Mixed-Orientation Solar Panel String Calculator

What happens if you string different-orientation solar panels together witout optimisers?

Calculations

Based on climate data for the geographic centre of Ireland.

Simulations model solar panel performance across 8760 hourly timepoints over the course of a year.

Global vs Local MPPT Search

MPPT (Maximum Power Point Tracking) is where a solar inverter tries to find the voltage/current combination that produces the most power overall from solar panels at any given moment.

Mixed orientations on a single string is a special case where the algorithm needs to use "global search", something that's not generally required where all panels are unshaded and face the same direction. If you have solar panels of different orientations connected to a single string without optimisers, then it's essential that you use global MPPT search in order to get the most from your solar panels. This option is available via the settings menu of most solar inverters.

What Happens When You Mix Solar Panel Orientations?

With local MPPT search: The orientation with less sunlight will generally limit the current (Amps) that the panels can generate. This typically results in substantially lower energy generation than if the two orientations of panels each had a separate string.

With global MPPT search: The inverter will "decide" whether to use all panels in series (sacrificing some current, depending on the degree of mismatch), or use only one of the orientations (activating bypass diodes so that the orientation with less sunlight gets idled). While still generally not as productive as two separate strings, this can get close, and certainly performs better for mixed-orientation strings without optimisers than local MPPT search.

Does it Make Sense to Mix Solar Panel Orientations Without Optimisers?

Arguably yes in some cases. You can avoid the cost and potential failure points of optimisers, while still getting around 90% of the production that you would if each orientation had its own string. In the era of low solar panel hardware costs, this is arguably a worthwhile trade-off.

Having a separate string for each orientation is not always feasible given hardware constraints. Most small solar inverters have no more than two strings, while many roofs have space for panels across three or four orientations.

In general, orientations that are relatively close (e.g. South and East) will work better together on a single no-optimiser string than orientations that are diametrically opposed (e.g. East and West).