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Grid-connected system definition

The "system" is defined as the set of components constituting the PV array—that is, the PV modules, strings, inverter, and connection to the grid.

Sub-array definition

You can define an unlimited number of different sub-arrays (add, copy, rename, move, and delete from the left of the dialog).

For a given sub-array: you must define your requirements, and PVsyst will automatically propose a suitable configuration.

The basic requirements for a subarray (i.e. the parameters you should input) are:

  • The desired nominal power, or alternatively the available area for installing modules (optional),
  • A PV module model, chosen in the database.
  • An inverter model, chosen in the database,
  • Possibly an optimizer, chosen in the database.

Then the program will choose the required number of inverters, according to a pre-defined PNomRatio (Pnom array/inverter ratio) of 1.25.

It will then propose a number of modules in series, and a number of strings in order to approach the desired power or available area.

The acceptable configurations for the number of modules in series/parallel are indicated in the dialog. They must meet the following requirements:

  • The minimum array voltage in worst temperature conditions (60°C) should not be under the inverter's voltage range for MPPT,
  • The maximum array voltage in worst temperature conditions (20°C) should not be above the inverter's voltage range for MPPT,
  • The maximum array voltage in open circuit (Voc at -10°C in Europe) should not exceed the absolute maximum voltage at the input of the inverter,
  • The maximum array voltage in open circuit (Voc at -10°C in Europe) should not exceed the allowed system voltage specified for the PV module.

NB: The voltage values calculated by PVsyst for amorphous modules are stabilized values after degradation. Initial values may be up to 15% higher during the first months. This should be considered when sizing the system, especially for absolute maximum voltages at the inverter input or for module insulation.

The inverter power sizing is a delicate and contested issue. PVsyst proposes a methodology based on predicted overload losses. This typically results in Pnom ratios below those recommended by inverter manufacturers, but they are closer to an economical optimum.

All these conditions are explicitly displayed on a system sizing graph, (button Show sizing).

You can now play with these parameters taking your own constraints into account. You can retrieve the automatic proposed values by clicking on the associated checkbox.

Warning messages are displayed if there are incompatibilities between chosen parameters. Red warnings indicate unacceptable conditions (simulation cannot be performed), and orange warnings are advisory. These color codes also appear on the System LED button.

NB: Sizing temperatures—as well as other parameters like the allowed loss when using highly overloaded systems—can be adjusted:

  • for your project in the project's parameters (Project's settings)
  • as default values for any new project: in the "Hidden parameters".

You can have a look at our FAQ "How to adjust the design temperatures" for reasonable values of these temperatures. In principle, except the Minimum temperature, you don't need to adjust them.

If desired, in a second phase of your project development, you can:

  • Modify the PV array specific loss parameters (thermal, wiring resistance, module quality, soiling, mismatch, IAM) using the Detailed Losses button.
  • Define a user's load profile to determine owner consumption and energy injected to the grid (net-metering). You will typically define an hourly profile to account for realistic daily production and consumption distributions.