Due to the structure of photovoltaic/thermal (PV/T) collectors, non-uniform distribution of solar irradiance and PV cell temperature is inevitable. In traditional models, uniform or 1D distribution ...of irradiance and temperature were adopted widely to analyze the output performance, which cannot obtain an accurate description on the dynamic behavior of the PV/T system. Thus, a novel 2D irradiance-temperature coupling model for the performance characterization of flat-plate PV/T system was proposed in this study. Results suggest that the non-uniform distribution of irradiance exerted a dramatic effect on photovoltaic efficiency but a modest influence on photothermic efficiency. As the ratio of frame shadow on PV cells changed from 0% to 80%, the photovoltaic efficiency decreased by 42.26% and the photothermic efficiency increased by 9.81%. By contrast, the flow rate had a stronger effect on the photothermic efficiency than the photovoltaic efficiency. As the flow rate increased from 0.005 kg/s to 0.03 kg/s (velocity changing from 0.0112 m/s to 0.0674 m/s in the copper tube), the photovoltaic efficiency increased from 9.46% to 9.54% and the photothermic efficiency improved from 32.62% to 35.83%. Moreover, a parallel electrical circuit layout has a greater total output with a value of 2594.99 MJ/m2.
•A 2D irradiance-temperature coupling model for PV/T modules is developed.•Influences of non-uniform irradiance distribution and temperature were confirmed.•Non-uniform distribution of irradiance affects the PV efficiency more dramatically.•Effect of different electric circuit layouts on the PV/T module was studied.•The model is expected to give a more objective description on PV/T performance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Photovoltaic/thermal (PV/T) hybrid utilization is a promising method for efficient solar energy harvesting. However, a low operating temperature is required for photovoltaic (PV) conversion to make ...PV efficiency at a high level, while a relatively high operating temperature is preferred for photothermal (PT) conversion to improve the quality of collected heat, which causes a temperature conflict and induces certain limitations on the efficiency and scale promotion of PV/T. Herein, a novel PV/T system is proposed based on the spectral beam splitting and serial thermal circuit to decouple the power generation and heat collection, which aims to reduce the intrinsic temperature conflict and improve efficiency. A combined thermal-electrical model of the PV/T system is developed and parametric analysis is performed. Predicted results show that the temperature of the solar cells is 7.7 °C lower than the outlet water temperature in the novel PV/T system, demonstrating the temperature-decouple effect. Compared with the traditional PV/T system, the outlet water temperature is 3.9 °C higher and the solar cell temperature is 9.4 °C lower in the proposed system, showing a comprehensive efficiency improvement of 17.9%. In summary, this work provides an alternative way for efficient PV/T utilization by decoupling the operating temperature of PV and PT processes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A novel vacuum PV/T collector has been proposed to improve overall efficiency.•A small-scale vacuum PV/T collector is fabricated for experimental demonstration.•The vacuum PV/T collector can ...decrease the heat loss by 16.08% compared with the air-gap PV/T collector.•Annual thermal energy gain of the vacuum PV/T is increased by 124.88%.
Photovoltaic/thermal (PV/T) technology can generate electricity and heat simultaneously and improve solar energy harvesting efficiency. However, flat-plate PV/T collectors have strong heat loss in cold conditions and the collected heat is low-grade thermal energy, which limits the practical application of the PV/T collectors on a large scale. Herein, the vacuum environment is introduced to the flat-plate PV/T collector, conductive and convective heat loss are blocked, improving the efficiency and operating temperature of the PV/T collector. In this paper, a novel design of the vacuum PV/T collector has been proposed and fabricated, which maintains both the upper and lower space of the absorber in a vacuum state without additional glass cover causing energy loss. Performance comparison between the vacuum PV/T collector and the air–gap PV/T collector has been conducted, demonstrating that the vacuum condition can decrease the heat loss coefficient by 16.08%. In addition, a combined thermal-electrical mathematical model is constructed and validated. The predicted results reveal that the annual thermal energy outputs of the vacuum PV/T collectors without and with ideal low emissivity coating are 124.88% and 346.58% higher than that of the air–gap PV/T collector when the operating temperature is 50 °C. In summary, the vacuum PV/T collector exhibits great potential in improving thermal performance while slightly reducing the output of electrical energy. This work contributes to extending the working time of the PV/T collector and guides the design of the new generation of highly efficient PV/T collectors.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Photovoltaic/thermal (PV/T) collectors can simultaneously generate electrical and thermal energy, but the overheating phenomenon often occurs in hot seasons, leading to poor electrical performance ...and shortened lifetime in PV modules. In this study, a thermal regulation strategy by switching the backplate is introduced into the conventional PV/T collector, which can adapt to different heat demands in different seasons by opening or closing the backplate, achieving better electrical performance in summer without affecting winter heating. Comparative experiments between the switchable and conventional PV/T collectors are conducted to observe the performance advantage. The results show that the maximum stagnation temperature of the switchable PV/T collector is 18.1 °C lower than the conventional one, which relatively improves electrical efficiency by 8.6%. Subsequently, an annual performance prediction by a validated mathematical model illustrates that the thermal performance of the switchable PV/T collector in the heating season is comparable to the conventional PV/T collector, but the electrical efficiency can be increased by 6.26% in the non-heating season. Moreover, further study shows the proposed strategy has efficient regulation in other types of PV/T collectors similarly, demonstrating the positive role of switchable backplate technology in enhancing electrical efficiency and addressing the seasonal contradiction in PV/T collector operation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A silica aerogel-based photovoltaic/thermal (PV/T) collector is proposed.•The aerogel-based PV/T collector significantly suppress radiation heat loss.•The thermal performance of the aerogel-based ...PV/T collector is enhanced by 46%.•The performance of aerogel-based PV/T is equivalent to that of spectrally selective PV/T with a thermal emissivity of 0.1.•The exergy efficiency of the aerogel-based PV/T collector is increased by16.2%.
Photovoltaic/thermal (PV/T) collector can convert incident sunlight into electrical and heat energy simultaneously. However, compared with the solar thermal collector, the radiative heat loss of the PV/T absorber is larger since the spectrally selective PV/T absorber is difficult to design and fabricate after introducing PV cells, which leads to lower thermal efficiency. Thus, an approach that can reduce the radiative heat loss of the PV/T collector without the requirement for spectrally selective PV/T absorber is emergently needed. Here, a novel aerogel-based PV/T collector is proposed to suppress radiative heat loss and improve efficiency by introducing the silica aerogel that is highly transparent to sunlight and opaque to infrared light, as well as ultra-low effective thermal conductive into the PV/T collector. A numerical model is established to evaluate the performance of the aerogel-based PV/T collector, and the results present that the heat loss of the PV/T collector at the operating temperature of 70°C can be dramatically reduced by approximately 75% after using the silica aerogel and the thermal efficiency can also be increased by 46%. Moreover, a parametric study is conducted to investigate the influence of solar radiation, ambient temperature, and emissivity of the PV/T absorber on the performance of the aerogel-based PV/T collector. This study is devoted to exploring a new method to suppress the radiative heat loss of the PV/T collector and enhance its solar harvesting performance correspondingly, which gives a reference for the design of high-performance PV/T utilization.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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