How do I Understand Optimal Voltage Drop Percentage? Q+A from NABCEP Advanced PV Installer Training

I have question about voltage drop. In my area, some sources say if Voltage drop is less than 3% it is ok, some sources say it must be not more than 2%. How do I understand optimal Voltage Drop %?

This question was asked recently by a student in our 40-hour Advanced Solar PV Installer Training. The following answer is from the course instructor Dr. Sean White:

With PV, voltage drop is never a safety issue and there are no restrictions in the code regarding voltage drop.

Voltage drop is not good and leads to a loss of power. Voltage drop can even make the inverter turn off.

I would say that it is not the job of the AHJ [authority having jurisdiction] to enforce performance. Maybe it should be, but the AHJ should be enforcing safety.

For some loads, as the voltage gets lower, the current will get higher, causing a safety issue for voltage drop with loads.

Many people get confused with PV, since there are a lot of factors that are reverse of normal electricity.

One way to look at voltage drop is if the price of an extra module is more than the price of a larger wire, then invest in the larger wire.

The rules that the AHJ should be enforcing are the wire sizing for current rules in articles 310 and 690.

This is not an unusual problem, it is a good question and it is silly that anyone would have a PV system that loses 3% of system power due to small wires.

Here is an article on the subject of voltage rise on PV inverter output circuits.

http://solarprofessional.com/articles/design-installation/voltage-rise-considerations-for-utility-interactive-pv-systems

Learn more about the 40-hour Advanced Solar PV Installer Training.