DC Voltage drop losses value with Bifacial Modules

[Sergio Alonso]

Good afternoon,

In the Ohmic Losses tab inside PV Field detailed losses parameters, we need to populate the ohmic Loss fraction at STC for the array. When working with bifacial modules, does this voltage drop value need to be calculated considering the bifacial gain effect on the Imp of the module, or does PVsyst consider this value as monofacial losses only and increases it internally with the hourly bifacial gain?

Should we just use the module Imp value or Imp*(1+Bifacial Gain%) for this parameter?

Thanks in advance.

[dtarin]

Ohmic loss inputs in PVsyst are up to the user to define, so you should be considering the current under bifacial conditions when sizing your cabling and determining voltage drops, etc. PVsyst will consider the hourly I^2 x R losses inclusive of bifacial gain, but this is not determining what the initial input is, that is determined by the user based on their design. 

[André Mermoud]

The ohmic fraction is defined as a percentage of a  "Reference Power".

Here the reference power is the STC power, but it could be any other power  (the ohmic fraction will be proportional to this reference power).

However this Ohmic loss specified as a percentage is not the basic data. The basic data is the resistance of the wires, derived from this Loss fraction.

The resistance is the same whatever the reference power chosen. 

This is fully explained in the Help "Project design > Array and system losses > AC ohmic loss from inverter to injection point".