Thermodynamic rating of an energy efficient chiller cum heater for metal hydride storage in hybrid photovoltaic - fuel cell (PVFC) system

Abstract

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.With dwindling energy resources which earth is having in the form of fossil fuels, today there is a scrupulous requirement of venturing alternative avenues, which can eventually share the ever-increasing energy demand. Solar photovoltaic is a reliable and clean source of energy. However due to its intermittent nature, it is vital to integrate solar photovoltaic with other sources of energy. Fuel cell technology because of its inherent environment friendly behavior has been an option that can fulfill this requirement. Present study deals with exploring the design challenges of integrating hydrogen fuel cell with solar photovoltaic. The continuous supply of hydrogen as fuel can be met in a safer and reliable manner through solid state storage of metal hydride system, with the hydrogen generated through an electrolyzer utilizing the PV (Photovoltaic) electricity. The challenges lie in dealing with the high-end exothermic reaction that occurs in the process of storing hydrogen in the metal hydride and the endothermic reaction that occurs in the process of extracting hydrogen. Therefore designing of an adequate cooling and heating arrangement for metal hydride storage system is also very important from efficient energy utilization point of view. Thermodynamic analysis of this cooling and heating circuit is reported for making an energy efficient PV/FC (Photovoltaic-fuel cell) system. The metal hydride unit is thermodynamically analyzed to critically ascertain the performance of the chiller that extracts the exothermic heat generation of the hydrides for the hydrogen storage to occur and the heater to achieve the reverse action. Several candidate approaches ranging from a simple back of the envelope calculations to sophisticated conjugate heat transfer analysis using CFD (Computational Fluid Dynamics) techniques are utilized to analyze the system. For the range of parameters considered, the study estimated the chiller and heater requirements of 250 W and 500 W respectively.