Recessed AC Combiner for (2) 25 kW Inverters

B

bellington

Senior Member
Location
Hahira, GA
Occupation
Consultant
Good morning.

I have (2) Chint 25 kW 480 3-phase inverters to pack into a very small space. They will use the Chint FlexOM Gateway. To provide adequate space for air flow, I am considering using a standard 480-volt 100-amp recessed electrical panel with (2) 40-amps 3-pole breakers, and an 80-amp main for combining AC output. The 100-amp panel output would then connect to an 80-amp breaker in a 250-amp panel with a 100-amp main that also provides power for 3 water heaters. The 250-amp panel would connect to an 600-amp panel in another building. The 600-amp panel is connected through the switch gear to the battery, other solar, and/or generator. It is located in the Bahamas and falls under Canadian Code.

Questions:

1. Is there a better option for combining the (2) inverter outputs?
2. Will a standard recessed panel work for a combiner?
3. Will I still be required to have a separate disconnect if the 100-amp panel main breaker would serve the same purpose?
4. If I wanted to remotely open the circuit with the BESS, how should I go about that?

Thanks,

Byron
 
A standard 480V panel would be fine for an AC combiner. Nothing more special is needed.

Question 3 depends on a various details of installation under the NEC, I can't speak to the Canadian code.

You could probably use contactors or perhaps shunt trip breakers open the circuit remotely. (Won't be too cheap at 480V.)

(Is there grid or not?)
 
bellington said:
.



1. Is there a better option for combining the (2) inverter outputs?
Click to expand...

Other option might be skipping the combiner and running the inverter outputs back to that 250 amp panel?

2. Will a standard recessed panel work for a combiner?
Click to expand...

Sure, at least for siemens, the minimum box size would be 20 by 32, 5.75 in deep.

3. Will I still be required to have a separate disconnect if the 100-amp panel main breaker would serve the same purpose?
Click to expand...
The combiner panel doesn't need a main breaker at least under the NEC
 
jaggedben said:
A standard 480V panel would be fine for an AC combiner. Nothing more special is needed.

Question 3 depends on a various details of installation under the NEC, I can't speak to the Canadian code.

You could probably use contactors or perhaps shunt trip breakers open the circuit remotely. (Won't be too cheap at 480V.)

(Is there grid or not?)
Click to expand...
Thanks for the response. The battery/solar/generator will be the grid, unless the submarine 13.2 kV cable from neighboring island gets repaired, or replaced (not very likely).
 
bellington said:
Thanks for the response. The battery/solar/generator will be the grid, unless the submarine 13.2 kV cable from neighboring island gets repaired, or replaced (not very likely).
Click to expand...
Kinda figured it was something like that.

Regarding opening the PV circuit from the BESS, not saying you shouldn't provide for it but I think primary control of the PV should probably be by frequency/voltage shifting.
 
electrofelon said:
Other option might be skipping the combiner and running the inverter outputs back to that 250 amp panel?



Sure, at least for siemens, the minimum box size would be 20 by 32, 5.75 in deep.


The combiner panel doesn't need a main breaker at least under the NEC
Click to expand...
"Other option might be skipping the combiner and running the inverter outputs back to that 250 amp panel?"

I think I would still need a common disconnect for both inverters and that panel provides power for (3) water heaters.
 
jaggedben said:
Kinda figured it was something like that.

Regarding opening the PV circuit from the BESS, not saying you shouldn't provide for it but I think primary control of the PV should probably be by frequency/voltage shifting.
Click to expand...
Thank you. Yes, agreed primary control should be through the inverter gateway. The remote contactor would be a last resort, all else fail situation, for the possibility of failed curtailment response from the inverter.
 
bellington said:
"...

I think I would still need a common disconnect for both inverters
Click to expand...

Why? Is the Canadian code specific about this?

and that panel provides power for (3) water heaters.
Click to expand...

So? In some US jurisdictions this would be no problem.

Unless it's just a preference for ease of quick response I don't see the need. Or unless the utility (if ever reconnected) would require it.
 
PWDickerson said:
Have you considered using a single larger inverter so you can skip the combiner panel altogether?
Click to expand...
This. A single inverter is always a better option, IMO, even if it is a bit underloaded with DC. I'd be willing to bet that a single inverter that can handle 50kW of modules will be less expensive than two 25kW inverters, not to mention that the interconnection would be simpler/cheaper as well.
 
ggunn said:
This. A single inverter is always a better option, IMO, even if it is a bit underloaded with DC. I'd be willing to bet that a single inverter that can handle 50kW of modules will be less expensive than two 25kW inverters, not to mention that the interconnection would be simpler/cheaper as well.
Click to expand...
The installer said they needed two to handle all the strings.
 
Chint's 25 kW inverter has terminals for 6 strings. Times 2 = 12 strings. Their 50 kW inverter has terminals for 15 strings. Input voltage ranges are the same for both inverters. Unless there is a case to use two inverters so there is redundancy built into the system, I would go with a single 50 kW inverter.
 
PWDickerson said:
Chint's 25 kW inverter has terminals for 6 strings. Times 2 = 12 strings. Their 50 kW inverter has terminals for 15 strings. Input voltage ranges are the same for both inverters. Unless there is a case to use two inverters so there is redundancy built into the system, I would go with a single 50 kW inverter.
Click to expand...
Depending on the module Isc he might not be able to double string all the inputs, and the DC fusing might get funky. The max input per MPPT is 68A, calculated by 1.25 times the combined Isc. But I am skeptical of the assertion that a 50kW Chint could not be strung using the modules that would fit on (2) 25kW Chint inverters.
 
ggunn said:
Depending on the module Isc he might not be able to double string all the inputs, and the DC fusing might get funky. The max input per MPPT is 68A, calculated by 1.25 times the combined Isc. But I am skeptical of the assertion that a 50kW Chint could not be strung using the modules that would fit on (2) 25kW Chint inverters.
Click to expand...
Is the system on a one or two family dwelling? A maximum adjusted string Voc of 600V instead of the inverter maximum of 1000V could be a factor. A 50kW PV system on a 480/277V service would be a very unusual for a residence, though.
 
Last edited:
Good afternoon to all,

Thanks for much for the comments. There are 695 72 W modules placed on 10 sections of mostly 6/12 roof. A large portion of the modules are on an almost east/west line, some on south side, with some having some north component. There will be some sections productive in the morning sun and useless in the evening sun and vice-versa. I'm not well versed in string arrangement, but the different orientations may have played a part in going with (2) 25 kW, rather than (1) 50 kW.

Regardless, the (2) 25 kW inverters are on site and waiting to be connected to the modules and the local grid. That won't change.

I am also not familiar with what a typical AC combiner panel would look like. My assumption was that it would be a surface mounted box. The (2) inverters mounted in the preferred locations would not have adequate air flow if I have to add another surface mounted box. That was the reason for my original question of using a standard recessed 480 service panel in place of whatever was typically used.

1. I think we have agreed a standard recessed panel will suffice. Thanks for that.
2. What does a typical AC combiner panel look like?
3. Or, are standard electrical panels normally used?

As always, I greatly appreciate your input!

Byron
 
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