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Optical splitting film-based spectral splitting concentrated photovoltaic thermal system (CPV/T) utilises the full spectrum of sunlight to obtain more useful energy and enables the PV cells and thermal absorber work at different temperature. In this work, an optical splitting film-based spectral splitting CPV/T under concentrated solar irradiance was devised and set up to utilise the full spectrum sunlight and decrease the temperature of CPV cell. The reflection bands of SiO2/TiO2 interference thin film matched well with the spectral response bands of the CPV cell, which could avoid the infrared light to heat CPV cell. Under concentrated solar irradiation, temperature of CPV, photoelectric and photothermal conversion efficiencies were tested. The overall energy and exergy conversion efficiencies were theoretically analysed. The results showed that the CPV cell with optical splitting film could reduce by 11.0 K, and power generation and photoelectric conversion efficiency of the CPV cell could improve by 9.4% and 1.3% under concentrated solar irradiation, respectively. The overall energy and exergy conversion efficiency of proposed system could achieve 18.85% and 14.61%, i.e., 5.8% and 1.5% higher than those of the CPV system without film under concentrated solar irradiation, respectively.

As ZnO nanoparticles had the advantages of high thermal conductivity and low cost, the possibility of using ZnO nanoparticles in spectral splitting photovoltaic/thermal (PV/T) systems was initially studied from the perspective of optical properties. Water–ZnO and glycol–ZnO nanofluids were prepared via a two-step method and used for model validation and stability testing. The scheme employed to investigate the optical properties and radiative transfer of the nanofluids was developed using Mie scattering theory combined with the Monte Carlo ray tracing (MCRT) method. The overall effective spectral transmittance coefficients of PV cells were utilized for comprehensive evaluation of the spectral transmittances of the nanofluids in spectral splitting PV/T systems. The overall effective spectral transmittance of a PV cell water-ZnO nanofluids was 21.54% higher than that those of cells containing water–polypyrrole and water–Cu9S5 nanofluids, respectively. The effects of the nanoparticle diameter, mass concentration and the optical length of the nanofluid on the spectral transmittance of glycol–ZnO nanofluid were also investigated.

The ultrasonic-assisted solar photochemical splitting of water had been explored in recent years to enhance hydrogen production efficiency. In this study, a photon-absorption-based study was conducted to investigate the mechanism of the ultrasonic-assisted solar photochemical splitting of water. An elaborate test bench for temperature-controlled, ultrasonic-assisted solar photochemical water splitting was designed, set up, and tested. A comparison of the hydrogen production between the ultrasonic-assisted and conventional solar photochemical splitting of water was carried out. The effective nanoparticle size before and after ultrasonic vibration, as well as after solar photocatalysis, was analyzed. Furthermore, the spectral absorptivity of the nanofluids before and after ultrasonic vibration, as well as after solar photocatalysis, was investigated by both experimental and numerical methods. The investigation indicated that the improved particle dispersion in the solution prepared by ultrasonication allowed the absorbance of more incoming sunlight. The amount of hydrogen produced by the ultrasonic-assisted hydrogen production was 3.45 times that of conventional solar photochemical splitting of water without pre-ultrasonicated. Besides, an effective spectral absorptivity coefficient was proposed as a modified measure of spectral absorptivity. In addition, the optimal particle diameter was optimized using the Monte Carlo ray tracing method to identify the best light absorption performance.

Photocatalysts currently in use are only able to utilize very small part of the solar spectrum that arrives at the earth's surface (mainly ultraviolet light). Most of the photons that are not absorbed by the photocatalysts are converted to heat. However, there is no consensus on the effect of reaction temperature on photo-thermo chemical synergetic catalysis, which has been studied herein using experimental investigations combined with thermodynamic analysis. An elaborate photo-thermo chemical reaction test rig was initially designed and set up that can test experimental variable while the other influence factors were kept constant. The effects of ultrasonic and operation temperature on Pt/TiO2 particle cluster distribution during the photo-thermo chemical synergetic catalytic water splitting process were analyzed by an upright microscope for the first time. The results indicated that the H2 production rate varies with reaction temperature, and 55 °C is the optimum temperature for the photo-thermo chemical synergetic catalytic water splitting process studied here. A maximum H2 production rate of 11.934 mmol/(h g) could be achieved using a classical Pt/TiO2 catalyst, when operating under the optimum reaction conditions.

Perovskite solar cell had the advantages of low cost, high efficiency and flexibility, which had significant development potential. Reducing the thickness of the perovskite absorber layer was a practicable method to reduce the content of toxic lead elements, however, an insufficient light absorption and low photocurrent were usually observed due to the shorten optical path length. In this study, SiO2 nanophotonic structure was introduced and designed by electromagnetic theory to allow the perovskite absorber layer to become thinner, while did not decrease its light absorption and photocurrent. The geometrical parameters of SiO2 nanophotonic structure was optimized by finite-difference time-domain (FDTD) method combined with particle swarm optimization algorithm to obtain the largest light absorption enhancement. When SiO2 nanophotonic structure was used, the perovskite solar cell with a 200 nm thickness perovskite absorber layer can generate the same photocurrent as the planar perovskite solar cell with a 300 nm thickness perovskite absorber layer, which can reduce toxic lead elements of perovskite material as high as 33%. The feasibility of applying SiO2 nanophotonic structure to different perovskite solar cells was further investigated.

Radiative cooling is a passive means of cooling that does not require the consumption of additional energy and has broad application potential. While experimental spectral measurements have been conducted, the daylighting of buildings, photovoltaic (PV) cells, and vehicles has seldom been considered. Here, we use spectrum-selective coatings to resolve the competing demands of daylighting (or appearance) and radiative cooling. A simple liquid blade-coating method that was inexpensive, convenient, and scalable was used to achieve radiative cooling with ultrahigh transmittance in visible light and excellent cooling performance. Resonant polar dielectric SiO2 microparticles with optimized volumetric fractions and diameters were randomly mixed into an acrylic resin and manually bladed at room temperature with natural evaporation drying. Spectrometry results showed that a mean visible light transmittance >91.3% was achieved, which was much higher than reported in previous studies; a mean emittance >93.7% within the “atmospheric window” was also reached. Over four days testing of a silver-plated aluminum sheet in a populous area at sea level, we achieved a maximum sub-ambient decrease in temperature of ~8.7 °C and a maximum cooling power of 108.49 W/m2.

Nanofluid-based spectral splitting concentrating photovoltaic thermal (CPV/T) system enables photovoltaic (CPV) cells and thermal absorbers to operate at different temperatures and realizes the utilization of full-spectrum sunlight. It is important to find one kind of low cost nanofluid that can be applied to nanofluid-based spectral splitting CPV/T system. In this study, the feasibility of using cost-effective glycol-ZnO nanofluid in spectral splitting CPV/T system was experimentally verified. A two-axis sun-tracking nanofluid-based spectral splitting CPV/T system was designed and fabricated. The solar energy conversion efficiency correlation coefficient was utilized to compare the thermodynamic performance of glycol-ZnO nanofluid-based spectral splitting CPV/T system with those of water-polypyrrole and water-Ag-SiO2 nanofluid-based spectral splitting CPV/T system. The effects of ZnO nanoparticles concentration in glycol-ZnO nanofluid on thermal and electrical performances were investigated. The cost comparisons of different types of nanoparticles were also conducted. The results indicated that the correlation coefficient of glycol-ZnO nanofluid-based spectral splitting CPV/T system was 0.218 and 0.05 higher than those of water-polypyrrole and water-Ag-SiO2 nanofluid-based spectral splitting CPV/T system, respectively. The cost of ZnO nanoparticles was 0.13%, 0.08% and 0.17% of cost of Au, Ag and polypyrrole nanoparticles, respectively.