CHP plant produces more than demand

[MarcoRP]

Hello,

I’m trying to create a simple model with a back-pressure CHP plant that must meet a specific heat demand. To set up the plant, I’ve used the CHPR~FX attribute to fix the ratio between heat and electricity production. I’ve assigned the electrical capacity to the STOCK attribute and the electrical efficiency to the EFF attribute.

There’s no electricity demand in the model, and the electricity export price is set to 0. In theory, this means the optimal behavior for the CHP plant should be to produce just enough heat to satisfy the demand, with electricity being a byproduct dictated by the CHPR~FX ratio.

However, the model shows the CHP plant producing around 26 PJ of heat annually, even though the total heat demand is only 5 PJ. I can’t figure out why this is happening—it seems like I’m missing something obvious, but I’m not sure what it is.


I have attached the model folder here.

[Antti-L]

That was a funny case.  Are you just trying make a trick on us all? 

Your dummy prices are set so astronomical that even Cplex gets tricked:
ACT_COST ' '/
'DK1'.2024.'IMPDEMZ'.'MDKK24' 8888000000000
'DK1'.2024.'IMPMATZ'.'MDKK24' 10000000000000000000
'DK1'.2024.'IMPNRGZ'.'MDKK24' 10000000000000000000
'DK2'.2024.'IMPDEMZ'.'MDKK24' 8888000000000
'DK2'.2024.'IMPMATZ'.'MDKK24' 10000000000000000000
'DK2'.2024.'IMPNRGZ'.'MDKK24' 10000000000000000000
/;

I tested with more sensible prices and indeed got sensible results.
ACT_COST ' '/
'DK1'.2024.'IMPDEMZ'.'MDKK24' 8888
'DK1'.2024.'IMPMATZ'.'MDKK24' 1000
'DK1'.2024.'IMPNRGZ'.'MDKK24' 1000
'DK2'.2024.'IMPDEMZ'.'MDKK24' 8888
'DK2'.2024.'IMPMATZ'.'MDKK24' 1000
'DK2'.2024.'IMPNRGZ'.'MDKK24' 1000
/;
So, your "issue" had actually nothing to do with VEDA or TIMES, or CHP modeling for that matter. 

[MarcoRP]

Thank you very much; that makes things much clearer. I hadn’t considered that at all. I initially set the dummy prices very high due to a mistake with energy outputs being in different units but forgot to lower them afterward.