Although inverters with Maximum Power Point Tracking (MPPT) are not as prevalent in Utility scale solar systems as they are on C&I and Residential solar systems, some power plants are designed with String inverters with multiple MPPTs.
PVcase GM doesn't yet have a specific Electrical System Type for string inverters with multiple MPPTs, but it is possible to adapt the "DC combiner - Inverter - Transformer" system type for this purpose.
Note: For the purposes of this tutorial, a Fixed Tilt system will be considered, because the string inverters with multiple MPPTs are more commonly used in power plants with that type of mounting system.
Electrical Devices
Before starting, it is necessary to complete Stringing in the first tab of the Electrical Design window. Once that is done, the Electrical devices tab will show the number of strings available in any specific PVcase PV area/s. This will allow for the System type field to become available and the "DC combiner - Inverter - Transformer" system type can be selected.
At this point, the user can input the preferred parameters in the Configuration section, taking into account, that where DC combiners are referenced, MPPTs should be considered: Strings per MPPT and MPPTs per Inverter.
Any of the multiple Placement type options can be selected depending on the user's preferences and system design, but the common Trench adjacent will work fine in many cases.
Numbering allows defining the desired direction in which devices and strings should be numbered. It is important to define this correctly to ensure proper allocation of strings to MPPTs. For Fixed Tilt systems, to reduce the impact of row to row shading in the performance of the power plant, it is preferred to define the Priority as Horizontal, in order to ensure that the strings at different heights on each frame go to separate MPPTs.
Also important, is that the Labeling is adjusted so that instead of DCB (DC combiner box), the labels show as MPPTs.
At this point, the generation of electrical devices can proceed by clicking Auto/Semi. When the layout is fairly regular, the Auto option could work fine, but if it is quite irregular, the Semi option will give the user more control over the MPPT arrangement. For this example, the Auto option will be used, but selecting each transformer block separately, so that each block can have its own group of strings and independent alignment line defined by the user, as this will ensure an adequate string to MPPT allocation.
Now it is possible to verify that:
-the Electrical Overview shows the correct allocation of electrical objects
-for each inverter, the MPPTs were properly allocated right next to it
-only strings at a specific frame height were allocated to each MPPT (by using Color Coding)
Cabling
If satisfied with the electrical design generated, the next step is to generate the cabling. To guarantee a proper routing of the cables, the adequate selection of trenches is critical.
Now it is possible to:
-verify the proper cable routing
-show the SLD (single line diagram) with cables lengths
-export the BoM (bill of materials) with cable quantities
Note: The reference to DCBs will not show in the layout, but it will remain in the Overview. If the user doesn't want for this reference to show in the SLD and BOM, they would need to be edited manually.