This project looks into the impact of data uncertainty on the techno-economic decisions of the actors in a future energy system, with flexibility sources. It considers three actors, namely the distribution system operator, aggregators (as potential operators of a demand response program), and end-users, like building energy managers and residential consumers. A comprehensive framework is developed to quantify the sensitivity of a hypothetical energy system with flexible sources, which might be put in place in the future, to unknown and inaccurate data. The proposed framework consists of three modules: a simulation module, a local sensitivity analysis (LSA), and a global sensitivity analysis (GSA). Hypothetical energy systems that harness the available flexibility from the demand side are simulated as optimization problems. Such models reflect the requirement of existing, or emerging actors in the system.