A parametric study of a renewable energy based multigeneration system using PEM for hydrogen production with and without once-through MSF desalination

The importance of renewable energy compared to fossil fuels is increasing due to growing energy demand and environmental challenges. Multi-generation systems use one or more energy sources and produce several useful outputs. The present study aims at investigating and comparing solar energy based multi-generation systems with and without once-through MSF desalination unit from the thermodynamic point of view. Firstly, hydrogen, electricity, and hot water for space heating and domestic usage are produced using the system, which consists of a parabolic trough collector, an organic Rankine cycle (ORC) and a PEM electrolyzer and heat exchanger as sub-systems. The performance of the entire system is evaluated from the energetic and exergetic points of view. Various parameters affecting hydrogen production rate and efficiency values are also investigated with the thermodynamic model implemented in the Engineering Equation Solver (EES) package. The system can produce hydrogen at a mass flow rate of 20.39 kg/day. The results of the study show that the energy and exergy efficiency values of the ORC are calculated to be 16.80% and 40% while those for the overall system are determined to be 78% and 25.50%, respectively. Secondly, once-through MSF desalination unit is integrated to the system between ORC evaporator and heat exchanger producing domestic hot water in the solar cycle in order not to affect hydrogen production rate while thermodynamic values are compared. Fresh water production capacity of the system is calculated to be at a volumetric flow rate of 5.74 m³/day with 10 stages.     

Development of an integrated thermochemical cycle-based hydrogen production and effective utilization

In this study, an assessment of a renewable energy-based hybrid sulfur-bromine cycle for hydrogen fuel production and effective utilization is performed since the present era requires lots of hydrogen for fueling many systems. Hydrogen, produced by the hybrid sulfur-bromine cycle, is supplied to the combustion subsystems by blending with natural gas for residential use. Solar and wind energy sources are potentially considered as renewable energies for green hydrogen production. Also, a drying unit is included with an incineration subsystem. A desalination unit is also integrated to produce freshwater for the community. In this way, electricity, heat, and clean water required both for the community and the subsystems are supplied. The integrated system is then assessed in terms of energy and exergy efficiencies. Here, 0.233 kg/s of natural gas and hydrogen blend and 1.338 kg/s of biomass are provided to the system. The energy and exergy efficiencies of the overall system are determined to be 64.43% and 32.24%.     

Exergoeconomic and environmental impact analyses of a renewable energy based hydrogen production system

In this study, exergoeconomic and environmental impact analyses, through energy, exergy, and sustainability assessment methods, are performed to investigate a hybrid version renewable energy (including wind and solar) based hydrogen and electricity production system. The dead state temperatures considered here are 10 °C, 20 °C and 30 °C to undertake a parametric study. An electrolyzer and a metal hydride tank are used for hydrogen production and hydrogen storage, respectively. Also, the Proton Exchange Membrane Fuel Cell (PEMFC) and battery options are utilized for electricity generation and storage, respectively. As a result, the energy and exergy efficiencies and the sustainability index for the wind turbine are found to be higher than the ones for solar photovoltaic (PV) system. Also, the overall exergy efficiency of the system is found to be higher than the corresponding overall energy efficiency. Furthermore, for this system, it can be concluded that wind turbine with 60 gCO₂/month is more environmentally-benign than the solar PV system with 75 gCO₂/month. Finally, the total exergoeconomic parameter is found to be 0.26 W/$, when the energy loss is considered, while it is 0.41 W/$, when the total of exergy loss and destruction rates are taken into account.     

Techno-economic analysis and optimization of a proposed solar-wind-driven multigeneration system; case study of Iran

This paper performs a thermo-economic assessment of a multi-generation system based on solar and wind renewable energy sources. This system works to generate power, freshwater, and hydrogen, which consists of the following parts: the solar collectors, Steam Rankine subsystem, Organic Rankine subsystem, desalination part, and hydrogen production and compression unit. Initially, the effects of variables including reference temperature, solar radiation intensity, wind speed, and solar cycle mass flow rate, which depend on weather conditions and affect the performance of the integrated system, were investigated. The thermodynamic analysis results showed that the overall study's exergy efficiency, the rate of hydrogen and freshwater production, and total cost rate are 33.3%, 7.92 kg/h, 1.6398 kg/s, and 61.28 $/h, respectively. Also, the net power generation rate in the Steam and Organic Rankine subsystems and wind turbines are 315 kW, 326.52 kW, and 226 kW, respectively. The main goal of this study is to minimize the total cost rate of the system and maximize the exergy efficiency and hydrogen and freshwater production rate of the total system. The results of optimization showed that the exergy efficiency value improved by 20.7%, the hydrogen production rate increased by 1%, and the total cost rate value declined by 2%. Moreover, the optimum point is similar to a region in Hormozgan province, Iran. So, this region is proposed for building the power plant.     

Exergy analysis of solar energy applications

Solar energy is a clean, abundant and easily available renewable energy. Usage of solar energy in different kinds of systems provides scope for several studies on exergy analysis. In the present work, a comprehensive literature review has been carried out on exergy analysis of various solar energy systems. The systems considered under study are solar photovoltaic, solar heating devices, solar water desalination system, solar air conditioning and refrigerators, solar drying process and solar power generation. The summary of exergy analysis and exergetic efficiencies is presented along with the exergy destruction sources.     

Energy and exergy analyses of OMW solar drying process

The energy and exergy analyses of the drying process of olive mill wastewater (OMW) using an indirect type natural convection solar dryer are presented. Olive mill wastewater gets sufficiently dried at temperatures between 34 °C and 52 °C. During the experimental process, air relative humidity did not exceed 58%, and solar radiation ranged from 227 W/m² to 825 W/m². Drying air mass flow was maintained within the interval 0.036–0.042 kg/s. Under these experimental conditions, 2 days were needed to reduce the moisture content to approximately one-third of the original value, in particular from 3.153 g_water/g_{dry matter} down to 1.000 g_water/g_{dry matter}.Using the first law of thermodynamics, energy analysis was carried out to estimate the amounts of energy gained from solar air heater and the ratio of energy utilization of the drying chamber. Also, applying the second law, exergy analysis was developed to determine the type and magnitude of exergy losses during the solar drying process. It was found that exergy losses took place mainly during the second day, when the available energy was less used. The exergy losses varied from 0 kJ/kg to 0.125 kJ/kg for the first day, and between 0 kJ/kg and 0.168 kJ/kg for the second. The exergetic efficiencies of the drying chamber decreased as inlet temperature was increased, provided that exergy losses became more significant. In particular, they ranged from 53.24% to 100% during the first day, and from 34.40% to 100% during the second.     

Evaluation of a hybrid photovoltaic-wind system with hydrogen storage performance using exergy analysis

This article presents and discusses the results of an exergy analysis conducted during the operation of a test-bed hybrid wind/solar generator with hydrogen support, designed and constructed at the Industrial Engineering School of the University of Extremadura, Badajoz (Spain). An exergy analysis is made of the different components of the system, calculating their exergy efficiencies and exergy losses, and proposing future improvements to increase the efficiency of the use of the surplus energy produced by the wind/solar generator. The results show the electrolyzer to have an acceptable efficiency (η_ex = 68.75%), but the photovoltaic modules a low exergy efficiency (η_ex = 8.39%) as also is the case, though to a lesser extent, for the fuel cell (η_ex = 35.9%).     

Design and analysis of an integrated concentrated solar and wind energy system with storage

This study analyzes a renewable energy‐driven innovative multigeneration system, in which wind and solar energy sources are utilized in an efficient way to generate several useful commodities such as hydrogen, oxygen, desalted water, space cooling, and space heating along with electricity. A 1‐km² heliostat field is considered to concentrate the solar light onto a spectrum splitter, where the light spectrum is separated into two portions as reflected and transmitted to be used as the energy source in the concentrated solar power (CSP) and concentrated photovoltaics (CPV) receivers, respectively. As such, CSP and CPV systems are integrated. Wind energy is proposed for generating electricity (146 MW) or thermal energy (138 MW) to compensate the energy need of the multigeneration system when there is insufficient solar energy. In addition, multiple commodities, 46 MW of electricity, 12 m³/h of desalted water, and 69 MW of cooling, are generated using the Rankine cycle and the rejected heat from its condenser. Further, the heat generated on CPV cells is recovered for efficient photovoltaic conversion and utilized in the space heating (34 MW) and proton exchange membrane (PEM) electrolyzer (239 kg/h) for hydrogen production. The energy and exergy efficiencies of the overall system are calculated as 61.3% and 47.8%, respectively. The exergy destruction rates of the main components are presented to identify the potential improvements of the system. Finally, parametric studies are performed to analyze the effect of changing parameters on the exergy destruction rates, production rates, and efficiencies.     

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.     

A new solar and geothermal based integrated ammonia fuel cell system for multigeneration

In this study, a new solar and geothermal based integrated system is developed for multigeneration of electricity, fresh water, hydrogen and cooling. The system also entails a solar integrated ammonia fuel cell subsystem. Furthermore, a reverse osmosis desalination system is used for fresh water production and a proton exchange membrane based hydrogen production system is employed. Moreover, an absorption cooling system is utilized for district cooling via available system waste heat. The system designed is assessed thermodynamically through approaches of energy and exergy analyses. The overall energy efficiency is determined to be 42.3%. Also, the overall exergy efficiency is assessed, and it is found to be 21.3%. The exergy destruction rates in system components are also analysed and the absorption cooling system generator as well as geothermal flash chamber are found to have comparatively higher exergy destruction rates of 2370.2 kW and 643.3 kW, respectively. In addition, the effects of varying system parameters on the system performance are studied through a parametric analyses of the overall system and associated subsystems.     

Thermoeconomic analysis and artificial neural network based genetic algorithm optimization of geothermal and solar energy assisted hydrogen and power generation

The study aims to optimize the geothermal and solar-assisted sustainable energy and hydrogen production system by considering the genetic algorithm. The study will be useful by integrating hydrogen as an energy storage unit to bring sustainability to smart grid systems. Using the Artificial Neural Network (ANN) based Genetic Algorithm (GA) optimization technique in the study will ensure that the system is constantly studied in the most suitable under different climatic and operating conditions, including unit product cost and the plant's power output. The water temperature of the Afyon Geothermal Power Plant varies between 70 and 130 °C, and its mass flow rate varies between 70 and 150 kg/s. In addition, the solar radiation varies between 300 and 1000 W/m² for different periods. The net power generated from the region's geothermal and solar energy-supported system is calculated as 2900 kW. If all of this produced power is used for hydrogen production in the electrolysis unit, 0.0185 kg/s hydrogen can be produced. The results indicated that the overall energy and exergy efficiencies of the integrated system are 4.97% and 16.0%, respectively. The cost of electricity generated in the combined geothermal and solar power plant is 0.027 $/kWh if the electricity is directly supplied to the grid and used. The optimized cost of hydrogen produced using the electricity produced in geothermal and solar power plants in the electrolysis unit is calculated as 1.576 $/kg H₂. The optimized unit cost of electricity produced due to hydrogen in the fuel cell is calculated as 0.091 $/kWh.     

Experimental study of a solar desalination pond as second stage in proposed zero discharge desalination process

This work represents the efficiency of a solar desalination pond as a second stage of proposed zero discharge desalination processes to reach fresh water and also concentrated brine from the effluent wastewater of the desalination unit of Mobin petrochemical complex. So a solar desalination pond is constructed after a pretreatment unit to concentrate the softened wastewater to about 20 wt%. The concentrated wastewater is as a suited feed for a forced circulation crystallizer. During one year, the effects of major parameters such as ambient temperature and solar insolation rate are investigated, experimentally. specific gravity in each layer of concentrated brine wastewater is evaluated. Also, evaporation rates are calculated theoretically and are verified by experimental data. Theoretical values predict evaporation rate accurately. Results show good agreement with experimental data. According to results, maximum evaporation rate is 5 l/m² day when the insolation rate is about 24,602 kJ/m² day Solar energy absorption factor on June is max. Also, experimental results show the best proposed time to gain highest thermal energy is on spring therefore performance efficiency of solar desalination pond promote on spring comparing with the other months. Extracted data for specific gravity prove the bottom of solar desalination pond, layer 1, is best zone for energy saving and energy utilization.Also, theoretical values of evaporation rate are calculated according to measured temperatures and related mass conservation equation. Comparison between theoretical and experimental values shows dusty weather, humidity and wind velocity affects on heat transfer coefficients approximately. So, deviations between theoretical data and measured values can be explained. Results show good agreements with experimental data.     

Large-scale time evaluation for energy estimation of stand-alone hybrid photovoltaic–wind system feeding a reverse osmosis desalination unit

In this study, energy and water production estimation on a large-scale time from Photovoltaic–Wind hybrid system coupled to a reverse osmosis desalination unit in southern Tunisia has been elaborated. The use of a hybrid system for desalination appears nowadays as a very promising solution for remote and arid areas. The produced energy is used for potable water production. For energy production, metrological data (wind speed, solar irradiance…) and steady-state models have been used. The obtained results show that the hybrid solution (solar and wind) gives an energy availability during the year, despite changing energy according to daytime, season and year. The reverse osmosis desalination unit powered by Photovoltaic–Wind hybrid system for producing potable water from brackish water is an appropriate solution to southern Tunisia (salinity about 6 g/l). For this, compositions of brackish feed water in Djerba region were selected. Double stage configuration in the desalination process using spiral modules is adopted extensively and validation of the steady-state models is presented.     

Thermodynamic analysis of a novel solar and geothermal based combined energy system for hydrogen production

The present study develops a new solar and geothermal based integrated system, comprising absorption cooling system, organic Rankine cycle (ORC), a solar-driven system and hydrogen production units. The system is designed to generate six outputs namely, power, cooling, heating, drying air, hydrogen and domestic hot water. Geothermal power plants emit high amount of hydrogen sulfide (H₂S). The presence of H₂S in the air, water, soils and vegetation is one of the main environmental concerns for geothermal fields. In this paper, AMIS(AMIS® - acronym for “Abatement of Mercury and Hydrogen Sulphide” in Italian language) technology is used for abatement of mercury and producing of hydrogen from H₂S. The present system is assessed both energetically and exergetically. In addition, the energetic and exergetic efficiencies and exergy destruction rates for the whole system and its parts are defined. The highest overall energy and exergy efficiencies are calculated to be 78.37% and 58.40% in the storing period, respectively. Furthermore, the effects of changing various system parameters on the energy and exergy efficiencies of the overall system and its subsystems are examined accordingly.     

Thermodynamics analysis of a hybrid system based on a combination of hydrogen fueled compressed air energy storage system and water electrolysis hydrogen generator

In front of the opportunity of the rapid development of renewable energy power generation, energy storage is playing a more important role in improving its utilization efficiency. In this paper, a hybrid energy system based on combination of hydrogen fueled compressed air energy storage system and water electrolysis hydrogen generator is proposed. The superfluous renewable energy power is charged by compressing the air and/or producing hydrogen through water electrolysis. A hydrogen combustor is introduced to raise the air temperature in the discharging process. A thermodynamic model of the proposed system is built. Energy and exergy analysis found that under the design condition, the proposed system can achieve a round trip efficiency of 65.11%, an exergy efficiency of 79.23%, and an energy storage density of 5.85 kWh/m³. The exergy loss of water electrolysis hydrogen generator and hydrogen combustor rank in the top two of all components. Sensitivity analysis indicates that the outlet temperature of hydrogen combustor and specific energy consumption of water electrolysis hydrogen generator are the crucial influencing factor of system performance.     

Integration of wind turbine with heliostat based CSP/CPVT system for hydrogen production and polygeneration: A thermodynamic comparison

In this study, two wind-solar-based polygeneration systems namely CES-1 and CES-2 are developed, modeled, and analyzed thermodynamically. CES-1 hybridizes a heliostat based CSP system with wind turbines while CES-2 integrates heliostat-based CPVT with wind turbines. This study aims to compare the production and thermodynamics performance of two heliostat based concentrated solar power technologies when hybridized with wind turbines. The systems have been modeled to produce, freshwater, hot water, electricity, hydrogen, and cooling with different cycles/subsystems. While the overall objective of the study is to model two polygeneration systems with improved energy and exergy performances, the performances of two solar technologies are compared. The wind turbine system integrated with the comprehensive energy systems will produce 1.14 MW of electricity and it has 72.2% energy and exergy efficiency. Also, based on the same solar energy input, the performance of the heliostat integrated CPVT system (CES-2) is found to be better than that of the CSP based system (CES-1). The polygeneration thermal and exergy efficiencies for the two systems respectively are 48.08% and 31.67% for CES-1; 59.7% and 43.91% for CES-2. Also, the electric power produced by CES-2 is 280 kW higher in comparison to CES-1.     

A super-efficient method for hydrogen production from seawater

A hybrid system to produce hydrogen from the seawater is proposed and the best condition of that to have the highest efficiency is found here. The hybrid system consists of parabolic trough collectors, reverse osmosis (RO) desalination system, and a thermochemical water decomposition unit with heat dissipation system by cooling towers. The main process is based on the cuprous chloride (five-step) cycle that is optimized compared to previous research works. The RO and Cu–Cl processes are simulated by ROZA and Aspen HYSYS software programs, respectively, which are linked to the developed MATLAB codes for other components. The optimum area of the parabolic trough collectors is found 2964.6 m². Furthermore, the foremost dimensions for two cooling towers are 40 and 20 m height, and 50 and 35 m base diameter, respectively. Additionally, according to the results, the proposed hybrid system enjoys a high level of both energy and exergy efficiency values at the same time. The total energy efficiency of the hybrid H₂ production system is 18%, while it has the exergy efficiency of 30%.     

Production of hydrogen for export from wind and solar energy,natural gas,and coal in Australia

Hydrogen production for export to Japan and Korea is increasingly popular in Australia. The theoretically possible paths include the use of the excess wind and solar energy supply to the grid to produce hydrogen from natural gas or coal. As a contribution to this debate, here I discuss the present contribution of wind and solar to the electricity grid, how this contribution might be expanded to make a grid wind and solar only, what is the energy storage needed to permit this supply, and what is the ratio of domestic total primary energy supply to electricity use. These factors are required to determine the likeliness of producing hydrogen for export. The wind and solar energy capacity, presently at 6.7 and 11.4 GW, have to increase almost 8 times up to values of 53 and 90 GW respectively to support a wind and solar energy only electricity grid for the southeast states only. Additionally, it is necessary to build-up energy storage of actual power >50 GW and stored energy >3000 GW h to stabilize the grid. If the other states and territories are considered, and also the total primary energy supply (TPES) rather than just electricity, the wind and solar capacity must be increased of a further 6–8 times. It is concluded that it is extremely unlikely that hydrogen for export could be produced from the splitting of the water molecule by using excess wind and solar energy, and it is very unlikely that wind and solar may fully cover the local TPES needs. The most likely scenario is production hydrogen via syngas from either natural gas or coal. Production from natural gas and coal needs further development of techniques, to include CO₂ capture, a way to reuse or store CO₂, and finally, the better energy efficiency of the conversion processes. There are several challenges for using natural gas or coal to produce hydrogen with near-zero greenhouse gas emissions. Carbon capture, utilization, and storage technologies that ensure no CO₂ is released in the production process, and new technologies to separate the oxygen from the air, and in case of natural gas, the water, and the CO₂ from the combustion products, are urgently needed to make sense of the fossil fuel hydrogen production. There is no benefit from producing hydrogen from fossil fuels without addressing the CO₂ issue, as well as the fuel energy penalty issue during conversion, that is simply translating in a net loss of fuel energy with the same CO₂ emission.     

Proof-of-concept study of an integrated solar desalination system

This paper describes the performance of a directly heated solar desalination system. The design concept is based on using a direct solar energy collection unit, integrated with flash evaporation and low temperature multi-effect distillation (LT-MED) equipment. Key parameters affecting desalination rate include flashing evaporation pressure, first effect distillation pressure and seawater temperature. The experimental results indicate that at flash evaporation pressure of 0.01 MPa, first effect distillation pressure of 0.004 MPa, and the temperature of solar-heated seawater of 78 °C, the system can reach steady state operation in 17 min. At steady state, desalination rate of 0.204 × 10⁻³ m³/min is obtained. On raising temperature from 70 to 78 °C, net increase in desalination rate of 0.165 × 10⁻³ m³/min is achieved. In contrast, the change of first effect distillation pressure only had minimum effect on desalination rate. Experimental results are in agreement with the theoretical analysis. If temperature continues to increase beyond 78 °C, scaling due to precipitation of CaSO₄ takes place. In this study, the techniques that prevent the system from scaling deposits are discussed.     

Evaluation of hydrogen production with iron-based chemical looping fed by different biomass

In this study, the iron-based chemical looping process driven by various biomasses for hydrogen production purposes is studied and evaluated thermodynamically through energy and exergy approaches. The overall system consists of some key units (combustor, reducers and oxidizer) a torrefier, a drying chamber, an air separation unit, a heat exchanger, and auxiliary units as well. The biomasses considered are first dried and torrified in the drying chamber and sent to reactors to produce hydrogen. The exergy and energy efficiencies of the iron based chemical looping facility are investigated comparatively for performance evaluation. The maximum exergy destruction and entropy production rates are calculated for the torrefaction process as 123.15 MW and 4926 kW/K respectively. Under the steady–state conditions, a total of 8 kg/s hydrogen is produced via chemical looping process. The highest energy efficiency is obtained in the looping of rice husk with 86% while the highest exergy efficiency is obtained in the looping using sugarcane bagasse with 91%, respectively.