Project design > Grid-connected system definition

The "system" is defined as the set of components constituting the PV-array, i.e. the PV modules, strings, inverter, up to the connection to the grid.

Sub-array definition:

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

For a given subarray: you have to define your requirements, and PVsyst will automatically propose a suited arrangement.

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

-	The desired nominal power, or alternatively the available area for installing modules,

-	A PV module model, chosen in the database.

-	The inverter model, chosen in the database,

Then the program will choose the required number of inverters, according to a pre-defined 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 choices for the number of modules in series/parallel are mentioned on the dialog. They should 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 the stabilized ones after degradation. The initial values may be up to 15% higher during the first months. This should be taken into account when sizing the system, especially concerning the absolute maximum voltages for the inverter input or the module insulation.

The inverter power sizing is a delicate and debated problem. PVsyst proposes a methodology based on the predicted overload losses. This usually leads to Pnom ratios far below those recommended by inverter's providers, but we think that 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 will be displayed if there are some incompatibilities between the chosen parameters. Red warnings are not acceptable (simulation cannot be performed) and orange warnings are indicative. These colours will be thrown back on the "System" LED's button.

NB: The sizing temperatures - as well as other parameters like the allowed loss when using highly overloaded systems - when may be adjusted :

- for your project in the project's parameters (button "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 step of the development of your project), you can

-	modify the PV-array specific loss parameters (thermal, wiring resistance, module quality, soiling, mismatch, IAM) with the "Detailed Losses" button.

-	define a user's load profile for determining the owner's own consumption and the injected (sold) energy to the grid (net-metering). You will usually define an hourly profile in order to take realistic daily production and consumption distributions into account.