Comprehensive comparative assessments of optimal distributed solar-energy systems for combined heat and power

In this paper, we present the results of techno-economic evaluations of a range of optimised solar energy systems for heat and/or power provision in buildings located in hot, solar-rich climatic regions. Hybrid photovoltaic–thermal (PVT), solar thermal (ST), photovoltaic (PV), and combined PV and ST (PV-ST) systems are assessed using annual simulations. The systems are evaluated for electricity generation, space heating, and domestic hot water supply for a hotel in Fayoum, Egypt, which serves as a representative case study. Multi-objective optimisations are conducted to maximise the annual energy-saving ratio while minimising the payback time. For each technology, four representative commercial products with a spread of performance and cost characteristics are selected for comparison. The results demonstrate that detailed techno-economic assessments are essential for identifying the most economical solution, as relying solely on systems with the lowest upfront cost can be misleading. Energetic analyses show that, for a constrained maximum installation area of 150 m², the best-performing PVT system outperforms the alternatives in terms of energy savings. Specifically, it achieves a maximum annual energy-saving ratio of 43 % across the available area. The economic assessments show that the proposed systems are profitable in the specified case study, i.e., payback < 25 years, if appropriately sized and operated. For the same energy savings, the PVT systems are the most profitable with the shortest payback time (min. 6.2 years) and lowest levelised cost of electricity (min. 0.028 $/kWh), thanks to their lower investment costs per unit displaced energy. The payback time and levelised cost PV-ST systems (min. 8.1 years, 0.036 $/kWh) are close to those of ST systems (min. 8.1 years, 0.035 $/kWh), while PV systems are less attractive in this context (min. 8.6 years, 0.041 $/kWh). From an environmental perspective, the CO₂ emission reduction potential of PVT systems is considerably higher (by 20–52 %) than those of all other systems, reaching a maximum of 31 tCO₂/year. The proposed systems, especially the PVT systems, show excellent decarbonisation potential and cost effectiveness, thus motivating further development for applications in buildings in such climate zones.