Nowadays, national decarbonisation strategies and policies aim to address climate change, defining pathways for the transition towards a net-zero emissions energy system. In this energy transition, all sectors must contribute. However, the electricity sector has the greatest potential to decarbonise: a fully decarbonised power sector is expected by 2050. To support policymakers in planning the evolution of energy systems, optimisation modelling tools are needed to capture key challenges and opportunities. In this thesis, long-term scenarios for Italy are analysed to achieve the imposed targets of emission reduction for the power sector. An hourly resolution power system spanning three years is modelled.