Can you tell me what HOMER assumes for the solar panels for effiency? And when using the monthly averages in the solar resource data, is HOMER assuming continuous power or does it take into account no sun at night at all?
Unless you are modeling the effect of temperature on the PV array, HOMER doesn't ask you for the PV array efficiency. You just specify the cost per kWp, and HOMER assumes that the power output is linear with solar radiation.
When you are modeling the effect of temperature on the PV array, HOMER does ask for the efficiency so that it can calculate how much of the solar radiation goes to heating the panel.
When you enter monthly average solar radiation data, HOMER synthesizes realistic hourly solar radiation data from those monthly averages. Yes, the synthetic radiation data does show the sun going down at night. You can see this if you click the Plot button on the Solar Resource Inputs window.