Wind Capacity Factors

Hi, I'm using the NREL SAM wind tool and have a question about wind capacity factors. In my model I have a wind farm made up of 3 rows with 8 turbines per row (24 total) with each turbine having a rated output of 4.5 MW. The average output over a given year is 38.78 MW and the tool claims a capacity of 108 MW and a capacity factor of 35.9%. That makes sense if you don't account for wake losses, but the maximum output over the year is 87.3 MW due to system losses. My question is - should the denominator in capacity factor (max capacity) by the maximum possible output of the wind farm or the maximum theoretical output? My research online seems to point to it being the maximum possible output but the NREL SAM tool seems to be using the theoretical max capacity number for the capacity factor calculation.
 

Hi Jim,

There are different ways to define the capacity factor, which is why it is not an ideal metric.

In SAM, the capacity factor reported by the wind power model is calculated as follows:

Capacity Factor = Annual AC Energy in Year 1 (kWh/yr) / ( System Nameplate Capacity (kW) * 8760 (h/yr) )

For more see the "Capacity Factor" topic in Help: samrepo.nrelcloud.org/help/mtp_capacity_factor.html

Best regards,
Paul.

Thanks Paul. So when NREL predicts capacity factors as they do on their "wind supply curves" site here:
Wind Supply Curves | Geospatial Data Science | NREL

Are those projected capacity factors based on nameplate capacity or maximum output?

Thanks for your help!

Hi Jim,

I would assume that those capacity factors are calculated from the nameplate capacity, but it's always best to check references to be sure.

Best regards,
Paul.