PV Module Voltage vs Battery Voltage

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Another advantage to using a transfer switch is that when the grid goes down and you’re in islanding mode you’re no longer stuck with 20% of the main breaker size. Your Pv and batteries can output their full power. So you could easily go from 7.6kw to 11kw with Pv and battery contributions on smaller systems.

If the house has a majority of gas appliances then you might not need a critical loads panel at all in this scenario. Some manufacturers sell load shed devices that prevent and/or prioritize heavy loads from running to prevent you from having to have a separate critical loads panel. If the house has lots of electric appliances then a critical loads panel would make more sense from a cost perspective.


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Regarding the backup loads panel... I'm assuming the feed from the PV array connects to a circuit breaker on the bottom of the panel? and the feed from the multimode inverter connects where?... to the main lugs of the panel, on the top? it seems like that's what the diagram I posted implies (post #10).
 
There's a variety of topologies to connect things in, and the diagram in post #10 isn't a very modern choice.

Typically these days there'd be a generation panel to combine the PV and the ESS connections, and that would a feeder from/to the generation panel would interconnect via a feeder splice to the feeder that goes from the MID to the backup loads panel.

Cheers, Wane
 
Grouch1980 said:
Regarding the backup loads panel... I'm assuming the feed from the PV array connects to a circuit breaker on the bottom of the panel? and the feed from the multimode inverter connects where?... to the main lugs of the panel, on the top? it seems like that's what the diagram I posted implies (post #10).
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You can use any 705.12 rule for busbars fed by multiple sources as you see fit. Since you would most likely control the panel layout , it is the most logical to put them at opposite ends of the busbar to take credit for the 120% rule. Another possible design you might choose, is to combine them in an AC combiner that is dedicated to the sources, and then feed a subpanel that is dedicated to the critical loads. A panel listed for the purpose of combining the two kinds of inverters might also do this, and let you tie them together without the restrictions of 705.12.

Where NEC 2020 applies, you might also use a power control systems as described in 705.13, to mitigate the total supplied current to a value that is acceptable to feed the critical loads panel.
 
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