Understanding inverter clipping
Why oversizing the array is common, and why it isn't free
Installers frequently size the DC array larger than the inverter's AC rating, since a modestly oversized array keeps the inverter producing closer to its rated capacity during more of the day, including hazy conditions and the shoulder hours around sunrise and sunset. This is one of the tradeoffs to weigh alongside the grid tie inverter sizing calculator when picking an inverter for a given array. The tradeoff is that on the clearest, highest-output days, the array's peak DC potential can exceed what the inverter can convert, and that excess above the inverter's ceiling is lost. This estimator quantifies that specific tradeoff in annual kWh terms.
Why the shape of the daily power curve matters
Clipping isn't an all-or-nothing event across the day. Array output rises and falls through daylight hours in roughly a bell shape, so clipping only occurs during the window near solar noon when output is highest, and the amount clipped tapers to zero at the edges of that window. This calculator models that shape with a simplified triangular profile to estimate both how many hours a day clipping occurs and how much energy is lost during that window, rather than assuming a flat loss all day.
Why the DC to AC ratio is the number to watch
The ratio between array DC size and inverter AC rating is the single biggest driver of how much clipping occurs. A ratio near 1.0 means little to no clipping, while ratios above roughly 1.25 to 1.3 start losing a noticeable percentage of annual production on the sunniest days. There's no universal "right" ratio; it depends on your site's typical weather, module orientation, and how much the installer is trying to compensate for shoulder-season and morning/evening underperformance. Once you have a percentage loss figure, the cost per kWh produced calculator can translate it into an actual annual dollar cost.
Why this is an estimate, not a guarantee
Real-world clipping depends on actual weather, not a clean bell curve every day. Cloudy days rarely reach the DC ceiling at all, while unusually clear, cool days (which boost module output) can clip more than this model predicts. Treat the output here as a useful way to compare different DC to AC ratios against each other, not as a precise forecast of your system's actual annual clipping loss. For a version based on real production data rather than a modeled curve, the inverter clipping output loss calculator looks at the same phenomenon from the other direction, and NREL's PVWatts calculator models clipping with considerably more technical precision.
What this tool doesn't cover
This estimator uses a simplified single daily profile repeated across the year, not an hour-by-hour simulation accounting for seasonal sun angle changes, cloud cover, or shading. It also doesn't account for inverter-specific clipping behavior, like power limiting curves that some inverters use to soften the clip, a topic the Department of Energy's inverter and grid services overview touches on more broadly. For AC-side losses once power leaves the inverter, pair this with the AC cable loss calculator and DC cable loss calculator for the full picture.