I am using PVWatts to model upsizing my existing solar system and the results PVWatts is giving me is surprising but I can't find my error. The inverter is a SolarEdge 7600H which supports up to 11.8 of DC kW.

In PVWatts if I put in my proposed new system in zip 92131 size of 11.36kW, Premium modules, system losses at 10. tilt 20 and azimuth of 142 and in Advanced put DC to AC Size Ratio to 1 I get a result of 19,455kWh/Year.

If I take 11,360/7600 I get a ratio just shy of 1.5. When I put that into PVWatts as the AC/DC ratio and recalculate it says I will get 18,565 from the system. So 18,565/19,455 is .954 or 95.4%.

So even with a 1.5x oversized system the result per PVWatts is I will get about 95% of the output even with a 1:1 inverter. This seems like too much production. I understand that PVWatts is a model and perhaps I'm using it wrong. Did I miss a step or foul my math? If not I'll stick with my current inverter.