Abstarct: Energy systems such as electricity and natural gas have been independently operated and planned. However, today, the benefits of integrating the energy infrastructures of electricity and natural gas have led in multi-energy systems (MES). These systems make possible simultaneous optimization of various forms of energy. Aiming to address customers’ demands for electrical and thermal energy, this thesis used an electricity grid, a natural gas network, and the solar power as inputs of a multi-energy system. The primary challenge in the application of a multi-energy system is its design according to the concept of energy security. Additionally, a system should be designed so as to address consumers’ demands for years. Therefore, a number of accessible transformation and storage technologies in various sizes and efficiency levels were made available to the designer. The system performance should both address subscribers’ demands and minimize costs and pollution. Pareto front was used to analyze variations. In order to increase system flexibility and consumers’ contribution to the problem objectives, a demand-side management program was implemented to help customers make informed decisions about their energy consumption and help the system designer reduce the peak load and modify load shape specifications.