PV System Calculations

[moe99]

Hello I'm a total newbie and I'm trying to understand how to calculate the following for a PV system:
1) Rated operating current
2) Rated operating voltage
3) Maximum Photovoltalic source voltage
4) Rated short-circuit current

My dad is an electrician and plans to setup the solar system, but he's away right now so I can't ask him to help.

I'm not sure if I have all the information to understand how to calculate this stuff ... let me know what I need and how I can calculate them.

I would be using 2 x 10 Q.PRO L-G4.2 315 PV panels linked together in parallel providing me with 6300 Watts for a 120/240V setup.
Using an Outback Randian Series Inverter/Charger GS8048A
2 x FLEXmax 80 MPPT


From my understanding I would assume these are the values:
1) Rated operating current: 30A
2) Rated operating voltage: 240V
3) Maximum Photovoltalic source voltage:
= 45.53 V x (1 + ((-31 °C – 25 °C) x -0.30% / °C))) x (20 panels/2)
= 53.27 V x 20 / 2
= 532.7 V
4) Rated short-circuit current: 30A

 

[ron]

You can use the inverter manuf sizing tool
http://outbackpower.com/outback-support/string-sizing-tool
You likely don't need an 8kW inverter with only 6.3kW of panels. Often folks use 0.8 or 0.9 times the wattage of the PV panels to determine the sweet spot for the inverter size.

 

[ggunn]

Hello I'm a total newbie and I'm trying to understand how to calculate the following for a PV system:
1) Rated operating current
2) Rated operating voltage
3) Maximum Photovoltalic source voltage
4) Rated short-circuit current

My dad is an electrician and plans to setup the solar system, but he's away right now so I can't ask him to help.

I'm not sure if I have all the information to understand how to calculate this stuff ... let me know what I need and how I can calculate them.

I would be using 2 x 10 Q.PRO L-G4.2 315 PV panels linked together in parallel providing me with 6300 Watts for a 120/240V setup.
Using an Outback Randian Series Inverter/Charger GS8048A
2 x FLEXmax 80 MPPT


From my understanding I would assume these are the values:
1) Rated operating current: 30A
2) Rated operating voltage: 240V
3) Maximum Photovoltalic source voltage:
= 45.53 V x (1 + ((-31 °C – 25 °C) x -0.30% / °C))) x (20 panels/2)
= 53.27 V x 20 / 2
= 532.7 V
4) Rated short-circuit current: 30A

These numbers are different depending on whether you are talking about the AC or DC side:

DC side:
Operating current is module Imp times the number of strings.
Operating voltage is module Vmp times the number of modules in a string.
Maximum voltage is cold temperature corrected module Voc times the number of modules in a string.
Maximum current is 1.25 times module Isc times the number of strings.

AC side:
Current is the nameplate maximum current of the inverter(s).
Voltage is the grid voltage.

 

[moe99]

You can use the inverter manuf sizing tool
http://outbackpower.com/outback-support/string-sizing-tool
You likely don't need an 8kW inverter with only 6.3kW of panels. Often folks use 0.8 or 0.9 times the wattage of the PV panels to determine the sweet spot for the inverter size.

I will take a look at this.

We plan to eventually increase the amount of panels in the future. I'm just trying to do a calculation for the 20 panels we have now. (Already bought the materials)

Looking at the panels specifications I 'think' I've calculated the Rated operating current, operating voltage, Max PV sourve voltage and short-circuit current. Hopefully someone can check my work/calculations.

1) Rated operating current: 8.46 A x 2 strings of 10 modules = 16.92 A
2) Rated operating voltage: 37.34 V x 10 modules per string = 373.4 V ( or I think it might just be 240V)
3) Maximum photovoltaic source voltage: 45.53 V x 10 modules per string x 1.1701 (temperature coefficient for my area) = 532.7 V
4) Rated Short-circuit current: 9.06 A x 2 strings of 10 modules = 18.12 A

These numbers I got from the picture I've attached.

 

[moe99]

These numbers are different depending on whether you are talking about the AC or DC side:

DC side:
Operating current is module Imp times the number of strings.
Operating voltage is module Vmp times the number of modules in a string.
Maximum voltage is cold temperature corrected module Voc times the number of modules in a string.
Maximum current is 1.25 times module Isc times the number of strings.

AC side:
Current is the nameplate maximum current of the inverter(s).
Voltage is the grid voltage.

I'm not entirely sure which the numbers we need to be honest. To be honest what happened is that we had an inspector come by to look at the setup and he told us everything is good to go, except we need to put a "marking for the PV system at the disconnecting means for the photovoltaic output circuit specifying: - Rated operating current - Rated operating voltage - Maximum photovoltaic source voltage - Rated short-circuit current."

Sorry for my lack of understanding. My dad is the one who knows all of the electrical stuff, I'm just helping out and trying to learn from the project in the process. Problem is my dad has a language barrier.

 

[ggunn]

I will take a look at this.

We plan to eventually increase the amount of panels in the future. I'm just trying to do a calculation for the 20 panels we have now. (Already bought the materials)

Looking at the panels specifications I 'think' I've calculated the Rated operating current, operating voltage, Max PV sourve voltage and short-circuit current. Hopefully someone can check my work/calculations.

1) Rated operating current: 8.46 A x 2 strings of 10 modules = 16.92 A
2) Rated operating voltage: 37.34 V x 10 modules per string = 373.4 V ( or I think it might just be 240V)
3) Maximum photovoltaic source voltage: 45.53 V x 10 modules per string x 1.1701 (temperature coefficient for my area) = 532.7 V
4) Rated Short-circuit current: 9.06 A x 2 strings of 10 modules = 18.12 A

These numbers I got from the picture I've attached.
View attachment 18379

For the most part it's good. Your Vmp is 37.24V, not 37.34V IIRC (I can't read it now), so that's a bit off, and I'll take your word for the temperature correction, but you've got the idea. Sorry if I was a bit short with you in the other thread.

 

[moe99]

For the most part it's good. Your Vmp is 37.24V, not 37.34V IIRC (I can't read it now), so that's a bit off, and I'll take your word for the temperature correction, but you've got the idea. Sorry if I was a bit short with you in the other thread.

BEAUTIFUL! Thank you! and no problem at all I understand and thanks for your help and patience.

So then the Rated operating voltage would be: 37.24 V x 10 = 372.4 V


I was wrong to assume the Rated operating voltage was 240V then, correct?

 

[ggunn]

BEAUTIFUL! Thank you! and no problem at all I understand and thanks for your help and patience.

So then the Rated operating voltage would be: 37.24 V x 10 = 372.4 V


I was wrong to assume the Rated operating voltage was 240V then, correct?

It depends. If you are labeling the AC disco for a string inverter, the operating voltage is the AC line voltage. If it is the DC disco it's the module Vmp times the number of modules in a string.

BTW, I usually round to the nearest whole amp/volt for labeling.