Techno-economic optimization of wind energy based hydrogen refueling station case study Salalah city Oman

Clean energy resources will be used more for sustainability improvement and durable development. Efficient technologies of energy production, storage, and usage results in reduction of gas emissions and improvement of the world economy. Despite 30% of electricity being produced from wind energy, the connection of wind farms to medium and large-scale grid power systems is still leading to instability and intermittency problems. Therefore, the conversion of electrical energy generated from wind parks into green hydrogen consists of an exciting solution for advancing the development of green hydrogen production, and the clean transportation sector. This paper presents a techno-economic optimization of hydrogen production for refueling fuel cell vehicles, using wind energy resources. The paper analyses three configurations, standalone Wind-Park Hydrogen Refueling Station (WP-HRS) with backup batteries, WP-HRS with backup fuel cells, and grid-connected WP-HRS. The analysis of different configurations is based on the wind potential at the site, costs of different equipment, and hydrogen load. Therefore, the study aims to find the optimized capacity of wind turbines, electrolyzers, power converters, and storage tanks. The optimization results show that the WP-HRS connected to the grid has the lowest Present Worth Cost (PWC) of 6,500,000 €. Moreover, the Levelized Hydrogen Cost (LHC) of this solution was found to be 6.24 €/kg. This renewable energy system produces 80,000 kg of green hydrogen yearly.     

Life cycle cost assessment of wind power–hydrogen coupled integrated energy system

Aiming at the economic evaluation of wind power-hydrogen coupled integrated energy system (WPHCIES), a life-cycle economic assessment method of integrated energy system is proposed. Firstly, the integrated scheme and operation mode of integrated energy system are given. Secondly, with the net profit of the integrated energy system in the whole life cycle as objectives and the energy flow and stable operation of the system as constraints, a mathematical model for the economic evaluation of the given integrated energy system in the whole life cycle is constructed, and the payback period and net profit of life cycle of the given system can be reckoned by the model. Finally, taking a wind farm in South China as background, the life cycle economic evaluation model of the proposed system is simulated and calculated, and the effects of both the ratio of hydrogen production from wind power and the ratio of hydrogen to fuel cell on the net profit of wind power-hydrogen coupled integrated energy system during the payback period and the whole life cycle are further analyzed. In addition, the comparison demonstrated that the capital return period of the wind farm can be reduced from 11 years to 8.13 years, and the cumulative net income can be increased from 0.67 billion yuan to 0.93 billion yuan by reasonably choosing the power ratio of hydrogen production from wind power.     

Effects of pressure levels in three-cascade storage system on the overall energy consumption in the hydrogen refueling station

Studies show that compared with the one-buffer system, the cascade storage system has lower energy consumption in high-pressure hydrogen refueling stations. In the present study, practical dynamic models of the whole hydrogen refueling process are established to evaluate the energy consumption. Accordingly, the filling performance of the three-cascade storage system and single tank storage system are analyzed. Moreover, the impact of the three pressure levels and the charging sequence of the three tanks on the energy consumption are investigated. The obtained results show that changing from one buffer to three tanks gives a total energy saving of approximate 34%. For the three-cascade storage system, the total energy consumption increases approximately linearly with the increase of the pressure of the high-pressure tank. Whereas it shows concave curve shape trends with the increase of low-pressure level and the medium-pressure level. Furthermore, the charging sequence from the low-pressure buffer to the high one decreases the total operation energy consumption to a value slightly lower than the adverse charge sequence.     

Dynamic planning and energy management strategy of integrated charging and hydrogen refueling at highway energy supply stations considering on-site green hydrogen production

The layout of electric vehicles charging stations and hydrogen refueling stations (HRSs) is more and more necessary with the development of electric vehicles (EVs) and progress in hydrogen energy storage technology. Due to the high costs of HRSs and the low demand for hydrogen, it is difficult for independent HRSs to make a profit. This study focuses on the dynamic planning of energy supply stations on highways in the medium and long term, considering the growth of EV charging demand and the change in the proportion of hydrogen fuel cell vehicles (HFCVs). Based on the perspective of renewable energy generators (REGs), this study seeks the dynamic optimal configuration and comprehensive benefits of adding HRS and battery to existing EVCS considering the travel rules of new energy vehicles (NEVs). The results show that (1) It is profitable for REGs to invest in HRSs; (2) The economy of investment in batteries by REGs depends on the source-load matching. It is feasible only when the output of renewable energy is difficult to meet the demand. (3) The business model of REGs producing hydrogen on-site and supplying both electricity and hydrogen is feasible.     

Performance assessment of an electrochemical hydrogen production and storage system for solar hydrogen refueling station

This paper investigates the performance of a hydrogen refueling system that consists of a polymer electrolyte membrane electrolyzer integrated with photovoltaic arrays, and an electrochemical compressor to increase the hydrogen pressure. The energetic and exergetic performance of the hydrogen refueling station is analyzed at different working conditions. The exergy cost of hydrogen production is studied in three different case scenarios; that consist of i) off-grid station with the photovoltaic system and a battery bank to supply the required electric power, ii) on-grid station but the required power is supplied by the electric grid only when solar energy is not available and iii) on-grid station without energy storage. The efficiency of the station significantly increases when the electric grid empowers the system. The maximum energy and exergy efficiencies of the photovoltaic system at solar irradiation of 850 W m-2 are 13.57% and 14.51%, respectively. The exergy cost of hydrogen production in the on-grid station with energy storage is almost 30% higher than the off-grid station. Moreover, the exergy cost of hydrogen in the on-grid station without energy storage is almost 4 times higher than the off-grid station and the energy and exergy efficiencies are considerably higher.     

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.     

Analysis of the economy of scale and estimation of the future hydrogen production costs at on-site hydrogen refueling stations in Korea

This paper deals with the analysis of the economy of scale at on-site hydrogen refueling stations which produce hydrogen through steam methane reforming or water electrolysis, in order to identify the optimum energy mix as well as the total construction cost of hydrogen refueling stations in Korea. To assess the economy of scale at on-site hydrogen stations, the unit hydrogen costs at hydrogen stations with capacities of 30 Nm³/h, 100 Nm³/h, 300 Nm³/h, and 700 Nm³/h were estimated. Due to the relatively high price of natural gas compared to the cost of electricity in Korea, water electrolysis is more economical than steam methane reforming if the hydrogen production capacity is small. It seems to be the best strategy for Korea to construct small water electrolysis hydrogen stations with production capacities of 100 Nm³/h or less until 2020, and to construct steam methane reforming hydrogen stations with production capacities of 300 Nm³/h or more after 2025.     

Effect of wind condition on unintended hydrogen release in a hydrogen refueling station

Ambient condition, especially the wind condition, is an important factor to determine the behavior of hydrogen diffusion during hydrogen release. However, only few studies aim at the quantitative study of the hydrogen diffusion in a wind-exist condition. And very little researches aiming at the variable wind condition have been done. In this paper, the hydrogen diffusion in different wind condition which including the constant wind velocity and the variable wind velocity is investigated numerically. When considering the variable wind velocity, the UDF (user defined function) is compiled. Characteristics of the FGC (flammable gas cloud) and the HMF (hydrogen mass fraction) are analyzed in different wind condition and comparisons are made with the no-wind condition. Results indicate that the constant wind velocity and the variable wind velocity have totally different effect for the determination of hydrogen diffusion. Comparisons between the constant wind velocity and the variable wind velocity indicate that the variable wind velocity may cause a more dangerous situation since there has a larger FGC volume. More importantly, the wind condition has a non-negligible effect when considering the HMF along the radial direction. As the wind velocity increases, the distribution of the HMF along the radial direction is not Gaussian anymore when the distance between the release hole and the observation line exceeds to a critical value. This work can be a supplement of the research on the hydrogen release and diffusion and a valuable reference for the researchers.     

Multi-objective optimization of large-scale grid-connected photovoltaic-hydrogen-natural gas integrated energy power station based on carbon emission priority

Establishing integrated energy systems is conducive for improving renewable energy utilization and promoting decarbonization. In this study, a grid-connected photovoltaic-hydrogen-natural gas integrated energy system is established to explore the effects of the configuration of the integrated energy system on its environment and economy. A multi-objective hierarchical optimization allocation model is developed, and an optimization strategy with carbon emission superior to total cost is established for the first time. Additionally, the economy, environment, and energy efficiency of the system are analyzed. A comparative study is performed using a strategy considering that the total cost is superior to carbon emission. A case study reveals that the levelized cost of electricity increases by 62.24%, levelized carbon emission of power decreases by 74.19%, and energy efficiency increases by 8.51%, as compared with those of the comparison strategy. Thus, the carbon emission of the system is reduced considerably, and the energy efficiency is improved. Although the cost of the system optimized by the proposed strategy is higher, it is economically feasible. Further analyses indicate that extending the grid-connected period would be infeasible, as it might increase the total cost and carbon emission of the system. Moreover, sensitivity analyses show that increasing the natural gas price or carbon tax base price will not reduce the carbon emission of the system.     

Model predictive control of an on-site green hydrogen production and refuelling station

The expected increase of hydrogen fuel cell vehicles has motivated the emergence of a significant number of studies on Hydrogen Refuelling Stations (HRS). Some of the main HRS topics are sizing, location, design optimization, and optimal operation. On-site green HRS, where hydrogen is produced locally from green renewable energy sources, have received special attention due to their contribution to decarbonization. This kind of HRS are complex systems whose hydraulic and electric linked topologies include renewable energy sources, electrolyzers, buffer hydrogen tanks, compressors and batteries, among other components. This paper develops a linear model of a real on-site green HRS that is set to be built in Zaragoza, Spain. This plant can produce hydrogen either from solar energy or from the utility grid and is designed for three different types of services: light-duty and heavy-duty fuel cell vehicles and gas containers. In the literature, there is a lack of online control solutions developed for HRS, even more in the form of optimal online control. Hence, for the HRS operation, a Model Predictive Controller (MPC) is designed to solve a weighted multi-objective online optimization problem taking into account the plant dynamics and constraints as well as the disturbances prediction. Performance is analysed throughout 210 individual month-long simulations and the effect of the multi-objective weighting, prediction horizon, and hydrogen selling price is discussed. With the simulation results, this work shows the suitability of MPC for HRS control and its significant economic advantage compared to the rule-based control solution. In all simulations, the MPC operation fulfils all required services. Moreover, results show that a seven-day prediction horizon can improve profits by 57% relative to a one-day prediction horizon; that the battery is under-sized; or that the MPC operation strategy is more resolutive for low hydrogen selling prices.     

Assessment of offshore liquid hydrogen production from wind power for ship refueling

Green hydrogen from electrolysis has become the most attractive energy carrier for making the transition from fossil fuels to carbon-free energy sources possible. Especially in the naval sector, hydrogen has the potential to address environmental targets due to the lack of low-carbon fuel options. This study aims at investigating an offshore liquefied green hydrogen production plant for ship refueling. The plant comprises a wind farm for renewable electricity generation, an electrolyzer stack for hydrogen production, a water treatment unit for demineralized water production, and a hydrogen liquefaction plant for hydrogen storage and distribution to ships. A pre-feasibility study is addressed to find the optimal capacities of the plant that minimize the payback time. The model results show that the electrolyzer capacity shall be set equal to a value between 80% and 90% of the wind farm capacity to achieve the minimum payback times. Additionally, the wind farm capacity shall be higher than about 150 MW to limit the payback time to values lower than 11 years for a fixed hydrogen price of 6 €/kg. The Levelized Cost of Hydrogen results to be below 4 €/kg for a wide range of plant capacities for a lifetime of the plant of 25 years. Thus, the model shows that this plant is economically feasible and can be reproduced similarly for different locations by rescaling the different selected technologies. In this way, the naval sector can be decarbonized thanks to a new infrastructure for the production and refueling of liquified green hydrogen directly provided on the sea.     

A numerical study of hydrogen leakage and diffusion in a hydrogen refueling station

Studies focused on the behavior of the hydrogen leakage and diffusion are of great importance for facilitating the large scale application of the hydrogen energy. In this paper, the hydrogen leakage and diffusion in six scenarios which including comparison of different leakage position and different wind effect are analyzed numerically. The studied geometry is derived from the hydrogen refueling station in China. Due to the high pressure in hydrogen storage take, the hydrogen leakage is momentum dominated. The hydrogen volume concentration with the variation of the leakage time in different scenarios is plotted. More importantly, profiles of the flammable gas cloud at the end of the leakage are quantitatively studied. Results indicate that a more narrow space between the leakage hole and the obstacle and a smaller contact area with the obstacle make the profile of the flammable gas cloud more irregular and unpredictable. In addition, results highlight the wind effect on the hydrogen leakage and diffusion. Comparing with scenario which the wind direction consistent with the leakage direction, the opposite wind direction may result in a larger profile of the flammable gas cloud. With wind velocity increasing, the profile of the flammable gas cloud is confined in a smaller range. However, the presence of the wind facilitates the form of the recirculation zone near the obstacle. With an increase of the wind velocity, the recirculation zone moves downward along the obstacle. Thus, the hydrogen accumulation is more prominent near the obstacle.     

Optimal operation of a photovoltaic generation-powered hydrogen production system at a hydrogen refueling station

As the popularity of fuel cell vehicles continues to rise in the global market, production and supply of low-carbon hydrogen are important to mitigate CO₂ emissions. We propose a design for a hydrogen refueling station with a proton exchange membrane electrolyzer (PEM-EL)-based electrolysis system (EL-System) and photovoltaic generation (PV) to supply low-carbon hydrogen. Hydrogen is produced by the EL-System using electricity from PV and the power grid. The system was formulated as a mixed integer linear programming (MILP) model to allow analysis of optimal operational strategies. Case studies with different objective functions, CO₂ emission targets, and capacity utilization of the EL-System were evaluated. Efficiency characteristics of the EL-System were obtained through measurements. The optimized operational strategies were evaluated with reference to three evaluation indices: CO₂ emissions, capacity utilization, and operational cost of the system. The results were as follows: 1) Regardless of the objective function, the EL-System generally operated in highest efficiency state, and optimal operation depended on the efficiency characteristics of the EL-System; 2) mitigation of CO₂ emissions and increase in capacity utilization of the EL-System required trade-offs; and 3) increased capacity utilization of the EL-System showed two opposing effects on hydrogen retail price.     

Large-scale integration of wind power into the existing Chinese energy system

This paper presents the ability of the existing Chinese energy system to integrate wind power and explores how the Chinese energy system needs to prepare itself in order to integrate more fluctuating renewable energy in the future. With this purpose in mind, a model of the Chinese energy system has been constructed by using EnergyPLAN based on the year 2007, which has then been used for investigating three issues. Firstly, the accuracy of the model itself has been examined and then the maximum feasible wind power penetration in the existing energy system has been identified. Finally, barriers have been discussed and suggestions proposed for the Chinese energy system to integrate large-scale renewable energy in the future. It is concluded that the model constructed by the use of EnergyPLAN can accurately simulate the Chinese energy system. Based on current regulations to secure grid stability, the maximum feasible wind power penetration in the existing Chinese energy system is approximately 26% from both technical and economic points of view. A fuel efficiency decrease occurred when increasing wind power penetration in the system, due to its rigid power supply structure and the task of securing grid stability, was left primarily to large coal-fired power plants. There are at least three possible solutions for the Chinese energy system to integrate large-scale fluctuating renewable energy in the long term: Redesigning the regulations to secure grid stability by means of diversifying the participants, such as including hydropower and CHP plants; integrating large-scale heat pumps combined with heat storage devices to satisfy district heat demands and developing electric vehicles to promote off peak electricity utilisation.     

Pilot-scale hydrogen energy utilization system demonstration: A commercial building case study on on-site green hydrogen production and use

A demonstration of the Hydro Q-BiC®, i.e., a pilot-scale green hydrogen energy utilization system consisting of 64.75-kW photovoltaic (PV) panels, a 5-Nm³/h water electrolyzer, 40 Nm³ of metal hydride hydrogen storage, 14-kW fuel cells, and 20-kW/20-kWh Li-ion batteries, is discussed here. We set up our hydrogen system in front of a market administration building with demands that differ from those of a typical business building. The purpose of this study is to demonstrate the practicability of the green hydrogen system. The demonstration tests include 24-h experiments with various weather conditions: clear, cloudy, and clear to rainy; the CO₂ reduction capability evaluation is based on the results. In all cases, the CO₂ reduction capability is shown to be better than that of the PV-only system. However, the utilization of grid power for hydrogen production is proven to be of concern in the event of drastic and unexpected changes in weather conditions. Simulating annual CO₂ emissions indicates that the Hydro Q-BiC® can reduce emissions by more than 50%. We believe our findings can develop the practical application of hydrogen energy systems for buildings.     

Numerical investigation of the leakage and explosion scenarios in China's first liquid hydrogen refueling station

Promoting fuel cells has been one of China's ambitious hydrogen policies in the past few years. Currently, several hydrogen fueling stations (HRSs) are under construction in China to fuel hydrogen-driven vehicles. In this regard, it is necessary to assess the risks of hydrogen leakage in HRSs. Aiming at conducting a comprehensive consequence assessment of liquid hydrogen (LH2) leakage on China's first liquid hydrogen refueling station (LHRS) in Pinghu, a pseudo-source model is established in the present study to simulate the LH2 leakage using a commercial CFD tool, FLACS. The effects of the layout of the LHRS, leakage parameters, and local meteorological conditions on the LH2 leakage consequence has been assessed from the perspectives of low-temperature hazards and explosion hazards. The obtained results reveal that considering the prevailing southeast wind in Pinghu city, the farthest low-temperature hazard distance and lower flammable limit (LFL) -distance occurs in the leakage scenario along the north direction. It is found that the trailer parking location in the current layout of the LHRS will worsen the explosion consequences of the LH2 leakage. Moreover, the explosion will completely destroy the control room and endanger people on the adjacent road when the leakage equivalent diameter is 25.4 mm. The performed analyses reveal that as the wind speed increases, the explosion hazard decreases.     

Optimization of a combined wind and solar power plant

The paper is concerned with determining the optimized active areas of a photovoltaic conversion system, of a group of electricity generating wind machines and the optimal capacity of a battery storage system for a combined power plant. Minimization of the total life-cycle cost of the system is the criterion to obtaining the optimized parameters of the system. The algorithm consists of generating the system costs corresponding to various values of the parameters and to use these costs in a search procedure to determine the minimum. Each point is generated by a simulation program describing the system behaviour.     

Effect of wind energy system performance on optimal renewable energy model-an analysis

The Optimal Renewable Energy Model (OREM) has been developed to determine the optimum level of renewable energy sources utilisation in India for the year 2020–21. The model aims at minimising costefficiency ratio and determines the optimum allocation of different renewable energy sources for various end-uses. The extent of social acceptance level, potential limit, demand and reliability will decide the renewable energy distribution pattern and are hence used as constraints in the model. In this paper, the performance and reliability of wind energy system and its effects on OREM model has been analysed. The demonstration windfarm (4 MW) which is situated in Muppandal, a village in the southern part of India, has been selected for the study. The windfarm has 20 wind turbine machines of 200 KW capacity. The average technical availability, real availability and capacity factor have been analysed from 1991 to 1995 and they are found to be 94.1%, 76.4% and 25.5% respectively. The reliability factor of wind energy system is found to be 0.5 at 10,000 hours. The OREM model is analysed considering the above said factors for wind energy system, solar energy system and biomass energy systems. The model selects wind energy for pumping end-use to an extent of 0.3153×10¹⁵ KJ.     

Optimal operation of an all-in-one EV station with photovoltaic system including charging,battery swapping and hydrogen refueling

The issue of electrification of transportation is discussed due to the possibility of depletion of conventional resources in the near future and environmental problems caused by carbon emissions. For this purpose, different options have been proposed for the electrification of electric vehicles (EVs). Each potential EV user can choose a different EV type according to his desire, so different EV types can be seen in the environment. However, one of the most important reasons why the prevalence of EVs has not increased is the scarcity of EV charging, swapping, or refueling stations. In this respect, there is a need for an all-in-one EV station (AiOEVS) that can serve all types of EVs around and that all users know to be able to meet their energy needs easily and in line with their wishes. In this study, the economically optimum energy management model via mixed-integer linear programming (MILP) approach of an AiOEVS including a photovoltaic (PV) system as well electrolyzer and consisting of three different parts (charging for plug-in EVs, swapping for swappable EVs, and refueling for hydrogen fuel-cell EVs (HFCEVs)) is proposed. Besides, energy is purchased from the grid with time-of-use electricity prices. The proposed optimum operating framework is beneficial for each party. Furthermore, the hydrogen tank, swappable batteries, and long-parking plug-in EVs provide operational flexibility. The AiOEVS owner obtains a net profit of 33.12% at the end of the day. Furthermore, when the capacity of the PV is doubled or tripled, the gain increases by 11.69% or 23.41%, respectively.