Correct use of existing

If the investment model is based on an existing capacity of a power plant using “existing”, no investment costs are calculated for this existing capacity. It is assumed that the power plant is virtually paid off. But operating costs are still incurred. How can you enter them?
Apart from that: In most cases not everything is invested at the beginning, but the costs are spread over e.g. 20 years. So if a power plant has not yet been paid off in full, you still have to pay annual costs even with existing capacity. So what is the benefit of “existing”? Or how do you use “existing” correctly? Is there an example of use?
Thanks for an answer!
Greetings, Amélie

This forum is for different topics so please use the oemof tag if it is an oemof question. In that case it is a solph specific question.

There are always different ways to reach the same goal. You can build groups of power plants with similar behavior and use a instance of the Transformer class for each group. If you have investment and existing capacity you can use just one instance and the existing parameter. We do not consider constant costs in the objective function, because it does not make any difference for the results and you can safely add them afterwards.

@aoberdorfer Useful to add relevant tags whenever you create a topic. I was going to add an oemof tag but couldn’t be sure this topic was actually about oemof. I think you should be able to add tags. If not, message me and I’ll do it instead. R.

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