Understanding your inverter size
Why the inverter is smaller than the array's rated wattage
An 8,000 watt DC array with a 1.20 ratio needs a 6.67 kW inverter. This is normal, not an error. Panels almost never produce their full rated wattage at once, since that number assumes lab test conditions of 25 degrees Celsius and a specific light spectrum that real rooftops rarely match exactly. Sizing the inverter smaller than the array's rated wattage lets the inverter run closer to its own full capacity more of the time instead of sitting underused for most of the day. This inverter figure is only half the system; the solar panel calculator covers sizing the array that feeds it in the first place.
What a DC to AC ratio actually trades off
A low ratio near 1.10 wastes very little potential output but leaves inverter capacity unused during average conditions. A high ratio near 1.30 uses the inverter more fully but clips a larger share of output during the sunniest hours of the sunniest days. Most manufacturers and installers land between 1.15 and 1.25 for residential systems as a practical middle ground. The inverter clipping loss estimator shows the actual energy lost at your specific ratio. The Department of Energy's technical overview of grid-connected inverters covers these inverter basics in more general terms.
Standard inverter sizes you'll actually find
Residential string inverters commonly come in sizes like 3.8 kW, 5.0 kW, 6.0 kW, 7.6 kW, 10 kW, and 11.4 kW, though exact lineups vary by manufacturer. Once this calculator gives you a target size, round up to the nearest size your preferred brand actually sells rather than assuming a custom size exists. The central inverter vs string inverter cost tool compares pricing across common size tiers.
When your setup needs a different sizing approach
Off grid and hybrid systems size differently than grid tie systems, since battery charging and backup loads factor into the total. If you're not running a straightforward grid tie system, use the off grid inverter sizing calculator or hybrid inverter sizing calculator instead of this general tool for a more accurate number.
What to check before you buy
Beyond total AC wattage, confirm the inverter's MPPT voltage window fits your string design and its maximum input current fits your parallel string count. The MPPT voltage window calculator and parallel strings current calculator check these two limits directly. Once the sizing is settled, the payback period calculator gives a rough sense of what the combined system is worth over time, and NREL's PVWatts calculator offers a more detailed production estimate before you finalize a purchase.