Capacity Factor of Generators

[ivyseidel]

I'm working with GenX v3.6 so it's possible this is updated or explained in newer versions.

I have realized I am missing some understanding on how capacity factor works in GenX. There does not seem to be a capacity factor input column in Generators_data.csv, and I am under the impression that Generators_variability.csv is meant to represent fuel availability for things like solar or wind power. In the example models provided, some natural gas generators are given a variability of 1 for each hour time step which reenforced the idea that this wasn't meant to represent Capacity factor.

There is also a write_capacityfactor in the documentation of newer versions, but this seems to be for combining the capacity factors of sites that have multiple generators on them and therefore wouldn't apply to v3.6.

The last thing I've considered is that the Cap_size and Existing_Cap_MW values are supposed to already have capacity factor applied and are not representative of nameplate capacity.

Would appreciate some clarity on this, thank you!

[cfe316]

Hi Ivyseidel,

Thanks for your query! I think GenX consistently uses "capacity factor" to refer to the ratio of the annual power output to the (nameplate) theoretical maximum annual output.
It uses "availability" or "variability" to refer to the ability to generate power during a given hour, due to external factors like sun or wind, while assuming that the plant is in good working order.

Are you interested in things like forced outages?
Confusingly, in at least one place (the description of the Capacity Reserve Margin
constraints) GenX also uses "availability" to describe the fraction of the time that a plant is normally operating, i.e. not subject to a forced outage. In other parts of the Capacity Reserve Margin constraints, this is synonymous with the "capacity derating factor", which is the value in the CapRes_x columns.

Generators_variability.csv is meant to represent fuel availability for things like solar or wind power.

This is correct.

some natural gas generators are given a variability of 1 for each hour time step.

This means that their full capacity is available to generate power. This could be lower, for example, during the summer for a coal plant where the river cooling water is hotter and so the power cycle efficiency decreases.

write_capacityfactor

This is in the older versions as well; it outputs capacityfactor.csv. This writes the annual average capacity factor; it's just the ratio sum(hourly power output) / (capacity * length_of_year).

Cap_size and Existing_Cap_MW

These are in terms of the nameplate capacity.

Are you interested in modeling something like a fleet of gas generators which are offline (due to some forced outages) 20% of the time, and also making sure that they contribute the correct amount of capacity to the capacity reserve margin?