• Energy Research

Abstract The operating temperature rise and the dust accumulation on the front side of solar panels especially in arid and semi-arid desert areas is a major issue that causes low performance and damage to photovoltaic cells. This experimental investigation aimed to improve the solar panel electrical performance mounted in new hybrid system PV/T Bi-fluid that combines both active cooling and self-cleaning technique simultaneously. This new hybrid system was actively cooled from the backside of the PV module by forced air circulation, while its front side was cooled and cleaned by flowing water. The impact of the operating temperature and global solar radiation intensity on the PV module output voltage, electrical current, electrical power output, and electrical efficiency was evaluated experimentally. Experimental results showed a decreasing linear relationship between electrical efficiency and the increase in PV module’s temperature i.e. reference case without cooling. Up to 15 °C was the average temperature decrease observed in the PV module mounted in the new hybrid system, compared to the reference case. Under the same operating conditions, and at the peak of the global solar irradiation i.e. G = 650 W/m2, an improvement of about 5.7% in electrical efficiency compared to the reference case was obtained. The average overall energy efficiency was found to be 85.3%, while the average exergy efficiency was roughly 14.7%. Several correlations have been proposed for calculation of electric current intensity, electrical energy output, and electrical efficiency, as a function of the average PV module temperature or global solar radiation intensity. A comparison between the reference case and the new hybrid PV/T Bi-fluid system was proved that this new hybrid system was very effective to maintain the electrical efficiency of the PV module at its highest record.

Abstract Thermal conductivity of nanofluids is a key thermophysical property, which depends on concentration and size of nanoparticles, temperature and thermophysical properties of the base fluid. Over last decades, several works have been done on the thermal conductivity of nanofluids while a number of numerical and theoretical models have been proposed. However, most of these models were not able to predict appropriately the thermal conductivity for a variety of nanofluids. In the present paper, using the Vaschy–Buckingham theorem, new correlations for predicting the thermal conductivity of nanofluids were developed based on the existing experimental data. The new correlation proposed took into account the Brownian motion, the variation of volume fraction, the temperature and the size distribution of nanoparticles. The expression developed successfully predicts the thermal conductivity of a variety of nanofluids, TiO2, Al2O3, Al, Cu, Fe, MWCNTs/EG, Al2O3, SiO2/methanol, TiO2, Al2O3, CuO, MWCNTs/water, Al2O3/radiator coolant, Al2O3/R141b, Al, CNTs/Engine Oil, and Cu/Therminol 66, and suits the data with a mean and standard deviation of 2.74%, 3.63%, respectively. The correlation was derived from 196 values of nanofluids thermal conductivity, 86% of them are correlated within a mean deviation of ±5%, while 98% of them belong to an interval of ±10%. Moreover, the proposed correlation has been tested on 284 values of thermal conductivity of different nanofluids, and the predicted values have been found in excellent agreement with the experimental ones with a mean deviation of 3%. The mean deviation between the correlated and the tested point found to be 2.94%. The present correlation will be a good tool for engineers in preparing the nanofluid for different applications in heat exchangers and thermal solar collectors.

Abstract Most of the incident solar energy on a PV panel is converted into waste heat. This consequently reduces the efficiency of PV system. Therefore, if certain portion of this waste heat can be utilized adding a thermoelectric generator (TEG) in the PV panel endowed by an efficient cooling system, the output performance of the system can be improved significantly. In this study, a new configuration of nanofluid-based PV/T-TEG hybrid system with cooling channel is proposed to convert certain portion of waste heat to electrical energy in order to improve the overall efficiency of hybrid system. Thus, the nanofluid acts as a coolant and absorbs the heat from the back side of TEG module raising its gradient of temperature, as well as the overall performance of the system. Through a numerical modelling approach, performance of the proposed innovative design has been investigated and compared with the conventional solar-harvesting technology systems. At the optimum value of solar concentration C , and maximum operating temperature of 35 Â ° C , the obtained results reveal that the electrical energy in NCPV/T-TEG configuration has been found higher by 10 % , 47.7 % and 49.5 % against NCPV/T, CPV and CPV/TEG-HS systems, respectively. Overall, the proposed design of NCPV/T-TEG hybrid system has potential for further development in high-concentration solar systems.

Abstract Photovoltaic/thermal (PV/T) solar systems, which produce both electrical and thermal energy simultaneously, represent a method to achieve very high conversion rates of sunlight into useful energy. In recent years, nanofluids have been proposed as efficient coolants and optical filter for PV/T systems. Aim of this paper is to theoretically analyze the life cycle exergy of three different configurations of nanofluids-based PV/T hybrid systems, and compare their performance to a standard PV and PV/T system. Electrical and thermal performance of the analyzed solar collectors was investigated numerically. The life cycle exergy analysis revealed that the nanofluids-based PV/T system showed the best performance compared to a standard PV and PV/T systems. At the optimum value of solar concentration C , nanofluid-based PV/T configuration with optimized optical and thermal properties produces ∼1.3 MW h/m 2 of high-grade exergy annually with the lowest exergy payback time of 2 years, whereas these are ∼0.36, ∼0.79 MW h/m 2 and 3.48, 2.55 years for standard PV and PV/T systems, respectively. In addition, the nanofluids-based PV/T system can prevent the emissions of about 448 kg CO 2 eq m −2 yr −1 . Overall, it was found that the nanofluids-based PV/T with optimized optical and thermal properties has potential for further development in a high-concentration solar system.

Abstract A detailed assessment analysis of 2.5 kWp photovoltaic (PV) system located in southern Algeria (Latitude 27.88 °N, Longitude −0.27 °E, Altitude 262 m) has been carried out in this paper in order to support the growth of grid-tied photovoltaic power plant implementation in the Saharan environment. The achievement of this analysis has been done by performing an accurate evaluation of the different impacts of the environment parameters on the operating performance of the grid-tied PV system. The data set covers 12 operating months and has been collected by our team from the Research Unit on Renewable Energy (URER-MS). The collected experimental data reveal that the environmental parameters variation has direct effect on the performance of both energy conversion efficiency and system losses. The grid was supplied with a power of 4322.65 kWh during the year 2015, where the annual average temperature was 28.30 °C. An important variation in performance parameters have been observed for different months. The yield values of max/min monthly average daily reference, array and final were; 7.68/5.7 kW h/kWp/day, 6.07/4.24 kW h/kWp/day and 5.75/3.98 kW h/kWp/day, respectively. The PV module, inverter and overall system efficiency reached; 14.19/11.10%, 95.34/93.94% and 13.53/10.50%, respectively. The experimental results indicate that the performance ratio (PR) varies from 66.66% to 85.93% and the annual average capacity factor was 7.91%.

Optical characteristics besides unique thermo-physical properties of nanoparticles have encouraged researchers to use nanofluids in solar energy collectors or reservoirs as electromagnetic wave absorbing media. Recently, different analyses and approaches have been proposed by researchers. However, the appropriate electro-magnetic phenomenon of nanofluids is not established till date because of the complex dependence between nanoparticles and base fluids. In this work, optical properties of nanofluids are discussed on the basis of published data; mostly used models are presented along with their limitations and applications.

An experimental study was performed to determine the thermal efficiency of an Evacuated Tube Solar Collector (ETSC) using water based Single Walled Carbon Nanotubes (SWCNTs) nanofluids. Experiments were carried out using SWCNTs nanofluids having volume concentrations of 0.05, 0.1, and 0.2 vol.%. The performance of the collector was compared with SWCNTs nanofluid and water using the flow rates of 0.008, 0.017, and 0.025 kg/s. The experiments were undertaken according to ASHRAE standard 93-2003. The results show that, the collector efficiency improved with SWCNTs nanofluids compared to water as a working fluid. The maximum efficiency found to be 93.43% for 0.2 vol.% SWCNTs nanofluids at a mass flow rate of 0.025 kg/s. The collector efficiency shows greater enhancement with the increasing volume fractions of SWCNT nanoparticles and flow rate. In conclusions, results suggest that SWCNTs nanofluids can be used as the working fluids in an ETSC to absorb heat from solar radiation and to convert solar energy into thermal energy efficiently.