Evaluation of system configurations for solid oxide fuel cell-based micro-combined heat and power generators in residential applications

The evaluation of solid oxide fuel cell (SOFC) combined heat and power (CHP) system configurations for application in residential dwellings is explored through modeling and simulation of cell-stacks including the balance-of-plant equipment. Five different SOFC system designs are evaluated in terms of their energetic performance and suitability for meeting residential thermal-to-electric ratios. Effective system concepts and key performance parameters are identified. The SOFC stack performance is based on anode-supported planar geometry. A cell model is scaled-up to predict voltage–current performance characteristics when served with either hydrogen or methane fuel gas sources. System comparisons for both fuel types are made in terms of first and second law efficiencies. The results indicate that maximum efficiency is achieved when cathode and anode gas recirculation is used along with internal reforming of methane. System electric efficiencies of 40% HHV (45% LHV) and combined heat and power efficiencies of 79% (88% LHV) are described. The amount of heat loss from small-scale SOFC systems is included in the analyses and can have an adverse impact on CHP efficiency. Performance comparisons of hydrogen-fueled versus methane-fueled SOFC systems are also given. The comparisons indicate that hydrogen-based SOFC systems do not offer efficiency performance advantages over methane-fueled SOFC systems. Sensitivity of this result to fuel cell operating parameter selection demonstrates that the magnitude of the efficiency advantage of methane-fueled SOFC systems over hydrogen-fueled ones can be as high as 6%.     

Economic and environmental assessment of phosphoric acid fuel cell-based combined heat and power system for an apartment complex

Economic and environmental potential of medium-scale combined heat and power (CHP) systems in the residential sector was assessed by introducing a 400 kW_el-scale phosphoric acid fuel cell (PAFC)-based CHP system into an apartment building in New York City. Simulation-based analyses were carried out under two different CHP operation strategies; electrical-load-following (ELF) and thermal-load-following (TLF). Technical and economic analyses indicated that ELF would be the appropriate operation mode for this CHP application. Economic analysis indicated that the CHP/ELF system operation could economically benefit users within 10 years under the present grid prices in New York City. However, because the CO₂ emission factor of the NY grid is very low (300 g/kWh), the CHP/ELF system operation would increase CO₂ emission. Achieving carbon neutrality in this application thus requires improvement in the utilization ratio of recovered heat.     

Modelling of waste heat recovery for combined heat and power applications

The current environmental context dictates to reduce the pollutant emissions by improving thermal efficiency of the energy production units. The authors present some studies of cogeneration applications using gas turbines and thermal engines. The on-going research concerns a detailed study of thermodynamic modelling cycles with energy recovery. These combined cycles with gas turbine and ICE can generate a potential increase of about 10% of the energy efficiency. They will generate a technological complexity and the over-charge must be estimated. At last, the authors insist on the necessary synergy between gas turbines and thermal engines.     

An integrated system framework for fuel cell-based distributed green energy applications

The environmental pollution and diminishing conventional fuel sources and global warming problems make it more attractive for considering renewables as alternative energy sources, such as solar, wind and micro hydro, etc. Recent advances in hydrogen and fuel cell technologies further facilitate these energy options to supply electrical power to various communities. Hydrogen fuel cell systems coupled with renewable energy sources stand out as a promising solution. This paper presents an integrated system framework for fuel cell-based distributed energy applications. Five components are included in this framework: a physical energy system application, a virtual simulation model, a distributed coordination and control, a human system interface and a database. The integrated system framework provides a means to optimize system design, evaluate its performance and balance supplies and demands in a hydrogen assisted renewable energy application. It can either be applied to a distributed energy node that fulfills a local energy demand or to an energy-network that coordinates distributed energy nodes in a region, such as a hydrogen highway. The proposed system framework has been applied in the first phase of our multi-phases project to investigate and analyze the feasibility and suitability of hydrogen fuel assisted renewable power for a remote community. Through integration with an available renewable energy profile database, the developed system efficiently assists in selecting, integrating, and evaluating different system configurations and various operational scenarios at the application site. The simulation results provide a solid basis for the next phase of our demonstration projects.     

A direct flame solid oxide fuel cell for potential combined heat and power generation

A sealant-free solid oxide fuel cell (SOFC) micro-stack was successfully operated inside a liquefied petroleum gas (LPG) flame during cooking. This micro-stack consisted of 4 single cells with infiltrated La_0.75Sr_0.25Cr_0.5Mn_0.5O_3-δ (LSCM) based composite anodes, achieving an open circuit voltage of 0.92 V and a peak power density of 348 mW cm⁻². This performance is significantly better than that of stack with its cathode operation outside flame. The results confirmed that the perovskite oxide anode showed good properties of carbon-free, redox-stability, quick-start (less than 1 min) and successful operation under a wide range of oxygen partial pressure. For comparison, the conventional Ni/yttria-stabilized zirconia (Ni/YSZ) anode was prepared and tested under the same conditions, showing an open circuit voltage of 0.915 V and a peak power density of 366 mW cm⁻², but obvious carbon deposition, poor stability and slow/difficult-start. The direct flame SOFC (DFFC) with a new configuration and design has a potential for combined heat and power generation for many applications.     

Oxy-hydrogen gas as an alternative fuel for heat and power generation applications - A review

One of the important goals in today's world is sustainable power generation by using low or zero polluting fuels and energy conversion devices. In this context, utilization of gaseous fuels in internal combustion (IC) engines is focused more due to their better fuel mixing ability with air, higher combustion efficiency, easier transportation, and lower pollutant formation. Liquefied petroleum gas (LPG), compressed natural gas (CNG), hydrogen, and biogas are considered as commonly available alternative gaseous fuels for IC engines. Yet, a search for other possible alternative gaseous fuels is continuing in the world. In recent years, Oxy-hydrogen (HHO) also known as Brown's gas has been explored by many researchers in the world, for the possibility of using it for heat and power applications. Because of this, a comprehensive review of the production of HHO using different generators and its utilization in heat and power applications has been carried out, and the discussions are presented in this paper.     

Feasibility analysis of fuel cells for combined heat and power systems in the tertiary sector

The aim of this paper is to present a feasibility analysis of the application of fuel cells for a combined heat and power system with grid connection in the tertiary sector. Although the analysis considers Spanish data, the methodology proposed is developed to be applicable at the EU level.The current legislative framework is analysed in order to establish the suitability of the payment scheme considered for the sale of surplus electricity from these systems. The paper also establishes criteria for the optimal design of distributed generation systems based on fuel cells from a technical, economic and environmental point of view, presenting the strategies that should be implemented to promote the future implantation of these systems and their progressive introduction to the market.     

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.     

Economic analysis of a combined heat and power molten carbonate fuel cell system

Fuel cells can be attractive for use as stationary combined heat and power (CHP) systems. Molten carbonate fuel cell (MCFC) power plants are prime candidates for the utilization of fossil based fuels to generate high efficiency ultra clean power. However, fuel cells are considerably more expensive than comparable conventional technologies and therefore a careful analysis of the economics must be taken. This work presents analysis on the feasibility of installing both a FuelCell Energy DFC^® 1500MA and 300MA system for use at Adams Thermal Systems, a manufacturing facility in the U.S. Midwest. The paper examined thoroughly the economics driving the appropriateness of this measure. In addition, a parametric study was conducted to determine scenarios including variation in electric and natural gas rates along with reduced installation costs.     

The anode supported internal cathode tubular solid oxide fuel cell: Novel production of a cell geometry for combined heat and power applications

An effective strategy for generating combined heat and power (CHP) systems is to use the combustion of hydrocarbons to provide fuel reforming and heat production for solid oxide fuel cell (SOFC) operation. Though tubular SOFCs (tSOFCs) are well suited to the thermal cycling associated with combustion systems, they have a geometric limitation which requires significant alteration to the combustion chamber. These alterations can be eliminated by producing an anode supported internal cathode-tSOFC (IC-tSOFC) which can be directly integrated into the chamber with minimal alterations. Novel methods used to produce IC-tSOFCs are discussed in this work. Scanning electron microscopy (SEM) and performance characterization are used to analyze fabricated cells. With a peak power density of 369 mW∙cm⁻², and an open circuit voltage (OCV) of 0.98 V, it is confirmed that novel production methods for IC-tSOFCs have been successful.     

Coordinated power control with virtual inertia for fuel cell-based DC microgrids cluster

This paper proposes a coordinated power control method with virtual inertia (VI) for fuel cell-based DC microgrids (MGs) cluster based on the multi-agent system (MAS) control frame. In the primary control layer, a local energy management strategy with virtual inertia is adopted to suppress the bus voltage disturbance, smooth the output power of fuel cell, as well as manage the power flow in the DC MG. In the secondary and tertiary control layers, a coordinated power control method based on MAS frame is implemented for the power flow among the sub-MGs. More specifically, the secondary voltage control loop is used for the bus voltage smooth control at the moment of microgrids interconnection, and the power flow tertiary control regular is applied for the battery SoC converge uniformly in finite time. Also, a fuel cell-based DC microgrids cluster real-time simulation platform is established to verify the control performance of the proposed coordinated power control method on the bus voltage smooth control, the SoC consistency control, load abrupt response and ‘plug and play’ capability.     

Practical modelling of micro combined heat and power applications for local authority district heating schemes

The primary purposes of this paper are to describe a practical model which can be used to assist economic evaluation of district heating proposals, with particular reference to potential micro combined heat and power (CHP) applications, and to discuss the results of applying this model to a proposal for a particular scheme. The problems of realistic simulation of demand patterns, and the sensitivity of micro-CHP project values to scale, fuel prices, differential purchase/selling tariffs for electricity, duty cycle and plant utilization factors are discussed. Of several options, two were shown to be economically viable, relative to existing methods of supply (gas-fired boilers); however, the margin of benefit is small relative to wisely chosen modern boiler installations. A brief discussion of alternative methods of finance is provided; ceteris paribus, the proposed scheme would not be likely to attract venture capital from would-be lease-hire agencies. There is scope however for pilot schemes, whose results could be used to define more closely the limits of uncertainty of, for example, annual availability and duty cycle influences on the cost economics of operations.     

Methanol decomposition fuel processor for portable power applications

A new fuel processor approach for portable fuel cell power sources significantly improves upon microreformers by overcoming the difficulties with heat deficiencies and contaminants in the product hydrogen. Instead of reforming, the processor uses methanol decomposition to enable the byproduct, carbon monoxide (CO), to be used as the heat source. A hydrogen permselective membrane segregates the CO for combustion in an integrated burner, maximizes the decomposition conversion, and provides pure hydrogen for a fuel cell. Discharging the CO-rich retentate through an ejector to draw combustion air into the burner greatly simplifies the system. High and stable hydrogen yields are attained with optimized catalysts and fuel compositions. The resultant simple, efficient, and self-heating processor produces 85% of the hydrogen content of the fuel. A 20 W autonomous power source based on this novel fuel processor demonstrates a fuel energy density >1.5 Wh g^?1_(electrical), nearly twice as high as microreformer power sources.     

Analysis of total energy system based on solid oxide fuel cell for combined cooling and power applications

A total energy system (TES) incorporating a solid oxide fuel cell (SOFC) and an exhaust gas driven absorption chiller (AC) is presented to provide power, cooling and/or heating simultaneously. The purpose for using the absorption chiller is to recover the exhaust heat from the SOFC exhaust gas for enhancing the energy utilization efficiency of the TES. A steady-state mathematical model is developed to simulate the effects of different operating conditions of SOFC, such as the fuel utilization factor and average current density, on the performance of the TES by using the MATLAB softpackage. Parametric analysis shows that both electrical efficiency and total efficiency of the TES have maximum values with variation of the fuel utilization factor; while the cooling efficiency increases, the electrical efficiency and total efficiency decrease with increase in the current density of SOFC. The simulated results could provide useful knowledge for the design and optimization of the proposed total energy system.     

住宅用固体氧化物燃料电池热电联供系统的设计与分析

固体氧化物燃料电池(SOFC)发电技术是一种能够直接将燃料中的化学能转化电能的绿色高效的新能源技术。将SOFC作为分布式能源的发电装置运用在家用热电联供系统,具有综合效率高、无污染、无噪声等优点。文章搭建了天然气重整制氢-SOFC热电联供系统,完成了基于SOFC的家用热电联供系统的设计与分析。文章根据用户夏冬季热电消耗数据,提出了一种以用户电消耗为核心的家用热电联供系统的运行方案,同时给出了蓄电池容量和水箱容积的推荐参数。与传统火力发电系统相比,采用天然气的SOFC热电联供系统更加节能。     

Pem fuel cells for transportation and stationary power generation applications

We describe recent activities at Los Alamos National Laboratory devoted to polymer electrolyte fuel cells in the contexts of stationary power generation and transportation applications. A low cost/high performance hydrogen or reformate/air stack technology is being developed based on ultra-low platinum loadings and non-machined, inexpensive elements for flow-fields and bipolar plates. On-board methanol reforming is compared to the option of direct methanol fuel cells in light of recent significant power density increases demonstrated in the latter.     

Hybrid fuel cell-based energy system with metal hydride hydrogen storage for small mobile applications

This paper describes the general architecture of a hybrid energy system, whose main components are a proton exchange membrane fuel cell, a battery pack and an ultracapacitor pack as power sources, and metal hydride canisters as energy storage devices, suitable for supplying power to small mobile non-automotive devices in a flexible and variable way. The first experimental results carried out on a system prototype are described, showing that the extra components, required in order to manage the hybrid system, do not remarkably affect the overall system efficiency, which is always higher than 36% in all the test configurations examined. In fact, the system allows the fuel cell to work most often at quasi-optimal conditions, near its maximum efficiency (i.e. at low/medium loads), because high external loads are met by the combined effort of the fuel cell and the ultracapacitors. For the same reason, the metal hydride storage system can be used also under highly dynamic operating conditions, notwithstanding its usually poor kinetic performance.     

Optimal design and operational tests of a high-temperature PEM fuel cell for a combined heat and power unit

Development of new materials for polymer electrolyte membranes has allowed increasing the operational temperature of PEM fuel cell stacks above 120 °C. The present paper summarizes the main results obtained in a research devoted to the design, fabrication and operational tests performed on a high-temperature PEMFC prototype. A 5-cell stack has been assembled with commercial Celtec P-1000 high-temperature MEAs from BASF Fuel Cells, but the rest of elements and processes have been developed at LIFTEC research facilities. The stack includes different novelties, such as the way in which reactant gases are supplied to the flowfield, the design of the flowfield geometry for both anode and cathode plates, the concept of block that eases the assembling and maintenance processes, and the heating strategy for a very fast start-up. The different procedures comprising the assembly, closing and conditioning stages are also widely described and discussed. Results obtained in the preliminary operational tests performed are very promising, and it is expected that the 30-cells HT-PEMFC stack will deliver an electric power 2.3 times larger than the one initially predicted.     

An emerging market in fuel cells? Residential combined heat and power in four countries

Global concerns about fossil fuel stocks and security of supply have stimulated governments and industry to explore the development of alternative sources of energy. This has led to the emergence of liberalised markets for energy and the growth of de-centralised generation and distribution systems. Within this context, the use of a sustainable technology, such as fuel cells, as a generator of heat and electricity for the residential market, is a significant market opportunity. Using a set of framework conditions to explain the diffusion of renewable energy technologies, this paper analyses recent developments in four leading industrial countries, and concludes that Japan and Germany are competing to be the lead country for the introduction of this technology. In the process, we highlight the impact of government and the extent to which the development of a fuel cell industry is being driven by incumbent large firms acting independently or in collaboration with a range of other companies across the value chain.     

Mini- and micro-gas turbines for combined heat and power

The use of mainframe gas turbines for power generation has increased in recent years and is likely to continue to increase. The proportion of power generation using combined heat and power is also growing mainly due to efficiency improvements and environmental benefits.

Mini- and micro-turbines offer a number of potential advantages compared to other technologies for small-scale power generation, particularly for distributed power generation, although there are some technical and non-technical barriers to the implementation of the technology. There is an uncertainty about their market potential but they could be used for power generation in the industrial, commercial and residential sectors. The market potential could increase substantially if the cost, efficiency, durability, reliability, and environmental emissions of the existing designs are improved.