This chapter highlights the significance of open-source energy system optimization models in enhancing the transparency and accessibility of energy system studies for policymakers. It provides a detailed example of the creation of a robust modeling framework. This includes guidance on selecting appropriate inputs, interpreting results, and connecting them to policy-relevant objectives such as the Sustainable Development Goals (SDGs), particularly SDGs 6 (water), 7 (energy), 8 (work and economic growth), 9 (industry), 13 (climate) and 15 (land). The focus is on the energy system optimization model TEMOA-Italy, a case study for Italy developed within the open-source framework TEMOA. The presented results explore the impact of possible future scenarios and energy policies on the power sector’s sustainability, showing that low emissions scenarios perform better than a base scenario concerning environmental aspects, but worse in terms of land use and social aspects like the quality of labor. Import dependence is also affected by the renewables’ penetration, due to the criticality of renewable technologies imports. The exclusion of carbon capture from the set of available new technologies improves geopolitical stability and reduces volume shortage risk.