To provide the progressive global demand for energy, the use of renewable energies is being rapidly developed. Since solar radiation is available in most parts of the earth, the photovoltaic (PV) power plant is one of the worthwhile solutions. As a deficiency, temperature rise in photovoltaic cells leads to a drop in their electrical output power. In this experimental study, the circulation of carbon black nanofluid was investigated as a coolant of PV modules. Both water and ethylene glycol (EG) were used as the base fluids. It is found that all modified cases generate more output power than the conventional one. For instance, water + carbon nanofluid yields 54% more output power compared with the conventional one. To make a real assessment of using nanofluid as a coolant, the electrical consumption by pump and fan must be counted. Therefore, in this study, the net output power is calculated. In the cases of EG and EG + carbon, the net output powers get lower than the conventional module. So, they are not justifiable. In this paper, a modified formula is proposed to calculate the exergy efficiency, in order to achieve more accurate results. Accordingly, from an exergy viewpoint, 16.3% and 4.5% in electrical and thermal exergy efficiencies are achieved, when water + carbon nanofluid was used. Moreover, the values of entropy generation and lost exergy were reported for all considered cases.

The present research work aims to investigate the energy saving aspects in cool thermal energy storage system (CTES) by improving the thermophysical properties of deionized (DI) water. The influence of phase change enthalpy, specific heat, thermal conductivity, and cooling rate of the DI water for the dispersion of chemically functionalized multi-walled carbon nanotubes (f-MWCNT) is studied experimentally. The covalent functionalization method is used to modify the surface of the multi-walled carbon nanotubes (MWCNT) with the use of concentrated nitric acid. The nanofluid phase change materials (PCMs) in different mass concentrations (0.25%, 0.50%, and 0.75%) were prepared by dispersions of the f-MWCNT in DI water. The minimum reduction in enthalpy (4.01%) was recorded for the nano-PCM with 0.75% f-MWCNT as compared to the base PCM with 0.5% of sodium dodecyl benzene-sulfonate (10%). The thermal conductivity enhancement of 53.15% and 28.2% was recorded in both states for the nano-PCM (with 0.75%) at the temperature of − 10 °C and 5 °C respectively. Also, the enhancement of 30% and 23% in cooling rate is recorded for the dispersion of maximum concentration of f-MWCNT at the HTF temperatures of − 8 °C and − 6 °C, respectively. It is proven from the above findings that the dispersion of f-MWCNT reduces the subcooling and facilitates the running of the CTES system at a higher operating temperature.

This work aims to develop a novel nanofluid using Therminol-55 (T-55) as heat transfer fluid and multi-wall carbon nanotubes (MWCNTs) as dispersants with various volume concentrations of 0.05, 0.1, 0.3, and 0.5% and assess its thermo-physical properties for solar-thermal applications. The pH values of nanofluid MWCNT/T-55 with various particle loading were too far-flung from the pH (I) value, which confirmed the good dispersion stability of nanofluid. The measured density shows tremendous deviation from predicted density with increasing MWCNT loading owing to the non-considering of microstructural parameters in Pak & Cho correlation predication. The highest augmentation in nanofluid thermal conductivity was 16.83% for 0.5 vol. % MWCNT at 60 °C. The maximum improvement in dynamic viscosity of nanofluid with 0.5 vol. % of MWCNT is found to be 44%, and this rise is reduced at higher temperatures. The thermal effectiveness of the nanofluids demonstrates that nanofluid with all volume fractions of MWCNTs was favorable at higher temperatures in the laminar region. Mouromtseff number ratio decreases with a rise in temperature and MWCNT volume concentration. It is concluded that the excellent thermo-physical properties and prolonged thermal stability of the MWCNT will be highly beneficial in improving the overall performance of various kinds of heat transfer fluids (HTFs) for process heating and solar-thermal applications.

Solar energy has been a vital renewable energy source for humanity for decades. Researchers have proposed many strategies to harness the same but solar photovoltaic (PV) is the only technology which has reached commercial scale and highly successful in meeting renewable energy goals of many countries. The major drawback of PV systems is that increase in the temperature of solar cell of the PV module beyond the threshold limit brings down its electrical efficiency (EE). Hence, this review paper discusses the different cooling techniques responsible for reducing the cell temperature, which in turn increases not only its EE, but also collection of the thermal energy that is otherwise considered to dampen the performance of the PV system. A brief study on PV with air cooling, photovoltaic thermal (PVT) with water cooling, PVT/PCM with and without fins, PVT integrated with nanofluids has been done in this review paper. PVT hybrid systems are the need of hour to get the optimum efficiency. Amongst the PVT systems, the performance analysis of PV integrated with the nanofluid is discussed and it is found to give the maximum cell temperature reduction. Since reduction in the cell temperature directly relates to better efficiency, PVT system using nanofluid as a cooling medium gives the best overall efficiency (OE) followed by PVT system incorporating water and air respectively. This review paper also gives spotlight to the real-time usages of PCM and nanofluids for the effective cooling ability especially in the case of PV module.

Energy demand in the present scenario is rising to meet the increasing demands of energy usage. On the other hand, the use for renewable energy sources now becomes essential to mitigate the climate change as well as to reduce gradual depletion of fossil fuels. Among these renewable energy sources, solar energy particularly solar thermal systems have phenomenal scope in present and future research. In solar thermal systems, concentrators are used to extract the energy from solar irradiation and convert it into useful form. Among different types of solar concentrators, the parabolic dish solar concentrator is preferred as it has high efficiency, high power density, low maintenance, and potential for long durability. In this paper, a detailed review has been carried out on the design parameters like focal length, concentration ratio, and rim angle of the parabolic dish solar concentrator system for achieving higher overall efficiency. The effects of different geometrical shapes of receivers on the overall heat transfer rates are discussed in this paper. Conical shaped receiver is having high overall optical and thermal efficiency comparing with other shapes of receivers. This study also shows that how the thermal performance of the receiver gets enhanced by 10–13% using nanofluids in place of general heat transfer fluids. The paper highlights different models using ray-tracing method for estimation and evaluation of the solar irradiation distribution on the receiver surface. The empirical relations for the design of parabolic dish solar concentrator system are derived for estimating overall concentrator efficiency and heat available at the receiver are given in this review. From the literature, the thermal performance of the receiver affecting the overall performance of the system is observed. Thermal losses due to geometrical properties and ordination of the receiver are explained in the observation section.

The present study aims to obtain the best modification of the hemispherical solar distillers that achieves the highest productivity with the lower inexpensive. To achieve this goal, this paper dealt with conducting a comparative study, operating performance analysis and an economic study of two different modifications, and comparing them with the reference distiller in order to obtain the best adjustments that achieve the highest productivity at the lowest cost. In the first modification, CuO nanoparticles with three different concentrations (0.1, 0.2, and 0.3%) were added to the basin water, to increase the intensity of absorbed solar energy, improve the thermal properties of basin fluid, and then increase the rate of vapor generation inside the distillation basin. In the second modification, water film glass cooling technology with three different flow rates (1.5, 2, and 2.5 L/h) was utilized to increase the water vapor condensation rate. In this experimental study, three hemispherical distillers were fabricated and tested under the same climate conditions at a 1-cm basin fluid depth, namely, conventional hemispherical solar still (CHSS), hemispherical solar still with glass cover cooling (HSS-C), and hemispherical solar still with CuO-water-based nanofluid (HSS-N). The experimental results presented that the average daily accumulative yield of CHSS is 3.85 L/m²/day, while the daily accumulative yield of HSS-N increases to 5.75, 6.40, and 6.80 L/m²/day with improvement 49.3, 66.2, and 76.6% at volume fraction 0.1, 0.2, and 0.3%, respectively. Also, the daily accumulative yield of HSS-C increases to 4.9, 5.35, and 5.7 L/m²/day with improvements of 27.3, 39, and 48% at water film flow rates of 1.5, 2, and 2.5 L/h, respectively. The cost of distilled water produced from CHSS is 0.0106 $/L, while the utilization of HSS-C (2.5 L/h) and HSS-N (0.3%) reduces the cost of distilled water to 0.0072 and 0.0066 $/L, respectively. Based on accumulative yield and economic analyzes, it is recommended that the modified HSS-N (0.3% volume fraction) be utilized to achieve the highest accumulative yield and the lowest price of the produced distilled water.

Solar energy is one of the cleanest sources of renewable energy that is easily accessible in vast geographical areas. As the efficiency of the common solar collectors is very low and is limited by the absorption properties of working fluid, enhancing the thermal performance of these collectors is one of the major challenges of developing parabolic solar thermal power plants. In recent decades, researches revealed that utilizing nanofluid as a novel working fluid has a dramatic effect on the thermophysical and optical properties of the fluid. In this study, the flow and temperature fields of water/magnetite and water/aluminum nanofluids are evaluated by solving the steady form of governing equations including conservation laws of mass, volume fraction transport equation, momentum equation, energy equation, and radiation transfer equation. Moreover, the two-phase Buongiorno model is utilized and Brownian motion, thermophoresis effects, and magnetophoresis movement are taken into account in the nanofluid simulation. The numerical results demonstrate that increasing nanofluid volume fraction and flow rate can increase the thermal performance of the collector tube. It is found that the thermal efficiencies reach maximum values of 151.03% and 158.58% for water/aluminum and water/magnetite nanofluids, respectively. Furthermore, increasing the volume fraction from 0 to 0.3% leads to rise of 24.41% and 21.36% in the maximum temperature of the collector. The effects of different parameters such as nanoparticle volume fraction, flow rate, and nanoparticle kind on the collector thermal and electrical efficiencies, thermal distribution, and entropy production have been studied.

Previous studies have shown insufficient dispersion and thermal stability of nanofluids for high-temperature carbon capture and storage applications. Compared to the other NPs, TiO₂ nanofluids exhibit superior stability due to their high zeta potential. In previous studies, TiO₂ nanofluids have shown superior performance in heat transfer and cooling applications along with importing the stability of other nanofluids like SiO₂ in form of nanocomposites. Therefore, in this study, a nanofluid formulation consisting of titania nanofluid in a base solution of ethylene glycol (EG) with different co-stabilizers such as surfactants was synthesized for better dispersion stability, enhanced electrical, and rheological properties especially for the use in high-temperature industrial applications which include carbon capture and storage along with enhanced oil recovery. The formulated nanofluid was investigated for stability using dynamic light scattering (DLS) study and electrical conductivity. Additionally, the formulated nanofluid was also examined for thermal stability at high temperatures using an electrical conductivity study followed by rheological measurements at 30 and 90 °C. At a high temperature, the shear-thinning behavior of EG was found highly affected by shear rate; however, this deformation was controlled using TiO₂ nanoparticles (NPs). Furthermore, the role of surfactant was also investigated on dispersion stability, electrical conductivity followed by viscosity results, and it was found that the nanofluid is superior in presence of anionic surfactant sodium dodecyl sulfate (SDS) as compared to nonionic surfactant Triton X-100 (TX-100). The inclusion of ionic surfactant provides a charged layer of micelles surrounding the core of a NP and it produced additional surface potential. Consequently, it increases the repulsive force between two adjacent NPs and renders a greater stability to nanofluid while nonionic surfactant allowed monomers to adsorb on the surface of NP via hydrophobic interaction and enhances the short-range interparticle repulsion, to stabilize nanofluid. This makes titania nanofluid suitable for widespread high-temperature applications where conventional nanofluids face limitations. Finally, the application of the synthesized titania nanofluids was explored for the capture and transport of CO₂ where the inclusion of the anionic surfactant was found to increase the CO₂ capturing ability of titania nanofluids by 140–220% (over the conventional nanofluid) while also showing superior retention at both investigated temperatures. Thus, the study promotes the role of novel surfactant-treated titania nanofluids for carbon removal and storage and recommends their applications involving carbonated fluid injection (CFI) to carbon utilization in oilfield applications.

Solar still, which uses solar renewable energy sources, especially solar energy, to produce pure water, is a promising technology as it is abundantly available and eco-friendly. Researchers have innovated in internal and external designs to enhance distillate productivity in solar desalination systems. The present review paper discusses the major internal modifications done in history and recent past to enhance the distillate output. Six sub-sections have been developed concerning historic internal modifications that discuss types of basin liners, water depth, stones, dyes, phase change materials, and weirs. It has been found that among all the historic internal modifications, phase change materials were the most effective with distillate yield enhancement of up to 80%. The limitation in distillate yield made the researchers to perform further modifications to enhance the productivity, and hence, recent internal designs have also been discussed. Recent internal modifications have six sub-sections: fins, wicks, nanofluids, nanostructures, dynamic modifications, and natural materials. Among the recent, dynamic modifications were the most efficient with productivity enhancement of up to 300%, with a maximum cumulative yield of 8.78 kg/m²/day for the rotating wick solar still compared to CSS which gave only 2.21 kg/m²/day. Such a kind of review work has not been performed till date, which covers all the internal design modifications in one paper exhaustively. Furthermore, gaps have been identified, and future perspectives have been presented in the conclusion section. It has been observed that nanostructures, nanoparticles, and dynamic modifications are the most promising internal modifications in recent times that can boost distillate productivity to a greater degree.

This work aims to explore the optical and thermal conversion characteristics of activated carbon—solar glycol nanofluids with various volume fractions namely 0.2, 0.4, and 0.6%, respectively. Kigelia africana leaves were synthesized into porous activated carbon nanomaterials by using the high-temperature sintering process and the pyrolysis process in a muffle furnace. The experimental investigation was carried out with different nanofluid concentrations by using the solar simulator. Nanofluids were heated with the assistance of a solar simulator test system and the convection/conduction heat loss was decreased by using the glass as an insulating material around the test section. Prepared nanofluid with 0.6 vol% activated carbon augmented the thermal conductivity by 14.36% at 60°C. The maximum temperature difference of 10°C was attained at 0.6% volume concentrations of nanofluid as compared with base fluid (solar glycol). In addition, maximum receiver efficiency of 94.51% was attained at 0.6% volume fractions of activated carbon-based nanofluid compared with solar glycol thru a light radiation time of 600 s. Moreover, activated carbon–based nanofluid exhibited significantly higher absorption efficiency as the majority of the radiation was absorbed by the nanofluid. It is concluded that activated carbon-based nanofluids could be a suitable low-cost highly stable material for developing working fluid for direct absorbance solar collector–based applications.