A method for optimal sizing of an electrolyzer directly connected to a PV module

A method for optimal sizing of an electrolyzer directly connected to a PV module or array is presented. By combining the electrolyzer cells in series and in parallel it is possible to closely match the electrolyzer polarization curve to the curve connecting PV system’s maximum power points at different irradiation levels. The method presented here is based on linear approximation of both curves. With such a method it is possible to achieve the power transfer efficiency of up to 99%. The effect of PV temperature on optimum electrolyzer sizing is also investigated. The optimum electrolyzer size decreases with the increase of the PV temperature for the same PV system size. It was found that it is better (in terms of the system efficiency and the hydrogen generation rate) to size the EL system for a higher PV operating temperature.     

Solar-powered regenerative PEM electrolyzer/fuel cell system

An electrolyzer/fuel cell energy storage system is a promising alternative to batteries for storing energy from solar electric power systems. Such a system was designed, including a proton-exchange membrane (PEM) electrolyzer, high-pressure hydrogen and oxygen storage, and a PEM fuel cell. The system operates in a closed water loop. A prototype system was constructed, including an experimental PEM electrolyzer and combined gas/water storage tanks. Testing goals included general system feasibility, characterization of the electrolyzer performance (target was sustainable 1.0 A/cm² at 2.0 V per cell), performance of the electrolyzer as a compressor, and evaluation of the system for direct-coupled use with a PV array. When integrated with a photovoltaic array, this type of system is expected to provide reliable, environmentally benign power to remote installations. If grid-coupled, this system (without PV array) would provide high-quality backup power to critical systems such as telecommunications and medical facilities.     

Predicting efficiency of solar powered hydrogen generation using photovoltaic-electrolysis devices

Hydrogen fuel for fuel cell vehicles can be produced by using solar electric energy from photovoltaic (PV) modules for the electrolysis of water without emitting carbon dioxide or requiring fossil fuels. In the past, this renewable means of hydrogen production has suffered from low efficiency (2–6%), which increased the area of the PV array required and therefore, the cost of generating hydrogen. A comprehensive mathematical model was developed that can predict the efficiency of a PV-electrolyzer combination based on operating parameters including voltage, current, temperature, and gas output pressure. This model has been used to design optimized PV-electrolyzer systems with maximum solar energy to hydrogen efficiency. In this research, the electrical efficiency of the PV-electrolysis system was increased by matching the maximum power output and voltage of the photovoltaics to the operating voltage of a proton exchange membrane (PEM) electrolyzer, and optimizing the effects of electrolyzer operating current, and temperature. The operating temperature of the PV modules was also an important factor studied in this research to increase efficiency. The optimized PV-electrolysis system increased the hydrogen generation efficiency to 12.4% for a solar powered PV-PEM electrolyzer that could supply enough hydrogen to operate a fuel cell vehicle.     

Technico-economic analysis of off grid solar PV/Fuel cell energy system for residential community in desert region

A technico-economic analysis based on integrated modeling, simulation, and optimization approach is used in this study to design an off grid hybrid solar PV/Fuel Cell power system. The main objective is to optimize the design and develop dispatch control strategies of the standalone hybrid renewable power system to meet the desired electric load of a residential community located in a desert region. The effects of temperature and dust accumulation on the solar PV panels on the design and performance of the hybrid power system in a desert region is investigated. The goal of the proposed off-grid hybrid renewable energy system is to increase the penetration of renewable energy in the energy mix, reduce the greenhouse gas emissions from fossil fuel combustion, and lower the cost of energy from the power systems. Simulation, modeling, optimization and dispatch control strategies were used in this study to determine the performance and the cost of the proposed hybrid renewable power system. The simulation results show that the distributed power generation using solar PV and Fuel Cell energy systems integrated with an electrolyzer for hydrogen production and using cycle charging dispatch control strategy (the fuel cell will operate to meet the AC primary load and the surplus of electrical power is used to run the electrolyzer) offers the best performance. The hybrid power system was designed to meet the energy demand of 4500 kWh/day of the residential community (150 houses). The total power production from the distributed hybrid energy system was 52% from the solar PV, and 48% from the fuel cell. From the total electricity generated from the photovoltaic hydrogen fuel cell hybrid system, 80.70% is used to meet all the AC load of the residential community with negligible unmet AC primary load (0.08%), 14.08% is the input DC power for the electrolyzer for hydrogen production, 3.30% are the losses in the DC/AC inverter, and 1.84% is the excess power (dumped energy). The proposed off-grid hybrid renewable power system has 40.2% renewable fraction, is economically viable with a levelized cost of energy of 145 $/MWh and is environmentally friendly (zero carbon dioxide emissions during the electricity generation from the solar PV and Fuel Cell hybrid power system).     

Modeling,control and simulation of a photovoltaic /hydrogen/ supercapacitor hybrid power generation system for grid-connected applications

Hybrid renewable energy systems (HRES) should be designed appropriately with an adequate combination of different renewable sources and various energy storage methods to overcome the problem of intermittency of renewable energy resources. Focusing on the inevitable impact on the grid caused by strong randomicity and apparent intermittency of photovoltaic (PV) generation system, modeling and control strategy of pure green and grid-friendly hybrid power generation system based on hydrogen energy storage and supercapacitor (SC) is proposed in this paper. Aiming at smoothing grid-connected power fluctuations of PV and meeting load demand, the alkaline electrolyzer (AE) and proton exchange membrane fuel cell (PEMFC) and SC are connected to DC bus of photovoltaic grid-connected generation system. Through coordinated control and power management of PV, AE, PEMFC and SC, hybrid power generation system friendliness and active grid-connection are realized. The validity and correctness of modeling and control strategies referred in this paper are verified through simulation results based on PSCAD/EMTDC software platform.     

Development of hybrid photovoltaic-fuel cell system for stand-alone application

In this paper we present firstly the different hybrid systems with fuel cell. Then, the study is given with a hybrid fuel cell–photovoltaic generator. The role of this system is the production of electricity without interruption in remote areas. It consists generally of a photovoltaic generator (PV), an alkaline water electrolyzer, a storage gas tank, a proton exchange membrane fuel cell (PEMFC), and power conditioning units (PCU) to manage the system operation of the hybrid system. Different topologies are competing for an optimal design of the hybrid photovoltaic–electrolyzer–fuel cell system. The studied system is proposed. PV subsystem work as a primary source, converting solar irradiation into electricity that is given to a DC bus. The second working subsystem is the electrolyzer which produces hydrogen and oxygen from water as a result of an electrochemical process. When there is an excess of solar generation available, the electrolyzer is turned on to begin producing hydrogen which is sent to a storage tank. The produced hydrogen is used by the third working subsystem (the fuel cell stack) which produces electrical energy to supply the DC bus. The modelisation of the global system is given and the obtained results are presented and discussed.     

The coupling factor: A new metric for determining and controlling the efficiency of solar photovoltaic power utilization

The production of electricity and hydrogen in a renewable fashion, such as using solar energy, can provide a clean and sustainable energy source for electric-powered vehicles, including fuel-cell and battery-electric vehicles. Our research on generating hydrogen and charging batteries using renewable solar photovoltaic (PV) electricity has led to the development of a simple and convenient new metric called the coupling factor that describes the fraction of the maximum PV power transferred to electrical loads. The keystone of the coupling factor concept is a regression model to calculate the maximum PV voltage, current, and power as a function of the instantaneous incident solar irradiance and the photovoltaic module temperature. The coupling factor can range from zero to one, i.e., no transfer of power from the PV system to the load, to complete transfer of the PV power. We describe the derivation of regression models to compute important PV electrical output variables, such as the open circuit voltage, the short circuit current, the maximum power point voltage, the maximum power point current, and the coupling factor as a function of the fundamental measured variables affecting those quantities. The models are derived for PV modules used in our previous research to power an electrolyzer and charge high-voltage batteries. In addition, we develop models for other modules using PV cell technologies different from those used in our PV system. Some of the calculated quantities are compared to measurements for our PV system. The usefulness of these quantities, and especially the coupling factor, in rating the transfer of PV power to electrolyzer and battery loads, is illustrated. Finally, we discuss how the predicted maximum power point voltage can be used for real-time control and efficiency optimization of a dynamic PV-load system.     

Evaluation of DCX converters for off-grid photovoltaic-based green hydrogen production

Photovoltaic (PV) to electrolyzer power systems are an attractive research topic since the PV produced power can be optimized by skipping power conversion into AC and producing a direct DC-DC interface. Existing DC-DC power conversion systems to directly interface the PV generation and Hydrogen (H₂) electrolyzer are mainly based in interleaved structures or multi-resonant converters. Soft-switching characteristics are also suitable for these conversion topologies and DCX converters are then serious candidates to be used. DCX provides an isolated high efficiency solution but the DCX-based two-stage converter topology must be optimized in order to obtain better efficiency and energy yield. In this work a detailed comparison of DCX topologies is given for a PV to H₂ application. The proposed optimized system is validated through simulation in a multi-string electrolysis system, showing the relevance of the solution for this application. The proposed approach reaches a global maximum efficiency of 98.2%.     

The importance of detailed data utilization on the performance evaluation of a grid-independent hybrid renewable energy system

In this study, a multi-source hybrid power system consisting of wind turbine (WT), photovoltaic (PV) solar unit, proton exchange membrane (PEM) FC and battery is proposed. The WT and PV generation systems are considered as the main power sources for utilizing the available renewable energy. The FC system is proposed as the back-up generation combined with electrolyzer unit and battery picks up the fast load transients and ripples. In such a hybrid system, energy management plays an important role for the overall system performance and durability. From this perspective, a fuzzy logic based intelligent controller is considered in this study. Besides, a detailed minute-scale meteorological and load demand data is utilized in the simulation process and the importance of utilization of such detailed data is presented. This detailed analysis may be valuable for evaluating the feasibility of grid-independent hybrid renewable energy units for upcoming power systems.     

Development of a renewable hydrogen economy: Optimization of existing technologies

There is an increasing need for new and greater sources of energy for future global transportation applications. One recognized possibility for a renewable, clean source of transportation fuels is solar radiation collected and converted into useable forms of electrical and/or chemical (hydrogen) energy. This paper describes methods for utilizing and combining existing technologies into systems that optimize solar energy collection and conversion into useful transportation fuels. Photovoltaic (PV)-electrolysis (solar hydrogen) and PV-battery charging systems described in this paper overcome inefficiencies inherent in past concepts, where DC power from the PV system was first converted to AC current and then used to power electrical devices at the point of generation, or fed back to the grid to reduce electricity costs. These past, non-optimized concepts included efficiency losses in power conversion and unnecessary costs. These drawbacks can be avoided by capitalizing on the unique feature of solar photovoltaic devices that match their maximum power point to the operating point of an electrolyzer or a battery charger without intervening power transformers. This concept is illustrated for two systems designed, built, and tested by General Motors for fueling a fuel cell electric vehicle and charging an automotive propulsion battery. Based on this research, we propose a scenario in which individual home-owners, businesses, or sites at remote locations with no grid electricity, can capture solar energy, store it as hydrogen generated via water electrolysis, or as electrical energy used to charge storage batteries. Such a decentralized energy system provides a home refueling option for drivers who only travel limited distances each day.     

Mass minimization of a discrete regenerative fuel cell (RFC) system for on-board energy storage

RFC combined with solar photovoltaic (PV) array is the advanced technologic solution for on-board energy storage, e.g. land, sky, stratosphere and aerospace applications, due to its potential of achieving high specific energy. This paper focuses on mass modeling and calculation for a RFC system consisting of discrete electrochemical cell stacks (fuel cell and electrolyzer), together with fuel storage, a PV array, and a radiator. A nonlinear constrained optimization procedure is used to minimize the entire system mass, as well as to study the effect of operating conditions (e.g. current densities of fuel cell and electrolyzer) on the system mass. According to the state-of-the-art specific power of both electrochemical stacks, an energy storage system has been designed for the conditions of stratosphere applications and a rated power output of 12 kW. The calculation results show that the optimization of the current density of both stacks is of importance in designing the light weight on-board energy system.     

A photovoltaic-powered water electrolyzer: its performance and economics

A prototype water electrolyzer designed to operate from a solar photovoltaic (PV) array without power conditioning was operated for three months at the Florida Solar Energy Center. A 1 kWpk PV array was used to operate the electrolyzer at internal gas pressure from 0 to 40 psig. Performance of the electrolyzer/PV array was measured and characterized in terms of charge efficiency and power efficiency calculated from the operating data. The economics of residential production of hydrogen for energy purposes were calculated and summarized. While the near-term outlook for this energy storage technique was not found to be favorable, the long-term outlook was encouraging.     

Model construction and energy management system of lithium battery,PV generator,hydrogen production unit and fuel cell in islanded AC microgrid

The external electrical characteristics of the lithium battery, PV generator, hydrogen production unit (HPU) and fuel cell in islanded AC microgrid are well analyzed with mathematic models, based on which an energy management system among the abovementioned elements is proposed by using the bus frequency signaling. Specifically, the functions of lithium battery with the variables of the residual capacity and instantaneous working power are well designed to deliver its operation information to other units. The P-f droop control strategy is designed for the PV generator to make it adaptively work off from the maximum power point to the reference power point. The control strategy of HPU can make it work from the maximum efficiency point mode to the allowable maximum power point mode to absorb PV output power as much as possible when the lithium battery is almost getting full charged. Similarly, the fuel cell controller can regulate its power generation from the maximum efficiency point mode to the maximum power point to supply the local load as much as possible when the lithium battery is almost getting full discharged. Finally, the proposed energy management system is verified based on RTLAB experimental platform to show the effectiveness of the proposed coordination control strategy.     

Modeling of a hybrid marine current-hydrogen active power generation system

This paper presents the modeling and the simulation of a hybrid marine current-hydrogen power generation system. The marine current power generation system consists of a fixed pitch marine current turbine directly coupled to a permanent magnet synchronous generator (PMSG). The generator is connected to a DC link capacitor via a controlled rectifier, which has two modes of operation. The first mode is the maximum power point tracking (MPPT) by using torque control when the generator runs below the rated speed. The second mode is the power limitation (at the rated value) when the generator runs above the nominal speed. The generated power is transferred from the DC-link to the load via an inverter to run the system in a stand-alone operation mode. An energy storage system must cover the difference between the generation and the consumption for this scheme. The hydrogen, compared with the different energy storage systems, exhibits characteristics more applicable for marine current power generation systems. When the generated power is higher than the load requirements, a Megawatt-scale proton exchange membrane (PEM) electrolyzer consumes the surplus energy for hydrogen generation. The generated hydrogen is stored in tanks to feed a PEM fuel cell system to generate power in case of shortage. Based on this topology and operation procedure, the overall system is called an active power generation system. The MW scale PEM electrolyzer model is presented based on state of the art and the literature of different scales PEM electrolyzer system modeling.     

家用并网光伏系统仿真与运行性能计算

设计了一个家用并网光伏系统并计算其年发电量以研究其运行性能。在设定指定地点地理位置并导入气象数据,并根据屋顶可用面积决定光伏阵列的排布和逆变器参数后,利用PVsyst软件对光伏系统进行模拟,并计算发电量。结果表明：所设计的光伏系统年发电量约为7 114 kW·h,发电效率为75.1%。结合调查数据发现,该光伏系统发电量超过了当地用户年平均用电量;光伏系统一年中日输出电量的变化趋势显示,光伏系统发电量高峰时的日发电量均值可达35 kW·h以上;而光伏系统发电量低谷时的日发电量均值不足20 kW·h;光伏系统各项损失在理论发电量中的占比变化趋势显示,每年6、7、8月系统的光伏阵列损失最大,其原因是夏季气温升高使得光伏阵列运行性能受到影响。该光伏系统发电量可以满足一般家庭的用电需求,且用户可以参考光伏系统发电量的变化趋势选择合理的用电方式。     

The dynamic modeling and the exergy assessment of hydrogen synthesize and storage system with the power-to-gas concept for various locations

In this article, the solar hydrogen storage is modeled and hourly investigated with TRNSYS software. The Photovoltaic (PV) panel is employed for green power generation that is consumed in the electrolyzer subsystem and produced hydrogen. Additionally, the required electricity at the lack of enough solar irradiation is supplied from the grid. The performance of the system is comparatively analyzed for three main cities. Results show that the maximum power generation by PV panel is about 1670 kW in June which approximately is the same for two cities. The energy and Faraday efficiency of electrolyzer changes between 0.85-0.89 and 0.89–0.92 respectively. The amount of hydrogen production reaches 1235 m³/h for one of them in May. The total amount of hydrogen production is 13,181 m³/year in Yazd, 13,143 m³/year in hot city, and 13,141 m³/year in most populated city.     

Battery-assisted low-cost hydrogen production from solar energy: Rational target setting for future technology systems

The massive implementation of renewable energy requires sophisticated assessments considering the combination of feasible technology options. In this study, a techno-economic analysis was conducted for hydrogen production from photovoltaic power generation (PV) utilizing a battery-assisted electrolyzer. The installed capacity of each component technology was optimized for the wide range of unit costs of electricity from the PV, battery, and proton-exchange membrane electrolyzer. Leveling of PV output by battery, the necessary capacity of electrolyzer is suppressed and the operating ratio of electrolyzer increases. The battery-assist will result in a lower hydrogen production cost when the benefit associated with the smaller capacity and higher operation ratio of the electrolyzer exceeds the necessary investment for battery installation. The results from this study indicated the cost of hydrogen as low as 17 to 27 JPY/Nm³ using a combination of technologies and the achievement of ambitious individual cost targets for batteries, PV, and electrolyzers.     

太阳能光伏-PEM水电解制氢直接耦合系统优化

利用水电解制氢进行氢储能是我国可再生能源弃电问题的解决方案之一。本文建立了太阳能光伏阵列与质子交换膜（proton exchange membrane, PEM）水电解直接耦合系统的分析模型,研究耦合系统优化运行工况。结果表明,天气变化易导致直接耦合系统工作点偏离光伏最大功率点,引起耦合失配并降低太阳能利用率。通过匹配太阳能光伏阵列串并联结构和水电解器工作槽数进行“粗调”,改变PEM水电解器工作温度进行“精调”,可使直接耦合系统工作在最大功率点附近,使系统能量损失最小。本研究为太阳能光伏-PEM水电解氢储能直接耦合技术的运行策略和优化奠定了理论基础。     

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.     

Modeling,control and simulation of a PV/FC/UC based hybrid power generation system for stand-alone applications

Different energy sources and converters need to be integrated to meet sustained load demands while accommodating various natural conditions. This paper focuses on the integration of photovoltaic (PV), fuel cell (FC) and ultra-capacitor (UC) systems for sustained power generation. In the proposed system, during adequate insolation, the PV system feeds the electrolyzer to produce hydrogen for future use and transfers energy to the load side if possible. Whenever the PV system cannot completely meet load demands, the FC system provides power to meet the remaining load. If the rate of load demand increases the outside limits of FC capability, the UC bank meets the load demand above that which is provided by PV and FC systems. The main contribution of this work is the hybridization of alternate energy sources with FC systems using long and short-term storage strategies with appropriate power controllers and control strategies to build an autonomous system, with a pragmatic design and dynamic model proposed for a PV/FC/UC hybrid power generation system. The model is developed and applied in the MATLAB^®, Simulink^® and SimPowerSystems^® environment, based on the mathematical and electrical models developed for the proposed system.