Building integrated photovoltaic (BIPV) systems constitute a key concept for the realization of sustainable buildings. However, these systems have limited efficiency and durability due to their insufficient cooling capabilities. To overcome this drawback, it is necessary to maintain the operating temperature as low as possible. This study investigates the effectiveness of a passive low-cost strategy to improve the photovoltaic module (PV) performance of naturally ventilated BIPV systems by decreasing the module operating temperature. This strategy consists of inserting twisted baffles on the rear side of a PV module to enhance its cooling performance. A numerical investigation was performed using Computational Fluid Dynamics (CFD) simulations in order to explore the module surface temperature and its electrical efficiency. The effects of solar irradiance, the number and position of twisted baffles, and twist ratio have been investigated. The results revealed that the average temperature of the PV surface decreases with the increase of the number of twisted baffles (N), which leads to an improvement in the electrical efficiency. Indeed, the optimum performance enhancement is attributed to N = 15, and the corresponding PV temperature was decreased from 312.66 K to 310.15 K and from 348.42 K to 342.64 K for a solar irradiance variation from 200 to 1000 W.m(-2), resulting in an improvement of 1.21-3.36% in electrical efficiency compared to the case without inserts. Concerning the effect of the twist ratio, it is shown that the optimum electrical efficiency improvement is reached for the lowest twist ratio, which is in the range of 1.7-6.1% for solar irradiance range from 200 to 1000 W.m(-2).

Nowadays, building integrated photovoltaic (BIPV) systems are considered as a key concept for sustainable buildings. But these systems present some drawbacks which are mainly related to the negative effects of the solar cells temperature on these systems electrical efficiency and life time. An attempt to reduce this effect and improve the performance of BIPV is presented in this paper. The proposed solution consists of solar cells cooling systems application. Different structures of the cooling duct such as square, triangular and cylindrical are so studied and their effect on the performance of corresponding solar system is discussed. Results show that for all tested configurations, the water cooled duct can effectively reduce the surface temperature of the PV panel, allow a uniform distribution of this temperature and consequently improve the corresponding system performance. Regarding the electrical performance, the cylindrical duct showed the best cooling effect which consequently presented the best electrical efficiency for the considered solar system. However, the triangular duct was found to better improve the thermal and thus the overall efficiency of the BIPV.

The exploitation of solar energy using hybrid photovoltaic/thermal (PVT) system can represent a viable choice for the rising energy demand. Due to the wide range of PVT applications, many designs have been developed to improve the solar system global performance by cooling PV cells. The proposed system offers a practical heat gain in addition to the electrical efficiency enhancement. The integration of optical water filters (OWF) in photovoltaic systems could be an advantageous solution for their performance improvement. In this work, three different optical water filter models are evaluated using Cinematic fluid dynamics CFD modeling and their effect on the global system operating is discussed. Three shapes of OWF models are considered. Model (I) is an OWF under the PV cell. Model II is an OWF which passes over and under PV cells with separated inputs. Model III consists of a double pass mode OWF. Results showed that the maximum photovoltaic efficiency is corresponding to model (III) and reaches 12.08% at 14 h. The paper highlighted the different impacts associated with different OWF models. The results showed a significant increase in water outlet temperature. Consequently, an enhancement of the PVT system thermal efficiency is achieved. Finally, various water-based nanofluid (Al2O3, Cu, Ag, Au) optical filters are elucidated. The optimal photovoltaic performance is obtained by the water-Au nanofluid which allowed an electrical efficiency varying between 2% and 10%. Nanofluid filters have thus been shown to improve the performance of the CPVS concentrated photovoltaic system, not only because of the thermodynamic properties but also as a spectrally separated cooling system.

In this paper, various designs of concentrating solar water heater systems are studied. Our reference system is an integrated collector storage (ICSSWH). The proposed changes concern the concentrating technology by considering a dish instead of a CPC reflector, and the design of the concentrating solar water heater (CSWH) by considering a vertical instead of the horizontal mounting of the cylindrical storage tank in addition to the removal of the glass covering the system. Numerical results of the water temperature evolution and distribution show that the solar system which consists of a dish with a vertical storage tank performs better than the other systems. Indeed, in this solar system, the water temperature achieves 365 K while that in the ICSSWH does not exceed 328 K. The optimum storage tank diameter for the hottest day of the year is also evaluated for the chosen concentrated solar water heater and its operating is simulated for a typical day of each season. Results show that a tank diameter of 0.14 m allows the best hot water production throughout all the year. So CFD results show a satisfactory performance of the dish-based system with a vertical storage tank of 0.14 m diameter and prove the suitability of this point-focus solar collector for a solar water heater application through all the year.

In this paper, a parabolic trough collector (PTC) is studied, and its thermal performance is compared to that of an integrated collector storage solar water heater (ICSSWH). The effect of the concentration technology is so investigated using computational fluid dynamics (CFD) simulations. Results show that the PTC presents higher useful heat and, consequently, higher water temperature relative to the ICSSWH. It is also shown that its main disadvantage is its fast temperature drop and, thus, its high night losses. This drawback can be limited by covering the storage tank with a particular material layer. Phase change materials (PCM) are so introduced, and a PTC in which the storage tank is covered with a PCM layer is studied. Three different materials, respectively, durene, methyl bromobenzoate, and octatricontane, and three PCM radiuses, respectively, 0.03, 0.04, and 0.04 m, are considered. Simulation results show that the latent heat storage unit presents better thermal performance than the sensible one. Concerning the phase change, it is noted that for methyl bromobenzoate, the melting temperature that is relatively the highest in comparison with other PCM is not reached, and the phase change does not occur. The thermal behavior is similar to that in the sensible unit in which the water temperature increases, reaches its maximum value, and decreases next. However, for the other PCM, the melting temperature is reached, and the solid/liquid transition occurs. We notice that in an isothermal behavior during all this period and even after its end, the water temperature decreases very slightly during the rest of the night. Durene can be so selected as the most appropriate PCM for this PTC's design relative to octatricontane as it allows higher useful heat and lower night losses. The effect of the PCM's radius shows that the best performance corresponds to the lowest value, which is 0.03 m.

a hybrid Other investigations Tiwari, were interested to hybrid phοtοvοltaic-thermal systems cοοled by forced air circulation [6-9] . In this solar system; the heat produced the PV is the by ABSTRACT This paper presents a numerical investigation of a novel Optical Water Filter (ΟWF) integration in a Concentrator Photovoltaic System (CPVS). The ΟWF consists of a water layer placed on top of the PV module that serves as a solar spectrum splitter and a heat absorber. The water layer transmits the visible and a part of the infrared radiation, while filtering the ultraviolet and some of the infrared radiation which are not used by the PV cells. In this paper, numerical simulations were carried out for different filter’s nature and dimension. Five water layers are considered, respectively 1 cm, 2 cm, 3 cm, 4 cm and 5 cm. Results showed the significant effect of the water layer thickness on the PV cell temperature and proved that the best total efficiency is obtained for the water thickness range of 3 cm to 5 cm for which it exceeds 50%. The article pointed out the effects of the inclination of CPVS and the solar irradiation for the different water thicknesses. It is shown that the filter does not change the known results of the CPVS but it influences the gain in electrical efficiency which can reach an average value of about 3%. Moreover; a comparison οf the performance of different working fluids (propylene glycol, ethylene glycol, water and coconut oil) for the optical filter was performed and the results showed that water and coconut oil are found the best filters. The study presents also the concept of energy-saving efficiency to evaluate and to provide criterion fοr checking the overall performance of PVT systems. It is found that the energy-saving efficiency of optical filters with coconut oil exceeds 0.7 fοr higher thickness layers than 2 cm. selective οptical filters [30] . Otanicar studied οptical prοperties of fοur liquids (water, ethylene glycol, prοpyleneglycοl and therminοl VP-1) cοmmοnly used in sοlar energy applicatiοns [31] . Joshi alsο suggested different ideas of systems with a selectiοn of easily available transparent liquids (water, cοcοnut oil, Al 2 Ο 3 Nanοfluid, silicοnοil) [32] . Tο determine which filter shοuld be cοnstructed, we shοuld take care οffοur aspects: οptical prοperties (absοrptiοn transmissiοn spectrum), aging effect which is related to the effect of cοntinuοus expοsure to sunlight, thermal prοperties (heat capacity, viscοsity, flammability) and ecοnοmical aspects (easily available, inexpensive for large-scale cοmmercial applicatiοn).

In this article, the effect of concentration technology on the thermal performance of a solar water heating system is investigated. A three-dimensional numerical simulation of a parabolic trough collector (PTC) is carried out using the commercial software ANSYS. The performance of a line-focus concentration system is compared to that of an integrated collector storage solar water heater. The PTC provides more useful heat but has higher nighttime thermal losses. It is proposed to reduce nighttime energy loss by insulating the PTC storage tank. The effects of the insulation coverage strategy and medium are discussed. Numerical results show that the thermal insulation material significantly influences heat transfer. Indeed, addition of glass wool reduces heat collection during the day and improves heat preservation at night, while adding an air-filled glass tube increases heat transfer during the day and reduces nighttime thermal losses. The effect of tank insulation coverage is also investigated. This solar system performs best when the upper half of the tank is insulated. The maximum water temperature is 360.5 K, the overall thermal loss coefficient is 9.38 W/m2 K, and the nighttime thermal loss coefficient is 6.2 W/m K. The optimum PTC configuration is one in which the upper half of the tank is insulated by a 0.01 m-thick layer of air that is held in place by glass. This optimized system provides 29% more useful heat, a lower overall heat loss coefficient of 14.9%, and a lower nighttime heat loss coefficient of 62% than the non-insulated-tank-based PTC.

Flat plane and concentrating photovoltaic systems are the two major technologies for sunlight direct conversion into electricity. This work compares the energy generation potential of concentrating and non-concentrating PV systems under a summer clear sky day of the Tunisian Saharan city Tozeur. A fixed PV panel directly exposed to the solar irradiance is firstly studied. An asymmetric compound parabolic concentrator was then designed and used to focus the solar irradiance on this PV panel, which collects so the reflected sunlight. The electrical performance of these systems is experimentally characterized, and results indicate that the concentrating PV system performs better regarding the system output and electrical efficiency. Similarly, a financial analysis is performed and justify our solar installation choice. Two 3D CFD models describing the performance of these solar systems are then developed and experimental data are used for these models validation. Based on the good agreement between the numerical and experimental results, the performance of these two systems is evaluated of a cloudy day, the effect of the weather conditions is so discussed and the optimum design is evaluated.

In this paper, we propose a numerical study of a tubular solar collector with a U-tube. A three-dimensional numerical model is developed. It was first used in order to study the efficiency of the solar collector and to evaluate the validity of the developed computational fluid dynamics (CFD) model by comparison with experimental results from the literature. For the numerical simulations, the turbulence and the radiation were, respectively, modeled using the standard k–ε model and the discrete ordinates (DO) model. This numerical model was then used to carry out a parametrical study and to discuss the effect of selected operating parameters such as the fluid mass flow rate, the absorber selectivity, and the material properties. Numerical results show that with the increase of the working fluid flow rate from 0.001 kg/s to 0.003 kg/s, the efficiency of the solar collector is improved (from 30% to 35%). Numerical results also show that the filled-type evacuated tube with graphite presents a best result in comparison with those found using the copper fin tube (η increases from 54% to 64%). Finally, we noted that the use of a high selective absorber surface adds to better performance in comparison with the black absorber tube. This is mainly due to the radiation losses reduction.

In this paper, a three-dimensional computational fluid dynamics model is developed to predict the thermal and electrical performance of a water-cooled concentrated photovoltaic (CPV) system. Based on the good agreement between the numerical results and experimental data from literature, an attempt was made to improve this system performance. Indeed, as the developed model is able to predict the thermal behavior of the different system components, many hot spots were detected in the cell module. In order to avoid this disadvantage while promoting solar cell cooling, the number of water cooling pipes of the CPV module was first increased and then a rectangular channel was employed. Numerical simulation results indicate the potential of the different modified systems for reducing these hot spots and the CPV module temperature, thus providing increased electrical and thermal efficiencies. The optimum design, which presents a solar cell temperature of 315.15 K and respectively a thermal and combined (thermal plus electrical) efficiency of 74.2% and 83.5%, is also evaluated.

The thermal performance of an integrated collector storage solar water heater (ICSSWH) is numerically examined using the numerical software Fluent 6.3. As this solar system presents the disadvantage of its high night thermal losses, a new strategy helping to reduce these losses is proposed. A particular system in which the storage tank is covered with an outer glass tube is studied and a parametric study is conducted in order to evaluate the optimal air spacing gap between the water tank and the covering glass tube which minimizes this system's heat losses. A 3D computational fluid dynamics (CFD) model interpreting this modified system is so developed and its thermal performance is compared to that of the noncovered tank based ICSSWH. The analysis of these solar systems daily performance shows that the modified ICSSWH is able to generate more thermal output and presents the advantage of its lower thermal losses. Regarding the night operating, this covered tank based ICSSWH is shown more effective in retaining higher temperatures for longer period, resulting so in lower night thermal losses. Results also suggest that the best performance corresponds to the lowest air gap spacing (L = 0.005 m).

In this paper, an experimental study of a concentrating photovoltaic/thermal system is carried out in a spring day of the Tunisian Saharan city Tozeur and this solar system thermal performance is evaluated for two water mass flow rates. A 3D CFD model interpreting this photovoltaic/thermal system is then developed and used to predict the temperature of the different components of this hybrid system. Numerical results of the water outlet temperature and PVT system thermal efficiency are compared to the experimental data and a good agreement is seen proving the validity of the developed CFD model. The temperature contours are also presented for different instants of the day, helping to understand the different phenomenon related to the photovoltaic/thermal conversion of the solar energy using this concentrating system.

The thermal behavior of an integrated collector storage solar water heater (ICSSWH) is numerically studied using the package Fluent 6.3. Based on the good agreement between the numerical results and the experimental data of Chaouachi and Gabsi (Renew Energy Revue 9(2):75–82, 2006), an attempt to improve this solar system operating was made by equipping the storage tank with radial fins of rectangular profile. A second 3D CFD model was developed and a series of numerical simulations were conducted for various SWH designs which differ in the depth of this extended surface for heat exchange. As the modified surface presents a higher characteristic length for convective heat transfer from the storage tank to the water, the fins equipped storage tank based SWH is determined to have a higher water temperature and a reduced thermal losses coefficient during the day-time period. Regarding the night operating of this water heater, the results suggest that the modified system presents higher thermal losses.

In this paper, we propose a numerical study of an integrated collector storage solar water heater (ICS-SWH). Two numerical models in three-dimensional modeling are developed. The first one which describes a sensible heat storage unit (SHSU), allowing validating the numerical model. Based on the good agreement between numerical results and experimental data from literature, and as this type of solar water heater presents the disadvantage of its high night losses, we propose to integrate a phase change material (PCM) directly in the collector and to study its effect on the ICSSWH thermal performance. Indeed, a second 3D CFD model is developed and series of numerical simulations are conducted for two kind (myristic acid and RT42-graphite) and three radiuses (R = 0.2 m, R = 0.25m and R = 0.3 m) of this PCM layer. Numerical results show that during the day-time, the latent heat storage unit (LHSU) performs better than the sensible one when myristic acid is used as PCM. Regarding the night operating of this solar system, it is found that the LHSU is more effective for both PCMs as it allows lower thermal losses and better heat preservation. (C) 2013 Elsevier Ltd. All rights reserved.

Hybrid conversion of solar radiation, which allows simultaneous conversion of sunlight into thermal and electrical energy in the photovoltaic/thermal collector, is one of the most promising techniques of solar energy exploitation. In this study, low concentrating photovoltaic (PV) and photovoltaic/thermal (PVT) systems were designed and tested for a given spring climatic condition of the Tunisian Saharan city Tozeur. The system is basically an asymmetric compound parabolic photovoltaic concentrator. As this system's performance deteriorates with rising the solar cells temperature, we proposed to convert it on a hybrid one in order to improve its electrical efficiency and to recuperate simultaneously thermal energy. The comparison of these systems operating confirmed the improvement of the electrical performance of the combined PVT system and its acceptable thermal energy production. A computational fluid dynamics "CFD" model which interprets the PVT system was then developed and validated against the experimental results, proving the validity of the developed model use to identify numerically this system limitations and predict the possible improvements. (C) 2013 Elsevier Ltd. All rights reserved.