Many countries rely on high levels of generation from Variable Renewable Energies (VREs) to decarbonise their power systems. However, scaling up VREs beyond a certain threshold generates new challenges in the already complex electricity system and renewables policy landscape.The thesis introduces a comprehensive set of indicators and associated index--the Power System Decarbonisation (PSD) Index, in view of informing policy adaptation for achieving higher integration of VRE generation while minimizing any negative impact. To develop the index, insights from other indicators such as the World Energy Trilemma and the Energy Architecture Performance Index are used. Unlike existing indices that focus on the energy sector at large, the PSD index is specific to the power sector and covers the system, market and policy dimensions. In addition to tracking the evolution of the indicators, we use a statistical approach to assess the determinants of specic key performance indicators in order to highlight critical interdependencies that have strategic implications. The thesis thus fills an important research gap with respect to data-driven and power system-wide analysis.