DC vs AC Capacity Factors

Hello SAM, 

From what I read, capacity factor calculations always use the actual AC kWh electricity generated in one year in their numerator. This AC electricity must contain the effect of the overall derate factor. The denominator, however, could be expressed in DC (after PV panels) or AC power (after inverter) multiplied by 8760 hours. Question: Does this mean that AC power should include the contribution of inverter efficiency only and not the entire derate factor?

Therefore, is the following, correct?

• Solar panel rated DC power = 100 kW-dc
• inverter efficiency = 95%
• Inverter output AC power = 95 kW-ac
• derate factor = 80%
• Power after overall derating = 80 kW-ac
• AC kWh generated in one year = 175,200 kWh-ac

DC CF = 175,200 kWh-ac / (100 kW-dc x 8760 h) = 0.2 or 20%

AC CF = 175,200 kWh-ac / (95 kW-ac x 8760 h) = 0.21 or 21%

And would this be incorrect: 

AC CF = 175,200 kWh-ac / (80 kWh-ac x 8760 h) = 0.25 or 25%

Many thanks!

Best,
Arman

Hi Arman,

I am not sure there is a "correct" way to calculate the capacity factor. Any use of the capacity factor should be accompanied by a description of how it was calculated.

In SAM, the capacity factor is based on the nameplate capacity of the array (rated DC power at Standard Test Conditions) or inverter (maximum AC power output). It does not apply any derating factor to the capacity term in the denominator.

Best regards,
Paul.