DC Voltage drop- 1900ft & wire size

[electro7]

Hi,

I am calculating wire size for a 220kw ground mount system that would be located around 1900ft away from the point of interconnection. I am looking at a module that has 8.66 amps at mmp with 14 mods per string, which would be around 434 volts. What size wire would I need to keep the voltage drop under 2%?

Also, does anybody know if you can do 1000 volt systems for commercial? I thought I heard it passed in the 2014 code, but was also wondering if it was a jurisdictional thing?

I was thinking to have the inverter near the point of connection and run the DC the 1900ft, thinking it would help with voltage drop. We are still in the design stage of this though, so any thoughts on what would be most cost effective would help out a lot.

Thanks!

 

[ggunn]

Hi,

I am calculating wire size for a 220kw ground mount system that would be located around 1900ft away from the point of interconnection. I am looking at a module that has 8.66 amps at mmp with 14 mods per string, which would be around 434 volts. What size wire would I need to keep the voltage drop under 2%?

Also, does anybody know if you can do 1000 volt systems for commercial? I thought I heard it passed in the 2014 code, but was also wondering if it was a jurisdictional thing?

I was thinking to have the inverter near the point of connection and run the DC the 1900ft, thinking it would help with voltage drop. We are still in the design stage of this though, so any thoughts on what would be most cost effective would help out a lot.

Thanks!

My Southwire Vd iPhone app says you will need #1 Al or #3 Cu for single strings at 1900' 434VDC (Vmp) and 8.7ADC (Imp), but most AHJ's will let you string it to 1000V these days. You definitely want your long run to be the DC one, especially if you go to 1000VDC, and depending on inverter considerations I would consider combining DC out at the array.

 

[BillK-AZ]

Did you consider DC combiners and larger wire?

How do you plan on handling 50-60 strings, 100-120 conductors over that distance? Conduit derating and the problems of so many parallel strings make this impractical.

Where did the 2% max DC drop come from?

Can you change the design so as to tradeoff wire cost against additional PV module strings, or even additional string inverters?

 

[jaggedben]

I think there was an article on this subject in Solar Pro, maybe also a whitepaper, a couple years back. The authors basically argued that the energy gained by reducing voltage drop was only a break-even on the extra expense for larger wire.

Aside from that, see Bill's comments.

 

[SolarPro]

Here's the SolarPro article on Optimal DC Cable Selection in PV System Designs.

And here's an article on 1,000 Vdc Utilization Voltages. You can build 1,000 Vdc commercial systems under any Code cycle, but it is easier under NEC 2014.