**How does HOMER take into account the inverter efficiency for an AC PV system? Should it be integrated in the derating factor?**

As far as HOMER is concerned, an AC PV array is something that turns solar radiation into AC power. You need to make sure that the values you specify in the PV window reflect that. If you have a $10,000 PV array rated at 12 kW DC and connected to a 90% efficient inverter, then you have a $10,000 PV array rated at 10.8 kW AC. All that matters to HOMER is the AC rating, so you should enter it like so: