PVSyst: inverter with multiple MPPT inputs

In PVSyst it is possible to configure an inverter with multiple MPPT inputs. Inverters can have balanced or unbalanced MPPT inputs.

In the first case the input powers are identical. In the second case, the inputs have different powers. We will carry out examples of projects using two types of inverters.

Case 1

• 9 kWp system;
• 30 300 Wp JA Solar modules;
• 1 Fronius Symo 8.2-3-M inverter (2 balanced MPPTs).

The following figure illustrates the project configuration screen. In PVSyst, the letter “M” distinguishes inverters that have multiple inputs.

In the “Inverter selection” section, the software informs that the chosen inverter has 2 MPPT inputs.

Let's use two strings of 15 modules, one for each input. As the strings are identical, no special care is required in this simulation for inverter configuration.

It is enough to select the option “Use multi-MPPT” and define “No. of MPPT inputs = 2”. In this case, the two inputs are identical and the software performs the simulation as if there were two identical inverters, each with half the total power.

Case 2

• 9 kWp system;
• 30 300 Wp JA Solar modules;
• 1 Fronius Symo 10.0-3-M inverter (2 unbalanced MPPTs).

The following figure illustrates the project configuration screen. In PVSyst, the letter “M” distinguishes inverters that have multiple inputs.

In the “Inverter selection” section, the software informs that the chosen inverter has 2 unbalanced MPPT inputs.

In this example, we will distribute 20 modules in the first input and 10 modules in the secondary input. As the quantities of strings in each input are different, it is better to separate the photovoltaic system into two sub-groups (sub-arrays), as we see in the following figures.

The “MPPT1” sub-group, with 20 modules, is associated with the main input of the inverter (higher power). In the example we find the message “The inverter is slightly oversized” (the inverter is slightly oversized), which is just a warning – this is because we could use a larger number of modules on this input, so it is working with a little slack.

The “MPPT2” sub-group, with 10 modules, is associated with the secondary input of the inverter (lower power).

Case 3

A third possibility in this type of simulation is to combine all inputs into one. This depends from one piece of equipment to another and the manufacturer should be consulted about this possibility.

Instead of multiple inputs, the inverter is used as if it had just 1 MPPT, adding the powers of the two inputs.

In the figure below, the inverter's secondary input is disabled, meaning that the powers will be added to a single input (eliminating the inverter's multiple MPPT feature – which can be useful in some projects where the two individual inputs are not necessary) .

The result of the sum of the powers (disabling the secondary input) is seen in the figure below. In this case, the total power of the inverter (10 kW) is made available entirely at the main input.