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When combining strings with a different azimuth in an off grid system, lets say NNE facing with North Facing and NNW facing (Southern Hemisphere), you catch the morning and evening sun better, this is called "Virtual Tracking" where fixed panels can start charging sooner in the day and stop charging later in the day enabling your battery dependent period to be shortened.

An example might be 9 panels facing in each of the three directions.

Now my question is regarding the electrical characteristics of this practice, if you were to combine the panel strings facing in different directions in the same sub-array, combiner and charge controller.

One assumes that each panel string (i.e. the ones facing different directions) produces a different current output at the same voltage, if this is the case, I guess their is no problem (although at the very start and end of the day, the voltage might not be the same which could cancel out the benefit of doing virtual tracking in the first place).

I guess that if the panels facing different directions (Azimuth) were grouped together on the same combiner and charge controller (i.e. different directions use different combiners), there would be no problem and everything is telling me that this is the only best practice way to implement virtual tracking to avoid imbalance and any electrical back-feeding between the panel strings.

Lets assume three ±45Voc panels are in each string and three strings are combined into one 150V MPPT charge controller, e.g. Outback FlexMax 80, what is going to happen electrically if we mix strings with panels facing different directions, i.e. one facing North, one facing NNE and facing NNW, will the worst performing string at any time of the day become the common denominator for sub array performance.

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It depends what your priorities are.

First, combine all panels with the same azimuth (same illumination) directly (series, parallel, mixed, doesn't matter), and make each different azimuth combination have the same nominal voltage.

If you want a long charging day, cheaply, then combine the different directions in parallel, each with a diode in series with it. This will prevent dark directions robbing power from illuminated ones. The brightest direction will deliver almost the entire load.

If you want the highest total output, and are willing to spend a little more, then connect each direction to its own MPPT controller, and combine their outputs. Then even poorly illuminated directions will add as much as their light permits to the total output.

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  • \$\begingroup\$ This is exactly what I though might happen, I am upgrading a system with 2 MPPT controllers one with 5 parallel strings of 3 panels and one with 4 parallel strings of 3 panels, each string is ± 140Voc and 525Wp, currently they face random directions. My upgrade will add a third charge controller enabling me to separate different directions on different charge controllers. \$\endgroup\$ – user207364 Dec 16 '18 at 21:23

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