Last December, Dr. Felix Müsgens of Brandenburg university of technology, my colleague from his visiting days at the OIES, had invited me to talk about energy market modelling in Cottbus. I was very honoured by the opportunity. At the same time, I felt challenged: what do I have to say to a professional audience, that is not
A. Something so general, that it does not need to be said;
B. Something so narrow, that nobody other than me could possibly be interested in it?
After some reflection, I have decided to talk about the most valuable skill that I have started to acquire, as a result of being immersed in the activity of modelling the energy industry.

I chose to talk about model formulation, the process that precedes the writing of equations or algorithms. More specifically, I decided to talk about the process of model formulation of decision support models in the power industry.

My presentation (shown below) can be divided into three parts:
1. General background information on the practice of modelling and on decision problems
2. Several ways of looking at the specific context we have for modelling: the operations of the electric power industry
3. After all the preparation above, we can finally dive into the heart of matter. Discussion of model formulation choices.

Why have I settled on these points? Because, when I was first starting out in this area, I found myself unable to answer very fundamental questions such as:
What am I doing? What is modelling?
Why am I doing this? Why am I building this model?
Why do I do it in this particular way? Why have I chosen this particular model formulation?

This presentation, in a way, is an answer for myself, four years ago. It is what I wish I knew back then. I hope it will be useful for you, my readers, in your work, in providing a way to think about what modellers do.