The climate change crisis requires immediate action on a global and national scale to mitigate theGreenhouse Gas (GHG) emissions. In the next decades, the energy system will experience a considerablerise in Renewable Energy Sources (RES), leading to more fluctuating electricity generation from weather dependent Intermittent Renewable Energy Sources (IRES). This requires more flexibility in the energy system on both the supply and demand side. Demand Side Management (DSM), and specifically the category Demand Response (DR) has received increased attention for its ability in increasing the energy system flexibility. The thesis investigates two methods of DR in a bottom-up energy planning graph-based framework. An indirect method utilising the inherent temporal resolution mapping in the graph-based framework and a direct method implementing a DR formulation. The two methods are analyzed in a case study representing the German energy system with 100% share of RES in Germany in the bottom-up energy planning model. The evidence from the study suggest that a direct modelling approach is better for modelling load shifting compared to the indirect method. Considerable insights have been gained with respect to individual DR measures and how it affect the demand with the direct method. The findings shows that DR measures from Washing Appliances and Heat Storage mapped to the residential and commercial sector demand has the biggest contribution of load shifting in the energy system. The results from the indirect approach suggest that a two and four hour time-step temporal resolution can give a general indication on total system cost reduction from increasing the flexibility in the model. The case studies show that DR can contribute in increasing the system flexibility in the future energy system with high shares of renewable energy.