Fuel cell micro-CHP techno-economics: Part 2 – Model application to consider the economic and environmental impact of stack degradation

This article presents a literature review regarding the mechanisms of fuel cell degradation, accompanied by the reported range of observed degradation rates in experimental, demonstration and early commercial systems. It then synthesises and exploits this information to investigate the influence of degradation on the economic and environmental credentials of fuel cell micro-combined heat and power (micro-CHP) for the UK residential sector. The investigation applies a techno-economic model developed in the companion article designed to demarcate the key characteristics of commercially successful systems. Two distinct modes of degradation are examined; one proportional to power density in the stack, and the other proportional to thermal-cycling rate of the stack. It is found that limiting the power-density related degradation rate is very important from economic and environmental viewpoints, but thermal-cycling related degradation is less important when thermal energy storage is available because cycling can be avoided. Furthermore it is noted that techno-economic studies that ignore degradation can overestimate the marginal value of a micro-CHP system with respect to the conventional alternative by up to 45% and the CO₂ emissions reduction potential by up to 57%, for performance degradation rates of 2% per MW_eh output. This conclusion is noteworthy because most techno-economic analyses of fuel cells ignore degradation, potentially providing misleading results. Finally it is concluded that existing commercial degradation targets, such as the SECA targets, are appropriate for achieving marketable systems.     

Performance of an innovative 120 kWe natural gas cogeneration system

The paper deals with an innovative (120 kWe, 195 kWt) natural gas (NG) combined heat and power (CHP) system, at present under development, which has been set up at the FIAT Centre of Research (CRF), Turin, Italy. The main characteristics of the CHP system are: the use of an automotive derived internal combustion engine, a high part load electrical efficiency due to a variable speed operation strategy and an advanced exhaust gas after-treatment to meet the most stringent pollutant emission regulations.     

Micro-generation systems and electrolysers for refuelling private bi-fuel cars at home

An assessment is presented of the prospective use of micro-generation systems in conjunction with electrolysers and hydrogen stores for refuelling private bi-fuel (gasoline/hydrogen) cars with hydrogen. For a range of system sizes and three power source operating modes, predictions are made of the annual travel range on hydrogen and the associated CO₂ savings. A basic system (Mode A) operating solely from the output of a photovoltaic array was found to generate sufficient hydrogen to allow a passenger vehicle with a fuel efficiency of 8.5 l/100 km (33 mpg) to travel 613 km annually per kW of PV installed. An alternative system (Mode B) that permitted network electricity to contribute to hydrogen production, provided that the CO₂ emission factor of the generated hydrogen was half that of gasoline, enabled an annual travel distance of 772 km per kW of PV installed. A hybrid micro-generation system comprising a PV and micro-CHP system (Mode C), where the electricity that would otherwise be exported from the dwelling was diverted to hydrogen production, achieved a more consistent hydrogen production rate across the year. This resulted in a lower on-site storage requirement; when compared with Mode A, it provided an additional annual travel distance on hydrogen of between 1285 and 1833 km. A utility factor was employed to indicate the extent to which a system design could deliver a given daily driving distance on hydrogen across the year. High utility factors (>70%) were only achievable for modest daily driving distances (10–17 km) for the considered range of PV sizes (1.7–8.5 kW).     

Combined heat and power in industry and buildings

Combined heat and power (CHP) has huge potential to deliver energy savings and emissions reductions, and in many cases cost reductions too. But the market and regulatory framework is the key to delivering large-scale installations, and government has a poor record in delivering an appropriate framework.     

Effect of heat-saving measures on the CO2 savings attributable to micro-combined heat and power (μCHP) systems in UK dwellings

This paper considers the relationship between heat-saving and micro-combined heat and power (μCHP) technological interventions for reducing the carbon footprint of existing domestic dwellings within the UK housing stock. The relationship between the annual heat requirement of individual dwellings and the CO₂ savings attributable to different μCHP systems is investigated (by means of predictive modelling based on heat and power demand datasets recorded on a 1-min time base for nine dwellings). An assessment is made of the effects of various heat-saving measures upon the annual CO₂ savings predictions for candidate μCHP system implementations, when applied to ‘domestic building variants’ (as defined within the Carbon Vision TARBASE research programme). The increasing application of heat-saving interventions serves to reduce the CO₂ savings solely attributable to a μCHP system. The magnitude of this effect is a function of the μCHP system's electrical efficiency and electrical power output. For example, a 1 kW prime mover of 10% electrical efficiency is predicted to reduce annual CO₂ emissions by 72 kg CO₂ for a dwelling with an annual heat requirement of 11.9 MWh, but if the identified set of heat-saving measures is implemented first the demand falls to 5.0 MWh and the μCHP system will actually result in an emissions increase of 100 kg CO₂ p.a. By comparison, relative savings of 467 and 294 kg CO₂ p.a. are predicted if this dwelling is fitted with a 1 kW prime mover of 30% electrical efficiency. Still greater savings are predicted for higher power output systems of high efficiency, but a relatively large proportion of the generated electricity (44–75% depending on the heat and electrical demand of the dwelling) must then be exported.     

Cost-effective operating strategy for residential micro-combined heat and power

It is commonly assumed that dispatch of micro-combined heat and power (micro-CHP) should be heat driven, where the unit turns on when a heat load is present, and turns off or modulates when there is little or no heat demand. However, this heat led operating strategy—typical of large-scale CHP applications—may not be economically justified as scale decreases. This article investigates cost-effective operating strategies for three micro-CHP technologies; Stirling engine, gas engine, and solid oxide fuel cell (SOFC), under reasonable estimates of energy prices. The cost of meeting a typical UK residential energy demand is calculated for hypothetical heat led and electricity led operating strategies, and compared with that of an optimal strategy. Using central estimates of price parameters, and with some thermal energy storage present in the system, it is shown that the least cost operating strategy for the three technologies is to follow heat and electricity load during winter months, rather than using either heat demand or electricity demand as the only dispatch signal. Least cost operating strategy varies between technologies in summer months. In terms of environmental outcomes, the least cost operating strategy does not always result in the lowest carbon dioxide emissions. The results obtained are sensitive to electricity buy-back rate.     

家用热电联产技术

文章介绍了家用热电联产的概念、特点和优势，论述了斯特林发动机的原理和结构，分析了基于斯特林发动机的家用热电联产系统的关键技术、应用前景及主要障碍。     

Modelling of an HTPEM-based micro-combined heat and power fuel cell system with methanol

A fuel cell-based combined heat and power system using a high temperature proton exchange membrane fuel cell has been modelled. The fuel cell is fed with the outlet hydrogen stream from a methanol steam reforming reactor. In order to provide the necessary heat to this reactor, it was considered the use of a catalytic combustor fed with methanol. The modelling aims to fit the hydrogen production to the demand of the fuel cell to provide 1 kW_e, maintaining a CO concentration always lower than 30,000 ppm. A system with 65 cells (45.16 cm² cell area) stack operating at 150 °C and hydrogen utilization factor = 0.9 (with O₂/methanol ratio = 2 at combustor; H₂O/methanol ratio = 2 and temperature = 300 °C at reformer) needed a total methanol flow of 23.8 mol h⁻¹ (0.96 L h⁻¹) to reach 1 kW_e, with a system power efficiency (LHV basis) ca. 24% and a CHP efficiency over 87%. The ability to recycle the non-converted hydrogen from the fuel cell anode to the combustor and to use the heat produced at the fuel cell for obtaining hot water increased the global energy efficiency.     

Investigation of a 5 kW micro-CHP PEM fuel cell based system integrated with membrane reactor under diverse EU natural gas quality

This work investigates the techno-economic assessment of a 5 kW micro-cogeneration system based on membrane reactor and PEM fuel cell flexible towards different natural gas qualities. The flexibility of the system is evaluated for four typical natural gas compositions from different European countries featuring an average condition and three extreme cases. The optimal system design conditions are determined together with performance variation as function of NG composition and load. The sweep gas and vacuum pump are explored as options to reduce the membrane surface area, outlining the efficiency advantages of the former (41.21% vs. 39.24%). Simulations at partial load show that the electric efficiency increases until 60–70% of the load in both cases, then quickly drops. Micro-CHP performance are used as input to determine the specific system target cost (€/kW) based on a yearly energy and economic analysis. The first reveals that the primary energy savings is always positive outlining the environmental benefit of FERRET system application respect to the reference separated production. The target cost considering its application to two dwellings is around 2000 €/kW.     

Multi-criteria evaluation of residential energy supply systems

In this paper, we consider the selection of a residential energy supply system as a multi-criteria decision-making problem, which involves both financial and environmental issues. Specifically, we compare micro-CHP (micro-cogeneration) heating with traditional heating systems through an evaluation that accounts for: (i) the decision-makers’ subjective preferences, (ii) uncertainties in the performance of micro-CHP heating systems (which are partly caused by the lack of long-term operational experiences) and (iii) the context-dependency of life-cycle costs and environmental burdens of heating systems. Motivated by these considerations, we employ the PAIRS multi-criteria decision-making methodology that captures incomplete information by way of interval-valued parameters and provides support for sensitivity analyses, too. Our comparative analysis of alternative heating systems suggests that micro-CHP is a reasonable alternative to traditional systems, particularly from the environmental point of view.