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Small-scale combined heat and power (micro-CHP or mCHP) plants generate heat in the process of localised electricity production that can usefully be captured and employed for domestic space and water heating. Studies of the relative merits of three alternative network-connected mCHP plants are reviewed based respectively on an Internal Combustion engine (ICE), a Stirling engine (SE), and a Fuel Cell (FC). Each plant will, in most cases, result in lower carbon dioxide (CO2) emissions, relative to those from the most efficient condensing boilers. In addition, they lead to operational cost savings for the consumer, depending on house type. However, their capital costs are presently more expensive than a conventional boiler, with the FC being prohibitively so. The ICE and SE variants display the greatest economic and environmental benefit. Nevertheless, the performance and costs associated with these innovative technologies have rapidly improved over the last decade or so. Comparisons are also made with heat pumps that are seen as a major low-carbon competitor by the United Kingdom (UK) Government. Finally, the potential role of micro-CHP as part of a cluster of different micro-generators attached to contrasting dwellings is considered. The review places mCHP systems in the context of the UK transition pathway to net-zero CO2 emissions by 2050, whilst meeting residential energy demand. However, the lessons learned are applicable to many industrialised countries. [ABSTRACT FROM AUTHOR]

• Techno-economic feasibility of a hybrid CHP system is considered in different house types. • Each hybrid CHP system is optimized individually for a different case. • The exergy efficiency for detached houses is highest among the three house types. • The proposed system achieves a CO 2 emission reduction rate ranging from 30% to 45%. • The hybrid CHP system achieves the lowest LCOE at 0.622 £/kWh for detached houses. In this study, a hybrid cogeneration system that combines photovoltaic-thermal (PV-T) collectors with a Stirling engine, and a battery-pack-based energy option is proposed for residential applications. The system's purpose is to fulfil the electrical and heating requirements of different types of houses in the United Kingdom, including detached, semi-detached and mid-terraced houses. This study includes a comprehensive assessment of the techno-economic feasibility and environmental impact of the proposed integrated energy system, after determining the appropriate sizing of the system's components for the three different house types. The exergy efficiency of the integrated system for detached houses (with a 1 kWe-Stirling engine plus 28 m2 of PV-T collector array) is found to be higher compared to that for the semi-detached and mid-terraced house configurations, with the highest efficiency of 22 %. In terms of economic performance, detached houses have the lowest levelized cost of electricity (0.622 £/kWh), levelized cost of heat (0.147 £/kWh), and levelized cost of total energy (0.205 £/kWh). Furthermore, the system demonstrates the maximum potential reduction in CO 2 emissions in detached houses. The achieved CO 2 emissions reduction rates for different house configurations fall within the range of 30 % to 45 %. The proposed hybrid cogeneration system shows promise as an effective and sustainable solution to meet the energy demands of various residential house types in the United Kingdom, offering improved efficiency, cost-effectiveness, and substantial reductions in carbon emissions for detached houses. [ABSTRACT FROM AUTHOR]

• A micro-CHP system integrating PVT collectors, a SE and energy storage is considered. • A transient model is developed to evaluate technoeconomic and environmental performance. • The primary energy savings and carbon emission reduction amount to 35% and 37%. • The discounted payback period of the system is 28 years. • The system has greater environmental benefits and a longer payback period than alternatives. This paper presents a comprehensive analysis of the energetic, economic and environmental performance of a micro-combined heat and power (CHP) system that comprises 29.5 m2 of hybrid photovoltaic-thermal (PVT) collectors, a 1-kW e Stirling engine (SE) and energy storage. First, a model for the solar micro-CHP system, which includes a validated transient model for the SE micro-CHP unit, is developed. Parametric analyses are performed throughout a year to evaluate the effects of key component sizes and operating parameters, including collector flow rate, storage tank size, SE micro-CHP flow rate, and battery capacity, on the energetic, economic and environmental performance of the proposed system using real hourly weather data, and thermal and electrical energy demand profiles of a detached house located in London (UK). The optimum component sizes and operating parameters are determined accordingly. The daily and monthly operating characteristics of the system are evaluated, and its annual performance is compared to those of a reference system (gas boiler plus grid electricity), as well as of other alternative solar-CHP systems including a PVT-assisted heat pump system and a standalone PVT system. The results indicate that the installation of such a system can achieve an annual electricity self-sufficiency of 87% and an annual thermal energy demand coverage of 99%, along with annual primary energy savings and carbon emission reduction rate of 35% and 37% relative to the reference system. Over 30 years of operation, the net present value (NPV) of the proposed system is £1990 and the discounted payback period is 28 years. The economics of the proposed system is very sensitive to utility prices, especially the electricity purchase price. Relative to the alternative solar systems, the proposed system offers greater environmental benefits but has a longer payback period. This implies that although the energy saving and emission reduction potential of the proposed system is significant, the initial/capital investment, especially of the SE CHP unit and the PVT collector array, are currently high, so efforts should focus on the cost reduction of these technologies. [ABSTRACT FROM AUTHOR]