Control System for Heat Generation in a Hybrid PV/T System

Abstract

The study analyzes the performance of a PV/T unit with a PCM attached to the rear side of the PV panel in direct contact. The unit works removing heat from the panel and using this heat for external applications. The PCM has a heat exchanger inserted to transfer heat removed from the PV panel and stored in the PCM to a water flow that circulates through the heat exchanger. The efficiency of the PV panel is increased because of the temperature control, and can be optimized through a control unit. Heat transferred to the PCM and to the water flow enriches the overall energy generation of the unit, thus improving the global performance of the PV/T system. A control unit has been designed to operate the PV/T system for optimum conditions, forcing the PCM to work at the melting temperature zone, so the operational temperature of the PV/T system remains constant. Since the PV panel and the PCM are in thermal equilibrium, the temperature of the PV panel can be set up at the optimum value if the appropriate PCM is selected. In our case, paraffin wax of medium density has been chosen as PCM, operating at a melting point of 48º C that corresponds to the typical value of the NOCT for a PV panel. The operating zone moves between 45.8ºC and 50.2ºC because of temperature measurement uncertainties. The use of the typical NOCT value makes the PV panel to work at its optimum efficiency point; this process is ruled by the control unit that assures the PCM does not operate out of the melting zone activating or deactivating the water flow that circulates throughout the heat exchanger. The system has been simulated to reproduce real operating conditions for different solar radiation levels. The results from the simulation tests have proved that the hybrid PV/T system improves the efficiency of the PV panel as well as the overall thermal and electric efficiency.