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A Novel Integration of Radiative Cooling into Photovoltaic/Thermal Panel in Buildings by Applying a Spectrally Selective Micro/Nano Coating

Periodic Reporting for period 1 - RC-PV/T (A Novel Integration of Radiative Cooling into Photovoltaic/Thermal Panel in Buildings by Applying a Spectrally Selective Micro/Nano Coating)

Reporting period: 2019-12-01 to 2021-11-30

Common solar photovoltaic/thermal (PV/T) collectors are unproductive at night and show low efficacy on hot days, while typical radiative cooling (RC) devices suffer from poor effectiveness in non-cooling seasons. In this context, this project proposes a novel idea of incorporating the RC scheme into a PV/T collector for combined solar energy and radiative cooling utilization. The developed novel collector, namely, RC-PV/T collector, runs as a solar PV/T collector to provide electricity and heat during the daytime and acts as an RC collector to harvest cooling energy during the nighttime.

Lighting, heating and cooling are essential for modern buildings, which has incurred a huge energy demand. In the EU, buildings consume around 40% of the total energy supply. To tackle this challenge, the EU has been endeavouring to implement effective policies and technologies for developing Zero Energy Buildings (ZEB) and is actively seeking collaboration with countries and personnel worldwide to promote its scientific excellence and societal impact. Therefore, it is of significance and urgency to develop effective technology for providing part of the energy consumed in buildings by green, renewable alternatives such as solar energy and radiative cooling energy. By integrating the RC-PV/T collector with building envelops properly, this tri-functional collector can supply domestic electricity and hot water throughout the year, provide hot air for space heating in winter daytime, and collect cold air for space cooling in summer nighttime, thereby showing a multifunction in renewable energy harvesting and good seasonal adaptability. The integrated RC-PV/T collector can also be more cost-effective than stand-alone RC collectors. Therefore, the RC-PV/T technology can contribute to decarbonization in buildings.

The overall objective of this project is to develop a novel tri-functional RC-PV/T prototype which is superior to the mono-functional PV or PT collector, RC device and dual-functional PV/T collector. The scientific objectives are: (1) to carry out micro/nano structural design, optimization and manufacturing of the spectrally selective RC-PV/T coating; (2) to develop a computerized mathematic model for the use in characterization and optimization of the RC-PV/T collector; (3) to conduct field experiments of the RC-PV/T collector under different working conditions; (4) to numerically evaluate the RC-PV/T collector for building integrated applications; (5) to carry out economic and environmental assessment of the building integrated RC-PV/T (BiRC-PV/T) system.
(1) An RC-PV/T coating which can meet the spectral requirements of daytime solar photovoltaic and photothermic conversions and nighttime radiative cooling has been prepared. The sample coating has a solar absorptivity of about 0.95 indicating an excellent solar PV/T efficiency. In addition, the coating shows high emissivity excluding the solar spectrum, including the most important “atmospheric window” range, indicating that it has great radiative cooling potential.
(2) A computerized model using MATLAB has been developed and used to characterize and optimize the overall performance of the RC-PV/T collector and system. The effect of some key structure parameters of the RC-PV/T collector and system, including the insulation thicknesses, initial water temperatures in the tank, packing factors, panel emissivity values, and tank volumes, has been studied. Furthermore, the annual performance of the RC-PV/T system has been investigated.
(3) Two types of RC-PV/T collectors and systems have been designed and manufactured to test the output performance of the RC-PV/T system in two cities (i.e. Nottingham and Hefei) with different climates and two different working modes (i.e. water heating/cooling and air heating/cooling).
(4) A building-integrated RC-PV/T system has been designed and studied using MATLAB and EnergyPlus software to evaluate the effectiveness of utilizing the RC-PV/T collectors in a single-family house in terms of electricity, heating, and cooling energy-saving.
(5) Economic and environmental assessments of the RC-PV/T system have been conducted and the performance comparison among the RC-PV/T, typical PV/T, and RC systems have been carried out. Results suggested that the RC-PV/T system shows the best economic and environmental performance among the three systems.

6 academic papers have been published/accepted in top journals during the project period. 4 more papers have been submitted to energy-related journals for possible publication. All these papers have acknowledged this MSCA project. As the scientific committee, keynote/invited speaker, or oral presenter, Dr. Hu has participated in 5 conferences/seminars/workshops. Aside from the above research studies, additional works highly related to this MSCA project have been done during the reporting period.
The developed RC-PV/T collector shows higher overall PV/T efficiency than the typical solar PV/T collector and presents greater cooling power than the typical RC devices. Therefore, the environmental benefit of the RC-PV/T collector in terms of the reduced CO2 emission is better than that of the typical PV/T and RC collectors. In addition, due to higher overall performance and better diurnal and seasonal adaptability, the cost payback period of the RC-PV/T collector is slightly shorter than the typical PV/T collector and significantly less than the stand-alone RC collector.
Photos of the RC-PVT collector
Schematic structure of the RC-PVT collector
Schematic diagram of the RC-PVT experimental system
Operative heating and cooling schemes of the building-integrated RC-PVT system during the days and n