The sun and outer space are the ultimate heat and cold sources for the earth, respectively. They have significant potential for renewable energy harvesting. In this paper, a spectrally selective ...surface structure that has a planar polydimethylsiloxane layer covering a solar absorber is conceptually proposed and optically designed for the combination of photothermic conversion (PT) and nighttime radiative sky cooling (RC). An optical simulation is conducted whose result shows that the designed surface structure (i.e., PT-RC surface structure) has a strong solar absorption coefficient of 0.92 and simultaneously emits as a mid-infrared spectral-selective emitter with an average emissivity of 0.84 within the atmospheric window. A thermal analysis prediction reveals that the designed PT-RC surface structure can be heated to 79.1°C higher than the ambient temperature in the daytime and passively cooled below the ambient temperature of approximately 10°C in the nighttime, indicating that the designed PT-RC surface structure has the potential for integrated PT conversion and nighttime RC utilization.
•The principle of spectrally selective approaches for cooling solar cells is analyzed.•Radiative cooling is a significant method for solar cells to dissipate waste heat.•Full-spectrum thermal ...management of solar cells is a novel way to cool solar cells passively.•The cooling effect of full-spectrum thermal management is better than radiative cooling.•Appropriate material is the biggest challenge for this new cooling technology.
Waste heat is generated in solar cells during the daytime because they operate with a limited electrical efficiency. Moreover, the generated heat increases the solar cells’ operating temperature, and this has an adverse effect on their electrical efficiency. Therefore, numerous cooling methods have been developed to cool solar cells, such as forced air/water flow, hybrid photovoltaic/thermal system, and phase change material based photovoltaic application. Recently, a novel concept of changing the solar cells’ spectral response to both sunlight and thermal radiation has been proposed and developed to provide a passive cooling method for solar cells, which has drawn much attention from materials science to engineering fields. In this paper, the recent advancements of such a spectrally selective approach to passively cool solar cells, including radiative cooling of solar cells and full-spectrum thermal management of solar cells are reviewed, analyzed, and discussed from fundamental principles to detailed demonstration. Furthermore, the technical challenges involved in developing this new cooling technology are discussed. This paper is devoted to give a systematic introduction to a new passive cooling technology for solar cells by controlling the spectral property of solar cells, aiming to open a new opportunity for solar cells’ cooling.
Solar concentrating system is an effective way of combing solar energy with the building to satisfy the needs besides of electricity and hot water, also includes building heating, refrigeration, ...dehumidification, which require higher quality heat source. This paper put forward a novel static asymmetric lens-walled compound parabolic concentrator (ALCPC), which is composed of the mirror CPC and lens-walled structure, and can make full use of the total internal reflection and specular reflection. The optical performance of the ALCPC under the real application condition was established by software Lighttools®. Furthermore, the optimization structure by rotating the absorber away from the wall at some specific angles was also adopted for a wider scope applications. The results showed that the ALCPC has a large acceptance angle of 59° with highest optical efficiency of around 90% for most of the incident angles and has a relatively uniform flux distribution. In addition, annual performance analysis of the ALCPC was also done for Beijing (39°54’N, 116°23’E). The ALCPC as a static concentrator would be a good solution for the building south wall integration.
A novel photovoltaic/radiative cooling (PV/RC) hybrid system based on a selective plate is proposed. This system can generate electricity via diurnal PV conversion and obtain cooling energy by ...radiative cooling. We introduce a comprehensive photonic approach to simultaneously reduce impractical solar radiation absorption of the selective plate and enhance its thermal radiation for the hybrid system. Initially, we design a photonic structure made of 1D multilayer stack and 2D photonic crystal, which can selectively reflect solar radiation and actively radiate heat to the outer space while maintaining its solar transmission in PV conversion band (0.3–1.1µm). Then, we demonstrate that applying the photonic structure to a monocrystalline silicon solar cell can obtain a diurnal electricity output of 99.2Wm−2 and generate a nocturnal RC power by 128.5Wm−2, indicating 6.9% and 30.5% higher than those of a bare cell. In addition, the potential cooling energy obtained is far more in this structure than in existing RC emitters, including daytime RC emitter reported in a recent research. Results indicate that a comprehensive photonic approach can be used to design spectral selective structures for advancing the applications of exploiting solar energy harvesting and radiative cooling utilization.
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•A PV/RC hybrid system based on a spectral selective plate is proposed.•A comprehensive photonic approach is developed for the PV/RC plate.•A thermal simulation is conducted, and the performance of the system is analyzed.•The designed PV/RC plate shows a significant performance for PV and RC.
Concentrated photovoltaic (CPV) technology as a typical PV application is becoming popular due to its advantages of high conversion efficiency and low cost etc. However an important issue for CPV ...technology is the non-uniformity on the illumination and the temperature which can finally influence the overall electrical efficiency of solar cells. This study presents the feature of the non-uniform illumination and temperature, and reviews the cause and harm of the non-uniform illumination and temperature. Then the specific effect on cell parameters of different solar cells is analyzed, and finally the improving methods for reducing this negative effect on concentrating solar cells are proposed. This review will help researchers to learn the effect of the non-uniformity on the illumination and the temperature, and common improvement method, which will benefit CPV design and optimization.
•It summarizes the characteristics of non-uniform illumination and temperature distribution.•It analyzes the effect of non-uniform illumination and temperature distribution on PV.•It illustrates the improvement methods to overcome the negative influences.
Radiative cooling of solar cells has been proposed in recent years and has elicited much interest from fields of materials science to engineering science. Herein, a silica micro-grating photonic ...cooler is proposed, designed, and fabricated to radiatively cool solar cells. It is shown that the micro-grating silica can not only improve the thermal emissivity of the bulk silica to over 0.9 required for enhanced radiative cooling of solar cells but also exhibits a slight anti-reflection effect for sunlight. The outdoor experiment demonstrates that the proposed cooler can passively reduce the temperature of the commercial silicon cell by 3.6 °C when applied on the top of the cell under solar irradiance range from approximately 830 W m−2 to 990 W m−2, even though the cell already possesses a strong thermal emissivity of 0.67 and such a cooler slightly enhance the light trapping effect of the cell. This work provides an alternative way to design the solar-transparent infrared-emissive cooler for enhanced radiative cooling of solar cells and shows its cooling potential.
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•A silica micro-grating photonic cooler is proposed to radiatively cool solar cells.•Grating silica exhibits emissivity over 0.9 and simultaneously has anti-reflection effect for sunlight.•A temperature reduction of 3.6 °C is realized for the commercial solar cell with the grating silica.
•It summarizes the building integrated solar concentrating systems according to different functions.•It introduces the demands, types, applications and structures of the building integrated solar ...concentrating systems.•It presents prospects/directions/policies around the world towards the building integrated solar concentrating systems.
In the building sector, concerns towards the vast energy consumption has promoted the development of renewable energy technologies. In this regards, the solar concentration devices show a promising concept for building applications. However, the solar concentrators for application in buildings have many restrictions, which are different from the traditional solar concentrators. The main objective of this paper is to present a concise review on the building integrated concentrating devices, that have their own characteristics and multiple functions. This paper made a classification based on device’s functions, i.e. building integrated concentrated photovoltaic systems (BICPV), building integrated concentrating solar thermal (BICST) and building integrated concentrating solar daylighting (BICSD) and the combination of functions, i.e. BICPV/T, BICPV/D, BICST/D and BICPV/T/D. At the same time, this paper presented an elaborate introduction of the demands, types and applications of the building integrated concentrating devices and prospects/ directions/ policies about these technologies around the world. The review would provide important information for the actual engineering of building integrated concentrating devices.
Transparent envelopes account for a large amount of energy consumption of buildings, especially in hot climate regions. Glass is one of the main materials in transparent envelopes, so modifying the ...radiative properties of the glass is an alternative way for building energy saving. Here, a semi-transparent radiative cooling (ST/RC) glass was proposed by integrating the selective utilization of solar energy and passive radiative cooling. Comparative experiments based on two small-scale boxes were performed, which shows that the indoor air temperature of the box with the ST/RC glass is lower than that with the ordinary glass and the maximum temperature difference reached 16.4 °C, indicating that ST/RC glass can reduce the waste heat generated in the indoor environment. Besides, the daylighting level with the ST/RC glass is decreased by approximately 2/3 to support comfortable daylighting. Moreover, large-scale modeling of the building located in the Maldives was conducted and results show that the energy consumption of building could be saved by 21%–66.5% when the glass is modified to transmit visible light, reflect other solar irradiance, and emit like a blackbody, which indicates that the strategy of using light and thermal management of glass has the potential to reduce the energy consumption of buildings.
•A strategy of light and thermal management of the glass for building energy saving is proposed.•A semi-transparent radiative cooling (ST/RC) glass is proposed and fabricated.•The temperature of the indoor air with ST/RC glass can be reduced by over 16 °C.•The electricity saving ranges from 21% to 65 % under the light and thermal management strategy of the glass.
Photovoltaic-thermoelectric (PV-TE) conversion is a promising method for power generation, which converts solar power into electricity using the photovoltaic (PV) effect of solar cells and ...simultaneously generates electricity by the Seebeck effect of the thermoelectric (TE) device based on the waste heat of solar cells. Here, the power generation of the PV-TE device at night is experimentally demonstrated using radiative cooling that harnesses the cold of the universe directly. The PV-TE device is constructed by attaching a TE device on the bottom of the glass-covered PV module, with a heat sink stuck on the opposite side of the TE device. The open-circuit voltage of the TE device integrated into the PV-TE device was measured to be approximately 9 mV, indicating that the PV-TE device can definitely generate electricity from the darkness. Moreover, a new configuration of the PV-TE device for continuous power generation in the day and night is conceptually proposed for further consideration. In summary, this work proves the possibility of the PV-TE device for nighttime power generation, which could provide an alternative pathway for a wide range of nighttime and all-day power-consumed applications, such as lower power sensors and monitors.
•Nighttime power generation of the PV-TE device was experimentally demonstrated.•An average output voltage of the PV-TE device was measured as 9 mV in night.•A new configuration of the PV-TE device for continuous power generation is proposed.•This work provides an alternative pathway for nighttime and all-day applications.
•The feasibility of hybrid utilization of photovoltaic and radiative cooling was demonstrated.•Outdoor experiment and simulation study was conducted for performance evaluation.•Daily average ...electrical efficiency was measured as 14.9% on a mostly sunny day.•The net cooling power was evaluated as 72.9 W·m−2 on a mostly clear night sky.
The concept of hybrid utilization of daytime photovoltaic (PV) conversion and nighttime radiative cooling (RC), namely, PV–RC, was proposed and experimentally demonstrated. A PV–RC hybrid module with a size of 1380 mm × 720 mm was manufactured and characterized, and a corresponding PV–RC hybrid system was established. The PV–RC hybrid system can generate electricity at daytime by PV conversion and simultaneously obtain cooling energy by nighttime RC. PV performance of the hybrid system was tested on a mostly sunny day, and measured results showed that the daily average electricity output and electrical efficiency were 94.0 W·m−2 and 14.9%, respectively. Besides, nighttime RC performance of the hybrid system was measured on a mostly clear night sky and net cooling power of the PV–RC system was evaluated as 72.94 W·m−2 when temperature of the PV-RC panel was equal to ambient air temperature. Furthermore, a validated thermal analysis model was used for parametric study and results show that nighttime RC performance will be enhanced by dry atmosphere and low parasitic cooling loss. In summary, this work presented an experimental and simulation study for PV–RC hybrid system, which acts as a demonstration project of a real system. This study is a new attempt towards a real-world application of comprehensive utilization of solar energy and RC, which provides a good choice for cooling demand dominated buildings.
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