The thesis of this paper is a techno-economics analysis of solutions regarding the energy sustainable city in the Republic of Croatia. This thesis is related to the course “Urban Energy System”, and the main reason why the example of an urban energy system smaller town like Požega in Požeško-slavonska county in the Republic of Croatia was taken and analyzed. The paper is divided into several parts, theoretical and practical. The theoretical part will include basic technologies and components of sustainable energy, primarily renewable energy technologies for electricity and heat productions and consumer technologies to reduce consumption and to promote sustainable development such as the use of smart devices, electric vehicles, and energy efficiency measures. The practical part which is the main and core part of the paper, includes reference to the city of Požega and the analysis that includes energy analysis of the city’s power and thermal energy system, analysis of natural resources as potential renewable energy sources, and techno-economic analysis of solutions such as biomass cogeneration and photovoltaic power plant that are considered to ensure the energy sustainability of the city. Domestic and foreign literature, internet sources, personal communication with companies related to the topic for the purpose of scientific research analysis of the city of Požega, computer simulation tool HOMER Pro, budget tools of Microsoft Excel software package Microsoft Office and other listed sources were used for the preparation of the thesis. Examples of energy plants such as biomass cogeneration and solar power plant were analyzed, supported by technical and economical calculations, references to EU Directives, laws and regulations of the Republic of Croatia, and analyzed as a solution for energy sustainability and independence of the city. At the end of the thesis, the impact of the potentially built power plants on the electricity and thermal power system of the city is presented and some advantages, disadvantages, but also the conditions that need to be ensured for such a solution to be feasible in the future. The analysis determined the energy sustainability of the city of Požega, which is considered to be a prerequisite for the creation of the cities of the future, the so-called smart cities that will use renewables, an advanced network, and ICT technology to manage energy within the system, and will be able to operate in the parallel as part of the energy systems or as autonomous micro-grid. Technical or energy analysis will take into account the installed capacity of the planned bioenergy, supply system with all consumers, analysis of load and natural resources in the observed area, and economic analysis will provide a framework and overview of financial costs and profitability of such projects through LCOE method and the approximate repayment time of required investments.