Prospects of fuel cell auxiliary power units in the civil markets

Auxiliary power units (APUs), i.e. devices designed to provide additional onboard power in vehicles, are believed to be an important entry point for fuel cell (FC) technology into commercial markets. Three technologies are under consideration for this market: solid oxide fuel cells (SOFCs), proton exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs). By using the concept of total addressable, potential and capturable markets, this paper discusses the opportunities and challenges of fuel cell auxiliary power units (FC APUs). A number of conclusions can be drawn. As FC APUs do not offer increased fuel efficiency when meeting electrical demand while the main engine is used for propulsion (as opposed to idling), applications on board transit vehicles such as buses seem limited. Potential markets begin to open up in vehicles that either have a very large electricity demand due to many high-energy onboard functions, such as luxury limousines, or that require electrical power whilst stationary. Examples in the latter category include law enforcement vehicles, recreational vehicles, and most importantly heavy duty trucks. Volume and start-up time seem to be the major technical challenges hindering the market penetration of FC APUs. However, whilst the functional benefits of FC APUs over existing technologies are limited, the former must also be able to compete on a cost basis. The intense activities of APU manufacturers suggest a confidence either in the potential for cost reductions or in the consumers’ willingness to pay. Similarly, the involvement of a number of big truck manufacturers casts doubt on the extent to which incumbents are taken by surprise by competence-destroying, disruptive and radical technologies like FC APUs.     

Dynamic evaluation of low-temperature metal-supported solid oxide fuel cell oriented to auxiliary power units

A metal-supported solid oxide fuel cell (SOFC) composed of a Ni–Ce_0.8Sm_0.2O_2−δ (Ni–SDC) cermet anode and an SDC electrolyte was fabricated by suspension plasma spraying on a Hastelloy X substrate. The cathode, an Sm_0.5Sr_0.5CoO₃ (SSCo)–SDC composite, was screen-printed and fired in situ. The dynamic behaviour of the cell was measured while subjected to complete fuel shutoff and rapid start-up cycles, as typically encountered in auxiliary power units (APU) applications. A promising performance – with a maximum power density (MPD) of 0.176 W cm⁻² at 600 °C – was achieved using humidified hydrogen as fuel and air as the oxidant. The cell also showed excellent resistance to oxidation at 600 °C during fuel shutoff, with only a slight drop in performance after reintroduction of the fuel. The Cr and Mn species in the Hastelloy X alloy appeared to be preferentially oxidized while the oxidation of nickel in the metallic substrate was temporarily alleviated. In rapid start-up cycles with a heating rate of 60 °C min⁻¹, noticeable performance deterioration took place in the first two thermal cycles, and then continued at a much slower rate in subsequent cycles. A postmortem analysis of the cell suggested that the degradation was mainly due to the mismatch of the thermal expansion coefficient across the cathode/electrolyte interface.     

A techno-economic comparison of fuel processors utilizing diesel for solid oxide fuel cell auxiliary power units

Ultra-low sulphur diesel (ULSD) is the preferred fuel for mobile auxiliary power units (APU). The commercial available technologies in the kW-range are combustion engine based gensets, achieving system efficiencies about 20%. Solid oxide fuel cells (SOFC) promise improvements with respect to efficiency and emission, particularly for the low power range. Fuel processing methods i.e., catalytic partial oxidation, autothermal reforming and steam reforming have been demonstrated to operate on diesel with various sulphur contents. The choice of fuel processing method strongly affects the SOFC's system efficiency and power density.This paper investigates the impact of fuel processing methods on the economical potential in SOFC APUs, taking variable and capital cost into account. Autonomous concepts without any external water supply are compared with anode recycle configurations. The cost of electricity is very sensitive on the choice of the O/C ratio and the temperature conditions of the fuel processor. A sensitivity analysis is applied to identify the most cost effective concept for different economic boundary conditions.The favourite concepts are discussed with respect to technical challenges and requirements operating in the presence of sulphur.     

Analysis and optimization of solid oxide fuel cell-based auxiliary power units using a generic zero-dimensional fuel cell model

Fuel-cell-based auxiliary power units can help to reduce fuel consumption and emissions in transportation. For this application, the combination of solid oxide fuel cells (SOFCs) with upstream fuel processing by autothermal reforming (ATR) is seen as a highly favorable configuration. Notwithstanding the necessity to improve each single component, an optimized architecture of the fuel cell system as a whole must be achieved. To enable model-based analyses, a system-level approach is proposed in which the fuel cell system is modeled as a multi-stage thermo-chemical process using the “flowsheeting” environment PRO/II™. Therein, the SOFC stack and the ATR are characterized entirely by corresponding thermodynamic processes together with global performance parameters. The developed model is then used to achieve an optimal system layout by comparing different system architectures. A system with anode and cathode off-gas recycling was identified to have the highest electric system efficiency. Taking this system as a basis, the potential for further performance enhancement was evaluated by varying four parameters characterizing different system components. Using methods from the design and analysis of experiments, the effects of these parameters and of their interactions were quantified, leading to an overall optimized system with encouraging performance data.     

Analysis of potential fuel consumption and emissions reductions from fuel cell auxiliary power units (APUs) in long-haul trucks

The idling of heavy-duty trucks results in additional emissions, fuel consumption, and cost. Small fuel cell auxiliary power units (APUs) (now in development) are promising alternatives to idling the main engine. A solid oxide fuel cell (SOFC) APU is particularly attractive, because in conjunction with a reformer, it could operate on widely available diesel fuel. Because fuel cell APUs may not only reduce environmental impacts, but also reduce operating costs, this application has been cited as an attractive early market niche for fuel cells. Our objective is to determine whether SOFC APUs are likely to soon be economically feasible for those trucks that idle most and what energy and environmental benefits are probable. We estimate the APU market size as a function of APU costs by applying Monte Carlo sampling and net present value (NPV) economic analysis to our ADVISOR-based vehicle fuel consumption model. Emissions and fuel economy benefits estimates are then presented as a function of varying market penetration levels, assuming installation on only new vehicles and removal at the end of the 4-year SOFC lifecycle. With modest economic incentives from government and continuing fuel cell technology improvements, we find that SOFC APUs might be economically feasible for up to 15% of the long-haul truck population (60,000 trucks) in the United States in the 2015 time frame, resulting in a 30% reduction of heavy-duty truck fuel use during overnight idling and a 40% reduction in oxides of nitrogen (NO_x) produced during idling.     

Environmental and economic analyses of fuel cell and battery-based hybrid systems utilized as auxiliary power units on a chemical tanker vessel

This study aims to investigate the environmental and economic impacts of implementing fuel cell and battery-based hybrid configurations. Phosphoric acid and molten carbonate fuel cell systems in the place of diesel generators of a large tanker to supply the vessel's total electricity demand. Environmental and economic analyses of the utilization of the specified fuel cell systems with LiNiCoALO₂ and LiNiMnCoO₂ chemical types of battery cells on a large marine vessel are provided in this paper. In addition, the assessment of the most suitable battery cell and charge-discharge hours for fuel cell systems is carried out with a grid-search algorithm. Six different fuel cell and battery configurations are investigated to obtain the optimum system layout. The results show that the CO₂ emissions could be reduced by up to 49.75% and the lowest electricity production cost is found as 0.181 $/kWh for the current fuel prices with the utilization of molten carbonate fuel cells and LiNiMnCoO₂ battery cells.     

The modeling of a standalone solid-oxide fuel cell auxiliary power unit

In this research, a Simulink model of a standalone vehicular solid-oxide fuel cell (SOFC) auxiliary power unit (APU) is developed. The SOFC APU model consists of three major components: a controller model; a power electronics system model; and an SOFC plant model, including an SOFC stack module, two heat exchanger modules, and a combustor module. This paper discusses the development of the nonlinear dynamic models for the SOFC stacks, the heat exchangers and the combustors. When coupling with a controller model and a power electronic circuit model, the developed SOFC plant model is able to model the thermal dynamics and the electrochemical dynamics inside the SOFC APU components, as well as the transient responses to the electric loading changes. It has been shown that having such a model for the SOFC APU will help design engineers to adjust design parameters to optimize the performance. The modeling results of the SOFC APU heat-up stage and the output voltage response to a sudden load change are presented in this paper. The fuel flow regulation based on fuel utilization is also briefly discussed.     

秸秆成型燃料生产设备系统及经济性分析

文章对万吨级秸秆成型燃料生产技术进行了研究,开发出的秸秆成型燃料生产技术系统由两部分组成:秸秆预处理技术与成型燃料生产技术。该技术分别采用单独的PLC控制,再由工控机统一控制,实现了生产过程的优化,提高了产量,改善了生产条件,降低了生产成本,通过进一步经济性分析,发现产品价格下降10%,原料与工资成本上升20%,其项目具有较强的抗风险能力。     

Techno-economic modelling of a solid oxide fuel cell stack for micro combined heat and power

Solid oxide fuel cell combined heat and power (CHP) is a promising technology to serve electricity and heat demands. In order to analyse the potential of the technology, a detailed techno-economic energy-cost minimisation model of a micro-CHP system is developed drawing on steady-state and dynamic SOFC stack models and power converter design. This model is applied it to identify minimum costs and optimum stack capacities under various current density change constraints. Firstly, a characterisation of the system electrical efficiency is developed through the combination of stack efficiency profiles and power converter efficiency profiles. Optimisation model constraints are then developed, including a limitation in the change of current density (A cm⁻²) per minute in the stack. The optimisation model is then presented and further expanded to account for the inability of a stack to respond instantaneously to load changes, resulting in a penalty function being applied to the objective function proportional to the size of load changes being serviced by the stack. Finally, the optimisation model is applied to examine the relative importance, in terms of minimum cost and optimum stack maximum electrical power output capacity, of the limitation on rate of current density change for a UK residential micro-CHP application. It is found that constraints on the rate of change in current density are not an important design parameter from an economic perspective.     

Techno-economic analysis of autotrophic microalgae for fuel production

It is well-established that microalgal-derived biofuels have the potential to make a significant contribution to the US fuel market, due to several unique characteristics inherent to algae. Namely, autotrophic microalgae are capable of achieving very high efficiencies in converting solar energy into biomass and oil relative to terrestrial oilseed crops, while at the same time exhibiting great flexibility in the quality of land and water required for algal cultivation. These characteristics allow for the possibility to produce appreciable amounts of algal biofuels relative to today’s petroleum fuel market, while greatly mitigating “food-versus-fuel” concerns. However, there is a wide lack of public agreement on the near-term economic viability of algal biofuels, due to uncertainties and speculation on process scale-up associated with the nascent stage of the algal biofuel industry.     

Conceptual design and selection of a biodiesel fuel processor for a vehicle fuel cell auxiliary power unit

Within the European project BIOFEAT (biodiesel fuel processor for a fuel cell auxiliary power unit for a vehicle), a complete modular 10 kW_e biodiesel fuel processor capable of feeding a PEMFC will be developed, built and tested to generate electricity for a vehicle auxiliary power unit (APU). Tail pipe emissions reduction, increased use of renewable fuels, increase of hydrogen-fuel economy and efficient supply of present and future APU for road vehicles are the main project goals. Biodiesel is the chosen feedstock because it is a completely natural and thus renewable fuel.Three fuel processing options were taken into account at a conceptual design level and compared for hydrogen production: (i) autothermal reformer (ATR) with high and low temperature shift (HTS/LTS) reactors; (ii) autothermal reformer (ATR) with a single medium temperature shift (MTS) reactor; (iii) thermal cracker (TC) with high and low temperature shift (HTS/LTS) reactors. Based on a number of simulations (with the AspenPlus^® software), the best operating conditions were determined (steam-to-carbon and O₂/C ratios, operating temperatures and pressures) for each process alternative. The selection of the preferential fuel processing option was consequently carried out, based on a number of criteria (efficiency, complexity, compactness, safety, controllability, emissions, etc.); the ATR with both HTS and LTS reactors shows the most promising results, with a net electrical efficiency of 29% (LHV).     

Technological aspects of an auxiliary power unit with internal reforming methanol fuel cell

Increasing source runtime, speeding up the transient response, while minimizing weight, volume and cost of the power supply system are key requirements for portable, mobile and off-grid applications of fuel cells. In this respect, Internal Reforming Methanol Fuel Cell (IRMFC) modules were designed, constructed and tested based on an innovative double reformer (DRef) configuration and metallic bipolar plates (BPPs) with unique arrangement. Recently developed cross-linked Advent TPS^® high-temperature membrane electrode assemblies (MEAs) were employed for fuel cell operation at 210 °C. Taking into account the requirement for a light-weight and low-volume stack, Cu-based methanol reforming catalyst were supported on carbon papers, resulting in ultra-thin reformers. The proposed configuration offered a significant decrease in the weight and volume of the whole power system, as compared with previous voluminous foam-based modules. Moreover, specifically designed bipolar plates were made of coated Al-metal alloys, which proved to be stable in the strong acidic environment at elevated temperatures. The prototype 32MEAs-32DRef IRMFC stack of 100 W including home-made insulation casing, was integrated for operation at 200–210 °C and at 0.2 A cm⁻², demonstrating the functionality of the unit. A power output of 100.7 W (3.14 W per cell; 0.114 W cm⁻²) was achieved in the last run following several on-off cycles. The volumetric power density of the IRMFC stack including insulation and casing is around 30 W per lt, being among the highest reported either in the case of portable or stationary applications. Overall, the observed stability of reformers and bipolar plates was satisfactory within the timeframe of the work undertaken. Specific targets for improvement of the efficiency were identified, and the main drawback had to do with low thermal and mechanical stability of the membranes under start-up/shut-down transient operation.     

Modeling and control of photovoltaic and fuel cell based alternative power systems

Photovoltaic (PV) systems and fuel cells (FCs) represent interesting solutions as being alternative power sources with high performance and low emission. This work presents a modeling and control study of two power generators; photovoltaic array and fuel cell based systems. An MPPT approach to optimize the PV system performances is proposed. The PV system consists of a PV array connected to a DC-DC buck converter and a resistive load. A maximum power point tracker controller is required to extract the maximum generated power. Based on Incremental Conductance (INC) principle, the idea of the proposed control is to use a Fuzzy Logic Controller (FLC) that allows the choice of the duty cycle step size which is used to be fixed in conventional MPPT algorithms. The variable step is computed according to the value of the PV power-voltage characteristic slope. The second working system comprises a controlled DC-DC converter fed by a proton exchange membrane fuel cell (PEMFC) and supplies a DC bus. The mathematical model of the PEMFC system is given. The converter duty cycle is adjusted in order to regulate the DC bus voltage. Obtained simulation results validate the control algorithms for both of studied power systems.     

Capacity configuration of battery energy storage as an alternative to thermal power units for frequency regulation

传统调频机组因其固有特性而不易实现实际出力与理论计算值相吻合,并且工作在经济运行区内,难以应对电力系统快速发展,新能源发电并入等引起的频率稳定问题.电池储能系统(battery energy storage system,BESS)具有快速,精确的功率响应能力等优势,从而成为新的辅助调频手段的关注热点.在探讨BESS参与电网一,二次调频的实现方法基础上,对与火电机组具备同等调频能力的BESS功率与容量进行配置,并提出了储能容量控制策略建议.示例计算和对比分析,验证了该配置方案的可行性和储能系统参与电网调频的可靠性,为新调频手段的选取与分析提供了借鉴.     

Biodiesel as alternative fuel: Experimental analysis and energetic evaluations

This paper presents the first results of an investigation carried out by the authors on the potentialities of biodiesel as an alternative fuel based on strategic considerations and field experiences in boilers and diesel engines.The operation of a biodiesel fuelled boiler has been checked for some months. The engines have been bench-tested and then installed on urban buses for normal operation. Distances, fuel consumption and emissions (CO₂, CO, HC and NO_X) have been monitored; in addition devices wear and tear, oil and air filters dirtiness and lubricant degradation have been checked.Further investigations have also been devoted to assess some environmental aspects of bio-diesel. In particular the benefit of biodiesel to the total net emission of CO₂ during the whole life cycle has been studied and the net energy requirement has been evaluated.Finally, the global environmental support to the production of biodiesel has been studied according to the emergy analysis.     

Analysis of the market for diesel PEM fuel cell auxiliary power units onboard long-haul trucks and of its implications for the large-scale adoption of PEM FCs

Proton exchange membrane fuel cells (PEM FCs) offer a promising alternative to internal combustion engines in road transport. During the last decade PEM FC research, development and demonstration (RD&D) activities have been steadily increasing worldwide, and targets have been set to begin their commercialisation in road transport by 2015–2020. However, there still is considerable uncertainty on whether these targets will actually be met. The picture is complex and market and technology issues are closely interlinked; investment in RD&D projects is essential but not sufficient; the development of suitable early markets is also necessary and policy is set to play an important role. Auxiliary power units (APUs) are generally regarded as one important early market for FCs in transport. This paper analyses the possible future market for diesel PEM FC APUs onboard long-haul trucks and its implications for the development of PEM FCs in general. The analysis, part of the project HyTRAN (EC Contract no. 502577), is aided by the use of a dynamic simulation model of technology and markets developed by the author. Results suggest that an interesting window of opportunity for diesel PEM FC APUs exists but this is subject to additional research particularly targeted at the rapid development of fuel processors.     

Techno-economic analysis of an autonomous power system integrating hydrogen technology as energy storage medium

Two different options for the autonomous power supply of rural or/and remote buildings are examined in this study. The first one involves a PV – diesel based power system, while the second one integrates RES and hydrogen technologies for the development of a self – sustained power system. The main objective is the replacement of the diesel generator and a comparison between these two options for autonomous power supply. Model simulations of the two power systems before and after the replacement, an optimization of the component sizes and a techno – economic analysis have been performed for the purpose of this study. A sensitivity analysis taking into account future cost scenarios for hydrogen technologies is also presented. The results clearly show that the Cost of Energy Produced (COE) from the PV – hydrogen technologies power system is extremely higher than the PV – diesel power system. However, the adopted PV – hydrogen technologies power system reduces to zero the Green – House Gas (GHG) emissions. Moreover, the sensitivity analysis indicates that COE for the latter system can be further reduced by approximately 50% compared to its initial value. This could be achieved by reducing critical COE’s parameters, such as PEM electrolyser and fuel cell capital costs. Hence, a possible reduction on the capital costs of hydrogen energy equipment in combination with emissions reduction mentioned above could make hydrogen – based power systems more competitive.     

Techno-economic analysis of compressed air energy storage power plant

压缩空气储能系统被认为是最具发展前景的大规模电力储能技术之一,具有广阔发展前景。本文建立了压缩空气储能系统的技术经济性计算模型,并针对蓄热式压缩空气储能系统应用于工业用户的情景,在有无补贴的两种计算条件下,进行了技术经济性分析。研究结果表明,在无补贴条件下,系统内部收益率为16.3%,投资回收期为9.2年;计算补贴时,系统内部收益率为23.8%,投资回收期为6.2年。同时本文还对该系统进行了盈亏平衡、敏感性等不确定性分析,找出影响系统经济性的敏感因素;并得出政策扶持对提高压缩空气储能电站的财务收益水平和抗风险能力具有重要的作用。本文的研究可以为压缩空气储能系统的研究和工程应用提供理论参考和工程指导。     

Coal gas as a feed fuel for phosphoric acid fuel cell power plants

Westinghouse Electric Corporation has assessed the effects of a number of coal gasification systems and their gas compositions on a 7.5 MW_(c) dc Phosphoric Acid Fuel Cell (PAFC) power plant. Both low and medium BTU synthesis gases were considered from various promising gasification processes. Degree of development or commercialization, technical complexity, availability and coal restrictions were taken into account. System studies performed on the 7.5 MW_(c) dc PAFC power plant for nonintegrated and integrated fuel conditioning systems are discussed for the various gasification processes. In all cases coal gas was assumed to be purchased “over-the-fence”. Representative characteristics for the derived coal gases and PAFC system performance data are presented. The direct capital costs of the PAFC power plant are evaluated for each system.     

大型火电厂厂用电系统若干问题的探讨

结合某些大型火力发电厂的厂用电系统中出现的问题,对厂用电系统中一些问题进行了分析,探讨厂用电系统中辅机工作电源分布对机组运行的影响,提出了厂用电系统保护配置、设备选型、辅机控制电源等方面应注意的问题。