TRNSYS simulation models for solar-hydrogen systems

A solar-hydrogen system is a kind of stand-alone power system (SAPS), which can supply low energy dwellings with energy. With TRNSYS (a transient system simulation program) it is possible to perform parametric studies to find possible system configurations for different climates and loads. The systems simulated in this study consist of a photovoltaic (PV) cell array, an electrolyzer, a hydrogen (H₂) storage, a fuel cell, a catalytic burner, a lead-acid battery, DC/DC converters, DC/AC inverters, diodes, a solar collector, and a water storage tank. The main equations for the PV cell, electrolyzer and fuel cell are provided, while the other models are only briefly described. Simulations are performed for conventional low energy dwellings located in northern latitudes and results for different system configurations and operation schemes are given. The results show that the size of the solar-hydrogen system for a conventional low energy house located in Trondheim, Norway (63°N), needs to be quite large. This is mainly due to the somewhat high energy requirements assumed, but also due to the low insolation available. Simulations of the same dwelling located in lower latitudes, in more favorable climates, and/or with lower energy needs (e.g., future dwellings), show how the size of the solar-hydrogen system can be significantly reduced. The study also illustrates the importance of minimizing the thermal and electrical loads before designing a solar-hydrogen system for energy self-sufficient buildings.     

Control analysis of renewable energy system with hydrogen storage for residential applications

The combination of an electrolyzer and a fuel cell can provide peak power control in a decentralized/distributed power system. The electrolyzer produces hydrogen and oxygen from off-peak electricity generated by the renewable energy sources (wind turbine and photovoltaic array), for later use in the fuel cell to produce on-peak electricity. An issue related to this system is the control of the hydrogen loop (electrolyzer, tank, fuel cell). A number of control algorithms were developed to decide when to produce hydrogen and when to convert it back to electricity, most of them assuming that the electrolyzer and the fuel cell run alternatively to provide nominal power (full power). This paper presents a complete model of a stand-alone renewable energy system with hydrogen storage controlled by a dynamic fuzzy logic controller (FLC). In this system, batteries are used as energy buffers and for short time storage. To study the behavior of such a system, a complete model is developed by integrating the individual sub-models of the fuel cell, the electrolyzer, the power conditioning units, the hydrogen storage system, and the batteries. An analysis of the performances of the dynamic fuzzy logic controller is then presented. This model is useful for building efficient peak power control.     

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.     

Monitoring and control of a hydrogen production and storage system consisting of water electrolysis and metal hydrides

Renewable energy sources such as wind turbines and solar photovoltaic are energy sources that cannot generate continuous electric power. The seasonal storage of solar or wind energy in the form of hydrogen can provide the basis for a completely renewable energy system. In this way, water electrolysis is a convenient method for converting electrical energy into a chemical form. The power required for hydrogen generation can be supplied through a photovoltaic array. Hydrogen can be stored as metal hydrides and can be converted back into electricity using a fuel cell. The elements of these systems, i.e. the photovoltaic array, electrolyzer, fuel cell and hydrogen storage system in the form of metal hydrides, need a control and monitoring system for optimal operation. This work has been performed within a Research and Development contract on Hydrogen Production granted by Solar Iniciativas Tecnológicas, S.L. (SITEC), to the Politechnic University of Valencia and to the AIJU, and deals with the development of a system to control and monitor the operation parameters of an electrolyzer and a metal hydride storage system that allow to get a continuous production of hydrogen.     

Simulation,economic and environmental evaluations of green solar parking (refueling station) for fuel cell vehicle

Energy storage is needed for renewable systems due to the intermittent nature of wind and solar energy. Hydrogen can be used to store variable renewable energy such as solar and wind energy. According to this fact, there is an increasing interest in use of solar-hydrogen systems for power supply in remote areas or other standalone applications. One of these applications is Hydrogen production station working by solar energy to use in fuel cell vehicle. Time consuming aspect of solar-hydrogen production is the most prominent reason for presenting a new scheme as a parking-refueling station for fuel cell vehicles in this study. To do this, Simulation, economic and environmental evaluations of the solar parking-refueling station are considered in this article. Because of using an independent hydrogen compression system, the suggested parking-refueling station can be used in a standalone area such as rural and military applications. Results show that the proposed system seems to be economic in present condition. It also illustrates that the Levelized Cost of Product (Km-Passenger) is in a range of 0.15–0.28 US$. Although using the tracker system is not economically efficient, the effect of such a structure is more obvious in the points far from tropical area.     

Electric round-trip efficiency of hydrogen and oxygen-based energy storage

An electrolyzer and a fuel cell have been integrated in a small-scale stand-alone renewable energy system to demonstrate that hydrogen can be used for long-term stationary energy storage. The economic and environmental performance of such a system is strongly related to the ability of the electrolyzer to convert electrical energy to hydrogen and the ability of the fuel cell to convert hydrogen back to electrical energy, which together define the round-trip efficiency of the hydrogen storage system. One promising way to improve the efficiency as well as to decrease the capital costs of the fuel cell is to recuperate the oxygen from the electrolyzer and use it as the fuel cell oxidant instead of compressed air. This paper presents the modifications made to the system in order to implement oxygen recuperation. The round-trip system efficiency was found to be 18% with oxygen recuperation and 13.5% without it.     

Miniaturization of spacecraft electrical power systems with solar-hydrogen power supply system

The concept of solar-hydrogen systems for spacecraft, orbital stations, lunar and Martian bases is currently receiving a new impetus. The supply of solar energy to energy receivers aboard space vehicles is limited. The number of everyday tasks and energy-intensive experiments on board space objects is growing with the development of astronautics. To perform energy-intensive work and experiments, energy consumption exceeds the incoming solar fluxes. The modern solar-hydrogen system ensures the reception, conversion and accumulation of excess incoming energy in the form of chemical energy - hydrogen. Cryogenics makes it possible to miniaturize the solar-hydrogen system. The safety of the cryogenic solar-hydrogen energy system is ensured by hydrogen concentration and leakage sensors.The article proposes a comprehensive solution for miniaturization of Power Conversion Unit (PCU) of Energy Power System (EPS) of spacecrafts (SC), which consists in a joint solution of four key problems of miniaturization of power devices: energy, structural, design and technological, system. Miniaturization of the solar-hydrogen energy system (SHES) is achieved by installing onboard hydrogen and oxygen microcryogenic refrigerators, as well as hydrogen and oxygen cryogenic tanks, water tank, electrolyzer and hydrogen fuel cells (FC). The accumulation of chemical hydrogen energy on board the orbiting spacecraft ensures reliable operation when entering the shadow. Storage of hydrogen in cryogenic form significantly reduces the volume required. A cryocooler based on the Stirling cycle provides the process of liquefying hydrogen after the electrolysis of distilled water. In addition, cryogenic temperatures of 20.2 K can be used to thermostat precision instruments placed on board the spacecraft, For example, to ensure the operation of the SQUID. A 3D - model of a voltage stabilization module (VSM), on the basis of which EEC can be produced with different output power and redundancy depth. We give an example of a complete structural scheme of the EEC, which allows implementing all the fulfillment of all the tasks, assigned to the EEC of the PCU SC.     

Hydrogen as a battery for a rooftop household solar power generation unit

Decentralization of electrical power generation using rooftop solar units is projected to develop to not only mitigate power losses along transmission and distribution lines, but to control greenhouse gases emissions. Due to intermittency of solar energy, traditional batteries are used to store energy. However, batteries have several drawbacks such as limited lifespan, low storage capacity, uncontrolled discharge when not connected to a load and limited number of charge/discharge cycles. In this paper, the feasibility of using hydrogen as a battery is analyzed where hydrogen is produced by the extra diurnal generated electricity by a rooftop household solar power generation unit and utilized in a fuel cell system to generate the required electrical power at night. In the proposed design, two rooftop concentrated photovoltaic thermal (CPVT) systems coupled with an organic Rankine cycle (ORC) are used to generate electricity during 9.5 h per day and the extra power is utilized in an electrolyzer to produce hydrogen. Various working fluids (Isobutane, R134a, R245fa and R123) are used in the ORC system to analyze the maximum feasible power generation by this section. Under the operating conditions, the generated power by ORC as well as its efficiency are evaluated for various working fluids and the most efficient working fluid is selected. The required power for the compressor in the hydrogen storage process is calculated and the number of electrolyzer cells required for the hydrogen production system is determined. The results indicate that the hybrid CPVT-ORC system produces 2.378 kW of electricity at 160 suns. Supplying 65% of the produced electricity to an electrolyzer, 0.2606 kg of hydrogen is produced and stored for nightly use in a fuel cell system. This amount of hydrogen can generate the required electrical power at night while the efficiency of electrolyzer is more than 70%.     

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.     

Solar powered residential hydrogen fueling station

This paper presents a conceptual design of a solar powered hydrogen fueling station for a single family home in Wallingford, Connecticut, USA. Sixty high-efficiency monocrystalline silicon photovoltaic (PV) solar panels (Total capacity: 18.9 kW) account for approximately 94.7% of the hydrogen home’s power consumption. The fueling station consists of a 165 bar high pressure electrolyzer for on-site production of 2.24 kg/day of hydrogen, three-bank cascade configuration storage tanks (4.26 kg of H₂ at 350 bar) and a SAE J2600 compliant hydrogen nozzle. The system produces 0.8 kg/day of hydrogen for a fuel cell vehicle with an average commute of 56 km/day (Fuel mileage: 71 km/kg H₂). Safety codes and standards applicable at the facility are described, and a well-to-wheel analysis is performed to contrast the carbon dioxide emissions of conventional gasoline and fuel cell vehicles. The energy efficiency obtained by incorporating a solar-hydrogen system for residential applications is also computed.     

Comparative transient simulation of a renewable energy system with hydrogen and battery energy storage for residential applications

Energy systems for the building sector nowadays are moving towards using renewable energy sources such as solar and wind power. However, it is nearly impossible to fully develop a multi-generation energy system for a building only relying on these sources without convenient energy storage, backup systems, or connection to the grid. In this work, using TRNSYS software, a model was developed to study the transient behavior of an energy system applicable for residential buildings to supply the heating, cooling, domestic hot water, and electricity in demand. This study contains the comparison of two methods of energy storage, a hydrogen fuel cell/electrolyzer package and a conventional battery system. This study also provides information on environmental impacts and economical aspects of the proposed system. The results show that for an HVAC system when using hydrogen storage system the capital cost is twice the cost of using a battery system. However, the hydrogen system shows better performance when used at higher loads. Hydrogen storage systems show higher performance when used at higher size units.     

Design and simulation of a solar-hydrogen system for different situations

In recent years, hybrid photovoltaic–fuel cell energy systems have been popular as energy production systems for different applications. A typical solar-hydrogen system can be modeled the electricity supplied by PV panels is used to meet the demand directly to the maximum extent possible. If there is any surplus PV power over demand, and capacity left in the tank for accommodating additional hydrogen, this surplus power is supplied to the electrolyser to produce hydrogen for storage. When the output of the PV array is not sufficient to supply the demand, the fuel cell draws on hydrogen from storage and produces electricity to meet the supply deficit.     

Impact of hydrogen energy storage on California electric power system: Towards 100% renewable electricity

Decarbonization of the power sector is a key step towards greenhouse gas emissions reduction. Due to the intermittent nature of major renewable sources like wind and solar, storage technologies will be critical in the future power grid to accommodate fluctuating generation. The storage systems will need to decouple supply and demand by shifting electrical energy on many different time scales (hourly, daily, and seasonally). Power-to-Gas can contribute on all of these time scales by producing hydrogen via electrolysis during times of excess electrical generation, and generating power with high-efficiency systems like fuel cells when wind and solar are not sufficiently available. Despite lower immediate round-trip efficiency compared to most battery storage systems, the combination of devices used in Power-to-Gas allows independent scaling of power and energy capacities to enable massive and long duration storage. This study develops and applies a model to simulate the power system balance at very high penetration of renewables. Novelty of the study is the assessment of hydrogen as the primary storage means for balancing energy supply and demand on a large scale: the California power system is analyzed to estimate the needs for electrolyzer and fuel cell systems in 100% renewable scenarios driven by large additions of wind and solar capacities. Results show that the transition requires a massive increase in both generation and storage installations, e.g., a combination of 94 GW of solar PV, 40 GW of wind, and 77 GW of electrolysis systems. A mix of generation technologies appears to reduce the total required capacities with respect to wind-dominated or solar-dominated cases. Hydrogen storage capacity needs are also evaluated and possible alternatives are discussed, including a comparison with battery storage systems.     

An experimental investigation of a PEM fuel cell to supply both heat and power in a solar-hydrogen RAPS system

The potential for both heat and power extraction from a PEM fuel cell is investigated experimentally and using computer simulation to improve the economics of a solar-hydrogen system supplying energy to a remote household. The overall average energy efficiency of the fuel cell was measured to be about 70% by utilizing the heat generated for domestic water heating, compared to only 35-50% for electricity generation alone. The corresponding round-trip energy efficiency of the hydrogen storage sub-system (electrolyzer, storage tank, and fuel cell) was raised from about 34% in a power-only application to about 50% in combined heat and power (CHP) mode. The economic benefit of using the fuel cell heat for boosting an LPG hot water system over a 30-year assessment period is estimated to be equivalent to about 15% of the total capital cost of the solar-hydrogen system. The stoichiometry of the input air, and the fuel cell operating temperature, were found to influence significantly the overall performance of the solar-hydrogen CHP system.     

Advanced controller design based on gain and phase margin for microgrid containing PV/WTG/Fuel cell/Electrolyzer/BESS

Nowadays, with the increase in the amount of power generation related to renewable energy resources, the need for energy storage and management is raised. In this regard, the hydrogen energy plays a critical role in the development of renewable technologies. In view of the above, advanced controller design is presented in this paper to effectively perform load frequency control of islanded fuel cell microgrid based on the wind turbine, photovoltaic, fuel cell, electrolyzer, battery energy storage systems, and residential and commercial loads. The controller design is based on the determination of the controller parameters that the fuel cell microgrid system will provide the desired dynamic properties. In the proposed controller design, virtual gain and phase margin testers are added to provide the desired dynamic properties. The controller's stable parameter plane is determined with the help of the stability boundary locus method, taking into account time delay, gain, and phase margin. First, the accuracy of the stable parameter plane determined for the proposed controller design is demonstrated by means of time domain and eigenvalue analyzes. Finally, in order to show the performance of the advanced controller design and the success of the fuel cell as a backup generator, analysis studies have been carried out using actual data of solar and wind, and appropriate changes of load in studied microgrid.     

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.     

Energy and cost analysis of a solar-hydrogen combined heat and power system for remote power supply using a computer simulation

A simulation program, based on Visual Pascal, for sizing and techno-economic analysis of the performance of solar-hydrogen combined heat and power systems for remote applications is described. The accuracy of the submodels is checked by comparing the real performances of the system’s components obtained from experimental measurements with model outputs. The use of the heat generated by the PEM fuel cell, and any unused excess hydrogen, is investigated for hot water production or space heating while the solar-hydrogen system is supplying electricity. A 5 kWh daily demand profile and the solar radiation profile of Melbourne have been used in a case study to investigate the typical techno-economic characteristics of the system to supply a remote household. The simulation shows that by harnessing both thermal load and excess hydrogen it is possible to increase the average yearly energy efficiency of the fuel cell in the solar-hydrogen system from just below 40% up to about 80% in both heat and power generation (based on the high heating value of hydrogen). The fuel cell in the system is conventionally sized to meet the peak of the demand profile. However, an economic optimisation analysis illustrates that installing a larger fuel cell could lead to up to a 15% reduction in the unit cost of the electricity to an average of just below 90 c/kWh over the assessment period of 30 years. Further, for an economically optimal size of the fuel cell, nearly a half the yearly energy demand for hot water of the remote household could be supplied by heat recovery from the fuel cell and utilising unused hydrogen in the exit stream. Such a system could then complement a conventional solar water heating system by providing the boosting energy (usually in the order of 40% of the total) normally obtained from gas or electricity.     

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.     

A solar hydrogen hybrid system with activated carbon storage

A solar hydrogen hybrid system has been developed to convert, store and use energy from renewable energy sources. The theoretical model has been implemented in a dynamic model-based software environment and applied to real data. A photovoltaic sub-system drives a residential load and, if a surplus of energy is available, an electrolyzer to produce hydrogen which is stored in a cluster of nitrogen-cooled tanks filled with activated carbons; when needed, hydrogen is used in a fuel cell to supply power to the load. Hydrogen storage is achieved through physisorption at low temperature and low pressures. Physisorption storage provides safer operations along with good gravimetric and volumetric capacities at costs comparable to or smaller than compression or liquefaction storage.     

Hydrogen as an energy carrier in stand-alone applications based on PV and PV–micro-hydro systems

The paper compares two different models of a hypothetical stand-alone energy system based only on renewable sources (solar irradiance and micro-hydro power) integrated with a system for the production of hydrogen (electrolyzer, compressed gas storage and proton exchange membrane fuel cell or PEMFC). The models of both systems have been designed to supply the electricity needs of a residential user in a remote area (a valley of the Alps in Italy) during a complete year of operation, without integration of traditional fossil fuel energy devices. A simulation model has been developed to analyze the energy performance of these systems. The technical feasibility and the behavior of the systems will be evaluated through the analysis of some data (e.g. the production and consumption of electricity along the year by the different components; the heat management; the production, storage and utilization of hydrogen).