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Highlights • Atmospheric plate thermosyphon (APT) cooling solar cells was first proposed. • APT can reduce the temperature of PV panels without parasitic energy consumption. • The maximum temperature difference was less than 6 °C. • The heat transfer resistance at the evaporator is between 0.00486 and 0.02368 K/W. Abstract Since the heat pipe has no parasitic energy consumption, it is an important method for cooling the photovoltaic. In this paper, a novel type of atmospheric plate thermosyphon (APT) cooling system has been designed, which can be used for the heat dissipation of the single or low concentrated solar cells. In the experiments, the non-condensable gas (NCG) was collected by a gas reservoir. The coolant, ethanol, formed a liquid film on the porous medium and directly cooled the photovoltaic panel. The effect of various parameters such as heat flux density, tilt angle and inlet temperature have been studied. The results demonstrated that APT cooling system could effectively reduce the temperature of PV cells, and the higher heat flux density was, the shorter start-up time. The temperature of evaporator was uniform, and the larger inclined angle was, the greater surface temperature difference which maximumly was 5.6 °C. The thermal resistance at the evaporator was between 0.00486 and 0.02368 K/W. [ABSTRACT FROM AUTHOR]

Thermal management is a critical issue for normal operation of dense-array solar cells in high concentration photovoltaic system. A cooling method of direct-contact liquid film was experimentally and numerically investigated. In the experiments, deionized water was adopted as coolant and an electric heating plate was optimal designed to simulate dense-array solar cells. A two-dimension model was derived to present the temperature distribution on the surface of the simulated solar cells and flow characteristic of liquid film. The effect of various inlet parameters such as water temperature, inlet width and velocity had been numerical studied. The experiment results suggest that the surface temperature is well controlled under 120 °C at corresponding conditions, with concentration ratios ranging from 300 to 500X. The numerical results show that inlet width has a crucial effect on the liquid film thickness. The subcooled boiling state is a necessary condition to ensure cooling effect. High water inlet temperature is preferable for better heat transfer performance and temperature uniformity. The best optimizing inlet velocity, width and temperature are 1.06 m/s, 0.75 mm and 75 °C, respectively. [ABSTRACT FROM AUTHOR]

This paper presents an optimized ethanol phase-change immersion cooling method to obtain lower temperature of dense-array solar cells in high concentrating photovoltaic system. The thermal performances of this system were compared with a conventional active water cooling system with minichannels from the perspectives of start-up characteristic, temperature uniformity, thermal resistance and heat transfer coefficient. This paper also explored the influences of liquid filling ratio, absolute pressure and water flow rate on thermal performances. Dense-array LEDs were used to simulate heat power of solar cells worked under high concentration ratios. It can be observed that the optimal filling ratio was 30% in which the thermal resistance was 0.479 °C/W and the heat transfer coefficient was 9726.21 W/(m 2 ·°C). To quantify the quality of energy output of two cooling systems, exergy analysis are conducted and maximum exergy efficiencies were 17.70% and 11.27%, respectively. The experimental results represent an improvement towards thermal performances of ethanol phase-change immersion cooling system due to the reduction in contact thermal resistance. This study improves the operation control and applications for ethanol phase-change immersion cooling technology. [ABSTRACT FROM AUTHOR]

This paper presented a new method of cooling dense-array solar cells in high concentrating photovoltaic system by direct-contact liquid film, and water was used as working fluid. An electric heating plate was designed to simulate the dense-array solar cells in high concentrating photovoltaic system. The input power of electric heating plate simulated the concentration ratios. By heat transfer experiments, the effect of water temperatures and flow rates on heat transfer performance was investigated. The results indicated that: the average temperature of simulated solar cells was controlled well below 80 °C under water temperature of 30 °C and flow rate of 300 L/h when concentration ratio ranged between 300X and 600X. The maximum temperature difference among temperature measurement points was less than 10 °C, which showed the temperature distribution was well uniform. The heat transfer coefficient reached up to 11.91 kW/(m 2 ·K) under concentration ratio of 589X. To improve heat transfer performance and obtain low average temperature of dense-array solar cells, lower water temperature and suitable water flow rate are preferred. [ABSTRACT FROM AUTHOR]

A new hybrid system that integrated a photovoltaic (PV) panel with a solar photo-Fenton (SPF) reactor was constructed to treat wastewater and generate electricity for the first time. The decolorization and photovoltaic performances of the hybrid system were tested outdoors by discoloring three dyes: Acid Red 26 (AR26), Malachite Green (MG) and Reactive Blue 4 (RB4). Lab scale experiments also had been done to confirm the impact of temperature on the SPF process. The lab scale results show that SPF process was more efficiency for decoloring the different dyes, compared with dark Fenton. The SPF followed a pseudo-first-order reaction and the reaction rate constant was improved about 3.5, 4.5 and 0.61 times for AR26, RB4 and MG respectively as the wastewater temperature increased from 20 to 50 °C. The decolorization difficulty of the three dyes followed this order: MG > AR26 > RB4. The results of the hybrid systems tested outdoors show that 200 mg/L MG had achieved 98.6% color removal after 3 h of treatment at a low catalyst dose (Fe 2+ = 5 mg/L) under sunlight. For 100 mg/L MG, 99.3% color removal was observed after 70 min. The treatment time required for decolorization of AR26 and RB4 was more shorter. In the present of the water layer, the wastewater temperature was increased and that of the hybrid system was decreased. The average output power of the hybrid system was more than 12 W and sufficient to drive the system during all of the outdoor experiments. Our results suggest that the system could realize decolorization of different dyes and automatic operation. [ABSTRACT FROM AUTHOR]

A new cooling method by directly immersing the solar cells into phase-change liquid was put forward to cool dense-array solar cells in high concentrating photovoltaic system. A self-running system was built to study the feasibility of temperature control and the effect of bubbles generated by ethanol phase change under concentration ratio ranged between 219.8× and 398.4×. The results show that the cooling system is self-regulating without consuming extra energy and ethanol flow rate reaches up to 180.6 kg/(s·m 2 ) under 398.4×. The temperature of solar cells distributes in the range between 87.3 °C and 88.5 °C, the surface heat transfer coefficient of electric heating plate is up to 23.49 kW/(m 2 ·K) under 398.4×. The bubble effect on electrical performance of triple-junction solar cells is reported and the results show that I sc and P max decline 10.2% and 7.3%, respectively. A model based on bubble images illustrates that light loss at the interface between ethanol and bubble is the main reason to cut down the electrical performance. [ABSTRACT FROM AUTHOR]

The waste heat of automotive exhaust gas would be directly transferred into electricity by thermoelectric modules (TEM) because of the temperature difference between heat exchanger and water tank. For the vehicle thermoelectric generator (TEG), the electrical power generation was deeply influenced by temperature difference, temperature uniformity and topological structure of TEG. In previous works, increasing the difference of temperature would significantly enhance the power generation of TEG and inserted fins were always applied to enhance heat transfer in heat exchanger. However the fins would result in a large unwanted back pressure which went against to the efficiency of the engine. In current studies, in order to enhance heat transfer rates and to avoid back pressure increase, a heat exchanger containing cylindrical grooves (the depth-to-width ratio is 0.25) on the interior surface of heat exchanger was proposed. The cylindrical grooves could increase the heat transfer area and enhance the turbulence intensity, meanwhile there was no additional inserts in the fluid to block the flow. The surface temperatures of water tank and heat exchanger with three internal structures, such as grooved surface, flat surface and inserted fins, were studied by numerical simulation at each row of thermoelectric modules. The results showed that comparing to other structures, heat exchanger with cylindrical grooves could improve the TEG efficiency at a low back pressure. The influence of the channel height on the TEG performance was investigated and the TEG with a channel height of 8 mm showed the best overall performance. It was also found that a portion of heat exchanger uncovered with thermoelectric modules at the downstream section could make the upstream section hotter and make full use of each TEM. [ABSTRACT FROM AUTHOR]

The objective of the study is to construct and evaluate a fixed PV (photovoltaic) cell integrated with SODIS (solar water disinfection) system to treat drinking water and generate electricity under different climate through experimental and simulation methods. The photovoltaic and disinfection performances of the hybrid system were studied by the disinfection of Escherichia coli . The applicability of the system in Lhasa and Chennai was evaluated by analyzing the daily radiation and predicting the daily water temperature and the system electricity output. The results confirm that the temperature would dramatically enhance the SODIS process and shorten the disinfection time, when the water temperature was above 45 °C. The PV cell in the hybrid system could work under low temperature because of the water layer and the generated electricity was much more than the system consumption. The simulation results show that the days with maximum water temperature above 45 °C were more than 60% of whole year in Chennai. The generated electricity of the hybrid system was 49682.3 W h and 45615.9 W h a year in Lhasa and Chennai respectively. It was sufficient to drive the system of whole year. The number of days which realized drinking water treatment was 324 days in Lhasa and 315 days in Chennai a year. [ABSTRACT FROM AUTHOR]

In order to better apply direct liquid-immersion cooling (LIC) method in temperature control of solar cells in high concentrating photovoltaic (CPV) systems, electrical characteristics of GaInP/GaInAs/Ge triple-junction solar cells immersed in dimethyl silicon oil of 1.0–30.0 mm thickness were studied experimentally under 500 suns and 25 °C. Theoretical photocurrent losses caused by spectrum transmittance decrease from spectral absorption of silicon oil were estimated for three series sub-cells, and an in-depth analysis of the electrical performances changes of the operated cell in silicon oil was performed. Compared with cell performances without liquid-immersion, the conversion efficiency and the maximum output power of the immersed solar cell in silicon oil of 1.0 mm thickness has increased from 39.567% and 19.556 W to 40.572% and 20.083 W respectively. However, the cell electrical performances decrease with increasing silicon oil thickness in the range of 1.0–30.0 mm, and the efficiency and the maximum output power of the cell have become less than those without liquid-immersion when the silicon oil thickness exceeds 6.3 mm. [ABSTRACT FROM AUTHOR]

Abstract: Direct liquid-immersion cooling of concentrator solar cells was proposed as a solution for receiver thermal management of concentrating photovoltaic (CPV) systems. This research investigates the performance and long-term stability of silicon CPV solar cells operated in De-ionized (DI) water, isopropyl alcohol (IPA), dimethyl silicon oil, and ethyl acetate, respectively. Current–voltage characteristics of silicon CPV solar cells are measured. The presence of a thin liquid layer (1.5mm) results in an increase in the silicon CPV solar cells efficiency by 8.5–15.2% from the reference value. With an increase of the liquid layer thickness above the cell surface up to 9mm, due to more incident light is absorbed by the thicker liquid layer, the degree of the improvements to the cell efficiency decreases, which also depends to a noticeable degree on the liquid species. Further, more power output from the cells operated in liquids is achieved under higher concentration ratio. The long-term cell performance is discussed through three separate liquid immersion tests. The results from 1.5mm test demonstrate that degradation of cells performance immersed in IPA and in ethyl acetate mainly occurs by a decrease of Jsc and efficiency during 170days of test. But the long-term organic liquids immersion test (180days) without silicone sealant involved gives confidence of the reliable performance of the silicon CPV solar cells operated in liquids except for DI water. Therefore, the observed performance decay of the cells in 1.5mm test is due to the interaction between the silicone sealant and IPA or ethyl acetate. However, long-term immersion results from 9mm test (100days) show that the stable electrical performance of the cell is difficult to be achieved when immersed in DI water, which is consistent with the previous report. [Copyright &y& Elsevier]

Abstract: Liquid immersion cooling for a cylindrical solar receiver in a dish concentrator photovoltaic system has been experimentally verified to be a promising method of removing surplus heat from densely packed solar cells. In the present study, a three-dimensional (3D) numerical simulation model of the prototype was established for better understanding the mechanism of the direct-contact heat transfer process. With the selection of standard k–ε turbulent model, the detailed simulation results of velocity field and temperature characteristics were obtained. The heat transfer performance of two structural modules (bare module and finned module) under actual weather conditions was simulated. It was found that the predicted temperature distribution of the two structural modules at the axial and lateral direction was in good agreement with the experimental data. Based on the validated simulation model, the influence of liquid flow rate and module geometric parameters on the cell temperature was then investigated. The simulated results indicated that the cell module with fin height of 4mm and fin number of 11 has the best heat transfer performance and will be used in further works. [Copyright &y& Elsevier]

Abstract: Direct de-ionized (DI) water immersion cooling has been verified to be an effective method of managing the operating temperature of silicon solar cells under concentration. However, the stable electrical performance is difficult to be achieved. Possible factors from bare cell self, materials for tabbing cells were investigated in this study for understanding the degradation mechanism. Long term immersion results showed that no significant degradation on bare cells operated in DI water at 65°C. When cells were tabbed using lead-based solder and flux, the short circuit current (Isc ) of cells decreased with exposure time, notably under sunlight, but it was not observed for cell open circuit voltage (Voc ). The epoxy tabbed cells test also demonstrated that the tabbed cells without lead-based solder and flux involved were also found drop in Isc , but with slower rate. The presence of lead and tin black oxides on the lead based-soldered tabbed cells and red deposition on the epoxy tabbed cells confirmed the occurrence of galvanic corrosion. However, particular cleaning recovers the I–V towards its initial values for the former tabbed cells, and partial recovery for the latter tabbed cells, which indicates that the cells are not damaged after long-time DI water immersion. [Copyright &y& Elsevier]

Abstract: Solar heating and nocturnal radiant cooling techniques are united to produce a novel solar heating and cooling system. The radiant panel with both heating and cooling functions can be used as structural materials for the building envelope, which realizes true building integrated utilization of solar energy. Based on the natural circulation principle, the operation status can be changed automatically between the heating cycle and the cooling cycle. System performances under different climate conditions using different covers on the radiant panel are studied. The results show that the novel solar heating and cooling system has good performance of heating and cooling. For the no cover system, the daily average heat collecting efficiency is 52% with the maximum efficiency of 73%, while at night, the cooling capacity is about 47W/m2 on a sunny day. On a cloudy day, the daily average heat collecting efficiency is 47% with the maximum of 84%, while the cooling capacity is about 33W/m2. As a polycarbonate (PC) panel or polyethylene film are used as covers, the maximum heat collecting efficiencies are 75% and 72% and the daily average heat collecting efficiencies are 61% and 58%, while the cooling capacities are 50W/m2 and 36W/m2, respectively. [Copyright &y& Elsevier]

Abstract: It is generally recognized that BIPV (building integrated photovoltaics) has the potential to become a major source of renewable energy in the urban environment. The actual output of a PV module in the field is a function of orientation, total irradiance, spectral irradiance, wind speed, air temperature, soiling and various system-related losses. In urban areas, the attenuation of solar radiation due to air pollution is obvious, and the solar spectral content subsequently changes. The urban air temperature is higher than that in the surrounding countryside, and the wind speed in urban areas is usually less than that in rural areas. Three different models of PV power are used to investigate the effect of urban climate on PV performance. The results show that the dimming of solar radiation in the urban environment is the main reason for the decrease of PV module output using the climatic data of urban and rural sites in Mexico City for year 2003. The urban PV conversion efficiency is higher than that of the rural PV system because the PV module temperature in the urban areas is slightly lower than that in the rural areas in the case. The DC power output of PV seems to be underestimated if the spectral response of PV in the urban environment is not taken into account based on the urban hourly meteorological data of Sao Paulo for year 2004. [Copyright &y& Elsevier]

• Active phase change cooling system was firstly applied in flat PV cooling. • Uniform temperature distribution was obtained with the combination of porous media. • 19.32% and 18.40% increase in electrical power and efficiency was found with APC cooling. • With the same parasitic energy consumption, APC cooling was more efficient than conventional air cooling. • The system was analyzed from the viewpoint of both energy and exergy. The photoelectric conversion efficiency of solar cells was significantly influenced by its operating temperature which promotes the studies in thermal management for photovoltaic (PV). This paper introduced a novel cooling method based on porous media applied in PV panel for thermal management and efficiency enhancement. An active phase change (APC) cooling system has been designed and fabricated to explore the possibility of cooling the PV panel, and ethanol was considered as the working fluid. By laboratory test, average temperature, temperature distribution, electrical performance of the PV panel as well as energy and exergy efficiency were analyzed in detail. The results demonstrated that the average temperature of the PV panel can be better managed by the APC cooling method compared with the uncooled conditions at different irradiation levels. Besides, increasing the non-condensable gas flow rates has a positive effect on the temperature reduction and maximum generated power of the PV panel. The obtained three-dimensional temperature distribution map proved that the temperature distribution was well uniform with the maximum temperature difference less than 5 °C. The maximum specific power improvement and percentage improvement in power generation were 21.37 W/m2 and 19.32%, respectively. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Easy and lower cost substrate surface modification method is proposed. • Uniform-distributed porous structure benefit for heat transfer advancement. • Dense-grooved structure is beneficial for heat transfer enhancement. • These structure benefit for lower surface wettability and small bubbles generation. Abstract A new point from modifying substrate structure of solar cells is proposed based on direct-contact phase-change immersion cooling to solve the heat dissipation problem of solar cells worked under high concentration ratios. An electric heating plate (EHP) is carefully designed to simulate the heat flux of solar cells under high concentration ratios (184.2 X). Easy and lower cost ways of electrochemical etching and mechanical drawing bench are adopted to modify substrate surface of simulated solar cells. The result of thermal measurement shows substrate, undergoing electrochemical etching for 2 h (CE-2) or mechanical drawing bench using 800 mesh (MDB-800), owns the lower wall average temperature (85.36 and 85.7 °C) and higher surface heat transfer coefficient (3008 and 2970 W/(m2 K)). SEM results reveal that CE-2 or MDB-800 has uniform-distributed porous or dense-grooved structure. These special structures show better surface wettability and provide more active nucleus sites for small bubbles generation as well as higher bubbles update frequency according to our modified surface wettability and quantitative analysis results. Our study reveals that the advanced heat transfer performance is attributed to substrate structure with uniform-distributed porous or dense-grooved of CE-2 or MDB-800. This work gives a theoretical guidance for heat transfer advancement investigation involved in surface characteristic. [ABSTRACT FROM AUTHOR]

This study presents a new solar-driven hybrid system that integrated a photo-electrochemical reactor with a photovoltaics (PV) panel for azo dyes’ decolorization and electricity generation. Full spectrum of sunlight is utilized to optimize the color removal of Acid Red 26 (AR26) in this hybrid system. Persulfate (PS, S 2 O 4 2− ) was selected as the photochemical oxidant and Ti/IrO 2 -Ta 2 O 5 electrode was used as the anode. Experiments were made to evaluate the efficiency of decolorization and the performance of PV panels in different reaction conditions outdoors. The results showed that the synergistic effect of two processes was observed for the AR26 decolorization. Comparing with the solar/persulfate process or the electrochemical process alone, the complete color removal time by the hybrid system decreased up to 50% and 44.4% respectively. In this system, the water layer in the flow channel cooled PV panels by absorbing the far infrared spectrum of sunlight, and the increased temperature of wastewater from 7 °C to 16 °C enhanced the decolorization efficiency of AR26. Moreover, the generated electricity by PV panels could satisfy the energy demand of electrochemical oxidation. [ABSTRACT FROM AUTHOR]

To increase the photocatalytic reaction rate and make full use of electricity generated by photovoltaics (PV), a water purification system (SOL&PID) with solar and ultraviolet-light emitting diode (UV-LED) powered by a hybrid PV photocatalytic reactor was designed and tested in this paper. The SOL&PID system is based on Solar Water Purification and Renewable Electricity Generation system (SOLWAT). Photovoltaic and photocatalytic performances of SOL&PID system were evaluated in comparison with SOLWAT by the degradation of Acid Red 26 (AR 26) and 4-chlorophenol (4-CP) using suspended TiO 2 . To assess the directly-coupled performance between PV and UV-LED array, the power consumption percentage of UV-LED array from the maximum output power of PV was analyzed. The results show an adequate coupling between the UV-LED array and the photovoltaics. More than 92% of the maximum output power generated by PV modules is used to drive the LED array. The photocatalytic reaction rate constants in SOL&PID system increase respectively 29–37% and 31–78% during AR 26 and 4-CP experiments, in comparison with SOLWAT system. Besides, the SOL&PID system achieved lower solar module temperature and lower UV-LED pin temperature than the reference systems by the addition of flow channel. [ABSTRACT FROM AUTHOR]