• Energy Research

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 CO2 emissions in detached houses. The achieved CO2 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. This work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC) [grant numbers EP/T022949/1, EP/M025012/1, and EP/R045518/1], and by the Royal Society via an International Collaboration Award 2020 [grant number ICA\R1\201302].

Dairy farming is one of the most energy- and emission-intensive industrial sectors, and offers noteworthy opportunities for displacing conventional fossil-fuel consumption both in terms of cost saving and decarbonisation. In this paper, a solar-combined heat and power (S–CHP) system is proposed for dairy-farm applications based on spectral-splitting parabolic-trough hybrid photovoltaic-thermal (PVT) collectors, which is capable of providing simultaneous electricity, steam and hot water for processing milk products. A transient numerical model is developed and validated against experimental data to predict the dynamic thermal and electrical characteristics and to assess the thermoeconomic performance of the S–CHP system. A dairy farm in Bari (Italy), with annual thermal and electrical demands of 6000 MWh and 3500 MWh respectively, is considered as a case study for assessing the energetic and economic potential of the proposed S–CHP system. Hourly simulations are performed over a year using real-time local weather and measured demand-data inputs. The results show that the optical characteristic of the spectrum splitter has a significant influence on the system''s thermoeconomic performance. This is therefore optimised to reflect the solar region between 550 nm and 1000 nm to PV cells for electricity generation and (low-temperature) hot-water production, while directing the rest to solar receivers for (higher-temperature) steam generation. Based on a 10000-m2 installed area, it is found that 52% of the demand for steam generation and 40% of the hot water demand can be satisfied by the PVT S–CHP system, along with a net electrical output amounting to 14% of the farm''s demand. Economic analyses show that the proposed system is economically viable if the investment cost of the spectrum splitter is lower than 75% of the cost of the parabolic trough concentrator (i.e., <1950 €/m2 spectrum splitter) in this application. The influence of utility prices on the system''s economics is also analysed and it is found to be significant. An environmental assessment shows that the system has excellent decarbonisation potential (890 tCO2/year) relative to conventional solutions. Further research efforts should be directed towards the spectrum splitter, and in particular on achieving reductions to the cost of this component, as this leads directly to an increased financial competitiveness of the proposed system.

This paper presents a thermoeconomic analysis of a solar combined heating and power (S-CHP) system based on hybrid photovoltaic-thermal (PV/T) collectors for the University Sport Centre (USC) of Bari, Italy. Hourly demand data for space heating, swimming pool heating, hot water and electricity provision as well as the local weather data are used as inputs to a transient model developed in TRNSYS. Economic performance is evaluated by considering the investment costs and the cost savings due to the reduced electricity and natural gas consumptions. The results show that 38.2% of the electricity demand can be satisfied by the PV/T S-CHP system based on an installation area of 4, 000 m 2 . The coverage increases to 81.3% if the excess electricity is fed to the grid. In addition, the system can cover 23.7% of the space heating demand and 53.8% of the demand for the swimming pool and hot water heating. A comparison with an equivalent gas-fired internal combustion engine (ICE) CHP system shows that the PV/T system has a longer payback time, i.e., 11.6 years vs. 3 years, but significantly outperforms the ICE solution in terms of CO2 emission reduction, i.e., 435 tons CO2/year vs. 164 tons CO2/year. These findings suggest that even though the economic competitiveness of the proposed PV/T S-CHP system is not yet favourable when compared to the alternative gas-fired ICE-based system, the S-CHP solution has an excellent decarbonisation potential, and that if this is of importance in the wider sense of energy-system decarbonisation, it is necessary to consider how the higher upfront costs can be addressed.

In recent years, new materials and absorber configurations have been proposed to improve the performance of hybrid photovoltaic-thermal (PV-T) collectors. This work analyses the fluid flow and the energy performance of an uncovered water-based PV-T collector with a roll-bond thermal absorber. A detailed CFD model was developed and the results were compared with the experimental performance features provided by the PV-T manufacturer. The fluid flow results show uneven flow distribution among the roll-bond microchannels which leads to areas with larger PV cell temperatures and thus a lower electricity generation. The PV-T collector layers were also modelled using the energy transfer equations layer-by-layer. The model was run for several water inlet temperatures and water flow-rates to obtain the thermal performance curve. The results show that the electrical efficiency of the PV-T collector is 14.5–10.3% larger than for a PV-only system for water inlet temperatures of 20–30 °C, respectively. The developed CFD model reproduces accurately the thermal performance of the PV-T collector, with a maximum error of 6.5% for inlet water temperatures of 20–60 °C. Therefore, this model can be used with confidence to propose alternative designs that achieve a homogeneous temperature distribution in the PV layer and improve the overall PV-T collector performance.

Abstract This paper presents a comprehensive analysis of the energetic, economic and environmental potentials of hybrid photovoltaic-thermal (PVT) and conventional solar energy systems for combined heat and power provision. A solar combined heat and power (S-CHP) system based on PVT collectors, a solar-power system based on PV panels, a solar-thermal system based on evacuated tube collectors (ETCs), and a S-CHP system based on a combination of side-by-side PV panels and ETCs (PV-ETC) are assessed and compared. A conventional CHP system based on a natural-gas-fired internal combustion engine (ICE) prime mover is also analysed as a competing fossil-fuel based solution. Annual simulations are conducted for the provision of electricity, along with space heating, swimming pool heating and hot water to the University Sports Centre of Bari, Italy. The results show that, based on a total installation area of 4000 m2 in all cases, the PVT S-CHP system outperforms the other systems in terms of total energy output, with annual electrical and thermal energy yields reaching 82.3% and 51.3% of the centre’s demands, respectively. The PV system is the most profitable solar solution, with the shortest payback time (9.4 years) and lowest levelised cost of energy (0.089 €/kWh). Conversely, the ETC solar-thermal system is not economically viable for the sports centre application, and increasing the ETC area share in the combined PV-ETC S-CHP system is unfavourable due to the low natural gas price. Although the PVT S-CHP system has the highest investment cost, the high annual revenue from the avoided energy bills elevates its economic performance to a level between those of the conventional PV and ETC-based S-CHP systems, with a payback time of 13.7 years and a levelised cost of energy of 0.109 €/kWh. However, at 445 tCO2/year, the CO2 emission reduction potential of the PVT S-CHP system is considerably higher (by 40–75%) than those of the all other solar systems (254–317 tCO2/year). Compared to the solar energy systems, the ICE-CHP system has the shortest payback time (6.2 years), but its CO2 emission reduction (25 tCO2/year) is significantly lower. A high carbon price is beneficial for improving the cost-competitiveness of the solar energy systems, boosting its market penetration and helping to meet any carbon emission targets.

The cost competitiveness of an optimised solar combined heating and power (S-CHP) system based on a novel PVT collector is assessed in three different locations (Zaragoza, London and Athens). A series of sensitivity analyses are undertaken to evaluate the extent of the influence of the several economic parameters on the cost competitiveness of the proposed solar solution, and evaluate the need for financial incentives to boost the installation of this technology, in particular in the residential sector. From the different systems components’ costs, the results show that the PVT collector price is the one that influences more the system economics, as it responsible of the highest share of the total investment (~38%). High market discount rates and/or low inflation rates significantly and negatively affect the system cost competitiveness, leading to higher payback times (PBTs). Government incentives, if correctly applied, have the potential to improve the system economics in the short-term. However, in low latitude locations these incentives might not be necessary as high irradiance levels and energy prices lead to reasonable PBTs. Finally, the analysis of potential future scenarios, considering a combination of several economic parameters, demonstrates that the S–CHP system cost competitiveness is feasible in the short term Peer Reviewed