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Energy system modeling is a commonly used method to provide policy recommendations and insight to transformation pathways of energy systems. However, the low open-source availability of the frameworks in practice often leads to low interpretability and transparency of energy modeling system configurations. The configuration of an energy model entails how its system components, such as power plants, storage systems and grids operate, and which parameters are used to define them. In order to understand the impact of different model configurations and working principles on the model output, a thorough comparison between various modeling frameworks is necessary. This work thereby consists of a comparison of five open-source energy system modeling frameworks (OS-ESMFs) oemof, GENeSYS-MOD, Balmorel, urbs and GENESYS-2 on the mathematical level and spotlights selected methodological differences in renewable energy system modeling. The comparison shows diversity in the complexity of selected system components and helps to define the best use-cases and scales of application for each framework. Impacts of modeled features on the results were demonstrated by implementing two harmonized scenarios depicting the German electricity system using each framework. While similar model results were obtained for both scenarios, some differences were present, especially in the long-term expansion planning model. Some of those differences could be traced back to the identified modeling differences.

Recent European and German climate targets call for a faster power system transition towards variable renewable energy sources. With the increasing importance of Open Science, several Open Source models have been developed in recent years. However, only a few studies exist that compare their performance against each other. Therefore, this study performs a comprehensive model comparison of five mature Open Source power sector models. For this purpose, we apply eight fully harmonized and simplified one-year scenarios for the German power sector, to analyze deviations in model results. First, an in-depth analysis of two base scenarios for 2016 and 2030 reveals that linear programming-based models differ substantially from models with pre-implemented dispatch orders. Other deviations occur across all models and are mainly caused by the indifferent use of flexibility options such as storage and transmission. Second, variations of parameters and characteristics with a political significance are individually applied to the 2030 base scenario to identify their impact on model results. This includes CO2 emission budgets, increased demands by sector coupling, coal exit strategies, and renewable generation shares. The results prove that some models are far more sensitive to these parameters than others, and renewable generation shares alone are not sufficient to reach desired effects in emission reductions. Finally, a comprehensive scenario for 2030 combines all measures to evaluate general trends that result from the most recent updates in German energy policy. Model results indicate that the new targets require substantially increased investments into renewable generation capacities, storage, and transmission.

Well-founded research is needed to gain sound insights into the relationship between energy and the environment in order to ensure a basis for responsible policy-making in the face of a climate crisis. Transparency in code and data is a prerequisite for reproducible research in energy modelling and its quality assurance and is embedded in the philosophy of open source energy modelling frameworks (OSEMFs). While the focus was on improving the quality of input data and comparing models to compare results, there has been a lack of research on the effects of the structural assumptions across different frameworks. This thesis analyses the structural differences and structural assumptions between the OSEMFs OSeMOSYS and oemof. The methodology applies a wholly harmonised experimental setup to allocate output differences to diverging contextual assumptions in the underlying different mathematical equations among the OSEMFs. Diverging results between OSEMFs based on different structural assumptions occurred in this thesis and traced back to their origin. OSeMOSYS's and oemof's underlying energy balance equations lead to the same results though, when diverging structural assumptions are removed. Already a single undocumented opaque assumption in the underlying mathematical equations among frameworks can have a noticeable influence on the optimisation results. The documentation of OSEMFs is still not comprehensive enough to facilitate investigations of this kind efficiently, and the documentation of assumptions embedded in OSEMFs’ mathematical equations needs to be more detailed. The thesis could identify opportunities to enhance the performance of OSeMOSYS and highlights the importance of correct framework documentations to ensure their usability in practice., Välgrundad forskning är fundamentalt för att få en god insikt i förhållandet mellan energi och miljö för att säkerställa en grund för ansvarsfullt beslutsfattande inför diverse klimatkriser. Transparens i kod och data är en förutsättning för reproducerbar forskning inom energimodellering, dess kvalitetssärkring och är inbäddad i filosifin som behandlas av Open Source Energy Modelling Frameworks (OSEMF). Den primära fokusen av rapporten behandlar förbättring av kvaliteten av inmatningsdata och att jämföra resultatet från olika modeller. Det visar sig även finnas forskningsbrister inom effekterna av de strukturella antagagendana i dessa ramverk. Examensarbetet analyserar strukturella skillnader och strukturella antagendan mellan OSEMF, OSeMOSYS och eomof. Metoden tillämpar en harmoniserad experimentell uppsättning för att fördela resultat skillnaderna mellan OSEMF och dess strukturella antaganden. Avvikande resultat mellan OSEMF baserad på olika strukturella antaganden inträffade i denna avhandling och spårades tillbaka till deras ursprung. OSeMOSYS och oemofs underliggande energibalansekvationer leder dock till samma resultat när avvikande strukturella antaganden tas bort. Enstaka odokumenterat osammanhängande antagande i de underliggande matematiska ekvationerna mellan ramarna kan ha ett märkbart inflytande på optimeringsresultaten. Enligt resultat av examensarbetet går det att påstå att dokumentationen av OSEMF ännu inte är tillräckligt omfattande för att underlätta undersökning inom forskningsområdet, samt att dokumentationen av antaganden, vilka är inbäddade i OSEMF:s matematiska ekvationer måste vara mer detaljerade. Denna studie lyckades identifiera möjligheter att förbättra prestandan hos OSeMOSYS samt poängterar vikten av korrekta ramdokumentation för att säkerställa programmets användbarhet i praktiken.