The time when the designs of PV systems were only developed in wide-open areas is coming to an end. Today, many PV systems are installed on rooftops across Australia that do not always face the same direction. But multiple orientation installations can be problematic. Let’s find out why.

Why multiple orientation designs are a problem for solar 

PV systems are designed in strings. 

Each string should have the same number of solar panels in order to reach the same voltage in every string, which is crucial to connect the modules to the inverter. 

However, sometimes the space restrictions of the house or commercial centre will not allow the designer to place all solar panels facing in the same direction. 

For instance, if the string is designed with 5 solar panels per string, the available space might only be enough to place 3 solar panels facing north and 2 modules facing west. 

The issue with this is that mismatch losses appear in the scenario due to different orientations at the moment of tracking the maximum power point (MPP) of the array.

In our example, if three modules face north and two face west, the P-V or I/V curve of that string will have an irregular shape and tracking the MPP will be very hard for the inverter’s MPPT algorithm, since irradiance values will be different in every module. 

Moreover, the less-producing orientation will affect the power production of the other modules, since they are located in the same string.

This disparity will create so-called mismatch losses between solar panels and they could have an important impact on the performance of the inverter and the PV system energy yields. 

Strings with different orientations connected to the same inverter are occasionally allowed, since the mismatch losses are expected to be lower than 2% (according to SMA and Fronius sources). 

However, solar panels with different orientations within the same string and connected to the same central inverter are regularly not accepted and are considered a bad design since mismatch losses are expected to be much larger.

What’s the solution?

If space and technical restrictions of your design force you to place solar panels with different orientations within the same string, the best solution is to install Module-Level Power Electronics (MLPE). 

One of these devices is the DC optimiser which is placed on the rear side of the module to independently track the maximum power point of the solar panel and send it to the inverter.

Tigo is one of the two main companies that offer DC optimizers. 

The latest version of DC optimisers is the TS4 series which can be found in several models. 

The TS4-O or TS4-L covers include all the features from the Monitoring (TS4-M) and from the Safety cover (TS4-S), but also includes a predictive I/V feature that allows the designing of PV systems with different orientations, without affecting the performance of the array. 

Basically, the TS4-O cover allows your solar panels to have an independent power output production that will not affect the rest of the solar panels on the same string under shading conditions, and that will reduce mismatch losses due to different orientations.

Also, an important detail to take into account when designing PV systems with multiple orientations is related to the minimum start voltage of the inverter. 

Having different orientations influences the temperature values of the solar panels since one section might be receiving solar radiation (east-facing modules during the early morning) and others might not, cooling them down (west-facing modules during the early morning). 

This affects the voltage of the string and in some cases, the shorter string might not be able to reach the minimum voltage of the inverter throughout the day.

With these conditions, you must make sure that the orientation with more solar panels will be able to turn on the inverter throughout the day. 

This orientation should be the one that faces closest to north (in Australia). 

If this is the case, to increase the performance of the system you can place the TS4-O optimisers on the orientation that has fewer solar panels. 

This feature is called Selective deployment and is unique from Tigo’s TS4 series.

The amazing thing about this feature is that the designer does not have to add an entire set of DC optimizers for all arrays, which reduces costs and makes the project more attractive to the customer.

Meanwhile, if both orientations are able to exceed the minimum inverter voltage completely, the advice is to deploy the DC optimizers in all the solar panels. This is particularly recommended for PV systems with east-west configurations split in half.

Conclusion

Selective deployment is a new feature from TS4-O DC optimizers. It presents many advantages when dealing with shading and multiple orientations within the same string. 

If the solar panels are placed in the same string and they have different orientations, the modules that are placed in the less-producing orientation will affect the performance of the others. 

For instance, if you place 6 modules to the north and 3 to the east, the ones facing east will reduce the power output of the other modules facing north throughout the day.

To rectify this problem, you can place TS4-O optimisers on the less-producing orientation panels (east) and they will not affect the power output of the others (north). 

Simply keep in mind that your design must take into account that the longer string should be able to exceed the startup voltage of the inverter on its own, or if the two strings in different orientations have the same number of panels, then place the optimisers on all the array.

For more information visit How Solar Works.

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