Skip to content

PVModule model: graphs

In the PV module definition dialog, the page "Graphs" shows the general behavior of the model. You can display the following sets of curves:

  • Current vs Voltage (often named "I/V curves")
  • Power vs voltage (often names "P/V curves"),
  • Efficiencies as a function of the irradiance.
  • Efficiencies as a function of the temperature.

These plots show sets of parametric curves, i.e. for different Irradiances, Temperatures, Series resistance or Shunt resistance,

Efficiencies as a function of the irradiance

This plot is used for the determination of the Rseries (mainly) and Rshunt (accessorily).

The relative efficiency as function of the irradiance is highly dependent on the Rserie.

For crystalline modules, the efficiency at 25°C is used as a reference for the determination of Rserie:

  • when measured (acc. to IEC 61853), the shape of the efficiency as function of the irradiance is very well represented by the one-diode model. We choose the Rserie representing this curve at best.
  • when low-light measurements are unavailable, PVsyst uses the relative efficiency for the determination of the default Rserie value, by imposing a relative efficiency (with respect to STC) of -3% under 200 W/m².

I/V curves in realistic conditions

The option "Module temperature according to irradiance" is aiming to show the module behavior in "realistic" conditions.

Usually people show this I/V graph at different irradiances, but for a same temperature.

This pedagogic tool tries to show the reality at sun. When the irradiance increases the module temperature will increase: here each curve is at a temperature corresponding to the thermal model of PVsyst:

Tmod = Tamb + (1/U) * Ginc * Alpha * (1-effic).

The main objective of this graph is to show that in real conditions, the Vmpp voltage is almost constant whatever the irradiance.

In this case for the Voc, the decrease due to temperature often overcomes the logarithmic increase due to irradiance.