Methylcyclohexane production under fluctuating hydrogen flow rate conditions

Energy storage using liquid organic hydrogen carrier (LOHC) is a long-term method to store renewable energy with high hydrogen energy density. This study investigated a simple and low-cost system to produce methylcyclohexane (MCH) from toluene and hydrogen using fluctuating electric power, and developed its control method. In the current system, hydrogen generated by an alkaline water electrolyzer was directly supplied to hydrogenation reactors, where hydrogen purification equipment such as PSA and TSA is not installed to decrease costs. Hydrogen buffer tanks and compressors are not equipped. In order to enable MCH production using fluctuating electricity, a feed-forward toluene supply control method was developed and introduced to the system. The electrolyzer was operated under triangular waves and power generation patterns of photovoltaic cells and produced hydrogen with fluctuating flow rates up to 7.5 Nm³/h. Consequently, relatively high purity of MCH (more than 90% of MCH mole fraction) was successfully produced. Therefore, the simplified system has enough potential to produce MCH using fluctuating renewable electricity.     

Assessment of solar and wind energy as motive for potential hydrogen production of Algeria country; development a methodology for uses hydrogen-based fuel cells

This study is based on method of storing the part of renewable energy in the hydrogen form for using in a fuel cell at the absence of solar radiation due to overcast day or in the night. In addition, the system advantage don't need a batteries compared with other systems. The present work is compared energy potential of the wind and solar with the results of hydrogen production and to address the various obstacles to study and evaluation. This work is assessment the renewable resources in various sites of Algeria, especially in Adrar area which is one regions of the high solar energy in the world, where the radiation rates exceed more than $2300kWh/m^2$ per year, the area is also characterized by high wind power. In fact, by these two energy sources (solar and wind) that it characterized by Adrar, it's interesting to combine electrical producing energy and hydrogen production. The studies indicate that there are the meteorological factors related to the nature of site (irradiation, temperature and wind speed) are linked to the generation of electricity by renewable energy. The results obtained showing that the hydrogen production related to the solar radiation values, where southern of Algeria has more hydrogen potential compared with the northern. The simulation results show that the energy supplied by a photovoltaic module type UDTS 50 can supply energy for ten electrolyzer cells which are connected in series with this module.     

Influence of process conditions on gas purity in alkaline water electrolysis

In this paper the influence of operating conditions on the product gas purity of a zero-gap alkaline water electrolyzer was examined. Precise knowledge of the resulting gas purity is of special importance to prevent safety shutdown when the electrolyzer is dynamically operated using a renewable energy source. The investigation in this study involves variation of temperature, electrolyte concentration and flow rate as well as different electrolyte management concepts. The experiments were carried out in a fully automated lab-scale electrolyzer with a 150 cm² zero-gap cell and approximately 31 wt% KOH at ambient and balanced cathodic and anodic pressure. The purity of the evolved gases was measured via online gas chromatography. It can be seen from the experiments that a temperature increase and flow rate decrease reduces the gas impurity when mixing catholyte and anolyte. A further reduction of gas impurity can be achieved when both cycles are being separated and a dynamic cycling strategy is applied.     

Development of large scale unified system for hydrogen energy carrier production and utilization: Experimental analysis and systems modeling

The world's largest class hydrogen energy carrier production, storage, and utilization system has been operated in order to obtain basic data for practical use of the system using renewable energy. In this system, an alkaline water electrolyzer is combined with hydrogenation reactors to produce methylcyclohexane (MCH). Since electrolyzer behavior directly affects hydrogenation reaction, behaviors of the 150 kW class water electrolyzer against fluctuating electricity inputs were experimentally investigated. The cell stack voltage and hydrogen flow rate changed following temporal changes of the input current, whereas the temperature response was slow due to the large heat capacity of the system. Hydrogenation reactors performance using the hydrogen from the electrolyzer are reported. Then, based on the experiment data, a numerical simulation model for the electrolyzer was developed, which predicts the experimental result using fluctuating electricity very well. Furthermore, using the simulator, the heat utilization from the hydrogenation reaction for the electrolyzer warm-up process was investigated.     

Experimental study on the external electrical thermal and dynamic power characteristics of alkaline water electrolyzer

As hydrogen production with a water electrolyzer is an effective way for renewable energy consumption, understanding the external electrical characteristics of water electrolyzer is of great significance for the modeling and simulation, system configuration, and control strategy of the system for hydrogen production by renewable energy. However, there are relatively fewer studies in this area. This paper presents the establishment of an experimental platform to conduct an experimental study on the static and dynamic voltage‐current characteristics and analyze the adjustability of the electric power of the traditional alkaline water electrolyzer, the relationship between the electrical characteristics and the electrolyte temperature, and operating point of the alkaline water electrolyzer. In addition, the mathematical fitting problem of the electrical characteristics of the alkaline water electrolyzer is discussed. The work could supply a reference to alkaline water electrolyzer intergrated application in renewable energy.     

New multi-physics approach for modelling and design of alkaline electrolyzers

This work presents a multi-physics model used for the design and diagnosis of the alkaline electrolyzers. The model is based on a new approach that allows to choose precisely the design parameters of a new electrolyzer even if it is not commercially available and predicting energy consumption, efficiency and rate of hydrogen production, taking into account to their physical state and various operating conditions. The approach differs from those of conventional models of the following: It allows the characterization of the electrolyzer based on its structural parameters in a relatively short time (few minutes) compared with the conventional approach which need experimental data collected for few weeks (Ulleberg). The approach allows describing a range of alkaline electrolyzers, while semi-empirical models found in literature are inherent to a specific electrolyzer. In addition, the model takes into account the variation of all structural parameters (geometry, materials and their evolution depending on operating conditions) and operational parameters of the electrolyzer (temperature, pressure, concentration, bulk bubbling and recovery rate of electrode surface by the bubble), while the models in the literature involve only the temperature. The developed multi-physics model was programmed in a Matlab Simulink^® environment and an alkaline electrolyzer’s simulation tool was developed. The simulation tool was validated using two industrial (Stuart and Phoebus) electrolyzers with different structures and power rates. Simulation results reproduced experimental data with good accuracy (less than 0.9%). The simulation tool was also used to compare the energy efficiency of two hydrogen production systems. The first one is based on atmospheric electrolyzer with a compressor for hydrogen storage and the second one is a barometric electrolyzer (under pressure) with its auxiliary devices to identify the effective mode of hydrogen production according to the physical state and operating conditions of the electrolyzer. The analysis of results revealed that the second mode of hydrogen production is more efficient and confirms the results of the literature based solely on the thermodynamic approach (K. Onda et al) without the input of the power consumed by power overvoltages.     

Optimized photovoltiac system for hydrogen production

Hydrogen, which can be produced by water electrolysis, can play an important role as an alternative to conventional fuels. It is regarded as a potential future energy carrier. Photovoltaic arrays can be used in supplying the water electrolysis systems by their energy requirements. The use of photovoltaic energy in such systems is very suitable where the solar hydrogen energy systems are considered one of the cleanest hydrogen production technologies, where the hydrogen is obtained from sunlight by directly connecting the photovoltaic arrays and the hydrogen generator. This paper presents a small PV power system for hydrogen production using the photovoltaic module connected to the hydrogen electrolyzer with and without maximum power point tracker. The experimental results developed good results for hydrogen production flow rates, in the case of using maximum power point tracker with respect to the directly connected electrolyzer to the photovoltaic modules.     

Levelized costs of energy and hydrogen of wind farms and concentrated photovoltaic thermal systems. A case study in Morocco

This work deals with the evaluation of levelized costs of energy and hydrogen of wind farms and concentrated photovoltaic thermal systems. The production of hydrogen is ensured by an alkaline water electrolyser supplied by the electric current generated by the renewable energy sources. The study is carried out on the basis of meteorological data from the Tangier region, in Morocco. Mathematical models are developed to assess the performance and efficiency of renewable sources in terms of energy and hydrogen production for different installed powers. The comparison between the current results and those of previous work shows that the discrepancy did not exceed 6% for both electrical and thermal efficiency of the concentrated photovoltaic/thermal system. The results show that the energy consumption ratios of the electrolyzer are 61 and 64 kWh.kg⁻¹ for wind and solar energy, respectively. Wind and solar hydrogen production efficiencies are also 66 and 62%, respectively. Results show that levelized costs of energy and hydrogen decrease with the increase in installed wind and photovoltaic capacity. The overall results also show that the Tangier region can produce energy and hydrogen at low cost using wind energy compared to concentrated photovoltaic installations. For the hybridization of the two green sources studied, this is highly recommended provided that the capacity of the electrolyzer to be installed is optimal in order to effectively improve the production of hydrogen.     

Thermodynamic assessment of modified Organic Rankine Cycle integrated with parabolic trough collector for hydrogen production

Hydrogen is one of the most clean energy carrier and the best alternative for fossil fuels. In this study, thermodynamic analysis of modified Organic Rankine Cycle (ORC) integrated with Parabolic Trough Collector (PTC) for hydrogen production is investigated. The integrated system investigated in this study consists of a parabolic trough collector, a modified ORC, a single effect absorption cooling system and a PEM electrolyzer. By using parabolic trough collector, solar energy is converted heat energy and then produced heat energy is used in modified ORC to produce electricity. Electricity is then used for hydrogen production. The outputs of this integrated system are electricity, cooling and hydrogen. By performing a parametric study, the effects of design parameters of PTC, modified ORC and PEM electrolyzer on hydrogen production is evaluated. According to the analysis results, solar radiation is one of the most important factor affecting system exergy efficiency and hydrogen production rate. As solar radiation increases from 400?W/m² to 1000?W/m², exergy efficiency of the system increases 58%–64% and hydrogen production rate increases from 0.1016?kg/h to 0.1028?kg/h.     

Analysis of hydrogen production from combined photovoltaics, wind energy and secondary hydroelectricity supply in Brazil

In this work, the technical and economical feasibility for implementing a hypothetical electrolytic hydrogen production plant, powered by electrical energy generated by alternative renewable power sources, wind and solar, and conventional hydroelectricity, was studied mainly trough the analysis of the wind and solar energy potentials for the northeast of Brazil. The hydrogen produced would be exported to countries which do not presently have significant renewable energy sources, but are willing to introduce those sources in their energy system. Hydrogen production was evaluated to be around 56.26 × 10⁶ m³ H₂/yr at a cost of 10.3 US$/kg.     

Modelization of hybrid systems with hydrogen and renewable energy oriented to electric propulsion in sailboats

This paper presents a conceptual model of a hybrid electric sailboat in which energy from electric grid is stored in batteries and energy from renewable energies (eolic, solar and hydro) is stored as hydrogen. The main objective of this model is to study the viability of electrifying traditional sailboats with internal combustion engines into hybrid systems with batteries and fuel cell. The most important advantage of this design is the possibility to reduce up to zero emissions of traditional sailboat. Conversion of renewable energy to hydrogen is performed through an electrolyzer and post conversion to energy is carried out by a fuel cell. The fuel cell with the batteries forms the hybrid system (batteries-fuel cell) for propulsion electrical energy supply. In order to model the boat dynamic and energy systems, modular mathematical models were developed under Matlab^®-Simulink^®, using a fixed-step solver for the simulation of global model. A simulated logic controller manages the global model. In this paper, many models have been used: some of them are based in literature models and others were developed from experimental data. A control strategy has also been developed to manage energy flows and then it has been embedded to Matlab^® language. The global model permits test the performance of the sailboat.     

Design and transient-based analysis of a power to hydrogen (P2H2) system for an off-grid zero energy building with hydrogen energy storage

In this study, zero energy building (ZEB) with four occupants in the capital and most populated city of Iran as one of the biggest greenhouse gas producers is simulated and designed to reduce Iran's greenhouse emissions. Due to the benefits of hydrogen energy and its usages, it is used as the primary energy storage of this building. Also, the thermal comfort of occupants is evaluated using the Fanger model, and domestic hot water consumption is supplied. Using hydrogen energy as energy storage of an off-grid zero energy building in Iran by considering occupant thermal comfort using the fanger model has been presented for the first time in this study. The contribution of electrolyzer and fuel cell in supplying domestic hot water is shown. For this simulation, Trnsys software is used. Using Trnsys software, the transient performance of mentioned ZEB is evaluated in a year. PV panels are used for supplying electricity consumption of the building. Excess produced electricity is converted to hydrogen and stored in the hydrogen tank when a lack of sunrays exists and electricity is required. An evacuated tube solar collector is used to produce hot water. The produced hot water will be stored in the hot water tank. For supplying the cooling load, hot water fired water-cooled absorption chiller is used. Also, a fan coil with hot water circulation and humidifier are used for heating and humidifying the building. Domestic hot water consumption of the occupants is supplied using stored hot water and rejected heat of fuel cell and the electrolyzer. The thermal comfort of occupants is evaluated using the Fanger model with MATLAB software. Results show that using 64 m² PV panel power consumption of the building is supplied without a power outage, and final hydrogen pressure tank will be higher than its initial and building will be zero energy. Required hot water of the building is provided with 75 m² evacuated tube solar collector. The HVAC system of the building provided thermal comfort during a year. The monthly average of occupant predicted mean vote (PMV) is between ?0.4 and 0.4. Their predicted percentage of dissatisfaction (PPD) is lower than 13%. Also, supplied domestic hot water (DHW) always has a temperature of 50 °C, which is a setpoint temperature of DHW. Finally, it can be concluded that using the building's rooftop area can be transformed to ZEB and reduce a significant amount of greenhouse emissions of Iran. Also, it can be concluded that fuel cell rejected heat, unlike electrolyzer, can significantly contribute to supplying domestic hot water requirements. Rejected heat of electrolyzer for heating domestic water can be ignored.     

Production price of hydrogen from grid connected electrolysis in a power market with high wind penetration.

In liberalized power markets, there are significant power price fluctuations due to independently varying changes in demand and supply, the latter being substantial in systems with high wind power penetration. In such systems, hydrogen production by grid connected electrolysis can be cost optimized by operating an electrolyzer part time. This paper presents a study on the minimization of the hydrogen production price and its dependence on estimated power price fluctuations. The calculation of power price fluctuations is based on a parameterization of existing data on wind power production, power consumption and power price evolution in the West Danish power market area. The price for hydrogen is derived as a function of the optimal electrolyzer operation hours per year for four different wind penetration scenarios. It is found to amount to 0.41–0.45 €/Nm³. The study further discusses the hydrogen price sensitivity towards investment costs and the contribution from non-wind power sources.     

Solar and wind energy in Poland as power sources for electrolysis process - A review of studies and experimental methodology

The production of hydrogen is still a major challenge, due to the high costs and often also environmental burdens it generates. It is possible to produce hydrogen in emission-free way: e.g. using a process of electrolysis powered by renewable energy. The paper presents the concept of a research, experimental stand for the storage of renewable energy in the form of hydrogen chemical energy with the measurement methodology. The research involves the use of proton exchange membrane electrolysis technology, which is characterized by high efficiency and flexibility of energy extraction for the process of electrolysis from renewable sources. The system consist of PV panel, PEM electrolyzer, battery, programmable logic controller system and optional a wind turbine. Preliminary experimental tests results have shown that the electrolyzer can produce in average 158.1 cc/min of hydrogen with the average efficiency 69.87%.     

Wind-powered 250 kW electrolyzer for dynamic hydrogen production: A pilot study

Alkaline water electrolysis is the most promising approach for the industrial production of green hydrogen. This study investigates the dynamic operational characteristics of an industrial-scale alkaline electrolyzer with a rated hydrogen production of 50 m³/h. Strategies for system control and equipment improvement in dynamic-mode alkaline electrolytic hydrogen production are discussed. The electrolyzer can operate over a 30%–100% rated power load, thereby facilitating high-purity (>99.5%) H₂ production, competitive DC energy efficiency (4.01–4.51 kW h/Nm³ H₂, i.e., 73.1%–65.0% LHV), and good gas–liquid fluid balance. A safe H₂ content of 2% in O₂ (50% LFL) can be guaranteed by adjusting the system pressure. In transient operation, the electrolyzer can realize minute-level power and pressure modulation with high accuracy. The results confirm that the proposed alkaline electrolyzer can absorb highly fluctuating energy output from renewables because of its capability to operate in a dynamic mode.     

Modeling of hydrogen production with a stand-alone renewable hybrid power system

Hydrocarbon resources adequately meet today’s energy demands. Due to the environmental impacts, renewable energy sources are high in the agenda. As an energy carrier, hydrogen is considered one of the most promising fuels for its high energy density as compared to hydrocarbon fuels. Therefore, hydrogen has a significant and future use as a sustainable energy system. Conventional methods of hydrogen extraction require heat or electrical energy. The main source of hydrogen is water, but hydrogen extraction from water requires electrical energy. Electricity produced from renewable energy sources has a potential for hydrogen production systems. In this study, an electrolyzer using the electrical energy from the renewable energy system is used to describe a model, which is based on fundamental thermodynamics and empirical electrochemical relationships. In this study, hydrogen production capacity of a stand-alone renewable hybrid power system is evaluated. Results of the proposed model are calculated and compared with experimental data. The MATLAB/Simscape^® model is applied to a stand-alone photovoltaic-wind power system sited in Istanbul, Turkey.     

Hydrogen production and storage analysis of a system by using TRNSYS

In this study, hydrogen production and storage were investigated. The Transient System Simulation Program (TRNSYS) and Generic Optimization Program (GenOpt) packages were combined for the design and optimization of a system that produces hydrogen from water and stores the hydrogen it produced in the compressed gas tank. The system design is based on the electricity grid. Electrical energy produced in photovoltaic (PV) panels was used to electrolyze water. The systems for Izmir, Istanbul and Ankara provinces which are in different climate zones of Turkey were optimized and the annual system performances based on the optimum angles were analyzed. For the mentioned provinces, the PV tilt angles which minimize electricity drawn from the grid at the electrolyzer are also investigated. The electrical energy produced in the photovoltaic panels, the hydrogen and oxygen amounts produced, the efficiency of the electrolyzer, the gas and pressure levels in the hydrogen tank were compared. According to the results of the analysis, the annual total power produced in photovoltaic panels is 42803.66 kW in İzmir, 42573.74 kW in Istanbul and 44613.95 kW in Ankara. Hydrogen levels produced in the system are calculated as 10488.39 m³ year⁻¹ in Izmir, 9824.70 m³ year⁻¹ in Istanbul, and 10368.65 m³ year⁻¹ in Ankara.     

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.     

Energy analysis of a class of copper–chlorine (Cu–Cl) thermochemical cycles

For separating water into hydrogen and oxygen through intermediate Cu–Cl compounds, the new system configurations for 5-step, 4-step and 3-step thermochemical cycles using electrolysis of CuCl/HCl or CuCl and Brayton cycle are addressed in Aspen Plus^® environment. To address the feasible predictions by thermodynamic systems, we found that (i) the pressure and temperature affect the product yields of CuO ¹ CuCl₂ and CuCl in the hydrolysis and oxygen production processes; (ii) the internal heat recovery ratio (IHRR) and the feed ratio of H₂O/CuCl₂ dominate the energy efficiencies and Cl₂ production, respectively. Based on the prescribed operating conditions, the comparative evaluations show that the 5-step Cu–Cl cycle using CuCl electrolyzer can ensure the highest energy efficiency while IHRR = 72%, the 3-step Cu–Cl cycle using CuCl electrolyzer can ensure the less equipment and the highest energy efficiency while IHRR = 100%. The 4-step Cu–Cl cycle using CuCl/HCl electrolyzer, where the electrolyzer prevents copper crossovers and safely produces the pure hydrogen gas at low temperature, has a high possibility of commercialization due to the lower grade heat requirement, the less number of equipment and the higher energy efficiency.     

Energy and exergy analyses and optimization study of an integrated solar heliostat field system for hydrogen production

In this paper, we propose an integrated system, consisting of a heliostat field, a steam cycle, an organic Rankine cycle (ORC) and an electrolyzer for hydrogen production. Some parameters, such as the heliostat field area and the solar flux are varied to investigate their effect on the power output, the rate of hydrogen produced, and energy and exergy efficiencies of the individual systems and the overall system. An optimization study using direct search method is also carried out to obtain the highest energy and exergy efficiencies and rate of hydrogen produced by choosing several independent variables. The results show that the power and rate of hydrogen produced increase with increase in the heliostat field area and the solar flux. The rate of hydrogen produced increases from 0.006 kg/s to 0.063 kg/s with increase in the heliostat field area from 8000 m² to 50,000 m². Moreover, when the solar flux is increased from 400 W/m² to 1200 W/m², the rate of hydrogen produced increases from 0.005 kg/s to 0.018 kg/s. The optimization study yields maximum energy and exergy efficiencies and the rate of hydrogen produced of 18.74%, 39.55% and 1571 L/s, respectively.