Maximum Photovoltaic System Voltage 690.7

[southern view energy]

I have a question revolving around table 690.7 If I am sizing a PV array and I have 15 solar modules in series that create a combined open circuit voltage of 525 Volts DC. (35 volts per panel) I know that my combined voltage cannot exceed 600 volts to be within code compliance. However. I am getting the feeling that this table says that I have to correct the 525 volt output rating to the local environment minimum temperatures which happen to be 4 to -4 degrees F. So does this mean that the correction factor (being 1.18) when applied to 525 Open Circuit Volts which happens to equal 619 volts (525 * 1.18 = 619) causes my system to be a code violation. The classes that I have taken in this area does not specify this. Any help is appreciated. Thanks.

 

[John Paul]

My opinion is that in Part II 690.7 Max Voltage section (A) outlines the calc to determine maximum PV system voltage with temperature correction "to determine the voltage rating of cables, disconnects, overcurrent devices, and other equipment." only.

Section C stipulates your Max PV system voltage which your system complies with.

 

[SeanD]

I have a question revolving around table 690.7 If I am sizing a PV array and I have 15 solar modules in series that create a combined open circuit voltage of 525 Volts DC. (35 volts per panel) I know that my combined voltage cannot exceed 600 volts to be within code compliance. However. I am getting the feeling that this table says that I have to correct the 525 volt output rating to the local environment minimum temperatures which happen to be 4 to -4 degrees F. So does this mean that the correction factor (being 1.18) when applied to 525 Open Circuit Volts which happens to equal 619 volts (525 * 1.18 = 619) causes my system to be a code violation. The classes that I have taken in this area does not specify this. Any help is appreciated. Thanks.

Yes, I have seen AHJ's apply this code section in the manner which you describe. Since the wires from the solar modules are typically rated at 600v this would be a code violation under 690.7 (A). I would redesign your system with 14 modules in series.

Though I will point out that the record low temps are typically found at from 3am-6am. A PV system isn't producing power then. But finding the answer to the lowest temp when a system will be producing maximum output is considerably more work, so most people (Including AHJ's) just work with the record low.

 

[iwire]

I agree, you may not exceed 600 volts at any time, even on the coldest days. There is no wording to allow over 600 volts 'when it's cold'.

 

[ty]

I agree with Sean and Bob.

Where did you get the '35 volts per panel'? Is it 35Voc?
Where did you get the record lowest temperature for your area?
Did you get it at weather.co, or weatherbase.com?

 

[southern view energy]

Art 690.7

Art 690.7

the voltage from the panel is the Voc. The temperature that I used is and estimate from living here for 20 years. I know that I need more accurate data for realistic outcome. The purpose for this question is that I am studying to take the NABCEP exam in march and I was trying to understand the significance of the chart when sizing a system for a potential client.

It is now my understanding that i need to size the string so that I don't have too many modules in series at Voc so that when the correction factor is applied, I do not exceed 600 Volts.

Thanks for the help.

 

[SeanD]

I typically go to weather.com. Punch in the customer's zip code. If you select monthly, there is a button toward the bottom that say averages. This section includes record low and high temperature data. The other option if your AHJ is solar savy, is ask them what temperature coefficient they want you to use.

 

[BruceF]

There are no inverters on the market that will allow you to string together panels up to 600V. If you go to the online sizing programs offered by the Inverter companies, they will show the max number panels from a number of specified manufacturers that are allowed for a particular inverter. In US, the max voltage will not approach 600V. In other words, you are likely to exceed the max voltage allowed by the inverter before you exceed the 600V max of the wiring.

Hope this makes sense.

 

[BillK-AZ]

Maximum Photovoltaic System Voltage 690.7

Maximum Photovoltaic System Voltage 690.7

At a recent Fronius inverter training session they stated that anytime an inverter experiences over 600vdc that fact is written to the non-volatile memory and voids the warranty if the unit is returned for repair and the damage is consistent with over 600 volts. Big brother is watching!