Optimal heat recovery during polymer electrolyte membrane electrolysis

Abstract

The severe reduction in the available fossil fuel resources highlights the need to make more use of renewable energy resources (RER), such as solar photovoltaic (PV) modules, wind turbines, hydro-turbines, etc. Hydrogen (H2) may be seen as a possible alternative fuel which can be produced from renewable energy, as mentioned and a promising contender in the energy storage domain. A hydrogen electrolyser harnesses the energy produced by the RER, in order to produce H2, which could be stored in its current form to be used at a later stage to generate electrical energy, by means of a fuel cell.In this paper, an optimal switching control of a solid polymer electrolyte membrane water electrolyser (PEMWE) water heating system is presented, in which actual historic exogenous data obtained from a weather station in the considered area is used as inputs for the established model.The main aim of this paper was to develop an optimal control model, which maximizes the removal of the undesired heat from the PEMWE and transferring it to the hot water storage tank (HWST), whilst ensuring sufficient hydrogen is being produced.Simulations of the optimal switching control of a PEMWE water heating system was conducted successfully with the SCIP (Solving Constrained Integer Programs) solver in the optimization toolbox in MATLAB.The optimal switching control model yields a daily energy consumption of 49.85 kWh by the PEMWE compared to an energy consumption of 48.86 kWh by the standard PEMWE system (baseline). The optimal switching control model resulted in 2.51 kg of hydrogen compared to 2.56 kg which is produced by the standard PEMWE system. Moreover, the optimal control model recovered 1.03 kWh of heat successfully which is transferred to the HWST.The optimal control model development and implementation for a PEMWE to maximize the thermal energy recovery from the PEMWE to the HWST whilst ensuring stable H2 production are presented as one of the main contributions to the study.Secondly, by recovering the generated heat from the PEMWE, the time period for the membrane to degrade to a thickness of 50% could be prolonged by 0.68 years, after which the membrane degradation occurs non-linearly.