Model for energy conversion in renewable energy system with hydrogen storage

A dynamic model for a stand-alone renewable energy system with hydrogen storage (RESHS) is developed. In this system, surplus energy available from a photovoltaic array and a wind turbine generator is stored in the form of hydrogen, produced via an electrolyzer. When the energy production from the wind turbine and the photovoltaic array is not enough to meet the load demand, the stored hydrogen can then be converted by a fuel cell to produce electricity. In this system, batteries are used as energy buffers or for short time storage. To study the behavior of such a system, a complete model is developed by integrating individual sub-models of the fuel cell, the electrolyzer, the power conditioning units, the hydrogen storage system, and the batteries (used as an energy buffer). The sub-models are valid for transient and steady state analysis as a function of voltage, current, and temperature. A comparison between experimental measurements and simulation results is given. The model is useful for building effective algorithms for the management, control and optimization of stand-alone RESHSs.     

Performance investigation of an integrated wind energy system for co-generation of power and hydrogen

In this paper, a wind turbine energy system is integrated with a hydrogen fuel cell and proton exchange membrane electrolyzer to provide electricity and heat to a community of households. Different cases for varying wind speeds are taken into consideration. Wind turbines meet the electricity demand when there is sufficient wind speed available. During high wind speeds, the excess electricity generated is supplied to the electrolyzer to produce hydrogen which is stored in a storage tank. It is later utilized in the fuel cell to provide electricity during periods of low wind speeds to overcome the shortage of electricity supply. The fuel cell operates during high demand conditions and provides electricity and heat for the residential application. The overall efficiency of the system is calculated at different wind speeds. The overall energy and exergy efficiencies at a wind speed 5 m/s are then found to be 20.2% and 21.2% respectively.     

Automatic management of energy flows of a stand-alone renewable energy supply with hydrogen support

This work deals with the design and construction of an automation system for controlling the electric energy flows that take place at the continuous current bus (DC Bus) of a wind–solar system with hydrogen support. The automation system is based on a Siemens PLC s7_313C_2DP. This PLC was equipped with a Micro Memory Card (MMC) of 2 MB in order to allow the massive storage of data related to the control and monitoring of the test-bed. This system has to perform the required switching between the components of the hybrid electric energy generator. These elements are: photovoltaic generator, wind-turbine generator, fuel-cell system, and electrolyzer.     

Techno-economic analysis of the integration of hydrogen energy technologies in renewable energy-based stand-alone power systems

A large number of stand-alone power systems that are based on fossil fuel or renewable energy (RE) based, are installed all over Europe. Such systems, often comprising photovoltaics (PV) and/or diesel generators provide power to communities or technical installations, which do not have access to the local or national electricity grid. The replacement of conventional technologies such as diesel generators and/or batteries with hydrogen technologies, including fuel cells in an existing PV-diesel stand-alone power system providing electricity to a remote community was simulated and optimised, using the hybrid optimisation model for electric renewables (HOMER) simulation tool. A techno-economic analysis of the existing hybrid stand-alone power system and the optimised hydrogen-based system was also conducted. The results of the analyses showed that the replacement of fossil fuel based gensets with hydrogen technologies is technically feasible, but still not economically viable, unless significant reductions in the cost of hydrogen technologies are made in the future.     

Techno-economic analysis for rustic electrification in Egypt using multi-source renewable energy based on PV/ wind/ FC

A technical-economic investigation based on mathematical modeling, simulation, and optimization approach is employed in this research to assemble an island combined renewable energy systems (CRES) consists of solar PV/Wind/Fuel Cell (FC) of a small-scale countryside area in Egypt. The intent of the proposed island CRES is to boost the share of renewable energy in the energy mix and to study the possibility of using fuel cells as a storage/backup system instead of using battery banks.Three combinations of CRES are presented in this research to select the most optimum one. The combinations of the hybrid systems are PV/FC, PV/WT/FC, and WT/FC. The performance and the total cost of the suggested CRES were optimized using Firefly Algorithm (FA). The results obtained from the FA are compared with those obtained from the Shuffled Frog Leaping Algorithm (SFLA) and the particle swarm optimization (PSO).The selected case study area with latitude and longitude of (29.0214 N, 30.8714 E) is identified for economic viability in this work.The simulation outcomes show that the solar PV/Wind/Fuel Cell combination incorporated with an electrolyzer for hydrogen production grants the excellent performance. The proposed system is economically viable with a levelized cost of energy of 0.47 $/kWh.     

Power management strategies for a stand-alone power system using renewable energy sources and hydrogen storage

A stand-alone power system based on a photovoltaic array and wind generators that stores the excessive energy from renewable energy sources (RES) in the form of hydrogen via water electrolysis for future use in a polymer electrolyte membrane (PEM) fuel cell is currently in operation at Neo Olvio of Xanthi, Greece. Efficient power management strategies (PMSs) for the system have been developed. The PMSs have been assessed on their capacity to meet the power load requirements through effective utilization of the electrolyzer and fuel cell under variable energy generation from RES (solar and wind). The evaluation of the PMS has been performed through simulated experiments with anticipated conditions over a typical four-month time period for the region of installation. The key decision factors for the PMSs are the level of the power provided by the RES and the state of charge (SOC) of the accumulator. Therefore, the operating policies for the hydrogen production via water electrolysis and the hydrogen consumption at the fuel cell depend on the excess or shortage of power from the RES and the level of SOC. A parametric sensitivity analysis investigates the influence of major operating variables for the PMSs such as the minimum SOC level and the operating characteristics of the electrolyzer and the fuel cell in the performance of the integrated system.     

PV output power fluctuations smoothing: The MYRTE platform experience

The MYRTE platform is one of the PEPITE project applications included in the PAN-H program of the French Research National Agency, under the reference ANR-07-PANH-012. This platform consists of a photovoltaic array, a fuel cell, an electrolyzer, tanks (H₂, O₂ and H₂O), a thermal management system and electricity converters associated to various sub-systems.     

Electrolytic hydrogen based renewable energy system with oxygen recovery and re-utilization

The Hydrogen Research Institute (HRI) has developed a stand-alone renewable energy (RE) system based on energy storage in the form of hydrogen. When the input devices (wind generator and photovoltaic array) produce more energy than is required by the load, the excess energy is converted by an electrolyzer to electrolytic hydrogen, which is then stored after stages of compression, purification and filtration. Conversely, during a time of input energy deficit, this process is reversed and the hydrogen produced earlier is reconverted to electrical energy through a fuel cell. The oxygen which has been produced by the electrolyzer during the hydrogen production is also stored at high pressure, after having gone through a purification and drying process. This stored oxygen can be re-utilized as oxidant in place of compressed air in the fuel cell. The modifications of the electrolyzer for oxygen storage and re-utilization of it as oxidant for the fuel cell are presented. Furthermore, the HRI has designed and developed the control system with power conditioning devices for effective energy management and automatic operation of the RE system. The experimental results show that a reliable autonomous RE system can be realized for such seasonal energy sources, using stored hydrogen as the long-term energy buffer, and that utilizing the electrolyzer oxygen by-product as oxidant in the fuel cell increases system performance significantly.     

Design and optimum energy management of a hybrid renewable energy system based on efficient various hydrogen production

Utilizing renewable energy resources is one of the convenient ways to reduce greenhouse gas emissions. However, the intermittent nature of these resources has led to stochastic characteristics in the generation and load balancing of the microgrid systems. To handle these issues, an energy management optimization for microgrids operation should be done to urge the minimization of total system costs, emissions, and fuel consumption. An optimization program for decreasing the operational cost of a hybrid microgrid consisting of photovoltaic array, wind unit, electrolyzer, hydrogen storage system, reformer, and fuel cell is presented. Two different methods of producing hydrogen are considered in this study to ensure the effectiveness of the developed methodology. In the microgrid system with high penetration of renewable energy resources, using storage technologies to compensate for the intermittency of these resources is necessary. To evaluate the functioning of the microgrid system, a mathematical model for each source is developed to coordinate the system operation involving energy conversion between hydrogen and electricity. Particle Swarm Optimization Algorithm is utilized to determine the optimum size and operational energy management within the system. It is evident from the results that there is about a 10% reduction in the amount of CH₄ consumption in reformer when the electrolyzer was employed in the system. It is observed that the CH₄ reduction in summer and fall is higher than other seasons (10.6% and 11.5%, respectively). The reason is that the highest RES production occurs in these seasons during a year. It is also worth mentioning that the electrolyzer technology would play a significant role in decreasing the CH₄ consumption in the microgrid system.     

Modeling and performance analysis of renewable hydrogen energy hub connected to an ac/dc hybrid microgrid

This paper proposes a system modeling and performance analysis of a renewable hydrogen energy hub (RHEH) connected to an ac/dc hybrid microgrid (MG). The proposed RHEH comprises a photovoltaic (PV)-based renewable energy source (RES) as the primary source, a proton exchange membrane fuel cell (PEMFC) as the secondary power source, and a proton exchange membrane electrolyzer (PEMELZ) that can generate and store hydrogen in a hydrogen tank. All these resources are directly connected at the dc bus of the ac/dc microgrids. The PEMFC operates and utilizes the hydrogen from the hydrogen tank when the energy generated by RES cannot meet the load demand. A coordinated power flow control approach has been developed for the RHEH to mitigate the mismatch between generation and demand in the ac/dc microgrid and produce renewable hydrogen when renewable power is in excess. The paper also proposes a modified hybrid Perturb & Observe-Particle Swarm Optimization (Hybrid PO-PSO) algorithm to ensure the maximum power point tracking (MPPT) operation of the PV and the PEMFC. The operation of the proposed RHEH is validated through simulations under various critical conditions. The results show that the proposed RHEH is effective to maintain the system power balance and can provide power-to-hydrogen and hydrogen-to-power when required.     

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.     

A renewable source based hydrogen energy system for residential applications

In this study, both concentrated solar power and wind energy systems are integrated with electrolyser, fuel cell and absorption cooling subsystems to supply power, cooling, heating and hydrogen to residential applications in an environmentally benign and efficient manner. These subsystems are integrated in a unique way to manage the excess power through water electrolysis to produce and store hydrogen. Integrated systems are thermodynamically analyzed, and their performance is assessed comparatively. Solar radiation intensity, inlet temperature and wind velocity are taken into account, and hence their effects on the system performance are investigated. The results of this study show that the present system appears to be efficient, environmentally friendly and hence sustainable.     

Green hydrogen: A new flexibility source for security constrained scheduling of power systems with renewable energies

Green hydrogen, i.e. the hydrogen generated from renewable energy sources (RES) will significantly contribute to a successful energy transition. Besides, to facilitate the integration and storage of RES, this promising energy carrier is well capable to efficiently link various energy sectors. By introduction of green hydrogen as a new flexibility source to power systems, it is necessary to investigate its possible impacts on the generation scheduling and power system security. In this paper, a security-constrained multi-period optimal power flow (SC-MPOPF) model is developed aiming to determine the optimal hourly dispatch of generators as well as power to hydrogen (P2H) units in the presence of large-scale renewable energy sources (RES). The proposed model characterizes the P2H demand flexibility in the proposed SC-MPOPF model, taking into account the electrolyzer behavior, reactive power support of P2H demands and hydrogen storage capability. The developed SC-MPOPF model is applied to IEEE 39-bus system and the obtained numerical results demonstrate the role of P2H flexibility on cost as well as RES's power curtailment reduction.     

Techno-economic analysis of RES & hydrogen technologies integration in remote island power system

The main objective of the present study is the integration of hydrogen technologies as an energy storage medium in a hybrid power system. The existing power system of the island of Milos, which is based on fossil fuel generators and a small wind park, is assessed in the context of this paper. System level simulation results, from both technical and economic point of view, are presented for the currently existing and the proposed island's hybrid power system. The latter integrates a higher number of wind turbines and hydrogen technologies as energy storage medium, and the two system architectures are being compared taking into account not only technical and economic parameters but also Green House – Gas (GHG) emissions, fossil fuels consumption and Renewable Energy Sources (RES) penetration increase. Moreover, a sensitivity analysis has been performed in order to determine the contribution of hydrogen technologies equipment costs; with the cost of energy produced (COE) being the critical parameter. Results show that COE for the proposed power system is higher than the existing one, but on the other hand GHG emissions and fossil fuel consumption are significantly reduced. In addition, RES penetration increases dramatically and the sensitivity analysis indicates that a further reduction in hydrogen technologies equipment and subsidy on wind turbine costs would make RES & Hydrogen-based systems economically competitive to the existing power system of the island.     

Techno-economic analysis of thermochemical water-splitting system for Co-production of hydrogen and electricity

The two-step thermochemical metal oxide water-splitting cycle with the state-of-the-art material ceria inevitably produces unutilized high-quality heat, in addition to hydrogen (H₂). This study explores whether the ceria cycle can be of greater value by using the excess heat for co-production of electricity. Specially, this technoeconomic study estimates the H₂ production cost in a hybrid ceria cycle, in which excess heat produces electricity in an organic Rankine cycle, to increase revenue and decrease H₂ cost. The estimated H₂ cost from such a co-generation multi-tower plant is still relatively high at $4.55/kg, with an average H₂ production of 1431 kg/day per 27.74 MW_th tower. Sensitivity analyses show opportunities and challenges to achieving $2/kg H₂ through improvements such as increased solar field efficiency, increased revenue from electricity sales, and a decreased capital recovery factor from baseline assumptions. While co-production improves overall system efficiency and economics, achieving $2/kg H₂ remains challenging with ceria as the active material and likely will require a new material.     

Techno-economic analysis of hydrogen transportation infrastructure using ammonia and methanol

The transformation from a fossil fuels economy to a low carbon economy reshapes how energy is transmitted. Since most renewable energy is harvested in the form of electricity, hydrogen obtained from water electrolysis using green electricity is considered a promising energy vector. However, the storage and transportation of hydrogen at large scales pose challenges to the existing energy infrastructures, both regarding technological and economic aspects. To facilitate the distribution of renewable energy, a set of candidate hydrogen transportation infrastructures using methanol and ammonia as hydrogen carriers were proposed. A systematical analysis reveals that the levelized costs of transporting hydrogen using methanol and ammonia in the best cases are $1879/t-H₂ and $1479/t-H₂, respectively. The levelized cost of energy transportation using proposed infrastructures in the best case is $10.09/GJ. A benchmark for hydrogen transportation infrastructure design is provided in this study.     

Techno-economic analysis of hydrogen production from dehydrogenation and steam reforming of ethanol for carbon dioxide conversion to methanol

Decreasing carbon dioxide (CO₂) emission by converting to higher-valued product has become of interest. Hydrogen (H₂) is an important feedstock required in thermochemical conversion of CO₂ to chemicals such as methanol. The cost and availability of H₂ affect the cost of CO₂ conversion. This study is focused on the process simulation of H₂ production from ethanol feedstock. Steam reforming of ethanol is compared with dehydrogenation of ethanol to H₂ with valued products including ethyl acetate and acetaldehyde. Form this study, steam reforming of ethanol presents the lowest cost of H₂ production at 1.58 USD/kg H₂ while dehydrogenation of ethanol presents the cost at 3.24 and 1.97 USD/kg H₂, respectively. Although presenting the lowest cost, steam reforming of ethanol provides a net positive CO₂ emission in the overall CO₂ conversion to methanol process. In contrast, ethanol dehydrogenation to H₂ and byproducts, ethyl acetate and acetaldehyde, promotes a net negative CO₂ emission of −819.20 kg/ton methanol and −5.42 kg/ton methanol, respectively. The results present a decreasing CO₂ emission with an increasing cost of H₂ production.     

Weather data and energy balance of a hybrid photovoltaic-wind system with hydrogen storage

This article presents and discusses the results of measurements of solar radiation and wind speed obtained during the operation of a test-bed hybrid wind/solar generator with hydrogen support designed and constructed at the Industrial Engineering School at the University of Extremadura, Badajoz (Spain). An energy balance analysis is made of the different components of the system, calculating their conversion efficiencies, and proposing future improvements to increase the efficiency of the use of the surplus energy produced by the wind/solar generator. The continued collection of this data series will make it possible to perform energy and exergy analyses to allow extrapolation of the results to real stand-alone applications providing an uninterrupted power supply to receptors isolated from the grid.     

Towards 100% renewable energy systems: Uncapping power system flexibility

Relying almost entirely on energy from variable renewable resources such as wind and solar energy will require a transformation in the way power systems are planned and operated. This paper outlines the necessary steps in creating power systems with the flexibility needed to maintain stability and reliability while relying primarily on variable energy resources. These steps are provided in the form of a comprehensive overview of policies, technical changes, and institutional systems, organized in three development phases: an initial phase (penetration up to about 10%) characterized by relatively mild changes to conventional power system operations and structures; a dynamic middle phase (up to about 50% penetration) characterized by phasing out conventional generation and a concerted effort to wring flexibility from existing infrastructure; and the high penetration phase that inevitably addresses how power systems operate over longer periods of weeks or months when variable generation will be in either short supply, or in over-abundance. Although this transition is likely a decades-long and incremental process and depends on the specifics of each system, the needed policies, research, demonstration projects and institutional changes need to start now precisely because of the complexity of the transformation. The list of policy actions presented in this paper can serve as a guideline to policy makers on effectuating the transition and on tracking the preparedness of systems.     

Techno-economic analysis of alternative processes for alcohol-assisted methanol synthesis from carbon dioxide and hydrogen

The novel methanol production from carbon dioxide (CO₂) and hydrogen (H₂) called alcohol-assisted process is simulated. Although the alcohol-assisted process allows the reduction in operating temperature and pressure, the subsequent product purification is complicated. Comparative studies between the conventional CO₂ hydrogenation and the alcohol-assisted processes are carried out (case I–V). The alcohol-assisted processes present the opportunity of increasing the CO₂ conversion per-pass and reducing 25% of the hydrogen consumption, the barriers in the conventional process. However, the product purifications remain challenging due to the azeotrope of methanol and by-products. Energy consumptions decrease in the feed and reaction sections of the alcohol-assisted processes but significant increase in the product purifications. The formation of by-products and the sequence of purification units affect process performance and economics. The obtained results indicate that the product purification and the catalyst development to increase methanol selectivity and produce an easy-separated by-product play key roles in the enhancement of the process feasibility.