Solar, Subpanels and Breakers

[spacemancw]

I have 2 questions, about my current set up and future setup.

1.)
I have 28 x 305W solar panels going into a SolarEdge 7600H grid-tied inverter.
The Inverter comes into the main panel on a 40a breaker, which sits in the very bottom slot of the busbar.
I also have sub-panel, ( HOM1224L125PC rated 125a ) that comes off the main panel. I have a 2-pole 100a breaker in the main panel feeding that sub-panel, over 3AWG wire.
My first question is, does the position of that 100a breaker in the main, matter?
Currently from the top down I have :
200a main breaker,
30a (incoming gas generator, in off position with interlock switch)
50a to barn and pool equipment
100a to sub-panel
a few more breakers
etc
etc
lastly, the 40a Solar.

I was wondering if the sub-panel should be further down, or right above the solar breaker.

2.)
My next question would render the first moot, if I go this way.
I am considering getting battery backup for the solar and doing AC coupling.
So the SolarEdge inverter would come into the sub-panel .. or in this case we'll call it a critical loads panel.
As I said that panel is rated 125a.
Then from the critical loads panel to a new hybrid inverter (EG12kpv), and then from the new inverter to the main panel.
And then batteries hanging off the EG12k.

So that new hybrid inverter would enter the main panel on a 40a breaker (8 AWG I think) because the 120% rule would still apply to the main breaker.
My question is can I feed the SolarEdge into the Critical loads panel on a 40a breaker?

28 x 305W Solar Panels > SE 7600H > 40a breaker > Critical Loads Panel (Rated 125amps) > EG12k > 40a breaker > Main Panel (Rated 200amps) <> Grid
Note: at this point that 3AWG wire from the subpanel to the 100a breaker in the main panel, would no longer be in play and I would take away the gas generator input from the main panel.

 

[wwhitney]

1) No

2) Yes, but to comply with the 120% rule in the main panel, you must limit the joint output of both inverters (the Solaredge and the EG4-12kPV) to at most 240V*40A/125% = 7.68 kW. If the EG4-12kPV is listed as a Power Control System and can monitor the Solaredge's output and adjust its output to always satisfy that overall limit while on-grid, that would work. Otherwise, you'd need a different configuration to accommodate the joint output power of both inverters.

Cheers, Wayne

 

[spacemancw]

This is the design I have seen out there and what I would like to try to achieve.
I believe it is a power control system.
It is has an automatic transfer switch so that if the grid goes down, it shuts the connection to the main panel, so no backfeed to the grid. So circuits in the main panel no long get power, stove, dryer pool pump.

It then gets power from the battery and tricks the SolarEdge into seeing a good sine wave, and so the solar panels keep producing energy.
When grid is up, the Solar is either powering the house, charging the batteries or sending excess back to the grid. The hope is to send less to the grid and as much as possible to the batteries.

At night, it knows there is no solar production and so draws from the batteries first before the grid.

So I'd say that's a Power Control System, but I will double check documentation.
And you can see from this diagram that aside from the grid itself, there is only one other power source going into the main panel, and that's the 40amp from the EG4-12kPV. So that, I would think satisfies the 120% rule.

 

[wwhitney]

And you can see from this diagram that aside from the grid itself, there is only one other power source going into the main panel, and that's the 40amp from the EG4-12kPV.

Do you know that the EG4-12kPV inverter supports AC coupling with PV inverters on its load-side AC connection? When the batteries are full, and there are no critical loads running, the EG4-12kPV needs to be able to pass through the AC power from its load side to its grid-side.

Typically hybrid inverters are designed to support DC connections to batteries and DC connections to the PV panels. The latter you obviously can't do (at least without rewiring your array), as you have Solaredge optimizers and so need to use the Solaredge inverter to support them.

If the EG4-12kPV does support the configuration you've shown, then there is still, at least on the face of it, the possibility that the Solaredge 7600 will put out 7.6 kW, while the EG-12kPV will put out an additional 8kW from the battery. So that is what you have to check, that the EG4-12kPV can be configured not to do that.

Cheers, Wayne

 

[spacemancw]

Yes it does support AC coupling.
And no it will not pull from the batteries while it is outputting solar power. It will charge the batteries.
If the batteries are charged, and solar is still producing and I am not using all the power, excess will go to the grid.
If grid is down and batteries are charged, and there is excess ... with nowhere to go, the EG4 will change the sine wave so that the solar will stop producing and then it will draw from the batteries.

 

[jaggedben]

The size of the breaker connecting the battery inverter to the main does not matter. Only the solar+battery output current matters. Hopefully the battery inverter supports more than a 40A connection to the main because (although I've done it a few times) 40A is kind of limiting.

 

[spacemancw]

1) No

2) Yes, but to comply with the 120% rule in the main panel, you must limit the joint output of both inverters (the Solaredge and the EG4-12kPV) to at most 240V*40A/125% = 7.68 kW. If the EG4-12kPV is listed as a Power Control System and can monitor the Solaredge's output and adjust its output to always satisfy that overall limit while on-grid, that would work. Otherwise, you'd need a different configuration to accommodate the joint output power of both inverters.

Cheers, Wayne

Apparently the EG4 12kPV is not listed as a Power Control System.
So where does that leave me?

 

[wwhitney]

The main panel is the sticking point, as you have to consider that you have 15.6 kW of inverters that can supply it. So are your main panel and the meter in the same enclosure, as is common in California? If not, you have more options.

If yes, then your options are either to (a) change out the main panel, (b) move all loads out of the main panel and install one of the largest branch circuit breaker in that panel, which size would limit your available grid power, so you'd need to confirm that a load calculation for your house comes out to less than that breaker size, or (c) limit your total installed inverter capacity to 32A * 240V = 7.68 kW. E.g. for (c) does SolarEdge still make a 7.68 kW inverter than supports batteries?

Cheers, Wayne

 

[spacemancw]

The main panel is the sticking point, as you have to consider that you have 15.6 kW of inverters that can supply it. So are your main panel and the meter in the same enclosure, as is common in California? If not, you have more options.

If yes, then your options are either to (a) change out the main panel, (b) move all loads out of the main panel and install one of the largest branch circuit breaker in that panel, which size would limit your available grid power, so you'd need to confirm that a load calculation for your house comes out to less than that breaker size, or (c) limit your total installed inverter capacity to 32A * 240V = 7.68 kW. E.g. for (c) does SolarEdge still make a 7.68 kW inverter than supports batteries?

Cheers, Wayne

But I don't have 15.6 kW of inverters. Only half that.
The SolarEdge is 7.6kw, it gives it to the EG4 ... which passes it on.
Yes, the EG4 has batteries but Solar and Battery power are never going at the same time.

 

[wwhitney]

But I don't have 15.6 kW of inverters.
The SolarEdge is 7.6kw, it gives it to the EG4 ... which passes it on.

Well, the EG4 has an 8 kW inverter, so absent further information, it could pass on the 7.6 kW and add 8 kW to that to get 15.6 kW

Yes, the EG4 has batteries but Solar and Battery power are never going at the same time.

I think you need the PCS listing for the NEC to recognize that. Without it, the NEC would treat it as 15.6 kW of inverters.

Cheers, Wayne

 

[jaggedben]

Right. What stops the battery inverter and solar inverter from both outputting full power at the same time?

 

[spacemancw]

Right. What stops the battery inverter and solar inverter from both outputting full power at the same time?

The battery inverter (EG412k) stops that.
It is intelligent enough to know not to do that. Battery power is only used when the solar is no longer producing (when it's dark), or when the grid is down, batteries are fully charged and there is excess solar with nowhere to go. The EG4 changes the sine wave to the solar, stops it from producing and then starts to draw from the batteries. How much it draws and when to turn the solar on again is customizable.

 

[wwhitney]

The battery inverter (EG412k) stops that.

Right, I looked at the manual briefly and it does support modes for which that would be true. Not sure if it actually supports the exact optimal limit (NEC-wise), which would be "export from the battery or AC-coupled solar up to 32A max", but it at least supports "do not export at all". [AC-coupled PV is done via the 3rd (after Grid and Load) miscellaneous AC connection, which can be used for generator, AC-coupled PV, or sheddable load. Whether "do not export at all" applies only to DC-connected sources, or also applies to AC-coupled PV I'm not clear on; but it doesn't matter as far as overloading the main panel, as the Solaredge alone will not do that, so it suffices for the EG4-12kPV to not export to its Grid connection from its inverter.]

But for the NEC to recognize that behavior, I believe the product has to have been listed as a PCS, which means the behavior has been tested to work as required. If it hasn't been so listed, I believe that NEC-wise you'd need to treat it as if could export its full rating simultaneously with the PV.

@jaggedben could perhaps confirm my comments in the previous paragraph.

Cheers, Wayne

 

[spacemancw]

It is possible for the EG4 12kPV to pull from your battery bank and send an additional 8kW back through the grid terminals on top of what is being AC coupled through the GEN port. However, you have to manually go into the settings of the inverter and enable "Forced Discharge" for the inverter to do this. If you do not enable this function, in my situation, the EG4 12kPV inverter will only be pushing a maximum of 7.6kW back out through the grid terminals.

 

[jaggedben]

It is possible for the EG4 12kPV to pull from your battery bank and send an additional 8kW back through the grid terminals on top of what is being AC coupled through the GEN port. However, you have to manually go into the settings of the inverter and enable "Forced Discharge" for the inverter to do this. If you do not enable this function, in my situation, the EG4 12kPV inverter will only be pushing a maximum of 7.6kW back out through the grid terminals.

I get that. We are just saying that, from the code standpoint, what confirms that is the equipment being a listed Power Control System. I'm struggling with a somewhat similar situation right now where I need to convince a utility that a solar system won't export and they want to know if the equipment is a listed PCS and it isn't. So I'm trying to convince them that the manufacturer's manual is enough and I don't know if they'll accept that.

One thing about a PCS is that the user is not supposed to be able to change the settings, and I think the manufacturer is supposed to be some sort of certification process for qualified people who can access those settings. Can you see how it might be a problem if anybody with the manual can turn on the 'Forced Discharge' feature, even if they are not qualified and don't understand how this might be bad for upstream equipment?

 

[spacemancw]

Yes absolutely, I see the problem with unqualified people making changes.
I see AC coupled systems all over youtube. Amy Beaudet, the queen of solar, does a video for it at

(she passed away in 2021). So it would seem that technically all AC coupled setups have this problem.