Thermosyphon Rankine cycle (TRC) is an environmentally friendly system for direct extraction of electrical power using low enthalpy heat sources. An enhanced design of the TRC system using impulse turbine was recommended, in this paper. Energy and exergy analysis of the TRC was formulated in order to estimate its optimum operating conditions. Also the data available in open literature were used to validate the TRC mathematical model. The results showed that the highest efficiency happens for the reaction turbine model at the turbine infinite speed; and for the impulse turbine at the turbine limited speed. The simulation results indicated that the present model can be able to increase the efficiency of the TRC system. (C) 2009 Elsevier Ltd. All rights reserved.