Understanding the output gap
Why shading hurts a string inverter more than you'd expect
Panels wired in series share one current path, and that current gets capped by the weakest panel in the string. If one panel out of ten sits in partial shade, it doesn't just lose its own output. It can drag down the output of the other nine panels connected to it in that string. This amplification effect is why a small amount of shading can cause a disproportionately large drop in a string inverter system's total output. The Department of Energy's inverter systems overview covers this string-wiring behavior in more general terms.
How microinverters and optimizers break that link
Microinverters convert power at each individual panel, so a shaded panel only loses its own output and doesn't pull down its neighbors. Power optimizers work similarly at the DC level, conditioning each panel's output before it reaches a shared string inverter. Both approaches trade the amplified mismatch penalty for a smaller, more predictable loss that scales directly with how much of the array is actually shaded.
When the output gap is too small to matter
On a fully unshaded, single-orientation roof, a string inverter and a microinverter system produce nearly identical annual output. The output gap only widens as shading and mismatch increase, so a roof with no trees, chimneys, or dormers in the way often doesn't justify the added cost of panel-level electronics on output alone. The power optimizer sizing calculator can help if you're weighing a middle option instead of full microinverters, and for a cost-only comparison rather than an output projection, the output calculator with microinverters looks at the same decision from that angle. NREL's PVWatts calculator can model the output difference at a finer level of detail than the estimate here.
Reliability is part of the real comparison too
Output isn't the only factor. Microinverters put more individual components on the roof, which means more potential points of failure over a 25-year system life, though each failure only affects one panel instead of a whole string. String inverters concentrate their electronics in one accessible location, which can make troubleshooting and replacement simpler. The inverter lifespan estimator and inverter warranty value calculator factor these long-term considerations into the decision. The output calculator with microinverters shows how this number plays out in real production.
What to do with this comparison
If your output gain from this tool is small, a string inverter with a good warranty is usually the more cost-effective choice. If the gain is significant, the extra upfront cost of microinverters or optimizers often pays for itself within a few years through the additional energy produced.