The possibility of exploiting low temperature liquid-dominated geothermal sources can considerably increase the use of this kind of renewable energy. Improvements in the performance of geothermal cycles are possible by using closed Rankine and Kalina cycles, whose working fluid may be a pure substance or a two-component mixture. In this paper three configurations of the Rankine cycle are examined and compared to conventional single and dual flash steam power plants. The Kalina cycle system no. 12 has also been studied. Results showed that there is a potential for optimisation of the performance, by modifying the main parameters, such as turbine inlet pressure and type of fluid.