Service Size for PV Systems

[adsmith]

where would i find the code requirements for an appopreatly sized service that would support a 24kw pv array

 

[Smart $]

where would i find the code requirements for an appopreatly sized service that would support a 24kw pv array

The only concise requirement I can think of is regarding supply side connection (i.e. ahead of service disconnect). 705.12(A), second sentence:

"The sum of the ratings of all overcurrent devices connected to power production sources shall not exceed the rating of the service."

There's no outright requirement for service rating when the PV system is connected to the load side of the service disconnect, but a good general design practice would be the same.

In the case of a 120/240V 24kW system, we're only talking 125A service rating anyway, though it could be a bit greater depending on inverter output rating and sizing the ocpd(s) at not less than 125%.

 

[GoldDigger]

where would i find the code requirements for an appopreatly sized service that would support a 24kw pv array

You should find that the only requirements on service size (unless you are making a line-side tap to connect the PV as mentioned above) will be those set by POCO as part of your interconnect agreement with them.
POCO is usually content with the service size being equal to or greater than the maximum output current of the PV system, but YMMV.
Note that the service current requirements corresponding to your 24kW system will depend on whether your system is delivering straight 240 or balanced 120 or balanced three phase 208Y/120 versus some form of unbalanced output.
And the size of the array (panels) is not relevant. It is the size/output capacity of the inverter(s) that counts. Under some conditions the array can deliver more than its rated power.

 

[ggunn]

where would i find the code requirements for an appopreatly sized service that would support a 24kw pv array

The number you need to start with is the next standard OCPD rating up from 125% of the maximum rated AC output current of your inverter(s), not the DC power rating of the PV array. Are you talking about a backfed breaker in a panel or a supply side tap? If it's a backfed breaker you need to look at 705.12(D)(2), colloquially known as the "120% rule". If it's a supply side tap, then the ceiling is the size of the service.

 

[GoldDigger]

The number you need to start with is the next standard OCPD rating up from 125% of the maximum rated AC output current of your inverter(s), not the DC power rating of the PV array. Are you talking about a backfed breaker in a panel or a supply side tap? If it's a backfed breaker you need to look at 705.12(D)(2), colloquially known as the "120% rule". If it's a supply side tap, then the ceiling is the size of the service.

Really not trying to pick nits, but in odd circumstances you could end up satisfying the 120% rule and still exceed the service rating when using backfed breakers. So even in that case there is still the requirement that the number not exceed the rating of the service.
Since adsmith may be starting from a zero knowledge state, I wanted to make the answer more complete.

 

[Smart $]

Really not trying to pick nits, but in odd circumstances you could end up satisfying the 120% rule and still exceed the service rating when using backfed breakers. So even in that case there is still the requirement that the number not exceed the rating of the service.
Since adsmith may be starting from a zero knowledge state, I wanted to make the answer more complete.

Sorry, but I have to disagree. 705.12(A) only applies to a supply side connection.

 

[jaggedben]

where would i find the code requirements for an appopreatly sized service that would support a 24kw pv array

The short answer is: Article 705 of the NEC.

 

[GoldDigger]

Sorry, but I have to disagree. 705.12(A) only applies to a supply side connection.

OK, so the NEC may not require it, but I do not know of any POCO that will not balk at a PV output larger than the service size, regardless of how it is connected.

 

[Smart $]

OK, so the NEC may not require it, but I do not know of any POCO that will not balk at a PV output larger than the service size, regardless of how it is connected.

I'll agree with that.

 

[texie]

where would i find the code requirements for an appopreatly sized service that would support a 24kw pv array

Regardless of what Art. 705 will allow, a far more limiting factor may be the POCO. Many POCO's have limits that vary with the circumstances for a given site.