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NCAP_AFC and NCAP_AFA
#1
Hi everyone !

I am curently leanrning how to use VEDA and the TIMES model.
I have a question about the two attributes NCAP_AFA and NCAP_AFC : I understand they represent the load factor of a process, the former modelling a sort of mean value over all the commodities that come out of a process, and the latter representing a sort of relative value, but I'm not sure actually .

Can someone tell me how to interpret these values ? i.e. How can I understand a process with both AFA and AFC defined ? Which one is to be taken in consideration when I want to know the loda factor of this one process over a specific commodity ?

Thanks for your help !    Smile
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#2
Have you not been reading the documentation, or under VEDA2, looking at Information → TIMES Attributes?

From both places you can find basic info, e.g. the descriptions:
NCAP_AFA: Annual availability factor relating the annual activity of a process to the installed capacity.
NCAP_AFC: Commodity-specific availability of capacity for commodity group cg, at given timeslice level.

In the documentation you can see also the equation formulations.

> How can I understand a process with both AFA and AFC defined?

As you already know, NCAP_AFA defines an ANNUAL utilization factor (min./max./fixed), while NCAP_AFC defines a commodity-specific availability at given timeslice level. Both are taken into consideration if both are defined, but if they happen to be both specified at the ANNUAL level and the bound type of NCAP_AFA is UP/FX, then they are (by default) multiplied and only the AFC constraint is generated, as you can see from the documentation. But optionally, you can define them independently also in that case.
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#3
(30-04-2021, 04:34 PM)Antti-L Wrote: Have you not been reading the documentation, or under VEDA2, looking at Information → TIMES Attributes?

From both places you can find basic info, e.g. the descriptions:
NCAP_AFA: Annual availability factor relating the annual activity of a process to the installed capacity.
NCAP_AFC: Commodity-specific availability of capacity for commodity group cg, at given timeslice level.

In the documentation you can see also the equation formulations.

> How can I understand a process with both AFA and AFC defined?

As you already know, NCAP_AFA defines an ANNUAL utilization factor (min./max./fixed), while NCAP_AFC defines a commodity-specific availability at given timeslice level. Both are taken into consideration if both are defined, but if they happen to be both specified at the ANNUAL level and the bound type of NCAP_AFA is UP/FX, then they are (by default) multiplied and only the AFC constraint is generated, as you can see from the documentation. But optionally, you can define them independently also in that case.


Thank you !
I will go deeper in the documentation, I first checked what was told about this question in it but I found difficult to understand the difference. That's why I asked it in the forum.
Regards,
Ange
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#4
(30-04-2021, 04:34 PM)Antti-L Wrote: Have you not been reading the documentation, or under VEDA2, looking at Information → TIMES Attributes?

From both places you can find basic info, e.g. the descriptions:
NCAP_AFA: Annual availability factor relating the annual activity of a process to the installed capacity.
NCAP_AFC: Commodity-specific availability of capacity for commodity group cg, at given timeslice level.

In the documentation you can see also the equation formulations.

> How can I understand a process with both AFA and AFC defined?

As you already know, NCAP_AFA defines an ANNUAL utilization factor (min./max./fixed), while NCAP_AFC defines a commodity-specific availability at given timeslice level. Both are taken into consideration if both are defined, but if they happen to be both specified at the ANNUAL level and the bound type of NCAP_AFA is UP/FX, then they are (by default) multiplied and only the AFC constraint is generated, as you can see from the documentation. But optionally, you can define them independently also in that case.


Yet, something I can't understand is the meaning of NCAP_AFC = -1, do you have any idea how we can interpret that physically ?
Thank you for your help
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#5
Where do you see such used?  In your model?  So, why do you use such, if you don't see it meaningful?

I do not know any use for such an NCAP_AFC parameter, except as an interpolation option. I have never seen anyone suggesting to define a negative availability factor, other than you.  Rolleyes
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#6
very good question Antti. @AngeBlanchard, where do you see this specified?
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#7
(30-04-2021, 10:46 PM)AKanudia Wrote: very good question Antti. @AngeBlanchard, where do you see this specified?


Yes it was an interpolation rule actually, 
thanks again for your help
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#8
Ok then.  I guess it is someone else's model, which you are trying to understand?

Anyway, just for the record some additional info:
Because NCAP_AFC(r,y,p,cg,tslvl) = X, where X ≤ 0, is more or less meaningless (even zero is meaningless, as it would cause a divide by zero in the equation), the TIMES code automatically changes any such values to INF or to 1 (the latter only if the process is a storage process and cg is a commodity). The value of INF causes the commodity to be simply omitted from the equation, whereas the value 1 is the default value for an availability factor. Zero availability factors additionally cause independent constraints to be generated for the cg in question, forcing the flows of cg to zero, which is clearly what a zero availability for cg should imply.

Hence, for NCAP_AFC, the cases where the value is converted to INF may in fact have a rare use case when the process has a flow in the PG that should nonetheless not be contributing to the capacity availability. An example would be a hydro power plant with a fixed inflow profile and a reservoir storage, where at times of flooding some of the inflow may me spilled when the storage is full and thus cannot contribute to electricity generation. The spill flow should therefore be removed from the power plant availability constraint, and that could be done by using a negative NCAP_AFC(r,y,p,NRG,tslvl). But one could also request independent AFC equations for the same purpose.

Finally, please note that NCAP_AF / NCAP_AFA / NCAP_AFS are the primary attributes for defining process availability and utilization factors on any timeslice levels. NCAP_AFC is quite rarely needed, e.g. for storage processes and some types of demand processes with flexible output shares.
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