Thermodynamic analysis of solar-based photocatalytic hydrogen sulphide dissociation for hydrogen production

The dissociation of gaseous hydrogen sulphide (H₂S) into its components is an energy intensive process. The process is studied in this paper with respect to the thermodynamic limits. The band gap of the catalyst and the nature of the solar radiation limit the proportion of incoming radiation that may be used for the reaction. The intensity of the incoming radiation and the reactor temperature are varied and the performance is studied. The exergy efficiency is determined as a function of the quantum efficiency of the photochemical process, and the catalyst band gap. It is shown that an optimum case exergy efficiency of up to 28% can be achieved for the process. With the current status of technology, an exergy efficiency value in the region of 0.4–1% is calculated, with a short-term improvement potential of up to 10%. Hydrogen sulfide has high energy content, but is not widely used due to its impact on environmental pollution. The proposed process in this paper is attractive as it allows that energy to be utilized, while degrading the highly toxic gas into less harmful products.     

Energetic and exergetic performance evaluations of a geothermal power plant based integrated system for hydrogen production

In this paper, we propose an integrated system aiming for hydrogen production with by-products using geothermal power as a renewable energy source. In analyzing the system, an extensive thermodynamic model of the proposed system is developed and presented accordingly. In addition, the energetic and exergetic efficiencies and exergy destruction rates for the whole system and its parts are defined. Due to the significance of some parameters, the impacts of varying working conditions are also investigated. The results of the energetic and exergetic analyses of the integrated system show that the energy and exergy efficiencies are 39.46% and 44.27%, respectively. Furthermore, the system performance increases with the increasing geothermal source temperature and reference temperature while it decreases with the increasing pinch point temperature and turbine inlet pressure.     

Exergetic assessment of solar hydrogen production methods

Hydrogen is a sustainable fuel option and one of the potential solutions for the current energy and environmental problems. Its eco-friendly production is really crucial for better environment and sustainable development. In this paper, various types of hydrogen production methods namely solar thermal (high temperature and low temperature), photovoltaic, photoelecrtolysis, biophotolysis etc are discussed. A brief study of various hydrogen production processes have been carried out. Various solar-based hydrogen production processes are assessed and compared for their merits and demerits in terms of exergy efficiency and sustainability factor. For a case study the exergy efficiency of hydrogen production process and the hydrogen system is discussed in terms of sustainability.     

Solar hydrogen production: A comparative performance assessment

Hydrogen is a sustainable fuel option and one of the potential solutions for current energy and environmental problems. Its eco-friendly production is really crucial for better environment and sustainable development. In this paper, various solar hydrogen production methods are discussed. A comparative performance assessment study of solar thermal and photovoltaic (PV) hydrogen production methods is carried out. It is found that the solar thermal hydrogen production via electricity production is an environmentally benign method and possesses higher exergy efficiency than PV hydrogen production. However, the latter is better in a way that it does not involve any moving parts. PV hydrogen production suffers lower exergy efficiency because of low PV efficiency.     

Development and assessment of a solar,wind and hydrogen hybrid trigeneration system

A solar-wind hybrid trigeneration system is proposed and analyzed thermodynamically through energy and exergy approaches in this paper. Hydrogen, electricity and heat are the useful products generated by the hybrid system. The system consists of a solar heliostat field, a wind turbine and a thermochemical copper-chlorine (Cu-Cl) cycle for hydrogen production linked with a hydrogen compression system. A solar heliostat field is employed as a source of thermal energy while the wind turbine is used to generate electricity. Electric power harvested by the wind turbine is supplied to the electrolyzer and compressors and provides an additional excess of electricity. Hydrogen produced by the thermochemical copper-chlorine (Cu-Cl) cycle is compressed in a hydrogen compression system for storage purposes. Both Aspen Plus 9.0 and EES are employed as software tools for the system modeling and simulation. The system is designed to achieve high hydrogen production rate of 455.1 kg/h. The overall energy and exergy efficiencies of the hybrid system are 49% and 48.2%, respectively. Some additional results about the system performance are obtained, presented and discussed in the paper.     

Preformance analysis of a water splitting reactor with hybrid photochemical conversion of solar energy

In this paper, a new hybrid system for hydrogen production via solar energy is developed and analyzed. In order to decompose water into hydrogen and oxygen without the net consumption of additional reactants, a steady stream of reacting materials must be maintained in consecutive reaction processes, to avoid reactant replenishment or additional energy input to facilitate the reaction. The system comprises two reactors, which are connected through a proton conducting membrane. Oxidative and reductive quenching pathways are developed for the water reduction and oxidation reactions. Supramolecular complexes [{(bpy)₂Ru(dpp)}₂RhBr₂] (PF₆)₅ are employed as the photo-catalysts, and an external electric power supply is used to enhance the photochemical reaction. A light driven proton pump is used to increase the photochemical efficiency of both O₂ and H₂ production reactions. The energy and exergy efficiencies at a system level are analyzed and discussed. The maximum energy conversion of the system can be improved up to 14% by incorporating design modification that yield a corresponding 25% improvement in the exergy efficiency.     

Thermodynamic analysis and experimental investigation of a unique photoelectrochemical hydrogen production system

In this study, we thermodynamically analyze and experimentally investigate a continuous type hybrid photoelectrochemical H₂ generation reactor. This system enhances solar spectrum use by employing photocatalysis and PV/T. Additionally, by replacing electron donors with electrodes to drive the photocatalysis, the potential of pollutant emissions are minimized. In this study, the present reactor is tested under electrolysis operation during which the present reactor is investigated under three different inlet mass flow rates (0.25, 0.50, and 0.75 g/s) and four different operating temperatures (20, 40, 60, and 80 °C). Some parametric studies are run by varying the environmental temperature between 0 and 40 °C. In addition, the impact of coating the membrane electrode assembly of the reactor with Cu₂O is investigated. The present results show that the highest energy and exergy efficiencies occur at the environmental temperature of 20 °C which is about 60% and 50%, respectively. The Cu₂O coated membrane gives a lot higher current readings, meaning that the coating makes the membrane more conductive and increases H₂ production by permitting ions at a higher rate.     

Analysis and performance assessment of a combined geothermal power-based hydrogen production and liquefaction system

In this paper, the thermodynamic study of a combined geothermal power-based hydrogen generation and liquefaction system is investigated for performance assessment. Because hydrogen is the energy of future, the purpose of this study is to produce hydrogen in a clear way. The results of study can be helpful for decision makers in terms of the integrated system efficiency. The presented integrated hydrogen production and liquefaction system consists of a combined geothermal power system, a PEM electrolyzer, and a hydrogen liquefaction and storage system. The exergy destruction rates, exergy destruction ratios and exergetic performance values of presented integrated system and its subsystems are determined by using the balance equations for mass, energy, entropy, energy and exergy and evaluated their performances by means of energetic and exergetic efficiencies. In this regard, the impact of some design parameters and operating conditions on the hydrogen production and liquefaction and its exergy destruction rates and exergetic performances are investigated parametrically. According to these parametric analysis results, the most influential parameter affecting system exergy efficiency is found to be geothermal source temperature in such a way that as geothermal fluid temperature increases from 130 °C to 200 °C which results in an increase of exergy efficiency from 38% to 64%. Results also show that, PEM electrolyzer temperature is more effective than reference temperature. As PEM electrolyzer temperature increases from 60 °C to 85 °C, the hydrogen production efficiency increases from nearly 39% to 44%.     

Dynamic modelling of a solar hydrogen system for power and ammonia production

A new configuration of solar energy-driven integrated system for ammonia synthesis and power generation is proposed in this study. A detailed dynamic analysis is conducted on the designed system to investigate its performance under different radiation intensities. The solar heliostat field is integrated to generate steam that is provided to the steam Rankine cycle for power generation. The significant amount of power produced is fed to the PEM electrolyser for hydrogen production after covering the system requirements. A pressure swing adsorption system is integrated with the system that separates nitrogen from the air. The produced hydrogen and nitrogen are employed to the cascaded ammonia production system to establish increased fractional conversions. Numerous parametric studies are conducted to investigate the significant parameters namely; incoming beam irradiance, power production using steam Rankine cycle, hydrogen and ammonia production and power production using TEGs and ORC. The maximum hydrogen and ammonia production flowrates are revealed in June for 17th hour as 5.85 mol/s and 1.38 mol/s and the maximum energetic and exergetic efficiencies are depicted by the month of November as 25.4% and 28.6% respectively. Moreover, the key findings using the comprehensive dynamic analysis are presented and discussed.     

Development and assessment of a novel solar heliostat-based multigeneration system

In this paper, a comprehensive study on thermodynamic analysis and assessment, through energy and exergy approaches, is conducted for a multigenerational solar based integrated energy system. The system proposed in this study is based on heliostat solar system integrated with steam turbine. The system is also integrated with seawater reverse osmosis desalination unit and absorption cooling system. The desalination unit operates with energy recovery through the utilization of Pelton turbine. The system produces cooling, heating, fresh water and hydrogen through electrolysis. It is furthermore designed to cover the demand of 4 MW electric power with the production of 1.25 kg/h of hydrogen and 90 kg/s of fresh water. The system advisor model software is applied on a case study for the solar heliostat optimization analysis.     

Experimental investigation of a solar tower based photocatalytic hydrogen production system

In this paper, production of hydrogen from concentrated solar radiation is examined by a laboratory scale solar tower system that is capable of handling continuous flow photocatalysis. The system is built and studied under a solar simulator with an aiming area of 20 × 20 cm². The fraction of solar spectrum useful for water splitting depends on the energy band gap of the selected photocatalyst. Two types of nano-particulate photocatalysts are used in this work: ZnS (3.6 eV) and CdS (2.4 eV). The effect of light concentration on photocatalysis performance is studied using Alfa Aesar 99.99% pure grade, 325 mesh ZnS nano-particles. An improved quantum efficiency of 73% is obtained as compared to 45% with the same sample under non-concentrated light in a previous study. Only 1.1% of the energy of the solar radiation spectrum can be used by ZnS catalyst. A mixture of CdS and ZnS nano-particulate photocatalysts (both Alfa Aesar 99.99% pure grade, 325 mesh) is used to conduct a parametric study for a wider spectrum capture corresponding to 18% of the incident energy. Hydrogen production increases from 0.1 mmol/h to 0.21 mmol/h when the operating conditions are varied from 25 °C and 101 kPa to 40 °C and 21 kPa absolute pressures. Furthermore, the implementation of a continuous flow process results in an improvement in the energy efficiency by a factor of 5.5 over the batch process.