Thermo-economic comparisons between solar steam Rankine and organic Rankine cycles

Among all concentrated solar power technologies, plants with parabolic trough collector and steam Rankine cycle are the most matured and established technology. Organic Rankine cycle is a promising option for modular scale power plants with low temperature heat sources. The decision of selection between steam Rankine and organic Rankine cycles is influenced by solar collector field characteristics and cost, steam Rankine cycle efficiency, and power block cost. In this paper, based on the condition of equality of the levelized cost of energy, a methodology for selecting working fluid through a novel graphical representation, called working fluid selection diagram, is proposed. The proposed methodology also includes selection between parabolic trough and linear Fresnel collector based plant, for a given working fluid of the Rankine cycle. Most of the methods, proposed in literature, require multiple simulations for selecting various design parameters and optimum configuration of the plant. The proposed working fluid and solar collector field selection diagrams can be used for quick suggestion about optimal configuration of a concentrated solar power plant, without any detailed simulations. Based on the thermodynamic and economic parameters, R113 and isohexane achieves levelized cost of energy close to the parabolic trough collector based plant with steam Rankine cycle. Effects of different parameters on selection of optimal configuration of a concentrating solar power plant are also studied. The analytical procedures developed for selecting solar collector field and working fluid of the power generating cycle are important during conceptual design of a concentrated solar power plant. These methodologies can be applied at the initial design stage to compare the alternative configurations and to reduce the search space related to various design parameters.