*2.3. Summary of Models*

A summary of the approaches for energy modeling is presented in Table 1. For the purposes of this research, we distinguish three conceptual levels for all energy models. The first one looks into the operational routines of power systems dealing with balancing supply and demand on an hourly (or even finer) basis. The second one reviews the development of long-term energy systems, mostly focusing on the technology mix and its implications for system reliability, environment, economics, and so forth. Both types of model take the system perspective. The third type is real options models, which take the investor's perspective to understand the effects of policies.


**Table 1.** Overview of different model types in energy studies and their usual design choices.

We highlight the importance of hybrid models that combine several conceptual levels to reveal new insights and to capture new phenomena. Peter and Wagner [19] were able to note and quantify the benefits of an anti-correlation of power generation from renewable energy by integrating the fine resolution of operational power system models into a longterm energy system model. In contrast, Rios et al. [31] were able to comprehensively capture realistic investment behavior on an energy system level by embedding the real options logic into a long-term energy system model. However, for the purpose of designing a support instrument for renewable energy sources to steer their deployment in favor of system reliability, we need a model that combines all three levels: operational detail, system-level evolution and realistic investment behavior—a hybrid three-tier model.
