Abstract
The daily increasing energy demand combined with global environmental issues has promoted the development of a photovoltaic thermal (PV/T) system with onsite electrical and thermal energy supply in buildings. However, suffering from massive radiative and convective heat losses, the overall efficiency of PV/T systems is relatively low (normally lower than 70%). In this paper, silica aerogel, a spectral selective porous material with high solar transmittance, extra-low thermal conductivity and low mid-infrared emissivity, is integrated into the upper surface of PV/T systems to reduce heat losses. Meanwhile, composite phase change material (PCM) with active heat-transfer enhancement strategies is integrated at the backside for accumulated heat dissipation. Subsequently, a three-dimensional numerical model based on the finite volume method and enthalpy-porosity method is established in the commercial software Ansys Fluent to simulate the dynamic performance. Dynamic heat-transfer mechanism is studied with solar energy harvesting analysis subjected to the typical weather conditions in Guangzhou, China. A series of comparative and parametric studies are performed for optimal structural design and operation. Results indicate that, the incorporation of aerogel and composite PCM with high thermal conductivity are beneficial to improve electrical and thermal efficiencies, while the integration of nanofluid shows negligible effects. The optimal results show the improvement on overall energy and exergy efficiencies by 40.2% and 1.5% in summer and by 42.4% and 0.43% in winter, together with annual CO2 mitigation of 104.1 kg/m2 and return on investment (ROI) of 0.169. This study provides a novel structural design and optimal operation on a novel aerogel-based PV/T-PCM system, together with guidelines on techno-economic-environmental performance improvement, promoting the solar energy harvesting for decarbonization transformations in buildings.
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