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.     

Modeling and control design of hydrogen production process for an active hydrogen/wind hybrid power system

This paper gives a control oriented modeling of an electrolyzer, as well as the ancillary system for the hydrogen production process. A Causal Ordering Graph of all necessary equations has been used to illustrate the global scheme for an easy understanding. The model is capable of characterizing the relations among the different physical quantities and can be used to determine the control system ensuring efficient and reliable operation of the electrolyzer. The proposed control method can manage the power flow and the hydrogen flow. The simulation results have highlighted the variation domains and the relations among the different physical quantities. The model has also been experimentally tested in real time with a Hardware-In-the-Loop Simulation before being integrated in the test bench of the active wind energy conversion system.     

Bond graph modeling,design and experimental validation of a photovoltaic/fuel cell/ electrolyzer/battery hybrid power system

This work presents a complete bond graph modeling of a hybrid photovoltaic-fuel cell-electrolyzer-battery system. These are multi-physics models that will take into account the influence of temperature on the electrochemical parameters. A bond graph modeling of the electrical dynamics of each source will be introduced. The bond graph models were developed to highlight the multi-physics aspect describing the interaction between hydraulic, thermal, electrochemical, thermodynamic, and electrical fields. This will involve using the most generic modeling approach possible for managing the energy flows of the system while taking into account the viability of the system. Another point treated in this work is to propose. In this work, a new strategy for the power flow management of the studied system has been proposed. This strategy aims to improve the overall efficiency of the studied system by optimizing the decisions made when starting and stopping the fuel cell and the electrolyzer. It was verified that the simulation results of the proposed system, when compared to simulation results presented in the literature, that the hydrogen demand is increased by an average of 8%. The developed management algorithm allows reducing the fuel cell degradation by 87% and the electrolyzer degradation by 65%. As for the operating time of the electrolyzer, an increment of 65% was achieved, thus improving the quality of the produced hydrogen. The Fuel Cell's running time has been decreased by 59%. With the ambition to validate the models proposed and the associated commands, the development of this study gave rise to the creation of an experimental platform. Using this high-performance experimental platform, experimental tests were carried out and the results obtained are compared with those obtained by simulation under the same metrological conditions.     

High temperature electrolysis using Molten Carbonate Electrolyzer

Molten Carbonate Fuel Cells (MCFC) are a well-developed and commercial technology that can operate also as an electrolyzer producing hydrogen from steam. In this study, a system for the production of hydrogen based on Molten Carbonate Electrolyzer (MCE) is presented. The system receives, as an external input, water and recovers internally the additional gas streams required as input to the electrolyzer. The system products are, separately, pure oxygen and hydrogen. A calculation sheet was implemented to analyze the energy equilibrium and gas mix compositions. The system can produce 0.074 Nl h^?1 cm^?2 of hydrogen with an inlet power density of 0.213 W cm^?2 for an energy consumption of 3.40 kWh Nm_H2^?3. Sensitivity studies on current density, utilization factors of both steam and CO₂ were analyzed considering energy equilibrium of the stack unit and the post processing processes. Results show how current density has higher impact on system equilibrium compared to the other parameters.     

Thermodynamic analyses of a solar-based combined cycle integrated with electrolyzer for hydrogen production

In the current study, a combined steam and gas turbine system integrated with solar system is studied thermodynamically. In addition, an electrolyzer is added to the integrated system for hydrogen production which makes the current system more environmental friendly and sustainable. This system is then evaluated by employing thermodynamic analysis to obtain both energetic and exergetic efficiencies. The parametric studies are also conducted to investigate the effects of varying operating conditions and state properties on both energy and exergy efficiencies. The present results show that while gas turbine can generate 312 MW directly, 151.72 MW power is generated by steam turbine using solar collectors and exhausted gases recovered from the gas turbine. Furthermore, by adding electrolyzer to the integrated system, a total of 131.3 g/s (472.68 kg/h) hydrogen is generated by using excess electricity which leads to more sustainability system.     

Experimental study of effect of anolyte concentration and electrical potential on electrolyzer performance in thermochemical hydrogen production using the Cu-Cl cycle

An important process in the copper-chlorine water splitting cycle for hydrogen production is electrolysis which occurs after a series of cycle steps that produce the constituents for the anolyte of the electrochemical cell. In this investigation, an anolyte mixture of HCl/CuCl/H₂O of varying concentrations is circulated through the electrolyzer to assist in optimizing its performance. It is observed that the concentration and temperature of the anolyte directly affect the process. The efficiency of the electrolyzer is adversely affected, after running a series of experiments, due to copper deposition on the membrane. An important implication of the results is that, to determine the optimal electrolyzer performance, one needs to vary the flow rate and the concentration of anolyte, for a given constant voltage source. In addition, this work demonstrates that aqueous CuCl₂ can be recovered from the waste solution exiting the electrolyzer and recycled to the hydrolysis reactor.     

Experiment and simulation of electrolytic hydrogen production: Case study of photovoltaic-electrolyzer direct connection

Hydrogen as an energy currency, carrier and storage medium can contribute to solve the problem of intermittent availability of renewable energies. In this paper, we study the production of hydrogen by a proton exchange membrane (PEM) electrolyzer (WE) using photovoltaic energy (PV) as source of electricity. Experiments were performed to model and optimize the direct-coupling system. Mathematical and empirical models based on experiments were used to simulate the system. RMSE was about 2% for the PV and WE. Optimization of direct connection was carried out to improve the system efficiency. However, it was noticed that the simulation of the system does not fit well the experimental results. Nevertheless, the RMSE is about 7%. In this study, we emphasize the need to develop appropriate models for hydrogen production system that operates in direct connection mode.     

A solar-powered,high-efficiency hydrogen fueling system using high-pressure electrolysis of water: Design and initial results

Hydrogen for fuel-cell electric vehicles (FCEVs) was produced using clean, renewable solar energy to electrolyze water. This report describes the design, construction, and initial performance testing of a solar hydrogen fueler at the GM Proving Ground in Milford, MI. The system used high-efficiency photovoltaic (PV) modules, a high-pressure (6500 psi, 44.8 MPa) electrolyzer, and an optimized direct connection between the PV and electrolyzer systems. This resulted in world-class solar to hydrogen efficiencies as high as 9.3% (based on H₂ lower heating value, LHV). The system could potentially supply approximately 0.5 kg of hydrogen per day from solar power for the average solar insolation in Detroit; more hydrogen would be produced in locations with more abundant sunshine. This is sufficient hydrogen to operate an FCEV for an average daily urban commute. Thus, the solar hydrogen fueler testing served as a “proof of concept” for clean, renewable hydrogen with potential applications including convenient, clean, quiet, small-scale home fueling of FCEVs (that can contribute to the growth of a future FCEV fleet) and fueling in remote locations where grid electricity is not available.     

Hydrogen perspectives in Italy: Analysis of possible deployment scenarios

The paper analyses Italian hydrogen scenarios to meet climate change, environmental and energy security issues. An Italy-Markal model was used to analyse the national energy–environment up to 2050. About 40 specific hydrogen technologies were considered, reproducing the main chains of production, transport and consumption, with a focus on transport applications. The analysis is based on the Baseline and Alternative scenario results, where hydrogen reaches a significant share. The two scenarios constitute the starting points to analyse the hydrogen potential among the possible energy policy options. The energy demand in the Baseline scenario reaches values around 240 Mtoe at 2030, with an average annual growth of 0.9%. The Alternative scenario reduces consumption down to 220 Mtoe and stabilizes the _CO2${\mathrm{CO}}_2$ emissions. The Alternative scenario expects a rapid increase of hydrogen vehicles in 2030, up to 2.5 million, corresponding to 1 Mtoe of hydrogen consumption. A sensitivity analysis shows that the results are rather robust.     

Modeling fermentative hydrogen production from sucrose supplemented with dairy manure

Our previous studies had shown that fermentative hydrogen production from sucrose could be improved with dairy manure as a supplement. In addition to contributing to nearly 10% more hydrogen yield at ambient temperature, dairy manure was shown to be capable of providing the required nutritional needs, buffering capacity, and hydrogen-producing organisms, improving the practical viability of fermentative hydrogen production. In this report, we present a kinetic model for fermentative hydrogen production from sucrose supplemented with dairy manure. This model includes hydrogen production from sucrose as well as from the soluble products hydrolyzed from particulate manure. The integrated model was calibrated using experimental data from one batch reactor and validated with dissolved COD, hydrogen, and volatile fatty acid data from four other reactors. Predictions by this model agreed well with the temporal trends in the experimental data, with r² averaging 0.85 for dissolved COD; 0.94 for total COD; 0.84 for hydrogen; 0.84 for acetic acid; and 0.89 for butyric acid; quality of fit in the case of propionic acid was lower with r² averaging 0.57.     

Development of a dynamic regenerative fuel cell system

The development of a regenerative Integrated Renewable Energy Experiment (IRENE) is presented. IRENE is a laboratory-scale distributed energy system with a modular structure which can be re-configured to test newly developed components for generic regenerative systems integrating renewable energy, electrolysis, hydrogen and electricity storage and fuel cells. A special design feature of this test bed is the ability to accept transient inputs from and provide transient loads to real devices as well as from simulated energy sources/sinks. The findings of this study should be of interest to developers of small-scale renewable-regenerative systems intended to displace fossil fuel systems.     

A solid oxide membrane electrolyzer for production of hydrogen and syn-gas from steam and hydrocarbon waste in a single step

This paper describes a novel solid oxide membrane (SOM) electrolyzer that can utilize the energy value in any hydrocarbon waste or reductant to lower the energy requirement for hydrogen production from steam. The SOM electrolyzer consists of a one-end closed oxygen-ion-conducting yttria stabilized zirconia (YSZ) tube with Ni-YSZ cathode coated on the outside and liquid metal anode inside the tube. The SOM electrolyzer is operated by feeding steam on the cathodic side and hydrocarbon reductant in the liquid metal anode. By feeding hydrocarbon waste it is possible to lower the chemical potential of oxygen in the liquid metal such that the SOM electrolyzer can spontaneously dissociate steam and generate hydrogen on the cathodic side and oxidize the hydrocarbon waste on the anodic side to produce syn-gas. The rate of these reactions can be increased by applying a small potential across the electrodes.     

Dynamic modeling of a solar hydrogen system under leakage conditions

Dynamic behaviors of an integrated solar hydrogen system have been modeled mathematically, which is based on a combination of fundamental theories of thermodynamics, mass transfer, fluid dynamics, and empirical electrochemical relationships. The model considers solar hydrogen system to be composed of three subsystems, i.e., solar cells, an electrolyzer, and a hydrogen tank. An additional pressure switch model is presented to visualize the hydrogen storage dynamics under a leakage condition. Validation of the solar hydrogen model system is evaluated according to the measured data from the manufacturer's data. Then, the overall was simulated by using solar irradiation as the primary energy input and hydrogen as energy storage for one-day operation. Finally, electrical characteristics and efficiencies of each subsystem as well as the entire system are presented and discussed.