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Up to version 6.12, the "Heterogeneous" option allowed to define arrays in 2 different orientations with some restrictions, especially when dealing with shadings.

From version 6.13 onwards, the "Orientation" dialog offers the opportunity to define up to 8 different orientations.

Definition of sub-arrays

When defining multi-orientation, you should define one or several "electrical" sub-arrays associated with each orientation (button "System").

The definition of sub-arrays includes the possibility to give a name, and associate an orientation when multi-orientation is specified.  

You can also define 2 different orientations for a given sub-array (see below  "Mixed orientation sub-arrays").

Definition of near shadings

When defining near shadings, you have to also define sensitive areas to receive the PV modules of each orientation, as defined in the sub-arrays.

During the elaboration of the 3D scene, you can create your fields  without any constraints.

However when quitting the 3D editor, PVsyst will check the coherence between your 3D definitions, the "Orientation" definitions and the electrical "Sub-array" specifications:

System overview tool

These inter-compatibilities may be difficult to establish when you have several orientations. Therefore, there is now a new tool available from several dialogs (button "System overview") that provides the main characteristics already established for the system. This tool shows 4 lists of parameters:

- Orientation parameters.

- Compatibility between System and Shadings, especially concerning orientations and areas for each orientation.

- System parameters: list of the sub-arrays, their orientation, number of modules, inverters, etc.

Each list is accompanied with possible error or warning messages.

NB: There is no limitations anymore on the orientations: a  "shading factor table"  is established for each orientation, and the 3D shading calculations are performed independently for each orientation.  

Mixed orientations sub-arrays

It is commonly admitted that on a given MPPT input, all the collectors should be perfectly identical and have the same orientation.

However when defining the orientation of a sub-array, you have the possibility to define "Mixed #1 and #2". This means that you can define a sub-array with some strings in the first orientation and some other ones in the second orientation, even when these strings belong to the same MPPT input.

The simulation will establish the I/V curve for the strings of each orientation, and add them (in current) in order to get the full MPPT behavior, taking a possible mismatch into account.  

This mismatch is usually not very important with strings in different orientation. However, you cannot specify modules of a given string in different orientations: in this case, the mismatch may be very high, and this is not allowed in PVsyst (this is not a good practice).

N.B.: You can only mix orientations #1 and #2, but you can define several sub-arrays with these mixed orientations. You can do adjustments of the configuration using the button "Orient distrib." (see Power Sharing)

Tool for Mixed orientation analysis

In "Tools", button "Electrical behaviour of PV arrays", you have a tool to understand the composition of different I/V curves on a MPPT input.  

This tool shows the characteristic of two sub-arrays, connected in parallel that can be different in orientation and collector's kind or number.

When connecting together the outputs of 2 different sub-arrays, the resultant characteristic will depend on incident irradiances on each of the sub-fields. It is therefore necessary to introduce a model for the irradiance, in such a way as to be able to evaluate simultaneous irradiances under realistic conditions along the day. The tool uses a clear day profile, but with the possibility of modulating the global amplitude and the rate of diffuse irradiation. The temperature of the modules is calculated according to the respective irradiances. The user may use the scroll bar to modify the time-of day in order to evaluate the dynamic behavior during the day when the orientations are different.

The graph shows the respective I/V characteristics of each sub-field and their resultant (current sum) when connected in parallel. The comment gives the nominal MPP value of each array, as well as their common value and the relative loss when connected in parallel. You can observe that when the array voltages are comparable the power loss is usually low, even for very different currents (different orientations along the day, or different parallel strings). In this case, the performances of each array are simply added together.

But for different voltages (different number of modules in series), the resultant characteristic shows two distinct maxima with a serious loss of power. This could also induce the MPP tracking device into error, as it may "choose" the secondary maximum.

When the arrays are expected to operate under different voltages (heterogeneous arrays, but also by partial shading effects), it is also very important to connect blocking diodes in each string. The dotted line shows the resulting behavior if these diodes are omitted: the production of the higher array may flow into the lower one, inducing a feeding power into the "overvoltage" region.