Hybrid System , PV, Battery, Generator, ATS Confused Designer? Parallel feeders &ocpd

[ggunn]

If feeding the grid is a possibility, then 705.12(D)(2), the so-called 120% rule, applies and the Heavy Loaded Panel is undersized. The maximum AC out to the grid is not clear from the manual I have, but can be 56A per SI and there are two on each phase (the SI is 120V), a 70A CB would be used for each SI. Smart $ seems correct.

This is correct. This system would have 4 70A backfed breakers on the main, two on each busbar. 140A is 20% of 700A, so 700A is the minimum size of the main. I don't recall if the main is that large.

Just a thought here... Is there any reason why two of the SI's couldn't be left off the main, but only connected to the battery bank and the protected loads panel?

 

[Smart $]

...

Just a thought here... Is there any reason why two of the SI's couldn't be left off the main, but only connected to the battery bank and the protected loads panel?

I don't see why not... but I would not do so without the blessing of the manufacturer. Also, 70A supply may be insufficient for protected panel loads at night... it is a 200A panel but loading has not been provided.

 

[ggunn]

I don't see why not... but I would not do so without the blessing of the manufacturer. Also, 70A supply may be insufficient for protected panel loads at night... it is a 200A panel but loading has not been provided.

I thought about that; I was thinking that there may be plug in loads that they could move from the main to the PL panel in the event of an outage.

 

[TrickleCharge]

The protected loads panel has various 15-20A ckts that are typical in the house. The heavy load is just carrying the a/c and large equipment, range, water heater. etc. Originally, one of my concerns was the 120% rule and deleting the second protected load panel would definately overload the buss rating espcially with not only the (4) SI but the 60A feed for the PV Inverter. Still waiting to get a response from UL on the SI. Also wondering about 240.15 in regards to having a means of disconnecting all ungrounded feeds going to the second panel. 4 pole breaker? Thanks again for everyone's input!

 

[jaggedben]

In reading an install manual (Version 2, downloaded in 2012) for the SI5048U it seems that the following statement by jaggedben:
May not be true, the SI can backfeed the grid. The manual states

The manual states exactly what you quoted, that "generators on the stand-alone grid side (Sunny Boys) can feed their energy into the grid". That is not referring to the Sunny Island. The Sunny Island itself does not backfeed the grid.

If feeding the grid is a possibility, then 705.12(D)(2), the so-called 120% rule, applies and the Heavy Loaded Panel is undersized. The maximum AC out to the grid is not clear from the manual I have, but can be 56A per SI and there are two on each phase (the SI is 120V), a 70A CB would be used for each SI. Smart $ seems correct.

You [didn't] have enough information to say if the Heavy Loads panel is undersized. The 120% calculation is done with the Sunny Boys output, not the Sunny Island. The output of any Sunny Boys in this system [had] not been stated. The rating of the breakers connecting the SIs to the Heavy Loads panel is as irrelevant as if they were connecting the Protected Loads subpanel without the SIs being present.

 

[jaggedben]

Originally, one of my concerns was the 120% rule and deleting the second protected load panel would definately overload the buss rating espcially with not only the (4) SI but the 60A feed for the PV Inverter.

If there is 60A of grid-tied inverter (Sunny Boy) on the stand alone side of the SIs, then indeed the the 200A Heavy Loads panel is too small unless its main breaker is smaller than 200A, which hasn't been definitively stated.

The Protected Loads panel would be fine at 200A because could only receive 140A from or through the SIs and 60A from the grid-tied inverters.

 

[jaggedben]

Just a thought here... Is there any reason why two of the SI's couldn't be left off the main, but only connected to the battery bank and the protected loads panel?

No technical reason, but presumably that is not the functionality that the customer desires.

 

[ggunn]

This is correct. This system would have 4 70A backfed breakers on the main, two on each busbar. 140A is 20% of 700A, so 700A is the minimum size of the main. I don't recall if the main is that large.

Just a thought here... Is there any reason why two of the SI's couldn't be left off the main, but only connected to the battery bank and the protected loads panel?

Upon further review...

It is NOT correct. As jaggedben pointed out, the aggregate output of the Sunny Boys (the total of their breaker ratings) is the number to be used in calculating the 120% of the busbar rating of the main panel, not the ratings of the Sunny Islands' interconnect breakers. Sorry; I must've been asleep at the switch yesterday.

 

[Smart $]

In reading an install manual (Version 2, downloaded in 2012) for the SI5048U it seems that the following statement by jaggedben:



May not be true, the SI can backfeed the grid. The manual states

If feeding the grid is a possibility, then 705.12(D)(2), the so-called 120% rule, applies and the Heavy Loaded Panel is undersized. The maximum AC out to the grid is not clear from the manual I have, but can be 56A per SI and there are two on each phase (the SI is 120V), a 70A CB would be used for each SI. Smart $ seems correct.

The manual states exactly what you quoted, that "generators on the stand-alone grid side (Sunny Boys) can feed their energy into the grid". That is not referring to the Sunny Island. The Sunny Island itself does not backfeed the grid.

You [didn't] have enough information to say if the Heavy Loads panel is undersized. The 120% calculation is done with the Sunny Boys output, not the Sunny Island. The output of any Sunny Boys in this system [had] not been stated. The rating of the breakers connecting the SIs to the Heavy Loads panel is as irrelevant as if they were connecting the Protected Loads subpanel without the SIs being present.

If there is 60A of grid-tied inverter (Sunny Boy) on the stand alone side of the SIs, then indeed the the 200A Heavy Loads panel is too small unless its main breaker is smaller than 200A, which hasn't been definitively stated.

...

Just to add a little clarity, the manual states...

Under specific conditions, the system can also temporarily feed energy from the off-grid
power system into the main power grid in the GridCharge operating mode

Also, the 120% rule is determined using 125% of the SBs' output rating [not the sum of breaker ratings; see exception to 705.12(D)(2)]

 

[shortcircuit2]

Ok here is the updated "simplified" version of the proposed installation. Thanks for the input!

View attachment 8398

In this drawing, could the deisel generator be backfed by the solar output to the grid when active during a utility power outage?

 

[Smart $]

In this drawing, could the deisel generator be backfed by the solar output to the grid when active during a utility power outage?

That can't happen. The transfer switch would prevent it.

Edit: above concerning back feed to utility grid. May have interpretted incorrectly... if you mean backfeeding the generator, yes. The manual covers this in fairly good detail. But with the gennie connected as depicted, and not directly to the SI's, the potential is the same as when connected to utility power.

 

[shortcircuit2]

That can't happen. The transfer switch would prevent it.

Edit: above concerning back feed to utility grid. May have interpretted incorrectly... if you mean backfeeding the generator, yes. The manual covers this in fairly good detail. But with the gennie connected as depicted, and not directly to the SI's, the potential is the same as when connected to utility power.

I haven't reviewed the manual, but this system shouldn't be designed with the generator connected as depicted. When all loads are satisfied and there is excess power from the solar, it would try to export to the grid...or generator as laid out in that drawing. The generator needs to be connected to the gen-input of the inverter/charge controllers during a utility outage. I'm not to familar with the Sunny Islands, but with Outback this is how it is done.

 

[shortcircuit2]

I guess I'm wrong about the generator after reading post #9 from ggunn...the SI's can be programmed to not backfeed the gen-set?

 

[ggunn]

I guess I'm wrong about the generator after reading post #9 from ggunn...the SI's can be programmed to not backfeed the gen-set?

Yes, it can. The only way the SB's can backfeed the generator is if the batteries are fully charged and the output of the SB's exceeds the demand from the loads. The SI knows the state of charge of the batteries and can be programmed to shut off the genny when the batteries reach a set state of charge.

 

[Smart $]

Yes, it can. The only way the SB's can backfeed the generator is if the batteries are fully charged and the output of the SB's exceeds the demand from the loads. The SI knows the state of charge of the batteries and can be programmed to shut off the genny when the batteries reach a set state of charge.

There seems to be some confusion here resulting from the SI's being capable of having a generator connected directly to them. The drawing furnished by the OPer shows the generator is not. As such, there is only a "grid" side and an "off-grid" side.

 

[ggunn]

There seems to be some confusion here resulting from the SI's being capable of having a generator connected directly to them. The drawing furnished by the OPer shows the generator is not. As such, there is only a "grid" side and an "off-grid" side.

Maybe I am confused. In the drawing in post #17, when the transfer switch is in the generator (off grid) position, the SI's are connected to the generator. Am I missing something?

Of course, the safe way to do this is to connect the Sunny Boys to the main service panel. They would shut down when the grid is down, but how significant is that? If the grid is up most of the time, the difference in the SB's contribution to the bottom line could very well be negligible and not worth the trouble and risk to the genny.

 

[sandsnow]

There is relay setup to shut down all other sources when genset is on.

Still not convinced the feeder going from heavy panel to protected panel through the SI is permitted by code.
300.3; 310.4; 240.15(i think); 408.16(i think)
Not sure of some sections as i am typing while captive in doctor waiting room.

 

[sandsnow]

There is relay setup to shut down all other sources when genset is on.

Still not convinced the feeder going from heavy panel to protected panel through the SI is permitted by code.
300.3; 310.4; 240.15(i think); 408.16(i think)
Not sure of some sections as i am typing while captive in doctor waiting room.

 

[Smart $]

Maybe I am confused. In the drawing in post #17, when the transfer switch is in the generator (off grid) position, the SI's are connected to the generator. Am I missing something?...

Nope... its my bad. I'm not familiar with the SI and just glancing through the manual I got the impression it had separate connections for utility and generator (AC1 and AC2). It does not (AC1 is loads/SBs, AC2 grid/generator).

 

[Smart $]

There is relay setup to shut down all other sources when genset is on.

Still not convinced the feeder going from heavy panel to protected panel through the SI is permitted by code.
300.3; 310.4; 240.15(i think); 408.16(i think)
Not sure of some sections as i am typing while captive in doctor waiting room.

Of what you cited, I don't see it. You'll have to elaborate.

(BTW, 408.16 is regarding switchboards in damp locations)