This installation tip was provided by Matthew Charles, senior applications engineer at Sungrow USA
The NEC requires that voltage drop within an electrical circuit (which equates to the loss the system incurs due to design choices) be no more than 5%. When it comes to fundamental PV system design, however, voltage drop is recommended to be less than 2% for both DC and AC circuits.
Minimizing system losses due to voltage drop ultimately comes down to inverter placement and conductor size, regardless of the DC and AC system voltages. String inverters are traditionally placed on the end of a row of modules, minimizing loss on the DC source circuit conductor runs. This can easily allow for a voltage drop around 1%. Some string inverters also allow the maximum DC conductors to be as large as a #8AWG, further providing opportunity to reduce the DC voltage drop. This seems beneficial, but the energy delivered at the P.U.C. (point of utility connection) is the main driver for BOS costs. Being able to deliver the energy that is contractually obligated will determine the number of inverters within an array and AC conductor sizes.
Having very small DC power loss due to voltage drop doesn’t do anything for the bottom line if the AC voltage drops are at or above 2% with very large conductor sizes, and creates the need for extra inverters to deliver the required energy at the P.U.C. Additionally, increasingly larger DC:AC ratios (the amount of DC power relative to the inverter’s AC output power capacity) help further the argument that a higher amount of DC voltage drop and power loss has negligible impact on the overall DC power capacity for the project.
The better option would be to allow the DC voltage drops to be close to 2% and increase the length of the DC conductor runs by co-locating the inverters near each other. Then have these groups as close as possible to the P.U.C. This will reduce the AC voltage drop and the possible need to use more inverters to deliver the required energy. With the increase of DC system voltages, DC conductor runs can be longer with the same voltage drop, with the benefit of reduced AC system losses and more energy delivered to the P.U.C.