Various Rankine cycle architectures for single fluids and other improved versions operating with ammonia/water mixture are presented in this paper. Untapped heat resources and their potential for driving organic Rankine cycles are outlined. The nature - state and temperature of the heat source significantly influences the choice of the type of organic Rankine cycle machine. The temperature appears as a critical parameter during the selection process. Modules differ from one another from technology, size and cost viewpoints. The investment cost of an ORC project includes machine, engineering, system integration, capital costs, etc. and is closely linked to the application.