Dynamic modeling and simulation of a small wind–fuel cell hybrid energy system

This paper describes dynamic modeling and simulation results of a small wind–fuel cell hybrid energy system. The system consists of a 400 W wind turbine, a proton exchange membrane fuel cell (PEMFC), ultracapacitors, an electrolyzer, and a power converter. The output fluctuation of the wind turbine due to wind speed variation is reduced using a fuel cell stack. The load is supplied from the wind turbine with a fuel cell working in parallel. Excess wind energy when available is converted to hydrogen using an electrolyzer for later use in the fuel cell. Ultracapacitors and a power converter unit are proposed to minimize voltage fluctuations in the system and generate AC voltage. Dynamic modeling of various components of this small isolated system is presented. Dynamic aspects of temperature variation and double layer capacitance of the fuel cell are also included. PID type controllers are used to control the fuel cell system. SIMULINK^TM is used for the simulation of this highly nonlinear hybrid energy system. System dynamics are studied to determine the voltage variation throughout the system. Transient responses of the system to step changes in the load current and wind speed in a number of possible situations are presented. Analysis of simulation results and limitations of the wind–fuel cell hybrid energy system are discussed. The voltage variation at the output was found to be within the acceptable range. The proposed system does not need conventional battery storage. It may be used for off-grid power generation in remote communities.     

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.     

Optimal configuration of power generating systems in isolated island with renewable energy

In isolated islands, usually diesel generators supply electric power. However, there are problems, e.g., a lack of fossil fuel, environmental pollution etc. So, isolated island, e.g. Miyako island, installs renewable energy power production plants. However, renewable energy power production plants are very costly. This paper presents an optimal configuration of power system in isolated island installing renewable energy power production plants. The generating system consists of diesel generators, wind turbine generators, PV system and batteries. Using the proposed method, operation cost can be reduced about 10% in comparison with diesel generators only from simulation results.     

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.     

Real-time energy management in an off-grid smart home: Flexible demand side control with electric vehicle and green hydrogen production

A real-time energy management system for an off-grid smart home is presented in this paper. The primary energy sources for the system are wind turbine and photovoltaics, with a fuel cell serving as a supporting energy source. Surplus power is used to generate hydrogen through an electrolyzer. Data on renewable energy and load demand is gathered from a real smart home located in the Yildiz Technical University Smart Home Laboratory. The aim of the study is to reduce hydrogen consumption and effectively utilize surplus renewable energy by managing controllable loads with fuzzy logic controller, all while maintaining the user's comfort level. Load shifting and tuning are used to increase the demand supplied by renewable energy sources by 10.8% and 13.65% from wind turbines and photovoltaics, respectively. As a result, annual hydrogen consumption is reduced by 7.03%, and the average annual efficiency of the fuel cell increases by 4.6%     

Simulation of a small wind fuel cell hybrid energy system

This paper describes simulation results of a small 500 W wind fuel cell hybrid energy system. The system consists of a Southwest Wind Power Inc. AIR 403 wind turbine, a Proton Exchange Membrane Fuel Cell (PEMFC) and an electrolyzer. Dynamic modeling of various components of this small isolated system is presented. Simulink is used for the dynamic simulation of this nonlinear 48 V hybrid energy system. Transient responses of the system to a step change in the load current and wind speed in a number of possible situations are presented. Analysis of simulation results and limitations of a wind fuel cell hybrid energy system are discussed.     

Multi-objective optimal design of hybrid renewable energy systems using PSO-simulation based approach

Recently, the increasing energy demand has caused dramatic consumption of fossil fuels and unavoidable raising energy prices. Moreover, environmental effect of fossil fuel led to the need of using renewable energy (RE) to meet the rising energy demand. Unpredictability and the high cost of the renewable energy technologies are the main challenges of renewable energy usage. In this context, the integration of renewable energy sources to meet the energy demand of a given area is a promising scenario to overcome the RE challenges. In this study, a novel approach is proposed for optimal design of hybrid renewable energy systems (HRES) including various generators and storage devices. The ε-constraint method has been applied to minimize simultaneously the total cost of the system, unmet load, and fuel emission. A particle swarm optimization (PSO)-simulation based approach has been used to tackle the multi-objective optimization problem. The proposed approach has been tested on a case study of an HRES system that includes wind turbine, photovoltaic (PV) panels, diesel generator, batteries, fuel cell (FC), electrolyzer and hydrogen tank. Finally, a sensitivity analysis study is performed to study the sensibility of different parameters to the developed model.     

Torsional torque suppression of decentralized generators using H∞ observer

The output power fluctuations of renewable energy plants such as wind turbine generators and photovoltaic systems cause frequency deviations and terminal voltage fluctuations. Furthermore, these power fluctuations also affect the turbine shaft of diesel generator and gas-turbine generators which are usually the main electric power systems in isolated islands. This paper presents a control strategy that achieves torsional torque suppression and power system stabilization. Since the measurement of the torsional torque is technically difficult and there is uncertainty in mechanical constants of the shaft torsional system, the torsional torque is estimated by using a H_∞ observer. The simulation results validate the effectiveness of the proposed control system.     

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.     

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.     

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.     

Frequency deviation control by coordination control of FC and double-layer capacitor in an autonomous hybrid renewable energy power generation system

In this paper, a novel control strategy for frequency control in stand-alone application based on coordination control of fuel cells (FCs) and double-layer capacitor (DLC) bank in an autonomous hybrid renewable energy power generation system is implemented. The proposed renewable energy power generation subsystems include wind turbine generator (WTG), photovoltaic system (PV), FC system and DLC bank as energy storage system. The system performance under different condition has been verified by using real weather data. Simulation results demonstrate the validity of proposed studied hybrid power generation system feeding isolated loads in power frequency balance condition.     

Torsional torque suppression of generator based on H∞ control theory in isolated power system

Renewable energy power plants, such as wind turbine generator and photovoltaic system, have been introduced in isolated power system recently. The output power fluctuations of wind turbine generator and load deviations result in frequency deviation and terminal voltage fluctuation. Furthermore, these power fluctuations also affect the turbine shafting of diesel generators and gas‐turbine generators, which are the main components of power generation systems in isolated islands. For stable operation of gas‐turbine generator, the torsional torque suppression as well as power system stabilization should be considered. In this paper, the control strategy that achieves torsional torque suppression and power system stabilization is presented based on H_∞ control theory. The effectiveness of the proposed control system is validated by numerical simulation results. Copyright © 2010 John Wiley & Sons, Ltd.     

Integrated bidding strategy of distributed energy resources based on novel prediction and market model

This paper presents an integrated operation model of renewable energy, distributed generators (DGs), energy storage, and demand response to overcome the challenges of renewable energy market participation. Additionally, an accurate prediction model for wind, photovoltaic (PV) power, and market price is introduced based on ensemble empirical model decomposition. In this model, radial basis function neural network (RBFNN) is used for the forecasting of subsignals from the analysis model. The training model of RBFNN is shaped based on the B-water cycle algorithm (WCA) optimization method. Additionally, by considering the adjusted market, demand response, and uncertainties analysis, this method reduced the economic damages of generators and loads. A case study test has consisted of a wind turbine, photovoltaic energy, fuel cell energy, demand response, and energy storage.     

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.     

Polygeneration microgrids: A viable solution in remote areas for supplying power,potable water and hydrogen as transportation fuel

This paper presents the concept and the design of a hybrid renewable energy polygeneration microgrid along with its technical and economical evaluation. The energy of the sun and the wind is harvested by photovoltaics and a wind turbine. Besides that, the components of the microgrid include a battery bank, a Proton Exchange Membrane (PEM) fuel cell, a PEM electrolyzer, a metal hydride tank, a reverse osmosis desalination unit using energy recovery and a control system. The microgrid covers the electricity, transport and water needs and thus its products are power, hydrogen as transportation fuel and potable water through desalination. Hydrogen and the desalinated water also act as medium to long term seasonal storage. A design tool based on TRNSYS 16, GenOpt 2.0 and TRNOPT was developed using Particle Swarm Optimization method. The economic evaluation of the concept was based on the discounting cash flow approach. The Monte Carlo Simulation method was used in order to take uncertainty into account. A technically feasible polygeneration microgrid adapted to a small island is financially profitable with a probability of 90% for the present and 100% at the medium term.     

Supplying the energy of islands with geopolitical positions using distributed generations to increase energy security

The islands usually face challenges in their energy supply due to their specific location. On islands that are distant from the land, power is typically provided by diesel generators. Therefore, oil tankers must regularly refuel the island in order to supply the necessary fuel for diesel generators. As a result, if the fueling procedure is not completed for whatever reason, the island will not receive the necessary energy, which will result in an unavoidable loss of load. Due to their strategic location, some of these islands are used as military islands to protect the nations and waterways. Given the vital role that these military islands play for nations, a delay in supplying the island with energy can seriously harm security, the economy, and other factors. Transferring fuel to these islands is typically difficult, and in some cases impossible, under certain circumstances, such as war. Therefore, reducing the island's reliance on fossil fuels as much as feasible is vital to ensure the energy security of these specific islands. Diesel generators provide electricity to Larak Island, which is situated in the Strait of Hormuz. Larak Island serves as a military island due to its geopolitical location, hence it is crucial to consistently provide Larak with electricity. Therefore, in this paper, a combination of distributed generations and system storage is used to supply the Larak island. The photovoltaic, wind and tidal plants are considered the main power plants, and fuel cells with electrolyzers and hydrogen tanks have also been used as storage systems. In addition, the diesel generator is considered the system backup. The considered objective functions to design and manage Larak island's power supply system are reducing diesel generators fuel consumption, reducing electricity cost, and reducing electricity outages and lost power generation of renewable resources.     

A wind-power fuel-cell hybrid system study on the non-interconnected Aegean islands grid

The current paper presents the study of coupling a wind-turbine with a fuel cell to improve the utilization of wind power in the non-interconnected Greek archipelago grid. A part of the energy produced by the wind-turbine is stored in the form of hydrogen and is then delivered to the consumption at constant power through a fuel cell. This decoupling between the wind potential and power delivery is necessary to increase the contribution of renewable energy sources to the small capacity grids of islands. The study presents the technology of the system and simulates its operation over a year using a specially developed software and actual wind speed input data. In this way, the energy availability can be estimated and is presented for hybrid installations of increasing size. The nominal size of the individual devices (electrolyser, fuel cell, hydrogen storage tanks) is then selected depending on the hybridisation level, that is the ratio of energy delivered directly from the wind-turbine over the energy delivered from the fuel cell. Results show that it is possible to replace conventional power stations with a hybrid system, delivering energy under constant power with fuel cell sizes that reach almost up to 1/3 of the nominal wind-turbine power and overall efficiencies that may exceed 60%.     

Analysis of the current methods used to size a wind/hydrogen/fuel cell‐integrated system: A new perspective

As an alternative to the production and storage of intermittent renewable energy sources, it has been suggested that one can combine several renewable energy technologies in one system, known as integrated or hybrid system, that integrate wind technology with hydrogen production unit and fuel cells. This work assesses the various methods used in sizing such systems. Most of the published papers relate the use of simulation tools such as HOMER, HYBRID2 and TRNSYS, to simulate the operation of different configurations for a given application in order to select the best economic option. But, with these methods one may not accurately determine certain characteristics of the energy resources available on a particular site, the profiles of estimated consumption and the demand for hydrogen, among other factors, which will be the optimal parameters of each subsystem. For example, velocity design, power required for the wind turbine, power required for the fuel cell and electrolyzer and the storage capacity needed for the system. Moreover, usually one makes excessive use of bi‐parametric Weibull distribution function to approximate the histogram of the observed wind to the theoretical, which is not appropriate when there are bimodal frequency distributions of wind, as is the case in several places in the world. A new perspective is addressed in this paper, based on general system theory, modeling and simulation with a systematic approach and the use of exergoeconomic analysis. There are some general ideas on the advantages offered in this method, which is meant for the implementation of wind/hydrogen/fuel cell‐integrated systems and in‐situ clean hydrogen production. Copyright © 2009 John Wiley & Sons, Ltd.     

The effect of the hysteresis band on power management strategies in a stand-alone power system

A stand-alone power system that consists of a photovoltaic array and wind generators for the exploitation of renewable energy sources (RES), and that is capable of storing excessive energy in the form of hydrogen via water electrolysis for subsequent use in a polymer electrolyte membrane (PEM) fuel cell is currently being installed at Neo Olvio of Xanthi in Greece. The performance of two power management strategies (PMSs) that utilize a hysteresis band in the operation of the integrated system over a typical 4-month period is assessed. The state-of-charge (SOC) level of the accumulator is the main parameter that governs the operation of the electrolyzer and the fuel cell. The introduction of a hysteresis band in the boundary limits of the SOC of the accumulator provides larger flexibility in the operation of the electrolyzer, the fuel cell, and the accumulator. In this way, the units can be protected from heavy and unnecessary utilization or irregular operation (reduction of frequent start-ups and shut-downs). The simulated results for the implemented PMSs revealed important information about the reliability of the load satisfaction, the total operation time that each subsystem undergoes, as well as about the hydrogen inventory in the integrated system. The study also identified the effect of variation of hysteresis band size on the system performance as an important feature for the development of an integrated control strategy.