Which model type to choose?

By now you have learned about system perspectives and how to build optimization models, and practiced with your first bottom-up energy system model. You followed the explanation of basic building blocks and learned how to design aggregated firm and market models. So the natural question you will likely ask at this point is: which is the best model type to choose for a specific problem?

There is no general answer to this question as it heavily depends on the problem you want to analyze. One advantage of modeling is that many roads lead to Rome. In many cases you will be able to address your problem with different model types.

If you focus on the main characteristics of the different model concepts and designs we discussed, you often get a good idea for which type of question they are well fitted.

For example, think about the scale of your question:

• Large scale energy system models often focus on capturing many technical bottom-up aspects.
• Firm-oriented models allow you to capture the behaviour of profit oriented companies and how their decisions are influenced by external aspects like prices or policy regulations.
• And market models focus on interaction of actors.

Or whether you are looking for qualitative or quantitative answers:

• Conceptual/theoretical models aim to understand mechanisms and arguments.
• Numerical models can provide scenario assessments and are fitted to represent specific real world markets or systems.

Or, how your mathematical formulation fits to your question:

• Optimization problems need something to optimize like profits or costs.
• Equilibrium problems capture the interaction of different actors.

With a bit of experience those considerations will become easier and a natural part of the back and forth between defining your research problem and designing your model.