Metal resistivity

The resistivity of wiring metals is strongly dependent on the temperature, which can widely vary due to dissipating currents.

The basic value is specified for pure metal, at 20°C :

Copper:

Rho = 1.68 E-8 * (1 + 0.0039 * (Temp - 20) [°C] ) [Ohm·m]

Default value:

Temp = 50°C => Rho[50°C] = 1.88 E-8 [Ohm·m]

= 18.8 [ mOhm·mm²/m]

Aluminium:

Rho = 2.82 E-8 * (1 + 0.0039 * (Temp - 20) [°C] ) [Ohm·m]

Default value:

Temp = 50°C => Rho[50°C] = 3.15 E-8 [Ohm·m]

= 31.5 [mOhm·mm²/m]

These values at 50°C are the default in PVsyst.

You can eventually modify these defaults in the Hidden parameters (for any new calculation version).

You can specify the resistivity value effectively used for the present calculation, when defining the detailed losses: button "Detailed Losses" / "Ohmic losses" / "Detailed computations" / "Wires".

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NB: until Version 6.25, there were an error in the thermal parameter, the default values were

Copper:

Rho[50°C] = 22 [mOhm·mm²/m]

Aluminium: :

Rho[50°C] = 33 [mOhm·mm²/m]

so that calculations performed before this version may have slightly overestimated wiring losses (error of about 17%).

However the resistivity increases when the copper is not quite pure, and we don't know the real resistivity of industrial wires.

I really don't remember where I had picked up these values (at beginning of PVsyst, in 1992). Perhaps in the data of a wire manufacturer for "real" metal ?