Modeling and parametric study of a 1 kWe HT-PEMFC-based residential micro-CHP system

A detailed thermodynamic, kinetic and geometric model of a micro-CHP (Combined-Heat-and-Power) residential system based on High Temperature-Proton Exchange Membrane Fuel Cell (HT-PEMFC) technology is developed, implemented and validated. HT-PEMFC technology is investigated as a possible candidate for fuel cell-based residential micro-CHP systems, since it can operate at higher temperature than Nafion-based fuel cells, and therefore can reach higher cogeneration efficiencies. The proposed system can provide electric power, hot water, and space heating for a typical Danish single-family household. A complete fuel processing subsystem, with all necessary balance-of-plant components, is modeled and coupled to the fuel cell stack subsystem. The micro-CHP system’s synthesis/design and operational pattern is analyzed by means of a parametric study. The parametric study is conducted to determine the most viable system/component design based on maximizing total system efficiency, without violating the requirements of the system. Four decision variables (steam-to-carbon ratio, fuel cell operating temperature, combustor temperature and hydrogen stoichiometry) were parameterized within feasible limits to provide insight on their effect on the overall performance of the proposed system under study and also to provide input on more efficient design in the future. The system is designed to provide maximum loads of 1 kW_e and 2 kW_th. A sensitivity analysis is applied to investigate the influence of the most important parameters on the simulated performance of the system.     

Experimental evaluation of the sensitivity to fuel utilization and air management on a 100 kW SOFC system

The tubular SOFC generator CHP-100, built by Siemens Power Generation (SPG) Stationary Fuel Cells (SFC), is running at the Gas Turbine Technologies (GTT) in Torino (Italy), in the framework of the EOS Project. The nominal load of the generator ensures a produced electric power of around 105 kW_e ac and around 60 kW_t of thermal power at 250 °C to be used for the custom tailored HVAC system.     

The calibration of a model for simulating the thermal and electrical performance of a 2.8 kWAC solid-oxide fuel cell micro-cogeneration device

The concurrent production of heat and electricity within residential buildings using solid-oxide fuel cell (SOFC) micro-cogeneration devices has the potential to reduce primary energy consumption, greenhouse gas emissions, and air pollutants. A realistic assessment of this emerging technology requires the accurate simulation of the thermal and electrical production of SOFC micro-cogeneration devices concurrent with the simulation of the building, its occupants, and coupled plant components. The calibration of such a model using empirical data gathered from experiments conducted with a 2.8 kW_AC SOFC micro-cogeneration device is demonstrated. The experimental configuration, types of instrumentation employed, and the operating scenarios examined are treated. The propagation of measurement uncertainty into the derived quantities that are necessary for model calibration are demonstrated by focusing upon the SOFC micro-cogeneration system’s gas-to-water heat exchanger. The calibration coefficients necessary to accurately simulate the thermal and electrical performance of this prototype device are presented and the types of analyses enabled to study the potential of the technology are demonstrated.     

Performance assessment of a Stirling engine plant for local micro‐cogeneration

In this paper, we evaluate the viability of a 9.5‐kW_e wooden pellet‐fueled Stirling engine‐based micro‐cogeneration plant as a substitute for small‐scale district heating. The district heating systems against which the micro‐cogeneration plant is compared are based either on a pellet‐fueled boiler or a ground‐source heat pump. The micro‐cogeneration and district heating plants are compared in terms of primary energy consumption, CO₂ emissions, and feasibility of the investment. The comparison also considers an optimally operated individual 0.7‐kW_e pellet‐fueled Stirling engine micro‐cogeneration system with exhaust gas heat recovery. The study is conducted in two different climates and contributes to the knowledge base by addressing: (i) hourly changes in the Finnish electricity generation mix; and (ii) uncertainty related to what systems are used as reference and the treatment of displaced grid electricity. Our computational results suggest that when operated at constant power, the 9.5‐kW_e Stirling engine plant results in reduced annual primary energy use compared with any of the alternative systems. The results are not sensitive to climate or the energy efficiency or number of buildings. In comparison with the pellet‐fueled district heating plant, the annual use of primary energy and CO₂ emissions are reduced by a minimum of 25 and 19%, respectively. Owing to a significant displacement of grid electricity, the system's net primary energy consumption appears negative when the total built area served by the plant is less than 1200 m². On the economic side, the maximum investment cost threshold of a CHP‐based district heating system serving 10 houses or more can typically be positive when compared with oil and pellet systems, but negative when compared with a corresponding heat pump system. Copyright © 2010 John Wiley & Sons, Ltd.     

Micro-combined heat and power in residential and light commercial applications

The cogeneration is worldwide considered as the major option to achieve considerable energy saving with respect to traditional systems. This paper deals with the application of micro-cogeneration (electrical power <15 kW) to small scale (residential and light commercial application) users; the state of art of this technology is considered and an energetic analysis of MCHP system regarding its utilization in conjuction with domestic household appliances is performed. Finally the test facility designed and built to evaluate the performance of micro-CHP system itself is described and the optimum operation mode to match the user’s thermal and electrical loads identified.     

Renewable and hydrogen energy integrated house

The residential sector accounts for about a third of the total world energy consumption. Energy efficiency, Renewable Energy Sources and Hydrogen can play an important role in reducing the consumptions and the emissions and improving the energy security if integrated (Efficiency, Res, Hydrogen) systems are developed and experimented. The paper analyzes a real residential 100 square meters house, where energy efficiency measures and RES technologies have been applied, sizing a hydrogen system (electrolyzer, metal hydrides and fuel cell) for power backup, taking into consideration its dynamic behavior, experimentally determined. The technologies used are already available in the market and, except hydrogen technologies, sufficiently mature. Through energy efficiency technologies (insulation, absorbers, etc), the maximum electrical and thermal power needed decreases from 4.4 kW_e to 1.7 kW_e (annual consumption from 5000 kWh to 1200 kWh) and from 5.2 kW_t to 1.6 kW_t (annual consumption from 14,600 kWh to 4500 kWh) respectively. With these reduced values it has been possible to supply the consumptions entirely by small photovoltaic and solar thermal plants (less than 10 m² each). The hydrogen backup even if remains the most expensive (versus traditional batteries and gasoline generator), satisfying all the electric needs for one day, increases the security and allows net metering. Moreover the low-pressure hydrogen storage system through metal hydrides guarantees system safety too. Finally the system modularity can also satisfy higher energy production.     

Design and performance evaluation of an innovative small scale combined cycle cogeneration system

This paper deals with an innovative natural gas (NG) combined cycle cogeneration system (150-kW_e, 192 kW_t). The system is made up of a combination of two interconnected combined heat and power (CHP) systems: a reciprocating internal combustion engine cogenerator (ICE CHP) as the topping cycle and a Rankine cycle cogenerator (RC CHP) which operates as the bottoming cycle on the exhaust gases from the ICE. The expander technology chosen for the Rankine cycle prime mover is a reciprocating single expansion steam engine with three cylinders in a radial architecture. The ICE is an automotive derived internal combustion engine with a high part-load electrical efficiency, due to a variable speed operation strategy and reduced emissions.     

The financial viability of an SOFC cogeneration system in single-family dwellings

In the near future, fuel cell-based residential micro-CHP systems will compete with traditional methods of energy supply. A micro-CHP system may be considered viable if its incremental capital cost compared to its competitors equals to cumulated savings during a given period of time. A simplified model is developed in this study to estimate the operation of a residential solid oxide fuel cell (SOFC) system. A comparative assessment of the SOFC system vis-à-vis heating systems based on gas, oil and electricity is conducted using the simplified model for a single-family house located in Ottawa and Vancouver. The energy consumption of the house is estimated using the HOT2000 building simulation program. A financial analysis is carried out to evaluate the sensitivity of the maximum allowable capital cost with respect to system sizing, acceptable payback period, energy price and the electricity buyback strategy of an energy utility. Based on the financial analysis, small (1–2 kW_e) SOFC systems seem to be feasible in the considered case. The present study shows also that an SOFC system is especially an alternative to heating systems based on oil and electrical furnaces.     

Improved modelling of the fuel cell power module within a system-level model for solid-oxide fuel cell cogeneration systems

A generic system-level model for SOFC cogeneration devices has been developed under the umbrella of an International Energy Agency/Energy Conservation in Buildings and Community Systems project known as Annex 42. This paper addresses a limitation of the Annex 42 model by developing a more refined semi-mechanistic treatment for the fuel cell power module (FCPM). The electrochemical, thermal, and reformation modelling methods as well as techniques for treating the FCPM's balance of plant are first described. The methods used to calibrate and validate the enhanced model using previously collected data from a 2.8 kW_AC prototype SOFC cogeneration device are then discussed. Excellent agreement was found between model predictions and the measurements. The new modelling capabilities are then demonstrated through a parametric study that examines the influences of fuel utilization, excess air ratio and stack temperature.     

The Sotacarbo coal gasification experimental plant for a CO2-free hydrogen production

Being hydrogen the most promising energy carrier for distributed power generation and being the coal-to-hydrogen technologies far from their large-scale application, mainly due to their high costs, Sotacarbo has recently built up a pilot platform for the combined production of hydrogen and electrical energy from coal. The platform includes two different units: a 5 MW_th demonstrative plant and a 200 kW_th pilot plant (feed with a maximum of 35 kg/h of coal).     

Performance and cost of automotive fuel cell systems with ultra-low platinum loadings

An automotive polymer-electrolyte fuel cell (PEFC) system with ultra-low platinum loading (0.15 mg-Pt cm⁻²) has been analyzed to determine the relationship between its design-point efficiency and the system efficiency at part loads, efficiency over drive cycles, stack and system costs, and heat rejection. The membrane electrode assemblies in the reference PEFC stack use nanostructured, thin-film ternary catalysts supported on organic whiskers and a modified perfluorosulfonic acid membrane. The analyses show that the stack Pt content can be reduced by 50% and the projected high-volume manufacturing cost by >45% for the stack and by 25% for the system, if the design-point system efficiency is lowered from 50% to 40%. The resulting penalties in performance are a <1% reduction in the system peak efficiency; a 2-4% decrease in the system efficiency on the urban, highway, and LA92 drive cycles; and a 6.3% decrease in the fuel economy of the modeled hybrid fuel-cell vehicle on the combined cycle used by EPA for emission and fuel economy certification. The stack heat load, however, increases by 50% at full power (80 kW_e) but by only 23% at the continuous power (61.5 kW_e) needed to propel the vehicle on a 6.5% grade at 55 mph. The reduced platinum and system cost advantages of further lowering the design-point efficiency from 40% to 35% are marginal. The analyses indicate that thermal management in the lower efficiency systems is very challenging and that the radiator becomes bulky if the stack temperature cannot be allowed to increase to 90-95 °C under driving conditions where heat rejection is difficult.     

An analysis of the legal and market framework for the cogeneration sector in Croatia

Following a strategic orientation towards sustainable development, the Government of the Republic of Croatia has changed its energy legislation and has put forward a framework for the systematic development and increased use of renewable energy sources and cogeneration. This paper focuses on changes in the regulatory context relevant to the cogeneration sector and also analyses the impact of energy market transition on cogeneration viability in municipal district heating, industry, services and the residential sector. Particular attention has been paid to the expected changes of heat, electricity and gas prices. We present a simple model for quantitative prediction of the cogeneration system profitability at different power levels under given national circumstances. Our findings support a need for a strong institutional support for initial penetration of the micro-cogeneration technologies into the Croatian energy system.     

Biodiesel fuel processor for APU applications

Tail pipe emission reduction, increased use of renewable fuels and efficient supply of auxiliary power for road vehicles using fuel cells have been the main drivers of the European project BIOFEAT (biodiesel fuel processor for a fuel cell auxiliary power unit for a vehicle). Within the project a biodiesel fuelled heat integrated fuel processor for 10 kW_e capacity has been designed and constructed. Demonstration tests showed a high quality reformate with less than 10 ppm of CO and a gross efficiency of 87%.     

5 kWe + 5 kWt reformer-PEMFC energy generator from bioethanol first data on the fuel processor from a demonstrative project

A power unit constituted by a reformer section, a H₂ purification section and a fuel cell stack is being tested c/o the Dept. of Physical Chemistry and Electrochemistry of Università degli Studi di Milano, on the basis of a collaboration with HELBIO S.A. Hydrogen and Energy Production Systems, Patras (Greece), supplier of the unit, and some sponsors (Linea Energia S.p.A., Parco Tecnologico Padano and Provincia di Lodi, Italy). The system size allows to co-generate 5 kW_e (220 V, 50 Hz a.c.) + 5 kW_t (hot water at 65 °C) as peak output. Bioethanol, obtainable by different non-food-competitive biomass, is transformed into syngas by a pre-reforming and reforming reactors couple and the reformate is purified from CO to a concentration below 20 ppmv, suitable to feed a proton exchange membrane fuel cell (PEMFC) stack that will be integrated in the fuel processor in a second step of the experimentation. This result is achieved by feeding the reformate to two water gas shift reactors, connected in series and operating at high and low temperature, respectively. CO concentration in the outcoming gas is ca. 0.4 vol% and the final CO removal to meet the specifications is accomplished by two methanation reactors in series. The second methanation step acts merely as a guard, since ca. 15 ppmv of CO are obtained already after the first reactor.     

Life-cycle energy consumption and greenhouse gas emissions for electricity generation and supply in China

The Well-to-Meter (WTM) analysis module in the Tsinghua-CA3EM model has been used to examine the primary fossil energy consumption (PFEC) and greenhouse gas (GHG) emissions for electricity generation and supply in China. The results show that (1) the WTM PFEC and GHG emission intensities for the 2007 Chinese electricity mix are 3.247 MJ/MJ and 297.688 g carbon dioxide of equivalent (gCO_2,e)/MJ, respectively; (2) power generation is the main contributing sub-stage; (3) the coal-power pathway is the only major contributor of PFEC (96.23%) and GHG emissions (97.08%) in the 2007 mix; and (4) GHG emissions intensity in 2020 will be reduced to 220.470 gCO_2,e/MJ with the development of nuclear and renewable energy and to 169.014 gCO_2,e/MJ if carbon dioxide capture and storage (CCS) technology is employed. It is concluded that (1) the current high levels of PFEC and GHG emission for electricity in China are largely due to the dominant role of coal in the power-generation sector and the relatively low efficiencies during all the sub-stages from resource extraction to final energy consumption and (2) the development of nuclear and renewable energy as well as low carbon technologies such as CCS can significantly reduce GHG emissions from electricity.     

Coupling a Stirling engine with a fluidized bed combustor for biomass

The paper deals with the integration between a kinematic Stirling engine and a fluidized bed combustor for micro-scale cogeneration of renewable energy. A pilot-scale facility integrating a 40 kW_t combustor and a γ-type Stirling engine (0.5 kW_e) was set up and tested to demonstrate the feasibility of this solution. The Stirling engine was installed at a lateral wall of the combustor in direct contact with the fluidized bed region. An experimental campaign was executed to assess the performance of the innovative integrated system. The experimental results can be summarized in: (a) very high combustion efficiency with biomass feeding, (b) elevated heat transfer rate to the engine, (c) a relatively small share (about 2 kW_t) transferred to the engine from the thermal power generated by the combustor (around 13 kW_t), (d) conversion to electric power close to the upper limit of the engine, (e) limited impact of the Stirling engine on the fluidized bed behavior, for example, temperature. From the analysis of measured variables, the dynamics is dominated by the fast response of the Stirling engine, which rapidly reacts to the slow changes of the fluidized bed combustor regime: the dynamic response of the tested facility as a thermal system was slow, the time constant being of the order of 10 minutes.     

Thermally driven cooling coupled with municipal solid waste-fired power plant: Application of combined heat,cooling and power in tropical urban areas

Energy recovery from flue gases in thermal treatment plants is an integral part of municipal solid waste (MSW) management for many industrialized nations. Often cogeneration can be employed for both enhancing the plant profitability and increasing the overall energy yield. However, it is normally difficult to justify traditional cogeneration in tropical locations since there is little need for the heat produced. The main objective of this article is to investigate the opportunities and potentials for various types of absorption technologies driven by MSW power plants for providing both electricity and cooling. Results show that cogeneration coupling with thermally driven cooling is sustainably and economically attractive for both electricity and cooling production. The thermally driven cooling provides significant potential to replace electrically driven cooling: such systems are capable of providing cooling output and simultaneously increasing electricity yield (41%). The systems are also capable of reducing the fuel consumption per unit of cooling in comparison with conventional cooling technology: a reduction of more than 1 MW_fuel/MW_cooling can be met in a small unit. MSW power plant coupled with thermally driven cooling can further reduce CO₂ emissions per unit of cooling of around 60% as compared to conventional compression chiller and has short payback period (less than 5 years).     

Exergetic analysis of solid oxide fuel cell and biomass gasification integration with heat pipes

This paper presents an exergetic analysis of a combined heat and power (CHP) system, integrating a near-atmospheric solid oxide fuel cell (SOFC) with an allothermal biomass fluidised bed steam gasification process. The gasification heat requirement is supplied to the fluidised bed from the SOFC stack through high-temperature sodium heat pipes. The CHP system was modelled in AspenPlus™ software including sub-models for the gasification, SOFC, gas cleaning and heat pipes. For an average current density of 3000 A m⁻² the proposed system would consume 90 kg h⁻¹ biomass producing 170 kW_e net power with a system exergetic efficiency of 36%, out of which 34% are electrical.     

On policy instruments for support of micro combined heat and power

The performance of residential micro combined heat and power (micro-CHP)—a technology to provide heat and some electricity to individual dwellings—is generally dependent on the magnitude of household thermal energy demand. Dwellings with larger and more consistent thermal consumption perform well economically and achieve greater greenhouse gas emissions savings. Consequently, the performance of micro-CHP is dependent on the level of thermal insulation in a dwelling. Therefore, emerging policy approaches regarding energy use in the residential sector, which generally support both energy efficiency measures such as thermal insulation and adoption of micro-CHP, may inadvertently incentivise micro-CHP installation where CO₂ reductions are meagre or not cost-effective. This article examines this issue in terms of the changes in economic and environmental performance that occur for three micro-CHP technologies under changing patterns of residential thermal insulation in the United Kingdom. The results of this analysis are used to comment on the structure of policy instruments that support micro-CHP. It is found that simultaneous support for energy efficiency measures and micro-CHP can be justified, but care must be taken to ensure that the heat-to-power ratio and capacity of the micro-CHP system are appropriate for the expected thermal demand of the target dwelling.     

Exploring domestic micro-cogeneration in the Netherlands: An agent-based demand model for technology diffusion

Micro-cogeneration (micro-CHP) is a new technology at the household level, producing electricity in cogeneration with domestic heating, thereby increasing the overall efficiency of domestic energy production. We have developed a prototypical agent-based simulation model for energy technologies competing for demand at the consumer level. The model is specifically geared towards the competition between micro-CHP and incumbent condensing boilers. In the model, both technologies compete on purchase price and costs of usage, to which various (types of) consumers decide on the installation of either technology.