Renewable energy integration and electrification of energy sectors are key strategies to decarbonise the energy system. However, the stochasticity of renewable energy technologies (e.g., photovoltaics (PV)) prevents them from supplying energy on demand and could cause issues for the electricity grid, thereby reducing their economic value. This thesis focuses on the roles which energy storage, flexibility options and sector coupling can play in decarbonising the Swiss energy system. The deployment of PV, lithium-ion and vanadium redox flow batteries are studied under different decarbonisation pathways scenarios, as well as the flexibility enabled by electric domestic hot water boilers and demand-side management with wet appliances and sector coupling.