PV Watts - Capacity Factor

Is the capacity factor in the PVWatts model represented as an AC or DC value?

The capacity factor for each of the performance models is described in the SAM Help system's Capacity Factor topic.

For all of the PV performance models, including PVWatts, the capacity factor is the Total AC kWh of electricity generated by the system in a year divided by the system's rated capacity in DC kW divided by 8,760 hours per year:

Capacity Factor = AC kWh/yr / DC kW / 8,760 h/yr

Best regards,
Paul.

I just started using SAM, and it seems like when I change the module efficiency (in several different models for PV and HCPV systems), the capacity factor changes, even for the same location. This seems counterintuitive to me, since both the rated/nameplate power rating and the output power for a given year will change in proportion to the module efficiency. Could you explain why the module efficiency would affect the capacity factor, and provide some further details as to how the CF is computed? Thanks very much!
Best,
Kelsey

Dear Kelsey,

First of all, welcome to SAM!

I assume you are using the Flat Plate PV model's "Simple Efficiency Module Model" option to change the module efficiency.

Without seeing your file, it is hard for me to know exactly what might explain this. Keep in mind that it is the system nameplate capacity (kW) that SAM uses to calculate the capacity factor, not the module capacity. It is a combination of the module efficiency and number of modules in the system that determines the system's nameplate capacity, not just the module efficiency (assuming the module area does not change). The system's output (kWh) might also be affected by inverter clipping if both systems have the same inverter capacity, but for some hours of the year, the one with more efficient modules has higher DC output that exceeds the inverter's rated input capacity. Inverter clipping would cause a non-linear relationship between kW capacity and kWh output.

As for a description of the capacity factor calculation, please follow the link in my original post above to see the description in the online copy of SAM's help system.

Best regards,
Paul.