Design and Dynamic Simulation of a Combined System Integration Concentrating Photovoltaic/Thermal Solar Collectors and Organic Rankine Cycle

Abstract

This study presents the design of a novel ultra-high efficient solar power system. The system is equipped with a concentrating PhotoVoltaic/Thermal (CPVT) solar collectors bottomed by an Organic Rankine Cycle (ORC). The basic idea is to use a high temperature CPVT device producing simultaneously electricity and hot diathermic oil. Then, this hot fluid is used to supply heat to the Organic Rankine Cycle producing additional electricity. The collector is based on a combination of a parabolic dish concentrating solar thermal collector and a high efficiency solar photovoltaic collector. Among the possible high-temperature PVT systems, this paper is focused on a system consisting in a dish concentrator and in a triple-junction PV layer. In particular, the prototype consists in a parabolic dish concentrator and a planar receiver. The system is equipped with a double axis tracking system. The bottom surface of the receiver is equipped with triple-junction silicon cells whereas the top surface is insulated. Similarly, the ORC subsystem is equipped with tube and shell heat exchangers, a pump and an expander. In order to analyze the performance of the CPVT collector and ORC cycle, detailed mathematical models were implemented. These models are based on zero-dimensional energy balances on the control volumes of the system. The simulation model allows one to calculate in detail the temperatures of the main components of the system and the main energy flows. Both CPVT and ORC models are integrated in a more complex dynamic simulation model, developed in TRNSYS environment. Here, additional components are included in the system: Pump, tank, controllers, valves, etc. The input parameters of the model include weather conditions (temperature, insolation, wind velocity, etc.) and the geometrical/material parameters of the systems. This novel system was compared with a more conventional one, consisting of a concentrating PV collector equipped with III-V cells. Results showed that such second system (only CPVT) is more profitable from an economical point of view, with a 20 years Net Present Value 15% higher than the novel system (CPVT+ORC). Conversely, the novel (ORC+CPVT) system produces 6% more electrical energy.