A mobile off-grid platform powered with photovoltaic/wind/battery/fuel cell hybrid power systems

Cross utilization of photovoltaic/wind/battery/fuel cell hybrid-power-system has been demonstrated to power an off-grid mobile living space. This concept shows that different renewable energy sources can be used simultaneously to power off-grid applications together with battery and hydrogen energy storage options. Photovoltaic (PV) and wind energy are used as primary sources and a fuel cell is used as backup power. A total of 2.7 kW energy production (wind and PV panels) along with 1.2 kW fuel cell power is supported with 17.2 kWh battery and 15 kWh hydrogen storage capacities. Supply/demand scenarios are prepared based on wind and solar data for Istanbul. Primary energy sources supply load and charge batteries. When there is energy excess, it is used to electrolyse water for hydrogen production, which in turn can either be used to power fuel cells or burnt as fuel by the hydrogen cooker. Power-to-gas and gas-to-power schemes are effectively utilized and shown in this study. Power demand by the installed equipment is supplied by batteries if no renewable energy is available. If there is high demand beyond battery capacity, fuel cell supplies energy in parallel. Automatic and manual controllable hydraulic systems are designed and installed to increase the photovoltaic efficiency by vertical axis control, to lift up & down wind turbine and to prevent vibrations on vehicle. Automatic control, data acquisition, monitoring, telemetry hardware and software are established. In order to increase public awareness of renewable energy sources and its applications, system has been demonstrated in various exhibitions, conferences, energy forums, universities, governmental and nongovernmental organizations in Turkey, Austria, United Arab Emirates and Romania.     

Design of an energy management technique for high endurance unmanned aerial vehicles powered by fuel and solar cell systems

A hybrid electric propulsion system with a power switching technique is tested in flights of long endurance unmanned aerial vehicle, interchanging power supply between fuel and solar cell systems. A fuel cell system consists of a sodium borohydride-based hydrogen generator, a 300 W scale proton-exchange membrane fuel-cell stack that is connected with a battery and a customized controller. The solar cell system consists of a maximum power point track device, a battery and 80 W solar arrays on each wing. These two power sources are controlled by a power switching technique using solid-state relays, which selectively permit either one of the two power sources, or both, to meet the load variation during flight. Using this method, both power sources are independently operated to deliver necessary power to satisfy the load demand, which means that it can extend flight endurance by alternating between solar and fuel cells with high-system reliability. The flight test is conducted over a period of 1.5 h to evaluate the designed hybrid power system by switching from fuel cell power to solar cell power, and vice versa, thereby proving system reliability as well as extending the operational time for flight.     

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.     

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.     

Operation planning of hydrogen storage connected to wind power operating in a power market

In this paper, a methodology for the operation of a hybrid plant with wind power and hydrogen storage is presented. Hydrogen produced from electrolysis is used for power generation in a stationary fuel cell and as fuel for vehicles. Forecasts of wind power are used for maximizing the expected profit from power exchange in a day-ahead market, also taking into account a penalty cost for unprovided hydrogen demand. During online operation, a receding horizon strategy is applied to determine the setpoints for the electrolyzer power and the fuel cell power. Results from three case studies of a combined wind-hydrogen plant are presented. In the first two cases, the plant is assumed to be operating in a power market dominated by thermal and hydropower, respectively. The third case demonstrates that the operating principles are also useful for isolated wind-hydrogen systems with backup generation.     

Battery or fuel cell support for an autonomous photovoltaic power system

This paper presents an overview of comparison between battery backup and fuel cell backup to supplement the fluctuating photovoltaic (PV) power under inclement weather conditions. In order to compare them effectively, it is done in the categories of common and different attributes. The common attributes such as fast load-response, modular production, high reliability and environmental acceptability are the reasons why those two generating sources are the most likely technologies for PV power backup. According to the detailed comparison in the aspects of efficiency, capacity (or efficiency) variation, operational flexibility and environmental externality, the fuel cell backup has more benefits over the battery backup for the purpose of supporting a weather-dependent PV power source.     

Fuel cells for airborne usage: Energy storage comparison

The global drone market is growing every year. The number of applications is increasing: from search and rescue, security, surveillance to science and research and unmanned cargo systems.A limiting factor for drone exploitation is that for the energy storage, normally, a battery is used and this solution affects flight time. A possible solution could be the utilization of fuel cells. This paper focuses on the utilization of fuel cells power as an alternative solution for drone propulsion.The aim of the study is to determine when it is more appropriate, in terms of mass, to use a battery or a hybrid (fuel cell + battery) system to power drones. To compare the different systems, a numerical simulation model has been developed in order to choose the best power system once the drone operation profile has been defined.The model allows comparing different type of fuels and battery systems. The data to tune the model have been taken from commercial products, today already available. The simulation model considers a light-weight open-air cathode PEM (Polymer Exchange Membrane) fuel cell. The stack power output is chosen according to the mission profile and rages from 200 W to 1000 W.The presented results show that, for the considered drone segment, multirotor drones with weight of 7 kg at take-off, lithium batteries are still the best choice for time flight shorter than about 1 h. A hybrid system, appears to be interesting for longer flights. For example, it has been calculated that a hybrid quadcopter drone with a mass of 7 kg, considering a flight profile that requires 1089 Wh can be powered with a 4.4 kg hybrid system composed by a 500 W and 1.4 kg PEM fuel cell system, 1.9 kg hydrogen composite pressure vessel and a 0.8 kg lithium battery. The same amount of energy can be stored in a lithium battery with a weight of about 6.6 kg. These means a weight saving of more than 30%. The hybrid system, in term of weight, is even more convenient for flight profiles that require more energy.     

Development and demonstration of a deployable apparatus for generating hydrogen from the hydrolysis of aluminum via sodium hydroxide

Emergency and backup power is often enabled through the use of petrochemical based fuels and combustion-based generator systems, and while reliable, these backup power systems fail when petrochemical supplies are disrupted due to refinery, oil outages, or transportation delays. Fuel cells in some cases can serve as a backup to these traditional generators, but they also are fuel-limited to supplies of available energy sources. Recent work conducted in our laboratories focused on the development of a “backup” emergency hydrogen generation system that could be employed when existing energy stockpiles have failed or depleted. Specifically, aluminum metal can be used to generate hydrogen for fuel cells via hydrolysis with sodium hydroxide. In this paper, we summarize the engineering work to produce a deployable aluminum to hydrogen generator which is capable of producing 3.75 kg of hydrogen per day from scrap aluminum feedstocks. The generator was built upon an aircraft deployable pallet, allowing for hydrogen to be generated remotely in cases of power and fuel outages.     

Fuzzy control based engine sizing optimization for a fuel cell/battery hybrid mini-bus

The fuel cell/battery hybrid vehicle has been focused for the alternative engine of the existing internal-combustion engine due to the following advantages of the fuel cell and the battery. Firstly, the fuel cell is highly efficient and eco-friendly. Secondly, the battery has the fast response for the changeable power demand. However, the competitive efficiency of the hybrid fuel cell vehicle is necessary to successfully alternate the conventional vehicles with the fuel cell hybrid vehicle. The most relevant factor which affects the overall efficiency of the hybrid fuel cell vehicle is the relative engine sizing between the fuel cell and the battery. Therefore the design method to optimize the engine sizing of the fuel cell hybrid vehicle has been proposed. The target system is the fuel cell/battery hybrid mini-bus and its power distribution is controlled based on the fuzzy logic. The optimal engine sizes are determined based on the simulator developed in this paper. The simulator includes the several models for the fuel cell, the battery, and the major balance of plants. After the engine sizing, the system efficiency and the stability of the power distribution are verified based on the well-known driving schedule. Consequently, the optimally designed mini-bus shows good performance.     

Distributed control of a user-on-demand renewable-energy power-source system using battery and hydrogen hybrid energy-storage devices

A user-on-demand power source based on renewable energy requires storage devices to balance power sources and power demands because of the fluctuation of power sources like solar cells or wind power generators. The role of the control system is defined as two different tasks: allowing a power-flow imbalance between demand and power sources; and balancing the power flow inside the system. Since this control is complicated, many control methods using precise calculation of the power balance have been proposed. An analogue-like distributed control method - named “modified DC-bus signalling” - for controlling a renewable-energy power source without the need for a central processing unit is proposed. The modified DC bus signalling method discussed in this paper is composed of a DC-bus line connected with a battery, water-splitting electrochemical cell, and a fuel cell for hydrogen-energy storage via converters. The proposed control method was demonstrated to be able to control step-like and random changes in input and output power. The battery compensated high-frequency fluctuations in power demand, and the electrochemical cell and fuel cell handled the remaining low-frequency ones, which were matched to their response speeds.     

A hierarchical energy management strategy for fuel cell/battery/supercapacitor hybrid electric vehicles

In this paper, a hierarchical energy management strategy (EMS) based on low-pass filter and equivalent consumption minimization strategy (ECMS) is proposed in order to lift energy sources lifespan, power performance and fuel economy for hybrid electrical vehicles equipped with fuel cell, battery and supercapacitor. As for the considered powertrain configuration, fuel cell serves as main energy source, and battery and supercapacitor are regarded as energy support and storage system. Supercapacitor with high power density and dynamic response acts during great power fluctuations, which relives stress on fuel cell and battery. Meanwhile, battery is used to lift the economy of hydrogen fuel. In higher layer strategy of the proposed EMS, supercapacitor is employed to supply peak power and recycle braking energy by using the adaptive low-pass filter method. Meantime, an ECMS is designed to allocate power of fuel cell and battery such that fuel cell can work in a high efficient range to minimize hydrogen consumption in lower layer. The proposed EMS for hybrid electrical vehicles is modeled and verified by advisor-simulink and experiment bench. Simulation and experiment results are given to confirm effectiveness of the proposed EMS of this paper.     

Improved performance and energy management strategy for proton exchange membrane fuel cell/backup battery in power electronic systems

The objective of this paper is to propose an approach to analyze the reliability of proton exchange membrane fuel cell and backup battery in the power electronic systems by improving the strategy of energy management. This approach is based on the research of critical causes generating the degradation of power sources in the power electronic application and their undesirable effect. The analysis of potential failure modes that affect the fuel cell and the auxiliary source is developed by using analysis tools such as the Failure Mode and Effects Analysis (FMEA). The undesirable factors have to be taken into account in designing the topology of power converter in order to improve the performance of a fuel cell power system. In this context the authors propose to integrate a multiphase converter to minimize the current ripple and ameliorate the dynamic response of exchange membrane fuel cell. The improvement of battery lifetime is also ensured by the incorporation of an appropriate charge cycle that promises the full state of charge and avoids the overcharge.     

Experimental investigation on the online fuzzy energy management of hybrid fuel cell/battery power system for UAVs

The hybrid powerplant combining a fuel cell and a battery has become one of the most promising alternative power systems for electric unmanned aerial vehicles (UAVs). To enhance the fuel efficiency and battery service life, highly effective and robust online energy management strategies are needed in real applications.In this work, an energy management system is designed to control the hybrid fuel cell and battery power system for electric UAVs. To reduce the weight, only one programmable direct-current to direct-current (dcdc) converter is used as the critical power split component to implement the power management strategy. The output voltage and current of the dcdc is controlled by an independent energy management controller. An executable process of online fuzzy energy management strategy is proposed and established. According to the demand power and battery state of charge, the online fuzzy energy management strategy produces the current command for the dcdc to directly control the output current of the fuel cell and to indirectly control the charge/discharge current of the battery based on the power balance principle.Another two online strategies, the passive control strategy and the state machine strategy, are also employed to compare with the proposed online fuzzy strategy in terms of the battery management and fuel efficiency. To evaluate and compare the feasibility of the online energy management strategies in application, experiments with three types of missions are carried out using the hybrid power system test-bench, which consists of a commercial fuel cell EOS600, a Lipo battery, a programmable dcdc converter, an energy management controller, and an electric load. The experimental investigation shows that the proposed online fuzzy strategy prefers to use the most power from the battery and consumes the least amount of hydrogen fuel compared with the other two online energy management strategies.     

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.     

Fully-integrated micro PEM fuel cell system with NaBH4 hydrogen generator

A fully-integrated micro PEM fuel cell system with a NaBH₄ hydrogen generator was developed. The micro fuel cell system contained a micro PEM fuel cell and a NaBH₄ hydrogen generator. The hydrogen generator comprised a NaBH₄ reacting chamber and a hydrogen separating chamber. Photosensitive glass wafers were used to fabricate a lightweight and corrosion-resistant micro fuel cell and hydrogen generator. All of the BOP such as a NaBH₄ cartridge, a micropump, and an auxiliary battery were fully integrated. In order to generate stable power output, a hybrid power management operating with a micro fuel cell and battery was designed. The integrated performance of the micro PEM fuel cell with NaBH₄ hydrogen generator was evaluated under various operating conditions. The hybrid power output was stably provided by the micro PEM fuel cell and auxiliary battery. The maximum power output and specific energy density of the micro PEM fuel cell system were 250 mW and 111.2 W h/kg, respectively.     

A metal hydride system for a forklift: Feasibility study on on-board chemical storage of hydrogen using numerical simulation

This paper describes a technical feasibility study of on-board metal hydride storage systems. The main advantages of these systems would be that of being able to replace counterweights with the weight of the storage system and using the heat emissions of fuel cells for energy, making forklifts a perfect use case. The main challenge is designing a system that supplies the required energy for a sufficiently long period. A first draft was set up and analyzed to provide a forklift based on a fuel cell with hydrogen from HydralloyC5 or FeTiMn. The primary design parameter was the required amount of stored hydrogen, which should provide energy equal to the energy capacity of a battery in an electric vehicle. To account for highly dynamic system requirements, the reactor design was optimized such that the storage was charged in a short time. Additionally, we investigated a system in which a fixed amount of hydrogen energy was required. For this purpose, we used a validated simulation model for the design concepts of metal hydride storage systems. The model includes all relevant terms and parameters to describe processes inside the system's particular reactions and the thermal conduction due to heat exchangers. We introduce an embedded fuel cell model to calculate the demand for hydrogen for a given power level. The resulting calculations provide the required time for charging or a full charge depending on the tank's diameter and, therefore, the necessary number of tanks. We conclude that the desired hydrogen supply times are given for some of the use cases. Accordingly, the simulated results suggest that using a metal hydride system could be highly practical in forklifts.     

Pre-feasibility study of stand-alone hybrid energy systems for applications in Newfoundland

A potential solution for stand-alone power generation is to use a hybrid energy system in parallel with some hydrogen energy storage. In this paper, a pre-feasibility study of using hybrid energy systems with hydrogen as an energy carrier for applications in Newfoundland, Canada is explained. Various renewable and non-renewable energy sources, energy storage methods and their applicability in terms of cost and performance are discussed. HOMER is used as a sizing and optimization tool. Sensitivity analysis with wind speed data, solar radiation level, diesel price and fuel cell cost was done. A remote house having an energy consumption of 25 kW h/d with a 4.73 kW peak power demand was considered as the stand-alone load. It was found that, a wind–diesel–battery hybrid system is the most suitable solution at present. However, with a reduction of fuel cell cost to 15% of its current value, a wind–fuel cell system would become a superior choice. Validity of such projection and economics against conventional power sources were identified. Sizing, performance and various cost indices were also analyzed in this paper.     

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.     

Modeling and Analysis of a Hydrogen Reformer for Fuel Cell Applications

Fuel cells that utilize hydrogen and oxygen to produce energy are promising power sources. However, there are operational difficulties in storing hydrogen. One way to alleviate this problem is to generate hydrogen in situ from a liquid fuel via steam reforming. In this paper, an ethanol reformer was modeled as a tubular non-isothermal, non-isobaric packed-bed reactor with an annular heat transfer jacket, operating at unsteady state. A suitable heat transfer jacket was designed that provides heat to the reformer by combustion of ethanol. The partial differential equations of the reformer model were solved numerically and model predictions of hydrogen generation were shown to be in good agreement with experimental data available in the literature for a laboratory-scale reformer. A commercial-scale reformer was designed using this high-fidelity model that can produce sufficient hydrogen to generate up to 5 kW of power when used in conjunction with a Ballard Mark V fuel-cell stack. Experimental data from the dynamic power consumption in a 3-bedroom house were used to validate the size of the reformer as well as a back-up battery that supplies power when the reformer is unable to meet the power demand.     

Fuel economy and life-cycle cost analysis of a fuel cell hybrid vehicle

The most promising vehicle engine that can overcome the problem of present internal combustion is the hydrogen fuel cell. Fuel cells are devices that change chemical energy directly into electrical energy without combustion. Pure fuel cell vehicles and fuel cell hybrid vehicles (i.e. a combination of fuel cell and battery) as energy sources are studied. Considerations of efficiency, fuel economy, and the characteristics of power output in hybridization of fuel cell vehicle are necessary. In the case of Federal Urban Driving Schedule (FUDS) cycle simulation, hybridization is more efficient than a pure fuel cell vehicle. The reason is that it is possible to capture regenerative braking energy and to operate the fuel cell system within a more efficient range by using battery.Life-cycle cost is largely affected by the fuel cell size, fuel cell cost, and hydrogen cost. When the cost of fuel cell is high, hybridization is profitable, but when the cost of fuel cell is less than 400 US$/kW, a pure fuel cell vehicle is more profitable.