Large Commercial PV voltage drop?

[mooreaaryan]

What’s the maximum allowable voltage drop for PV systems large commercial type.
I see 5% 3% 2% 1%. But still not sure what answer is true or most correct

 

[PWDickerson]

There is no max allowable voltage drop. We try to shoot for 2%, which is conservative. I think a lot of installers are ok going higher than that. We do almost entirely residential, so the distances are relatively short, and 2% is easy to hit. It is not too hard to calculate the additional wire cost in order get to a lower voltage drop and compare that with the additional energy the system would generate over its life. When you do the math, it is often cost effective to accept a relative high voltage drop. You have to be careful with your AC voltage drop, because this results in the inverter operating at a higher AC voltage relative to the serivce equipment, and if the building is already operating toward the high end of the acceptable utility range, the voltage drop from the inverter to the servcie could increase the inverter AC voltage beyond its operating range, causing it to shut down. This isn't a problem on the DC side of the inverter.

 

[jaggedben]

There is no code rule.

Engineering wise the only hard limit would be if somehow your voltage drop caused the voltage to drop below the inverter's operating window.

Years ago there was a paper in Solar Pro magazine that argued with math that in large PV systems avoiding voltage drop will never pay for the extra copper/aluminum. Although it ultimately would depend on the price of conductor compared to the price you're getting for a kwh generated, on any given project.

 

[tortuga]

I always thought 130.5(c) of the California energy Code covered just about everything in CA but I dont know about solar:

Voltage drop. The maximum combined voltage drop on both installed feeder conductors and branch circuit
conductors to the farthest connected load or outlet shall not exceed 5 percent

 

[jaggedben]

I really don't think that covers solar DC conductors.

 

[pv_n00b]

When you work on larger C&I projects the maximum Vd is often specified in the scope document, like a 2% Vd. Strangely enough, I see people doing average Vd to hit a spec. If doing the average there could be one string with 10% Vd as long as there were many strings with a Vd less than 2%. I don't agree with this, but I see it pretty often.