MODELLING OF AN ORGANIC RANKINE CYCLE SOLAR-THERMAL POWER PLANT

Abstract

The purpose of this research is to present a comprehensive numerical model for the conversion of solar energy from sunlight to target mechanical energy of the Organic Rankine Cycle. The terminal processes include intermediate conversion of solar energy to thermal energy in the collector, and from thermal to mechanical work at the turbine. The model also incorporates thermal energy storage. Organic Rankine cycles have unique properties that are well suited for solar power generation. The thermodynamic potential of a varying Organic Rankine Cycle’s working fluids and configurations is analysed. Also, a specific thermodynamic model for STORC power plants is developed in Matlab Simulink ® software and presented. The methodology was implemented based on an existing plant design, which demonstrates opportunities for further optimisation and usability of current design practice. The model has the following elements: the first element is the solar resources model which sources the insolation energy and meteorological input at an instance of time for a specific location to the system. The second element is the solar collector model that accepts output from the solar resources model and presents the output of exit temperature of the collector fluid, the collector efficiency and the useful heat energy gained. The third element is the fluid transfer and storage model that shows the retention and regulation of system heat and temperature from the inlet to the outlet. The last item is the Organic Rankine Cycle model that presents the performance for the expected output power required with a varying fluid and configuration property diagram. Based on the study outcome, the integrated model was created to analyse the variations in geographic, geometrical properties with thermo-physical properties for a specific period of the possible power output from the plant. Case studies on the sensitivity and performance analysis show that the plant will provide more power and higher efficiencies with a larger aperture width of the collector than to the length of the collector. Furthermore, power outputs are higher for elevated and high Direct Normal Irradiance (DNI) locations than those locations with lower elevation and DNI. The report also discusses other results from the analysis of the effect on the model performance.