force SE to be needed). Similarly, if the Key is a new product. It behooves them to design it to be maximally compliant with panel level RSD. Otherwise they hamstrung themselves with the sales they can make in the US/Canada.

 

[y0bailey]

Dunno, a little confused by your phrasing there actually, it doesn't match my mental model of how the optimizers and RSDs work.

MLPE = module level power electronics. Basically any panel level thing you connect to the DC outputs of the solar panels. The way optimizers and RSDs work is, they sit between the solar panel and the string, and can "fully disconnect" the string (more accurately, they drop the voltage down to 1V so that there is some standby power available to bootstrap the system). A solar panel will have something like 30-60VOC, and since the MLPE is direct connected there is no engineering reason it needs to operate at 1V input voltage.

What year did you install your optimizers? What was the NEC in effect? Do you have the original plans / can you request them from installer or city? That often has this type of detail included. (I bet your AHJ is more incentivized to help you, since you pay them tax dollars every year and your installer is probably in a GTFO mode about dealing with an old customer).

You can also short circuit this research by calling someone at SE, they should know the answer given your part number of the SE optimizers and the Key. If you find the right department.

If SE was trying to sell the optimizers after the PANEL LEVEL (key point, there is also ARRAY LEVEL which is one NEC revision earlier IIRC) RSD requirement came in for NEC, then they MUST be compliant with panel level, otherwise they can't sell it in the US (or would be limited to selling to the jurisdictions still on the array level rules, or to people with ground mounts that are exempt. And in the latter case, this would usually be people with bad engineering skills since they should have put the ground mounts away from shade etc that would force SE to be needed). Similarly, if the Key is a new product. It behooves them to design it to be maximally compliant with panel level RSD. Otherwise they hamstrung themselves with the sales they can make in the US/Canada.

Install year was around 2018-2019...somewhere in there.
The optimizers are solar edge P320-5NC4ARS

The spec sheet states:

• Automatic module DC voltage shut-down for installer and firefighter safety. Each optimizer has an internal temperature sensor which detects if it gets over 185 degrees °F - and they shut down, if reached.

I guess another thing to confirm is that the SolarEdge Key even disable safeDC in my optimizers. I think it can as the manual states it will do the pXXXl optmizers?

 

[zanydroid]

NEC 2017 is where RSD came into play... if you shut down your inverter and test the voltage on the DC terminals (WITH A METER RATED TO 600V) you'll have your answer. It would have 1V * number of series panels.

SafeDC sounds like just the same 1V output as SunSpec-style RSD devices output in standby mode, except with a silly name given to it for marketing reasons.

Not sure what you mean by disable SafeDC. Lots of double negatives. The default safe mode of MLPE with RSD capability is to output 1VDC until they receive the activation signal from the transmitter. And then they will automatically drop back down to 1VDC or 0V if they ever lose the signal (IE, the fire melted the inverter, subpanel, transmitter; or someone hit the rapid shutdown switch).

 

[y0bailey]

NEC 2017 is where RSD came into play... if you shut down your inverter and test the voltage on the DC terminals (WITH A METER RATED TO 600V) you'll have your answer. It would have 1V * number of series panels.

SafeDC sounds like just the same 1V output as SunSpec-style RSD devices output in standby mode, except with a silly name given to it for marketing reasons.

Not sure what you mean by disable SafeDC. Lots of double negatives. The default safe mode of MLPE with RSD capability is to output 1VDC until they receive the activation signal from the transmitter. And then they will automatically drop back down to 1VDC or 0V if they ever lose the signal (IE, the fire melted the inverter, subpanel, transmitter; or someone hit the rapid shutdown switch).

In order to have the SolarEdge optimizers work with non-SolarEdge Inverters, the SafeDC has to be disabled.

My plans depend on that being possible on my optimizers, so I can use them with the EG4-18kpv without getting on my roof and swapping optimizers (not gonna happen).

 

[zanydroid]

Can you share your original documentation source that SafeDC has to be disabled? Since to me I cannot unambiguously translate from that English description to the functional behavior in engineering terms (IE, why is it done that way, what is the sequencing for system startup, etc). It doesn't 100% make sense to me.

Yes, I understand what you're trying to do.

FWIW it's actually not that painful to swap MLPE. I just installed panels on my single story roof, 25 degree pitch, and it's much less daunting than I thought. Managed to get the panels up and manipulate the panels solo (install microinverters and PV jumpers), without help. That said, OSHA and company insurance would probably frown on sending out a solo crew to do it.

 

[y0bailey]

Can you share your original documentation source that SafeDC has to be disabled? Since to me I cannot unambiguously translate from that English description to the functional behavior in engineering terms (IE, why is it done that way, what is the sequencing for system startup, etc). It doesn't 100% make sense to me.

Yes, I understand what you're trying to do.

FWIW it's actually not that painful to swap MLPE. I just installed panels on my single story roof, 25 degree pitch, and it's much less daunting than I thought. Managed to get the panels up and manipulate the panels solo (install microinverters and PV jumpers), without help. That said, OSHA and company insurance would probably frown on sending out a solo crew to do it.

https://www.solaredge.com/sites/default/files/se_key_datasheet.pdf

 

[zanydroid]

Busted link, got a mirror?

 

[zanydroid]

Ah I found it

"optimizers power with operate to Inverter SolarEdge-non allowing mechanism SafeDCTM s’optimizer power Disables" as a bullet point on a spec sheet... Low quality info IMO.

I'll only go so far with this, without full installation manual or talking to a support engineer.

 

[zanydroid]

Now, the fact that it says "One-time commissioning" does very strongly imply that it permanently disables the RSD.

So either you need to find a continuously transmitting device to maintain SafeDC

OR

You need to confirm that your existing permit does not have panel level RSD + and your AHJ will allow you to maintain that state with an inverter swap. In principle that makes sense but your AHJ makes the rules.

 

[zanydroid]

What about this

"SolarEdge Safety & Monitoring Interface"

 

[Quattrohead]

What about this

"SolarEdge Safety & Monitoring Interface"

I have Solaredge optimizers that came with my panels, I thought about using the SMI too but you cannot find them in this country.
Why not just AC couple the Solaredge system into the EG4 18k, out to your breaker box and not touch anything else ?

 

[y0bailey]

Now, the fact that it says "One-time commissioning" does very strongly imply that it permanently disables the RSD.

So either you need to find a continuously transmitting device to maintain SafeDC

OR

You need to confirm that your existing permit does not have panel level RSD + and your AHJ will allow you to maintain that state with an inverter swap. In principle that makes sense but your AHJ makes the rules.

The key itself has a button to turn safe DC back on, and the manual has instructions to do so as well... So I think I can re enable it if needed. Makes this a little less frightening so I can fix my mistake.

But I do think I'm losing RSD fully.

Time for RSD research.

 

[y0bailey]

I have Solaredge optimizers that came with my panels, I thought about using the SMI too but you cannot find them in this country.
Why not just AC couple the Solaredge system into the EG4 18k, out to your breaker box and not touch anything else ?

Are you using them with a non-solaredge inverter?

 

[y0bailey]

I have Solaredge optimizers that came with my panels, I thought about using the SMI too but you cannot find them in this country.
Why not just AC couple the Solaredge system into the EG4 18k, out to your breaker box and not touch anything else ?

Sorry I didn't see the second half of your statement.

I don't really want to couple and have another point of failure.... I'm on my third solar edge inverter in the 4-5 years my system has been up and I kinda want the thing off my house.