120% Rule for Hubrid System (PV, Battery, Gen)

[TrickleCharge]

I have a proposal for design on a hybrid system that includes PV, Batteries, and Gen. Im trying to figure out where the 120% rule plays out in this system per 690.64. I have labeled the points 1, 2, and 3 that I think play into this rule. Number 3 location has the PV feed. Number 2 has 125A breaker that comes from the midnite solar unit (which includes the batteries). The main service is 200A however they are only installting (1) 175A main breaker (this will be the only breaker in this panel. Thanks for the input!

 

[Smart $]

I have a proposal for design on a hybrid system that includes PV, Batteries, and Gen. Im trying to figure out where the 120% rule plays out in this system per 690.64. I have labeled the points 1, 2, and 3 that I think play into this rule. Number 3 location has the PV feed. Number 2 has 125A breaker that comes from the midnite solar unit (which includes the batteries). The main service is 200A however they are only installting (1) 175A main breaker (this will be the only breaker in this panel. Thanks for the input!

The simplest way to determine is the first point on the service/alternate source side where loads can be supplied from all sources. From what I can determine, that point is #3, though I'm uncertain why you have two red boxes.

 

[TrickleCharge]

At point 3 the supply is from the PV. What about supply from the battery inverters (point 2?) I accidentally had 2 boxes at point 3.

 

[GoldDigger]

At point 3 the supply is from the PV. What about supply from the battery inverters (point 2?) I accidentally had 2 boxes at point 3.

1. As far as I know the Sunny Island used without Sunny Boy inverters is not capable of sending power back to the grid, so there will not be any backfeed at the main panel from them.
2. I am not sure just what the nature of the PV supply on the protected loads panel is. But if they are pure grid-tied inverters, we need to know what kind and how they are interconnected (other than by AC) to the Sunny Island, etc.
3. To the extent that you have PV or battery which can feed back into the grid, it should be connected on the POCO side of the ATS or some other means used to make sure that it does not try to backfeed the generator.

 

[jaggedben]

I'm going to assume that this is related to the previous thread you started, and that there are some number of SMA Sunny Boy inverters connected to the 60A solar subpanel, and that the 60A breaker is properly sized for their output, not smaller or larger.

I'm also going to assume, as Golddigger stipulated, that the SIs do not backfeed the heavy loads panel or the grid, but that the Sunny Boy's can, through the SIs and Midnite equipment. I believe that is correct.

I'm also going to assume that the system is properly configured per SMA and Midnite's instructions, that the generator will be properly controlled by the SI master and not get backfed, etc. etc. etc.

In that case here are the minimum ratings required for each of the panelboards:
3) The protected loads panel = (60A+125A)/1.2 = 154.2A
2) The "heavy loads panel" = (60A+175A)/1.2 = 195.8A
1) Main service panel - is not subject to the 120% rule, just needs to be rated minimum 175A

So all of those panels are as they should be in the drawing.

 

[Smart $]

At point 3 the supply is from the PV. What about supply from the battery inverters (point 2?) I accidentally had 2 boxes at point 3.

It appears to me by what you have drawn, the reduced load panel can be supplied by sources other than the PV system. Being a load panel makes it distribution equipment under 705.12(D), and subject to the 705.12(D)(2) requirement.

Regarding the point brought up about backfeeding the grid... If the hybrid controller is not utility interactive at any time, then the 120% rule is rendered moot. Yet, if both the PV system and utility can supply the reduced load panel simultaneously... that by definition is interactive. It does not matter whether the system backfeeds any power to the utility.

 

[TrickleCharge]

Thanks all for the input! There is a low voltage cable from the SI that communicates with the ATS and Gen so that the generator cannot be backfed.