A flexible model integration approach for evaluating tradeoffs between CO2 emissions and cost in solid oxide fuel cell‐based building energy systems

A simulation framework for flexible evaluation of various distributed building energy systems based on the integration of component device simulation models is presented. Device technology models were constructed for a solid oxide fuel cell (SOFC), a gas turbine, a double pipe heat exchanger, and a compressor. A scheme is proposed for defining model interfaces in order to improve the flexibility and accessibility of the models. Based on that scheme, interfaces are defined for each device model. The component device models are integrated to construct system models of (1) a hybrid system combining an SOFC and a gas turbine (SOFC/GT system) and (2) a stand‐alone SOFC system. The integrated model of the SOFC/GT system is then used to carry out a multi‐objective optimization in order to study the tradeoffs between cost and CO₂ emissions of the SOFC system operation for a given electricity demand. Through these analyses, the optimal configuration of the SOFC/GT system and the optimal operation conditions of the SOFC system for the given electricity demand were explored. Copyright © 2005 John Wiley & Sons, Ltd.     

A modularized framework for solving an economic–environmental power generation mix problem

This paper presents a modularized simulation modelling framework for evaluating the impacts on economic cost and CO₂ emissions resulting from the introduction of a solid oxide fuel cell (SOFC) system into the existing mix of centralized power generation technologies in Japan. The framework is comprised of three parts: a dual‐objective linear programming model that solves the generation best‐mix problem for the existing power generation technologies; a nonlinear SOFC system model in which the economic cost and CO₂ emissions by the SOFC system can be calculated; and the Queuing Multi‐Objective Optimizer (QMOO), a multi‐objective evolutionary algorithm (MOEA) developed at the EPFL in Switzerland as the overall optimizer of the combined power supply system. Thus, the framework integrates an evolutionary algorithm that is more suitable for handling nonlinearities with a calculus‐based method that is more efficient in solving linear programming problems. Simulation experiments show that the framework is successful in solving the stated problem. Moreover, the three components of the modularized framework can be interconnected through a platform‐independent model integration environment. As a result, the framework is flexible and scalable, and can potentially be modified and/or integrated with other models to study more complex problems. Copyright © 2004 John Wiley & Sons, Ltd.     

Study on zero CO2 emission atmospheric pressure SOFC hybrid power system integrated with OTM

In order to further reduce the energy consumption of CO₂ capture from the traditional SOFC hybrid power system, based on the principle of energy cascade utilization and system integration, a zero CO₂ emission atmospheric pressure solid oxide fuel cell (SOFC) hybrid power system integrated with oxygen ion transport membrane (OTM) is proposed. The oxygen is produced by the OTM for the oxy‐fuel combustion afterburner of SOFC. With the Aspen‐plus software, the models of the overall SOFC hybrid power systems with or without CO₂ capture are developed. The thermal performance of new system is investigated and compared with other systems. The effects of the fuel utilization factor of SOFC and the pressure ratio between two sides of OTM membrane on the overall system performance are analyzed and optimized. The research results show that the efficiency of the zero CO₂ emission atmospheric pressure SOFC hybrid power system integrated with OTM is around 58.36%, only 2.48% lower than that of the system without CO₂ capture (60.84%) but 0.96% higher than that of the zero CO₂ emission atmospheric pressure SOFC hybrid system integrated with the cryogenic air separation unit. Copyright © 2014 John Wiley & Sons, Ltd.     

Dynamic modeling of a SOFC/MGT hybrid power system based on modified OIF Elman neural network

Solid oxide fuel cell (SOFC) integrated into micro gas turbine (MGT) cycle is a promising power‐generation technology. This article proposes a modified output–input feedback (OIF) Elman neural network model to describe the nonlinear temperature and power dynamic properties of the SOFC/MGT hybrid system. A physics‐based mathematical model of a 220 kW SOFC/MGT hybrid power system is used to generate the data required for the training and prediction of the modified OIF Elman neural network identification model. Compared with the conventional Elman neural network, the simulation results show that the modified OIF Elman identification model can follow the temperature and power response of the SOFC/MGT hybrid system with higher prediction accuracy and faster convergent speed. Copyright © 2010 John Wiley & Sons, Ltd.     

Parameter optimization study on SOFC‐MGT hybrid power system

This paper mainly studied the solid oxide fuel cell (SOFC)–micro gas turbine (MGT) hybrid power system. The key parameters that greatly influence the overall system performance have been studied and optimized. The thermodynamic potential of improving the hybrid system performance by integrating SOFC with the advanced thermal cycle system is analyzed. The optimization rules of main parameters of SOFC‐MGT hybrid power system with the turbine inlet temperature (TIT) of MGT as a constraint condition are revealed. The research results show that TIT is a key parameter that limits the electrical efficiency of hybrid power system. With the increase of the cell number, both the power generation efficiency of the hybrid cycle power system and TIT increase. Regarding the hybrid system with the fixed cell number, in order to get a higher electrical efficiency, the operating temperature of SOFC should be enhanced as far as possible. However, the higher operating temperature will result in the higher TIT. Increasing of fuel utilization factor is an effective measure to improve the performance of hybrid system. At the same time, TIT increases slightly. Both the electrical efficiency of hybrid power system and TIT reduce with the increase of the ratio of steam to carbon. The achievements obtained from this paper will provide valuable information for further study on SOFC‐MGT hybrid power system with high efficiency. Copyright © 2010 John Wiley & Sons, Ltd.     

Solid oxide fuel cell-lithium battery hybrid power generation system energy management: A review

The solid oxide fuel cell (SOFC)/lithium battery hybrid energy structure uses lithium batteries as the energy buffer unit to ensure that the SOFC can operate safely and stably when the load power increases suddenly. For the SOFC/lithium battery hybrid power generation system, a real-time energy management strategy based on power prediction is discussed, and an in-depth summary is made from system construction, power prediction, energy distribution, and power tracking. In the hybrid power generation system, the SOFC system and the lithium battery influence each other. Research the appropriate energy management strategies and realize real-time energy distribution and tracking of hybrid power generation systems in order to improve system performance and economy. This has become a key issue in the current SOFC hybrid power generation system research field.     

A multiple objective linear programming model for power generation expansion planning

The planning of new units for electrical power generation is a problem which involves different and conflicting aspects. Besides cost, security issues and environmental concerns must be explicitly incorporated into the models. In this way mathematical models become more realistic, and they enhance the decision maker's comprehension of the complex and conflicting nature of the distinct aspects of the problem. A multiple objective linear programming model for power generation expansion planning is presented. The model considers three objective functions (net present cost of the expansion plans, reliability of the supply system, and environmental impacts) and three categories of constraints (load requirements, operational restrictions and budget). Three generating technologies are considered for power system expansion: oil, nuclear and coal.     

Part load operation of SOFC/GT hybrid systems: Stationary analysis

In a global energetic context characterized by the increasing demand of oil and gas, the depletion of fossil resources and the global warming, more efficient energy systems and, consequently, innovative energy conversion processes are urgently required. A possible solution can be found in the fuel cells technology coupled with classical thermodynamic cycle technologies in order to make hybrid systems able to achieve high energy/power efficiency with low environmental impact. Moreover, due to the synergistic effect of using a high temperature fuel cell such as solid oxide fuel cell (SOFC) and a recuperative gas turbine (GT), the integrated system efficiency can be significantly improved. In this paper a steady zero dimensional model of a SOFC/GT hybrid system is presented. The core of the work consists of a performance analysis focused on the influence of the GT part load functioning on the overall system efficiency maintaining the SOFC power set to the nominal one. Also the proper design and management of the heat recovery section is object of the present study, with target a global electric efficiency almost constant in part load functioning respect to nominal operation. The results of this study have been used as basis to the development of a dynamic model, presented in the following part of the study focused on the plant dynamic analysis.     

A combined modeling approach for wind power feed-in and electricity spot prices

Wind power generation and its impacts on electricity prices has strongly increased in the EU. Therefore, appropriate mark-to-market evaluation of new investments in wind power and energy storage plants should consider the fluctuant generation of wind power and uncertain electricity prices, which are affected by wind power feed-in (WPF). To gain the input data for WPF and electricity prices, simulation models, such as econometric models, can serve as a data basis.This paper describes a combined modeling approach for the simulation of WPF series and electricity prices considering the impacts of WPF on prices based on an autoregressive approach. Thereby WPF series are firstly simulated for each hour of the year and integrated in the electricity price model to generate an hourly resolved price series for a year. The model results demonstrate that the WPF model delivers satisfying WPF series and that the extended electricity price model considering WPF leads to a significant improvement of the electricity price simulation compared to a model version without WPF effects. As the simulated series of WPF and electricity prices also contain the correlation between both series, market evaluation of wind power technologies can be accurately done based on these series.     

Modelling and evaluation of building integrated SOFC systems

This study presents the final results of a series of modelling steps which are undertaken for the performance assessment of the building cogeneration and polygeneration systems using solid oxide fuel cell (SOFC). Based on earlier work, generic SOFC cell stack and system models were developed and employed to analyze different SOFC systems configurations for optimal efficiencies, this SOFC system model is used to derive performance input data for transient whole-building and energy system simulation tools which contain simpler SOFC system models. These steps are shortly summarized here. Then the final step, the evaluation of building integrated co- and polygeneration SOFC systems in terms of primary energy demand and CO₂ emissions, employing such tools, is presented here for a polygeneration system with typical heating and cooling loads, and electricity demand profiles, for different SOFC systems, including a comparison to current standard technologies.     

A performance analysis of integrated solid oxide fuel cell and heat recovery steam generator for IGFC system

Solid oxide fuel cell (SOFC) is a promising technology for electricity generation. Sulfur-free syngas from a gas-cleaning unit serves as fuel for SOFC in integrated gasification fuel cell (IGFC) power plants. It converts the chemical energy of fuel gas directly into electric energy, thus high efficiencies can be achieved. The outputs from SOFC can be utilized by heat recovery steam generator (HRSG), which drives the steam turbine for electricity production. The SOFC stack model was developed using the process flow sheet simulator Aspen Plus, which is of the equilibrium type. Various ranges of syngas properties gathered from different literature were used for the simulation. The results indicate a trade-off efficiency and power with respect to a variety of SOFC inputs. The HRSG located after SOFC was included in the current simulation study with various operating parameters. This paper describes IGFC power plants, particularly the optimization of HRSG to improve the efficiency of the heat recovery from the SOFC exhaust gas and to maximize the power production in the steam cycle in the IGFC system. HRSG output from different pressure levels varies depending on the SOFC output. The steam turbine efficiency was calculated for measuring the total power plant output. The aim of this paper is to provide a simulation model for the optimal selection of the operative parameters of HRSG and SOFC for the IGFC system by comparing it with other models. The simulation model should be flexible enough for use in future development and capable of predicting system performance under various operating conditions.     

Study on a zero CO2 emission SOFC hybrid power system integrated with OTM using CO2 as sweep gas

A new zero CO₂ emission solid oxide fuel cell (SOFC) hybrid power system integrated with the oxygen ion transport membrane using CO₂ as sweep gas is proposed in this paper. The pure oxygen is picked up from the cathode outlet gas by the oxygen ion transport membrane with CO₂ as sweep gas; the oxy‐fuel combustion mode in the afterburner of SOFC is employed. Because the combustion product gas only consists of CO₂ and steam, CO₂ is easily captured with lower energy consumption by the condensation of steam. With the aspen plus soft, this paper builds the simulation model of the overall SOFC hybrids system with CO₂ capture. The exergy loss distributions of the overall system are analyzed, and the effects of the key operation parameters on the overall system performance are also investigated. The research results show that the new system still has a high efficiency after CO₂ recovery. The efficiency of the new system is around 65.03%, only 1.25 percentage points lower than that of the traditional SOFC hybrid power system(66.28%)without CO₂ capture. The research achievements from this paper will provide the valuable reference for further study on zero CO₂ emission SOFC hybrid power system with higher efficiency. Copyright © 2013 John Wiley & Sons, Ltd.     

Modelling of heat transfer and fluid flow in the hot section of gas turbines used in power generation: A comprehensive survey

Power generation is one of the major industries or businesses globally. Although, at present, a major attention has been paid towards the sustainable energy technologies, both gas and steam turbines are still heavily used in the power generation sector worldwide. Usually, gas turbines are used to drive an electrical power generator in simple systems, or they are used in combined cycle plants together with steam turbines. This paper presents a comprehensive review on modelling of heat transfer and fluid flow in hot section of gas turbines used in the power generation sector. Visibly, heat transfer and fluid flow characteristics directly affect the thermal efficiency and the overall performance of the gas turbines. Hence, existing models relating to heat transfer and fluid flow inside gas turbines are discussed in detail. Primarily, methods relating to the first principle modelling, empirical modelling, and finite element modelling are reviewed comprehensively, and then, a discussion is provided together with a comparison among models in terms of their advantages and disadvantages. Moreover, some existing issues such as the environmental impact are discussed which still remain as challenges to the power generation industry together with some of the possible future directions for improvements.     

Simulation of energy use in buildings with multiple micro generators

This paper focuses on the detailed modelling of micro combined heat and power (mCHP) modules and their interaction with other renewable micro generators in domestic applications based on an integrated modular modelling approach. The simulation model has been developed using Matlab/Simulink and incorporates a Stirling engine mCHP module embedded in a lumped-parameter domestic energy model, together with contributions from micro wind and photovoltaic modules. The Stirling cycle component model is based on experimental identification of a domestic-scale system which includes start up and shut down characteristics. The integrated model is used to explore the interactions between the various energy supply technologies and results are presented showing the most favourable operating conditions that can be used to inform the design of advanced energy control strategies in building. The integrated model offers an improvement on previous models of this kind in that a fully-dynamic approach is adopted for the equipment and plant enabling fast changing load events such as switching on/off domestic loads and hot water, to be accurately captured at a minimum interval of 1 min. The model is applied to two typical 3- and 4-bedroom UK house types equipped with a mCHP module and two other renewable energy technologies for a whole year. Results of the two cases show that the electrical contribution of a Stirling engine type mCHP heavily depends on the thermal demand of the building and that up to 19% of the locally-generated electricity is exported whilst meeting a similar percentage of the overall annual electricity demand. Results also show that the increased number of switching of mCHP module has an impact on seasonal module efficiency and overall fuel utilisation. The results demonstrate the need for the analysis of equipment design and optimal sizing of thermal and electrical energy storage.     

Modeling and control of a SOFC-GT-based autonomous power system

In this article, a dynamic, lumped model of a solid oxide fuel cell (SOFC) is described, as a step towards developing control relevant models for a SOFC combined with a gas turbine (GT) in an autonomous power system. The model is evaluated against a distributed dynamic tubular SOFC model. The simulation results confirm that the simple model is able to capture the important dynamics of the SOFC and hence it is concluded that the simple model can be used for control and operability studies of the hybrid system. Several such lumped models can be aggregated to approximate the distributed nature of important variables of the SOFC. Further, models of all other components of a SOFC-GT-based autonomous power system are developed and a control structure for the total system is developed. The controller provides satisfactory performance for load changes at the cost of efficiency.     

Effects of operating and design parameters on the performance of a solid oxide fuel cell–gas turbine system

We present a steady‐state thermodynamic model of a hybrid solid oxide fuel cell (SOFC)–gas turbine (GT) cycle developed using a commercial process simulation software, AspenPlus?. The hybrid cycle model incorporates a zero‐dimensional macro‐level SOFC model. A parametric study was carried out using the developed model to study the effects of system pressure, SOFC operating temperature, turbine inlet temperature, steam‐to‐carbon ratio, SOFC fuel utilization factor, and GT isentropic efficiency on the specific work output and efficiency of a generic hybrid cycle with and without anode recirculation. The results show that system pressure and SOFC operating temperature increase the cycle efficiency regardless of the presence of anode recirculation. On the other hand, the specific work decreases with operating temperature. Overall, the model can successfully capture the complex performance trends observed in hybrid cycles. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermodynamic modeling and exergy investigation of a hydrogen-based integrated system consisting of SOFC and CO2 capture option

The current study deals with the thermodynamic modeling of an innovative integrated plant based on solid oxide fuel cell (SOFC) with liquefied natural gas (LNG) cold energy supply. For the suggested innovative plant the energy, and exergy simulations are fully extended and the plant comprehensively analyzed. According to mathematical simulations of the proposed plant, a MATLAB code has been extended. The results indicate that under considered initial conditions, the efficiencies of SOFC and net power generation calculated 58% and 78%, respectively and the CO₂-capture rate is obtained 79 kg/h. This study clearly shows that the integrated system reached high efficiency while having zero emissions. In addition, the efficiencies and net amount of power generation, cooling or heating output and SOFC power generation are discussed in detail as a function of different variables such utilization factor, air/fuel ratio, or SOFC inlet temperature. For enhancing the power production efficiency of SOFC, the net electricity, and CCHP exergy efficiency the plant should run in higher utilization factor and lower air/fuel ration also it's important to approximately set SOFC temperature to its ideal temperature.     

The role of hydrogen in achieving the decarbonization targets for the UK domestic sector

To meet the UK's decarbonization targets the introduction of novel integrated renewable energy generation, storage and demand management systems is required. In this paper the current role of fuel cells in the British domestic sector is discussed using simulation results of a solid oxide fuel cell (SOFC) system in a typical British single dwelling. 17% of carbon dioxide emissions are saved and 69% of the electricity generated by the SOFC system is exported to the grid for this single dwelling according to simulation results. Additionally, the same SOFC system is integrated with photovoltaic technology in a 7 home zero carbon community. The community approach adds a significant benefit given it increases the amount of electricity generated by the SOFC system which is used onsite by 128%, being the price of imported electricity 3 times higher than the export tariff. Then, a combination of short-term and long-term energy storage strategies is suggested by means of a lithium-ion battery and polymer electrolyte membrane (PEM) electrolyser which increased the self-consumption by 118%. According to simulation results, a 6 kW PEM electrolyser with an annual efficiency of 66% only generates 19% of the hydrogen which is consumed by the SOFC system which was used to meet the peak demand using PV generation.     

The development of a PEMFC hybrid power electric vehicle with automatic sodium borohydride hydrogen generation

This paper describes the development of a hybrid Proton Exchange Membrane Fuel Cell (PEMFC) electric vehicle consisting of a 3 kW PEMFC, PV arrays, secondary battery sets, and a chemical hydrogen generation system. We first integrate a hybrid PEMFC electric vehicle and design power management strategies. The on-board hydrogen generation system can provide sufficient hydrogen for continuous operation of the PEMFC, and the performance tests demonstrate the effectiveness of the integrated system in providing sustainable power for driving. We then use Matlab/SimPowerSystem? to develop a simulation model and adjust the model parameters using experimental data. The results indicated that the model can effectively predict system responses and can be used for performance evaluation. We also use the simulation model to estimate the mileage and costs of the developed electric vehicle, and we discuss the impacts of component sizes on system costs and travelling ranges.     

Impact of wind power in autonomous power systems—power fluctuations—modelling and control issues

This paper describes a detailed modelling approach to study the impact of wind power fluctuations on the frequency control in a non‐interconnected system with large‐scale wind power. The approach includes models for wind speed fluctuations, wind farm technologies, conventional generation technologies, power system protection and load. Analytical models for wind farms with three different wind turbine technologies, namely Doubly Fed Induction Generator, Permanent Magnet Synchronous Generator and Active Stall Induction Generator‐based wind turbines, are included. Likewise, analytical models for diesel and steam generation plants are applied. The power grid, including speed governors, automatic voltage regulators, protection system and loads is modelled in the same platform. Results for different load and wind profile cases are being presented for the case study of the island Rhodes, in Greece. The scenarios studied correspond to reference year of study 2012. The effect of wind fluctuations in the system frequency is studied for the different load cases, and comments on the penetration limits are being made based on the results. Copyright © 2010 John Wiley & Sons, Ltd.