Performance of Solar-Thermal Organic Rankine Cycle (STORC) Power Plant with a Parabolic Trough System

Abstract

Modelling of the Organic Rankine Cycle (ORC) technology reduces the cost of testing and optimisation by providing tools for the evaluation and optimisation of existing and proposed ORC plants. This paper presents the thermodynamic potential for Solar-Thermal Organic Rankine Cycle (STORC) power plants by using Matlab Simulink® and Thermolib library software. The methodology was implemented based on existing plant designs in South Africa, which demonstrate opportunities for further optimisation of the available plants.

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 ORC 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 thermophysical properties for a specific period of the possible power output from the plant. The resource model extrapolates the required values of the specific weather data from the given set from databases. The thermal collector model applies heat and other energy transfer principles to estimate the useful heat gain, temperature of fluid at exit and the efficiency of the collector. The graphs of the storage tank show the changes in enthalpy and temperature of fluid before entering and after leaving the storage tank. Power output variation and property diagrams from the model results provided a tool for the case studies on the sensitivity and performance analysis and 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.