Experimental assessment of a residential scale renewable–regenerative energy system

An experimental assessment of a hydrogen based regenerative (electrolyser-fuel cell) system is presented. The experiment was conducted on a residential scale Integrated Renewable Energy Experiment (IRENE) test-bed under conditions that are representative of the real demands that would be placed on a solar based, regenerative system, with a focus on dynamic operation under transients in both load and renewable energy supply profiles. A control algorithm employing bus voltage constraints and device current limitations is outlined. Results for a 2 week operating period indicate that the system response is very dynamic but repeatable.     

Application of regenerative fuel cells for space energy storage: a comparison to battery systems

A major advantage of regenerative fuel cells compared with battery systems arises from the decoupling of their rated power and their capacity, which determines the storage system. The mass of battery systems is related to the energy stored, whereas the masses of regenerative fuel cell systems are mainly determined by their rated power. On the other hand, average power and total energy are not independent variables, since they are correlated by the period of discharge of the electrochemical cells. Thus a comparison of the different approaches to storage can be given, by evaluating system masses as a function of power requirement and period of discharge. Since space power applications are considered, the charging and discharging periods can be expressed in terms of orbit altitudes.     

Fuel cells and load transients

Fuel cells are static energy conversion devices that convert the chemical energy of fuel into electrical energy directly. Compared with conventional power generation systems, they have many advantages, such as high efficiency, zero or low emission (of pollutant gases), and flexible modular structure. Fuel cells are expected to play an important role in future distributed generation (DG) applications. Fuel cell DGs (FCDGs) can either be connected to a utility grid for network reinforcement or installed in a remote area to supply stand-alone power. In this article, a load transient mitigation controller is described for hybrid PEMFC-battery power generation systems. The hybrid FCDG is controlled in a way that during a load transient, the fuel cell provides the steady-state part of the load, and the battery will supply the transient part of the load. The proposed technique can be especially useful in fuel cell vehicles (motor starting and accelerating) as well as in stationary applications, where load transients are unavoidable. The load transient mitigation controller is applicable to other types of FCDGs     

Regenerative braking for fuel cell hybrid system with additional generator

The fuel cell hybrid system for automobiles consists of a fuel cell/battery or fuel cell/super-capacitor. The motor in the regenerative braking system revives electrical energy instead of dissipating heat during braking. In this study, an additional generator in a fuel cell/battery hybrid system is equipped and tested as an alternative to using a motor for regenerative braking. The fuel cell hybrid system uses the Nexa™ Power Module from Ballard Power Systems Inc. and a Ni-MH battery from Global Battery Co., Ltd. In the hybrid system, the battery's voltage undershoots, while the fuel cell's voltage does not undershoot. In this study, the fuel cell hybrid system is affected by the load share rates due to the SoC of the battery. Therefore, the SoC of the battery needs to be managed. Also, the dynamic performance of the fuel cell is more stable when comprising the hybrid system. In addition, the efficiency of regenerative braking by using the generator is 63.8%. This shows that the efficiency is significantly improved compared with the 24.2% efficiency of regenerative braking using the motor.     

A 100-W class regenerative fuel cell system for lunar and planetary missions

The Japan Aerospace Exploration Agency (JAXA) is developing polymer electrolyte fuel cell (PEFC) systems that can be operated under isolated low-gravity and closed environments. In the present study, we combine the PEFC with an electrolyzer in order to realize a regenerative fuel cell. Ideally, if a single cell can be operated as a fuel cell and the cell can be made reversible through the electrolysis reaction, then compact, lightweight regenerative fuel cell systems can be realized. A unitized regenerative fuel cell was prepared, and its operability was demonstrated. During 100-W class operations, a stable fuel cell and electrolysis reaction was observed.     

Multi-pressure absorption cycles in solar refrigeration:: A technical and economical study

A technical and economical study of regenerative absorption chillers with multi-pressure cycle has been undertaken as solar operated refrigeration systems. Referred to as advanced absorption chillers they represent one of the new technology options that are under development. Advanced absorption cooling technology offers the possibility of chillers with thermal COPs of 1.5 or greater at driving temperatures of 140°C, which reduces the collector area and the heat rejection requirements compared to current absorption cooling technology. Two different absorption systems have been considered. The first is an advanced, double-effect regenerative absorption cooling system, driven at 140°C, whose efficiency is about 55% of the Carnot efficiency. The second is an ideal, single-effect regenerative absorption system that achieves 70% of the Carnot efficiency driven at 140°C or 200°C. To evaluate the solar performance of a thermally driven chiller requires a separate analysis of the solar availability for a given location compared to the required monthly average solar input. In this analysis different systems, including the vapour compression chillers, have been compared in terms of the thermal and electrical energy input. An effective electrical COP may be computed assuming that the ratio of electrical energy cost to thermal energy cost is four, which is typical of today’s fossil fuel costs. The effective electrical COPs of different technical options can then be compared. Those systems with higher electrical COPs will have lower energy costs. If solar is to be competitive, then the cost of delivered solar thermal energy should be less than the cost of delivered fossil thermal energy.     

Numerical and experimental studies on unitized regenerative proton exchange membrane fuel cell

Increasing energy need and running out of fossil-based fuels direct us to renewable energy resources. Although hydrogen is not an energy source by itself, it is an energy carrier with a high specific heat capacity. As it is used as fuel in unitized regenerative PEM fuel cells, water is separated in electrolyzer mode and stored by producing hydrogen when there is no need for energy. In this study, performance tests on the unitized regenerative PEM electrolyzer/fuel cell were carried out and numerical modelling has been performed. The validity of the developed model was confirmed by the results of the experimental study. Before starting the performance tests, the cell's leakproofness tests were carried out, and the appropriate torque force was optimized, reducing the contact resistance that causes performance loss. The material selection of the cell components and corrosion-resistant materials that can operate in both electrolyzer and fuel cell modes were preferred.In this study, 0.019 slpm of hydrogen and 0.0095 slpm of oxygen gas is produced in the electrolyzer mode, while a power density of 0.353 W/cm² is obtained in the fuel cell mode at 80 °C, from a unitized regenerative PEM fuel cell with a 5 cm² active area, whose cell elements are combined with a 3 Nm clamping torque by using 12 bolts.     

Energy management strategy based on fuzzy logic for a fuel cell hybrid bus

Fuel cell vehicles, as a substitute for internal-combustion-engine vehicles, have become a research hotspot for most automobile manufacturers all over the world. Fuel cell systems have disadvantages, such as high cost, slow response and no regenerative energy recovery during braking; hybridization can be a solution to these drawbacks. This paper presents a fuel cell hybrid bus which is equipped with a fuel cell system and two energy storage devices, i.e., a battery and an ultracapacitor. An energy management strategy based on fuzzy logic, which is employed to control the power flow of the vehicular power train, is described. This strategy is capable of determining the desired output power of the fuel cell system, battery and ultracapacitor according to the propulsion power and recuperated braking power. Some tests to verify the strategy were developed, and the results of the tests show the effectiveness of the proposed energy management strategy and the good performance of the fuel cell hybrid bus.     

Transient recognition control for hybrid fuel cell systems

Hybrid power systems combining fuel cells with fast energy storage devices are good solutions to the fuel cell load-following problem. Hybrid systems may also offer efficiency and reliability advantages. In this paper, we propose a power control scheme for hybrid systems that exploits feed-forward information about the steady-state behavior of incoming load transients. The method uses a modified cluster-weighted modeling (CWM) algorithm to build a load transient recognition model. The model is formulated sequentially and can provide useful feed-forward information in real time. Simulation and experimental results are provided that demonstrate the effectiveness of the transient recognition model and the proposed power control scheme for hybrid fuel cell systems.     

A fuel cell city bus with three drivetrain configurations

Three fuel cell city buses of the energy hybrid- and power hybrid-type were re-engineered with three types of drivetrain configuration to optimize the structure and improve the performance. The energy distribution, hydrogen consumption, state of charge (SOC) and the power variation rate were analyzed when different drivetrain configurations and parameters were used. When powered only by a fuel cell, the bus cannot recover the energy through regenerative braking. The variation of the fuel cell power is large and frequent, which is not good for the fuel cell. When the fuel cell is linked to a battery pack in parallel, the bus can recover the energy through regenerative braking. The energy distribution is determined by the parameters of the fuel cell and the battery pack in the design stage to reduce the power variation rate of the fuel cell. When the fuel cell and DC/DC converter connected in series links the battery pack in parallel, energy can be recovered and the energy distribution can be adjusted online. The power variation rate of both the fuel cell and the battery pack are reduced.     

Efficiency and weight trade-off analysis of regenerative fuel cells as energy storage for aerospace applications

Both efficiency and mass are important characteristics of an energy storage system, particularly for aerospace applications. This paper reports the results of a trade-off analysis conducted to optimize the design of regenerative fuel cell systems used in conjunction with a PV array. The operating efficiency of both the fuel cell and electrolyzer may be traded against the stack mass, by selecting a higher or lower nominal cell potential, thus operating at higher or lower current density. The results suggest that the highest roundtrip efficiency does not necessarily provide the highest specific energy of the energy storage subsystem. Further, the highest specific energy of the energy storage subsystem does not result in the lowest mass of the entire power system. Maximum roundtrip efficiency of 34% and maximum specific energy of 555 Wh/kg are achievable under certain conditions, but the minimum system mass is achieved at the roundtrip efficiency of 33% and specific energy of the energy storage system of 500 Wh/kg. Such a regenerative fuel cell system would be comparable in terms of total system mass to an advanced battery system that is 80% efficient, but has specific energy of 200 Wh/kg.     

Experimental investigation of fuel cell dynamic response and control

An experimental study of the dynamic response of a commercial fuel cell system is presented in this work. The primary goal of the research is an examination of the feasibility for using fuel cells in a load-following mode for vehicular applications, where load-following implies that the fuel cell system provides the power necessary for transient responses without the use of additional energy storage elements, such as batteries or super-capacitors. The dynamic response of fuel cell systems used in the load-following mode may have implications for safe and efficient operation of vehicles. To that end, a DC–DC converter was used to port the power output of the fuel cell to a resistive load using a pulse-width-modulating circuit. Frequency responses of the system were evaluated at a variety of DC offsets and AC amplitudes of the PWM duty cycle from 1 out to 400 Hz. Open-loop transient responses are then evaluated using transitions from 10% to 90% duty cycle levels, followed by dwells at the 90% level and then transitions back to the 10% level. A classical proportional–integral controller was then developed and used to close the loop around the system, with the result that the fuel cell system was driven to track the same transient. The controller was then used to drive the fuel cell system according to a reference power signal, which was a scaled-down copy of the simulated power output from an internal combustion engine powering a conventional automobile through the Federal Urban Driving Schedule (FUDS). The results showed that the fuel cell system is capable of tracking transient signals with sufficient fidelity such that it should be applicable for use in a load-following mode for vehicular applications. The results also highlight important issues that must be addressed in considering vehicular applications of fuel cells, such as the power conditioning circuit efficiency and the effect of stack heating on the system response.     

An integrated approach to hydrogen economy in Sicilian islands

CNR–ITAE is developing several hydrogen and fuel cell demonstration and research projects, each intended to be part of a larger strategy for hydrogen communities settling in small Sicilian islands. These projects involve vehicle design, hydrogen production from renewable energy sources and methane, as well as implementation strategies to develop a hydrogen and renewable energy economy. These zero emission lightweight vehicles feature regenerative braking and advanced power electronics to increase efficiency. Moreover, to achieve a very easy-to-use technology, a very simple interface between driver and the system is under development, including fault-recovery strategies and GPS positioning for car-rental fleets. Also marine applications have been included, with tests on PEFC applied on passenger ships and luxury yacht as power system for on-board loads. In marine application, it is under study also an electrolysis hydrogen generator system using seawater as hydrogen carrier. For stationary and automotive applications, the project includes a hydrogen refuelling station powered by renewable energy (wind or/and solar) and test on fuel processors fed with methane, in order to make the power generation self-sufficient, as well as to test the technology and increase public awareness toward clean energy sources.     

Electrical integration of renewable energy into stand-alone power supplies incorporating hydrogen storage

A stand-alone renewable-energy system employing a hydrogen-based energy store is now being commissioned within the HaRI project at West Beacon Farm, Leicestershire, UK. The interconnection of the various generators, loads and storage system is made through a central DC busbar: an arrangement that is believed to be unique within systems of this type and scale. The rotating generators, such as the wind turbines, are connected through standard industrial drives operating in regenerative mode, while the DC devices—electrolyser, fuel cell and solar photovoltaic array—employ custom DC–DC converters. This paper reviews the design philosophy of the electrical system and the various converters required. Modelling and simulation of the system is discussed along with practical lessons learnt from its implementation and some initial results are presented.     

Analysis of fuel cell hybrid locomotives

Led by Vehicle Projects LLC, an international industry–government consortium is developing a 109 t, 1.2 MW road-switcher locomotive for commercial and military railway applications. As part of the feasibility and conceptual-design analysis, a study has been made of the potential benefits of a hybrid power plant in which fuel cells comprise the prime mover and a battery or flywheel provides auxiliary power. The potential benefits of a hybrid power plant are: (i) enhancement of transient power and hence tractive effort; (ii) regenerative braking; (iii) reduction of capital cost.Generally, the tractive effort of a locomotive at low speed is limited by wheel adhesion and not by available power. Enhanced transient power is therefore unlikely to benefit a switcher locomotive, but could assist applications that require high acceleration, e.g. subway trains with all axles powered.In most cases, the value of regeneration in locomotives is minimal. For low-speed applications such as switchers, the available kinetic energy and the effectiveness of traction motors as generators are both minimal. For high-speed heavy applications such as freight, the ability of the auxiliary power device to absorb a significant portion of the available kinetic energy is low. Moreover, the hybrid power plant suffers a double efficiency penalty, namely, losses occur in both absorbing and then releasing energy from the auxiliary device, which result in a net storage efficiency of no more than 50% for present battery technology.Capital cost in some applications may be reduced. Based on an observed locomotive duty cycle, a cost model shows that a hybrid power plant for a switcher may indeed reduce capital cost. Offsetting this potential benefit are the increased complexity, weight and volume of the power plant, as well as 20–40% increased fuel consumption that results from lower efficiency.Based on this analysis, the consortium has decided to develop a pure fuel cell road-switcher locomotive, that is, not a hybrid.     

Model validation and performance analysis of regenerative solid oxide cells for energy storage applications: Reversible operation

The need for electrical energy storage (EES) is being driven by the deployment of increasing amounts of intermittent renewable energy resources. In addition to their fuel flexibility, high efficiency, scalability, and long-term cost outlook, reversible (regenerative) solid oxide cell (rSOC) systems have the potential for round-trip efficiencies competitive with the other available energy storage technologies. Accordingly, the focus of the current study is to investigate modeling methods for high temperature rSOCs in order to facilitate future endeavors related to establishing optimal operating conditions and system designs. Previously developed solid oxide fuel cell (SOFC) and solid-oxide electrolytic cell (SOEC) models are integrated to form a general rSOC model. The model is first calibrated and validated based on the available experimental data in the extant literature. The validation results show that the fitting parameters extracted from the calibration study can precisely simulate the cell behavior under various operating conditions. The effects of key operating parameters, such as temperature, gas composition and fuel utilization, on the voltage–current density performance characteristic and thermoneutral voltage are then investigated. It is also observed that the total electrochemical losses of the cell can be significantly different in each operating mode (fuel cell and electrolyzing) under certain operating conditions. Advantages of pressurized operation on thermal management are also discussed.     

Calculating transient wall heat flux from measurements of surface temperature

Wall heat fluxes can be derived from time resolved measurements of the surface temperature. This paper describes an analytical approach to calculate the heat flux from an analytical solution of the one-dimensional transient energy equation with transient boundary conditions using the Laplace transformation. The results are compared to simple test cases for which the heat fluxes are given in literature. The method is used to calculate the heat flux from a fuel spray to a wall at diesel engine conditions.     

Simulation and modeling of copper-chlorine cycle,molten carbonate fuel cell alongside a heat recovery system named regenerative steam cycle and electric heater with the incorporation of PID controller in MATLAB/SIMULINK

MCFC (molten carbonate fuel cell) is a relatively new kind of fuel cell that may be utilized in both local and large-scale energy distribution and generating systems. MCFCs are largely regarded as a viable source of renewable energy. Making an MCFC is a time-consuming and costly process. Mathematical modeling and efficiency simulations are essential to appropriately maximize its performance. Regenerative cycle, copper-chlorine cycle, and electric heater with PID controller is also studied to integrate them with MCFC to increase the efficiency of the overall system. Copper–Chlorine cycle is integrated to provide a stable stream of hydrogen and oxygen for the fuel cell. The Molten Carbonate fuel cell of stack 100 generates 1.203 MW of power at Voltage of 1.2 V each. Waste Heat recovery system is installed named regenerative Steam cycle which produces 2.94 MW of power. The total efficiency of system is 57% and the total extracted power is 4.143 MW. MATLAB/Simulink R2020a is used for modeling of multigeneration system with use of Engineering Equation Solver.     

Analysis of transient response of a unit proton-exchange membrane fuel cell with a degraded gas diffusion layer

The transient response characteristics and durability problems of proton-exchange membrane fuel cells are important issues for the application of PEM fuel cells to automotive systems. The gas diffusion layer is the key component of the fuel cell because it directly influences the mass transport mechanism. In this study, the effects of GDL degradation on the transient response of the PEM fuel cell are systematically studied using transient response analysis under different stoichiometric ratios and humidity conditions. With GDLs aged by the accelerated stress test, the effects of hydrophobicity and structural changes due to carbon loss in the GDL on the transient response of PEM fuel cells are determined. The cell voltage is measured according to the sudden current density change. The degraded GDLs that had uneven hydrophobicity distributions cause local water flooding inside the GDL and induce lower and unstable voltage responses after load changes.     

Performance assessment of a biogas fuelled molten carbonate fuel cell-thermophotovoltaic cell-thermally regenerative electrochemical cycle-absorption refrigerator-alkaline electrolyzer for multigenerational applications

In recent years, there has been increasing interest in fuel cell hybrid systems. In this paper, a novel multi-generation combined energy system is proposed. The system consists of a molten carbonate fuel cell (MCFC), a thermally regenerative electro-chemical cycle (TREC), a thermo photovoltaic cell (TPV), an alkaline electrolyzer (AE) and an absorption refrigerator (AR). It has four useful outputs, namely electricity, hydrogen, cooling and heating. The overall system is thermodynamically modeled in a detailed manner while its simulation and modeling are done through the TRNSYS software tool. Power output, cooling-heating and produced hydrogen rates are determined using energetic and exergetic analysis methods. Results are obtained numerically and plotted. The maximum power output from the system is 16.14 kW while maximum energy efficiency and exergy efficiency are 86.8% and 80.4%,. The largest exergy destruction is due to the MCFC.