This thesis explores the current development of geothermal power plant technologies, with a particular emphasis on the importance of implementing renewable energy sources such as geothermal energy due to its inexhaustibility. The thesis is divided into three main parts: theoretical, research, and calculation. The theoretical part describes geothermal energy and geothermal power plants, including different types of plants such as dry steam, flash steam, and binary cycle power plants. It analyzes the conditions necessary for the successful construction of geothermal power plants, investment risks, and environmental impacts. The current state of installed geothermal power plant capacities worldwide and in Croatia is also presented, along with a consideration of their advantages, disadvantages, and costs. The research part focuses on the current state of geothermal power plant technologies. The technology readiness levels (TRL) of key components in geothermal power plants are presented, and the most important manufacturers of modern geothermal equipment are listed. The leading manufacturers of geothermal equipment and their specifications are examined, with a particular emphasis on the selection of materials for optimal operation of geothermal equipment in harsh working conditions. The calculation part of the thesis includes a techno-economic and thermodynamic efficiency calculation for Croatia's first geothermal power plant, Velika 1, located in Ciglena, along with a detailed description of its technical configuration and performance.