Thermally integrated energy storage system for hybrid fuel cell electric bike: An experimental study

The hybrid fuel cell/battery technology is an attractive option for a sustainable mobility with zero emissions. In fact, this solution owns system scalability features and high efficiency and, compared to battery electric solutions, it offers advantages in terms of flexibility of use and fast charging times. However, the thermal management for the battery in this type of powertrain is a crucial issue, since operating temperatures can significantly affect safety and performance. In this study, an innovative system aimed at providing high storage energy density and improving the battery pack performance of hybrid fuel cell/battery vehicles is investigated for use on-board of a plug-in fuel cell electric bike. The proposed system, developed by the authors in previous studies, integrates the battery pack with a hydrogen storage based on metal hydrides. The idea behind this solution is to exploit the endothermic desorption processes of hydrogen in metal hydrides to cool down the battery pack during operation. An experimental analysis is conducted to assess the thermal management capabilities of this system: by considering a typical duty cycle designed on the base of road test measurements, battery pack temperature profiles are evaluated and compared against those from a control experiment where no battery thermal management is enabled (i.e. no hydrogen desorption from the metal hydride tank). The results show that, beside enhancing the on-board stored energy capacity, the proposed system represents an effective solution to provide an efficient thermal management for the battery pack, with significant advantages in terms of attainable riding range.     

Data results and operational experience with a solar hydrogen system

A solar hydrogen system is presented able to provide uninterrupted 200 W_e power to an isolated application. It is composed of a photovoltaic generator, a battery set, an electrolyser, a metal-hydride system for hydrogen storage and a fuel cell. Batteries are charged with the photovoltaic array and the fuel cell, and discharged with the electrolyser and the application load. The fuel cell switches on when the state of charge of the batteries is low, until they are recovered to a predetermined level. The electrolyser produces H₂ at 30 bar, enough to feed directly the metal hydrides, avoiding pressurization steps. Metal hydrides work under pressure control in the temperature range 0–40 °C. Kinetics of absorption–desorption of hydrogen is observed as an important limiting aspect for this kind of storage. The system is able to convert about 6–7% of total solar energy irradiated in 1 year. Results and evaluation after 1-year operation are shown. Energy management is found to be a critical issue to improve the behavior of the system.     

Experimental study of hydrogen storage with reaction heat recovery using metal hydride in a totalized hydrogen energy utilization system

Experimental results for hydrogen storage tanks with metal hydrides used for load leveling of electricity in commercial buildings are described. Variability in electricity demand due to air conditioning of commercial buildings necessitates installation of on-site energy storage. Here, we propose a totalized hydrogen energy utilization system (THEUS) as an on-site energy storage system, present feasibility test results for this system with a metal hydride tank, and discuss the energy efficiency of the system. This system uses a water electrolyzer to store electricity energy via hydrogen at night and uses fuel cells to generate power during the day. The system also utilizes the cold heat of reaction heat during the hydrogen desorption process for air conditioning. The storage tank has a shell-like structure and tube heat exchangers and contains 50 kg of metal hydride. Experimental conditions were specifically designed to regulate the pressure and temperature range. Absorption and desorption of 5,400 NL of hydrogen was successfully attained when the absorption rate was 10 NL/min and desorption rate was 6.9 NL/min. A 24-h cycle experiment emulating hydrogen generation at night and power generation during the day revealed that the system achieved a ratio of recovered thermal energy to the entire reaction heat of the hydrogen storage system of 43.2% without heat loss.     

Test of hybrid power system for electrical vehicles using a lithium-ion battery pack and a reformed methanol fuel cell range extender

This work presents the proof-of-concept of an electric traction power system with a high temperature polymer electrolyte membrane fuel cell range extender, usable for automotive class electrical vehicles. The hybrid system concept examined, consists of a power system where the primary power is delivered by a lithium ion battery pack. In order to increase the run time of the application connected to this battery pack, a high temperature PEM (HTPEM) fuel cell stack acts as an on-board charger able to charge a vehicle during operation as a series hybrid. Because of the high tolerance to carbon monoxide, the HTPEM fuel cell system can efficiently use a liquid methanol/water mixture of 60%/40% by volume, as fuel instead of compressed hydrogen, enabling potentially a higher volumetric energy density.     

Experimental and numerical investigation of heat transfer in Li‐ion battery pack of a hoverboard

Li‐ion cells are used for energy storage and conversion in electric vehicles and a variety of consumer devices such as hoverboards. Performance and safety of such devices are severely affected by overheating of Li‐ion cells in aggressive operating conditions. Multiple recent fires and accidents in hoverboards are known to have originated in the battery pack of the hoverboard. While thermal analysis and measurements have been carried out extensively on large battery packs for electric vehicles, there is relatively lesser research on smaller devices such as hoverboards, where the extremely limited thermal management design space and the critical importance of user safety result in severe thermal management challenges. This paper presents experimental measurements and numerical analysis of a novel approach for thermal management of the battery pack of a hoverboard. Measurements indicate that temperature rise in cells in the pack can be as large as 30°C at 4C discharge rate, which, although unlikely to be a standard discharge rate, may result from a malfunction or accident. A novel thermal management approach is investigated, wherein careful utilization of air flow generated by hoverboard motion is shown to result in significant temperature reduction. Measurements also indicate the key role of the metal housing around the battery pack in thermal management. Measurements are found to be in good agreement with finite element simulations, which indicate that the battery pack can be cooled as effectively in presence of a perforated metal casing as without the casing at all. Experimental data and simulation model presented here offer critical insights into the design of hoverboard thermal management and may result in safer, high performance hoverboard battery packs.     

Application of hydrides in hydrogen storage and compression: Achievements,outlook and perspectives

Metal hydrides are known as a potential efficient, low-risk option for high-density hydrogen storage since the late 1970s. In this paper, the present status and the future perspectives of the use of metal hydrides for hydrogen storage are discussed. Since the early 1990s, interstitial metal hydrides are known as base materials for Ni – metal hydride rechargeable batteries. For hydrogen storage, metal hydride systems have been developed in the 2010s [1] for use in emergency or backup power units, i. e. for stationary applications.With the development and completion of the first submarines of the U212 A series by HDW (now Thyssen Krupp Marine Systems) in 2003 and its export class U214 in 2004, the use of metal hydrides for hydrogen storage in mobile applications has been established, with new application fields coming into focus.In the last decades, a huge number of new intermetallic and partially covalent hydrogen absorbing compounds has been identified and partly more, partly less extensively characterized.In addition, based on the thermodynamic properties of metal hydrides, this class of materials gives the opportunity to develop a new hydrogen compression technology. They allow the direct conversion from thermal energy into the compression of hydrogen gas without the need of any moving parts. Such compressors have been developed and are nowadays commercially available for pressures up to 200 bar. Metal hydride based compressors for higher pressures are under development. Moreover, storage systems consisting of the combination of metal hydrides and high-pressure vessels have been proposed as a realistic solution for on-board hydrogen storage on fuel cell vehicles.In the frame of the “Hydrogen Storage Systems for Mobile and Stationary Applications” Group in the International Energy Agency (IEA) Hydrogen Task 32 “Hydrogen-based energy storage”, different compounds have been and will be scaled-up in the near future and tested in the range of 500 g to several hundred kg for use in hydrogen storage applications.     

Analysis of cooling and heating characteristics of thermal management system for fuel cell bus

Vehicle thermal management system (VTMS) is an important part of the safe operation of fuel cell vehicles (FCVs). In this work, an integrated thermal management system was proposed for a fuel cell bus, with 80 kW fuel cell and 105 kWh battery. Liquid cooling is adopted for fuel cell, battery and motor. The model of VTMS was based on AMESim software. Two modes, including cooling and heating, were simulated for VTMS under different ambient conditions. The simulation is performed under a modified New European Driving Cycle (MNEDC), in which the running time is 1180 s and the distance is 10437 m. Results show that the VTMS could fulfill the temperature requirement for both modes. In cooling mode, ambient temperature of 34 °C, 37 °C and 40 °C are considered. The equivalent hydrogen consumption (EHC) is 505.68 g, 522.93 g and 539.48 g respectively. In heating mode, the ambient temperature is set to be −10 °C, −5 °C, 0 °C, and the corresponding EHC is 840.16 g, 783.64 g and 707.53 g, respectively. Besides, EHC at different heating target temperature for the fuel cell and battery was investigated. Results show that reducing the target heating temperature of fuel cell by 10 °C consumes less hydrogen than reducing the target heating temperature of battery by 5 °C. It is hoped that the results of this work will play a positive role in extending driving range.     

Dynamic analysis of a PEM fuel cell hybrid system with an on-board dimethyl ether (DME) steam reformer (SR)

Low-temperature polymer electrolyte membrane fuel cell (PEMFC) acts as a promising energy source due to the non-pollution and high-energy density. However, as hydrogen supply is a major constraint limiting the wide spread of fuel cell vehicles, a dimethyl ether (DME)-steam on-board reformer (SR) based on catalytic reforming via a catalytic membrane reactor with a channel structure is a possible solution to a direct hydrogen supply. The DME-SR reaction scheme and kinetics in the presence of a catalyst of CuO/ZnO/Al₂O₃+ZSM-5 are functions of the temperature and hydrocarbon ratio in the hydrogen-reforming reaction. An electric heater is provided to keep the temperature at a demanded value to produce hydrogen. As there is no available analysis tool for the fuel cell battery hybrid vehicle with on-board DME reformer, it is necessary to develop the tool to study the dynamic characteristics of the whole system. Matlab/Simulink is utilized as a dynamic simulation tool for obtaining the hydrogen production and the power distribution to the fuel cell. The model includes the effects of the fuel flow rate, the catalyst porosity, and the thermal conductivity of different subsystems. A fuel cell model with a battery as a secondary energy storage is built to validate the possible utilization of on-board reformer/fuel cell hybrid vehicle. In consideration of time-delay characteristic of the chemical reactions, the time constant obtained from the experiment is utilized for obtaining dynamic characteristics. The hydrogen supplied by the reformer and the hydrogen consumed in the PEMFC prove that DME reformer can supply the adequate hydrogen to the fuel cell hybrid vehicle to cope with the required power demands.     

Discharge dynamics of coupled fuel cell and metal hydride hydrogen storage bed for small wind hybrid systems

In small hybrid wind systems, excess wind energy is stored for later use during the deficit power generation. Excess wind energy can be stored as hydrogen in a metal hydride storage bed and reused later to generate power using a fuel cell. This paper deals with the discharge dynamics of the coupled fuel cell and metal hydride storage bed during the power extraction. Thermal coupling of the fuel cell and metal hydride bed is also discussed. The waste heat generated in the fuel cell is removed using a water coolant. The exit fuel cell coolant stream is passed through the metal hydride storage bed to supply the necessary heat required for desorption of hydrogen from the bed. This will also lead to a reduction in the load on the radiator. The discharge dynamics and the thermal management of the coupled system are demonstrated through a system simulation model developed in Matlab/Simulink platform.     

Dynamic analysis of PEM fuel cells and metal hydrides on a zero-emission ship: A model-based approach

As the interest in hydrogen and PEM fuel cells is growing, it is crucial to define the best technology for fuel storage, especially in the transportation field. Metal hydrides show different benefits, including the possibility of thermally coupling the hydrogen storage and utilization systems: fuel cells require heat subtraction for ensuring proper operation, while metal hydrides require heat to activate the hydrogen release reactions. This work describes the integration of PEMFCs and metal hydrides on board a zero-emissions ship, with a special focus on their thermal coupling; a model-based approach is developed to ensure the system's feasibility at different load demands for the vessel, including transient conditions. The study is based on the real application of an innovative zero-emissions ship (ZEUS) financed by Fincantieri-Isotta Fraschini S.p.A, where the total power installation is set at 144 kW by PEMFC and 50 kg of hydrogen are stored by metal hydrides.     

Thermal conductivity measurements of magnesium hydride powder beds under operating conditions for heat storage applications

One of the major issues of the change in energy politics is the storage of renewable energy in order to facilitate a continuous energy supply to the grid. An efficient way to store energy (heat) is provided by the usage of Thermochemical Energy Storage (TES) in metal hydrides. Energy is stored in dehydrogenated metal hydrides and can be released by hydrogenation for consumption. One prominent candidate for high temperature (400 °C) heat storage is magnesium hydride. It is a well-known and investigated material which shows high cycling stability over hundreds of cycles. It is an abundant material, non-toxic and easy to prepare in bigger scales. One of the major drawbacks for heat storage applications is the low heat transfer capability of packed beds of magnesium hydrides. In this work we present results of effective thermal conductivity (ETC) which were measured under hydrogen pressure up to 25 bar and temperatures up to 410 °C in order to meet the operating conditions of magnesium hydride as a thermochemical heat storage material. We could show that the effective thermal conductivity of a magnesium hydride – hydrogen system at 410 °C and 25 bar hydrogen increases by 10% from 1.0 W m⁻¹ K⁻¹ to 1.1 W m⁻¹ K⁻¹ after 18 discharging and charging cycles. In dehydrogenated magnesium hydride this increase of the thermal conductivity was found to be at 50% from 1.20 W m⁻¹ K⁻¹ to 1.80 W m⁻¹ K⁻¹ at 21 bar hydrogen. These data are very important for the design and construction of heat storage tanks based on high temperature metal hydrides in the future.     

Metal hydride materials for solid hydrogen storage: A review

Hydrogen is an ideal energy carrier which is considered for future transport, such as automotive applications. In this context storage of hydrogen is one of the key challenges in developing hydrogen economy. The relatively advanced storage methods such as high-pressure gas or liquid cannot fulfill future storage goals. Chemical or physically combined storage of hydrogen in other materials has potential advantages over other storage methods. Intensive research has been done on metal hydrides recently for improvement of hydrogenation properties. The present review reports recent developments of metal hydrides on properties including hydrogen-storage capacity, kinetics, cyclic behavior, toxicity, pressure and thermal response. A group of Mg-based hydrides stand as promising candidate for competitive hydrogen storage with reversible hydrogen capacity up to 7.6 wt% for on-board applications. Efforts have been devoted to these materials to decrease their desorption temperature, enhance the kinetics and cycle life. The kinetics has been improved by adding an appropriate catalyst into the system and as well as by ball-milling that introduces defects with improved surface properties. The studies reported promising results, such as improved kinetics and lower decomposition temperatures, however, the state-of-the-art materials are still far from meeting the aimed target for their transport applications. Therefore, further research work is needed to achieve the goal by improving development on hydrogenation, thermal and cyclic behavior of metal hydrides.     

Performance analysis of a hybrid solar-hydrogen-retired EV batteries (REVB) energy system with thermal-electrical loops

Utilizing solar energy is an efficient method to provide hybrid renewable energy system with sufficient thermal/electrical energy. Meanwhile, the rapid development of electrical vehicles leads to an excess of retired electric vehicles. As a combination of the abovementioned two conceptions, this study proposed and examined a hybrid solar-hydrogen-retired electrical vehicle battery energy system to meet thermal and electrical loads for small-scale usage. The novelty of this research is delivered as follows: first of all, the proposed hybrid energy system supplies both thermal and electrical energy to small-scale end users; secondly, the retired electrical vehicle batteries are recycling to relieve the pressure of battery demand; thirdly, an energy management strategy to regulate the complicated hybrid energy system is designed. The results show that with assistance of fuel cell as an energy storage unit, solar energy can basically satisfy the annual thermal/electrical load with maximum monthly energy supplement of 1220.43 MJ and 1572.75 kWh, respectively. However, the solar radiation serving as single energy source is not very reliable for large-scale utilization. Although the state of charge does not fluctuate greatly, the small range charge/discharge between 59% and 63% can still guarantee the normal operation of the proposed hybrid energy system.     

Dynamic behaviour of Li batteries in hydrogen fuel cell power trains

A Li ion polymer battery pack for road vehicles (48 V, 20 Ah) was tested by charging/discharging tests at different current values, in order to evaluate its performance in comparison with a conventional Pb acid battery pack. The comparative analysis was also performed integrating the two storage systems in a hydrogen fuel cell power train for moped applications. The propulsion system comprised a fuel cell generator based on a 2.5 kW polymeric electrolyte membrane (PEM) stack, fuelled with compressed hydrogen, an electric drive of 1.8 kW as nominal power, of the same typology of that installed on commercial electric scooters (brushless electric machine and controlled bidirectional inverter). The power train was characterized making use of a test bench able to simulate the vehicle behaviour and road characteristics on driving cycles with different acceleration/deceleration rates and lengths. The power flows between fuel cell system, electric energy storage system and electric drive during the different cycles were analyzed, evidencing the effect of high battery currents on the vehicle driving range. The use of Li batteries in the fuel cell power train, adopting a range extender configuration, determined a hydrogen consumption lower than the correspondent Pb battery/fuel cell hybrid vehicle, with a major flexibility in the power management.     

An operational high temperature thermal energy storage system using magnesium iron hydride

Metal hydrides have been demonstrated as energy storage materials for thermal battery applications. This is due to the high energy density associated with the reversible thermochemical reaction between metals and hydrogen. Magnesium iron hydride (Mg₂FeH₆) is one such material that has been identified as a thermal energy storage material due to its reversible hydrogenation reaction at temperatures between 400 and 600 °C. This study demonstates an automated thermal battery prototype containing 900 g of Mg₂FeH₆ as the thermal energy storage material with pressurised water acting as the heat transfer fluid to charge and discharge the battery. The operating conditions of the system were optimised by assessing the ideal operating temperature, flow rate of the heat transfer fluid, and hydrogen pressures. Overall, excellent cyclic energy storage reversibility was demonstrated between 410 and 450 °C with a maximum energy capacity of 1650 kJ which is 87% of the theoretical value (1890 kJ).     

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.     

Lightweight reactor design by additive manufacturing for preheating applications using metal hydrides

Thermal energy storage systems based on metal hydrides can be a solution for preheating fuel cells (FCs). They can provide thermal energy at temperatures below −20 °C during startup, while heat at 50 °C during operation is sufficient for regeneration. The challenge of such a system in mobile applications is the final weight specific thermal power. In this study, a reactor design based on additive manufacturing techniques for ~300 g of metal hydride is presented. Here, a reactor (passive) to hydride (active) mass ratio of 0.97 is realized, still reaching high weight specific thermal power of up to 2.1 kW/kg_MH at −20 °C and 8 bar (LmNi_4.91Sn_0.15). Considering the example of preheating a FC from −20 °C in ~120 s, the performance of LaNi₅ and LmNi_4.91Sn_0.15 is studied. While LaNi₅ requires higher regeneration temperatures than LmNi_4.91Sn_0.15 (>40 °C compared to >20 °C), its performance is less sensitive to operative variations due to its nearly ideal thermodynamic characteristic.     

The potential for integration of hydrogen for complete energy self-sufficiency in residential buildings with photovoltaic and battery storage systems

This paper presents an analysis of energy production in a pilot building located in Slovenia, which is a typical residential house with an installed photovoltaic (PV) system and pilot battery storage system. Energy management system gathers data from smart meters every 15 min. As the pilot building location is in central Europe, complete energy self-sufficiency cannot be provided. The most problematic period of energy production with photovoltaic systems is winter. Solar radiation during the winter is much lower than in the summer and sometimes snow covers photovoltaic panels and disables energy production. Energy production and energy consumption are analyzed for one year. This study shows that complete self-sufficiency can be achieved by supplementing photovoltaic systems with hydrogen fuel cells. The amount of hydrogen, which would suffice for complete self-sufficiency for the whole period, is calculated according to the analyzed data. A synergy between photovoltaic system and hydrogen fuel cells is a step forward to complete self-sufficiency with renewable energy sources. The share of self-sufficiency of a hybrid PV fuel cell system would be 62.13%, meaning that there is no possibility for complete self-sufficiency from the pilot system. The shortage of hydrogen is 144.24 kg for one year and for achieving complete energy self-sufficiency, PV system should be bigger. A hybrid system with photovoltaic system, battery storage system and hydrogen fuel cells can be a solution for complete self-sufficiency. From an economic point of view, such systems are accessible for commercial use. The initial investment is relatively high, because of the high cost of the hydrogen storage tank.     

200 NL H2 hydrogen storage tank using MgH2–TiH2–C nanocomposite as H storage material

MgH₂-based hydrogen storage materials are promising candidates for solid-state hydrogen storage allowing efficient thermal management in energy systems integrating metal hydride hydrogen store with a solid oxide fuel cell (SOFC) providing dissipated heat at temperatures between 400 and 600 °C. Recently, we have shown that graphite-modified composite of TiH₂ and MgH₂ prepared by high-energy reactive ball milling in hydrogen (HRBM), demonstrates a high reversible gravimetric H storage capacity exceeding 5 wt % H, fast hydrogenation/dehydrogenation kinetics and excellent cycle stability. In present study, 0.9 MgH₂ + 0.1 TiH₂ +5 wt %C nanocomposite with a maximum hydrogen storage capacity of 6.3 wt% H was prepared by HRBM preceded by a short homogenizing pre-milling in inert gas. 300 g of the composite was loaded into a storage tank accommodating an air-heated stainless steel metal hydride (MH) container equipped with transversal internal (copper) and external (aluminium) fins. Tests of the tank were carried out in a temperature range from 150 °C (H₂ absorption) to 370 °C (H₂ desorption) and showed its ability to deliver up to 185 NL H₂ corresponding to a reversible H storage capacity of the MH material of appr. 5 wt% H. No significant deterioration of the reversible H storage capacity was observed during 20 heating/cooling H₂ discharge/charge cycles. It was found that H₂ desorption performance can be tailored by selecting appropriate thermal management conditions and an optimal operational regime has been proposed.     

Selection of metal hydrides for a thermal energy storage device to support low-temperature concentrating solar power plants

Metal hydrides have become more and more significant both as hydrogen storage devices and as basic elements in energy conversion systems. Besides the well-known rare earth hydrides, magnesium alloys are very promising in the field of thermal energy storage for concentrating solar power plants. There is interest in analysing the performances of such materials in this context; for this purpose, a numerical model to describe hydrogen absorption and desorption processes of a metal hydride has been connected to a model elaborated with the help of Cycle-Tempo software to simulate a CSP plant operation. The integration of this plant with four metal hydride systems, based on the combination of two low-temperature hydrides (LaNi₅, LaNi_4.8Al_0.2) and two high-temperature hydrides (Mg, Mg₂Ni) has been studied. The investigation has taken into account CSP overall performances, transfer surfaces and storage efficiencies, to determine the feasibility of designed plants. Results show that the selection of the optimal hydrides must take into account hydride operation temperatures, reaction enthalpies, storage capacities and kinetic compatibility. In the light of the calculated parameters, a solar ORC plant using R134a as the working fluid is a valuable choice if matched to a storage system composed of LaNi₅ and Mg₂Ni hydrides.