Solar photovoltaic power generation will play a dominant role as jurisdictions around the world move toward a future decarbonized economy. For decarbonised power systems that rely on variable renewable energy, flexibility will be one of the most valued services needed by the greater electricity system. This thesis presents the modelling approach and results of a production cost model of British Columbia to examine the implications of large penetrations of rooftop solar PV on the electricity system. The modeling approach focuses on accurate modelling representations of hydro system flexibility, with differentiation made between storage hydro and run-of-river hydro assets. Current literature gives little attention to the exact representation of hydro-dominant system flexibility as it is often assumed to be almost completely flexible.