Keep east-facing modules and west-facing modules out of the same series string. The two faces see different sun at the same hour. In series, they are forced to share one current, and the dimmer face sets it. Give each orientation its own MPPT input, or use module-level electronics so each module can sit at its own point. This page does not name a best azimuth. Annual energy by compass direction belongs to the tilt article, after a weather file, not to a slogan.
One series string carries one current
A string is modules wired in series. What that wiring does, and why voltage adds while current does not, is in what a solar string is. Put an east module and a west module in that series and the morning current has to pass through the west module, which is still in weaker sun. The afternoon reverses the problem. The bright face cannot push its current through the dim face. Bypass diodes inside a module can route around a shaded group of cells. They do not give two compass directions two currents inside one string.
Shade from a tree or a vent is a different problem, with its own account in how shade affects PV output. Two orientations are not "a bit of shade." They are two irradiance curves sharing hardware that can hold only one current.
Separate trackers, or accept one shared voltage
An MPPT input holds one operating voltage and slides it to pull more power from whatever is attached. What MPPT does is the longer account. Two faces on one input have to agree on that voltage. Separate inputs let the east string and the west string sit at different points at 9 a.m. and again at 4 p.m.
Paralleling a finished east string with a finished west string on a single tracker is a compromise: currents can add, but the tracker still picks one voltage for both. Accept that only when the inverter manual and the person signing the design both accept it. The arrangement this page treats as the clean split is a tracker per orientation, or electronics at the module.
Module-level gear, without crowning a winner
A microinverter or a DC optimizer gives each module its own operating point, so an east module and a west module need not share a string current. How a string inverter and a microinverter differ, including what fails where, is in string inverter versus microinverter. This roof decision does not pick that winner. It only refuses the mixed series string. If the inverter has two trackers and you have two faces, assign one face to each tracker and say so on the one-line.
An east face produces earlier and a west face later. For a building that uses power at those hours, the spread can raise the share consumed on site. Self-consumption is where that bill effect is explained. Whether east, west, or south yields more energy on this roof is a model of your weather file and your tilt. Run that question in tilt and orientation. Do not let a contractor mix the strings and call the compass direction optimized.
Count the trackers before the modules go up. An inverter datasheet that says two MPPT inputs may still restrict how the strings are paired: current per input, voltage window, and whether the two inputs may be loaded unevenly. East and west are uneven by nature, morning and afternoon. If the manual wants the inputs balanced, this roof may need a different inverter or module-level gear, not a clever series jumper between the faces. Write the assignment on the one-line so the next person does not tidy the two faces into one series run.
