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Membrane distillation (MD) assisted by heat pump exhibits a favorable energy performance in water production, but it consumes huge precious electricity. In this work, a nanofluid filtered concentrating photovoltaic/thermal (CPV/T) technology is proposed to integrate with heat pump membrane distillation (HPMD) system for electricity/water cogeneration. Solar energy cascade utilization is considered in the system where electricity generated by CPV/T powers heat pump for MD heat recovery, and the collected thermal energy is used to heat seawater. A comprehensive study is carried out by establishing models of the receiver, direct contact membrane distillation (DCMD) and heat pump to investigate the performance of the nanofluid filtered solar membrane distillation system using heat pump. Results show that the seawater of 350.3 K is fed to the DCMD module while the electrical efficiency is above 12.2%. MD parametric analysis and equivalent specific thermal energy consumption (eSTEC) optimization are performed. We found that HPMD operates at the lowest eSTEC of 607.8 kWh·m−3 at heating temperature of 338 K and feed flow rate of 0.04 kg s−1. An overall system efficiency of 61% is obtained, and the comparison of permeate flux and energy consumption demonstrates advantages of the proposed system over other hybrid MD technologies. [ABSTRACT FROM AUTHOR]

Few studies focus on the stability and the optical characteristics optimization of the nanofluid filters for photovoltaic/thermal (PV/T) systems. In this work, a propylene glycol (PG) based nanofluid filter consisting of Ag@SiO 2 nanoparticles was fabricated for both Si and GaAs solar cells and the stability was assessed. Results show that PG based Ag@SiO 2 nanofluids retain their optical properties after subjecting to solar radiation, high temperature heating and ambient storage for 60 days. Further, an optimization routine based on Mie scattering theory and Lambert Beer law was proposed for selection of the best particle concentration and optical path distance of the nanofluid. The filtering efficiencies more than 43% and 35% are achieved for Si and GaAs solar cells, respectively. Finally, the filtering performance of nanofluids with the best nanofluid parameters was discussed in PV/T systems. The optimized nanofluids combined with Si cells achieve the value of merit function (MF) of 1.51 when Ag@SiO 2 /PG-DI nanofluid with particle concentration of 30 mg/L and optical path distance of 42 mm. It is higher than the value obtained in literature. For GaAs cells, the Ag@SiO 2 /PG-DI nanofluid filter with 23 mg/L particle concentration and 50 mm optical path distance produces the highest MF of 1.38. • Stability of propylene glycol based Ag@SiO 2 nanofluids demonstrated experimentally. • Optimization routine proposed to select best concentration & optical thickness. • Filtering efficiencies more than 43% and 35% achieved for Si and GaAs solar cells. • Maximum MF of 1.51 for Si cell when Ag@SiO 2 /PG-DI nanofluid with 42 nm & 30 mg/L. • Maximum MF of 1.38 for GaAs cell when Ag@SiO 2 /PG-DI nanofluid with 50 nm & 23 mg/L. [ABSTRACT FROM AUTHOR]

Over the past few years, a growing interest has surfaced about the PV/T systems based on nanofluid filter. Some palsmonic nanofluids including Ag, Au and Cu nanoparticles are proposed as the optical filter of PV/T system. To identify the best nanofluid parameters for Si and GaAs solar cell, an optical model of the nanofluids based on Mie scattering theory and Lambert Beer law are developed. Results show that the absorption peak of Ag nanoparticle displays a red-shift trend with the increase of particle diameter and refractive index of base fluid. Adjusting the optical path-length is one efficient way to regulate the optical properties. A maximum merit function (MF) of 1.375 can be achieved for Si cells when Ag/propylene glycol (PG)+CoSO 4 nanofluid is used as the optical filter with nanoparticle diameter of 20 nm, concentration of 20 mg/L and optical path-length of 22 mm. The investigation of the best Ag nanofluid filter for GaAs cells reveals that PG base fluid with Ag nanoparticle diameter of 20 nm, concentration of 1 mg/L and optical path-length of 60 mm can achieve a MF value of 1.342. The optimized MF values for Cu and Au nanofluids are slight higher than that for Ag nanofluid. [ABSTRACT FROM AUTHOR]

The distributed solar powered membrane distillation (SPMD) system for water/electricity co-production is a valuable solution for relieving energy pressure in remote areas but it suffers from a complicated operation mechanism. This paper performs a comprehensive parameter analysis and user-oriented optimization on a nanofluid filtered solar membrane distillation system using heat pump to enhance its competitiveness. Response surface methodology is employed to examine the interactions of the influencing factors on the system performance, and the plots reveal significant interactions, particularly on equivalent specific thermal energy consumption (eSTEC). An artificial neural network is integrated with genetic algorithm to perform single and multi-objective system performance optimization. The results show that maximum system exergy efficiency, permeate flux and minimum eSTEC are 19.39 %, 35.8 kg·m−2·h−1 and 463.5 kWh·m−3, respectively. Furthermore, the technique for order preference by similarity to an ideal solution is utilized, based on performance indicator weight derived from the analytical hierarchy process, to offer a user-oriented optimal solution. It demonstrates that after optimization, the system exergy efficiency and permeate flux are improved by 9.9 % and 30.2 %, respectively, along with a reduction of eSTEC by 5.7 %. This research contributes to advancing solar-to-water/electricity efficiency and offering valuable insights for the development of SPMD systems. • Comprehensive analysis and user-oriented optimization on a new SPMD is conducted. • RSM employed to examine interactions of influencing factors on system performance. • ANN integrated with GA performs single and multi-objective system optimization. • Exergy efficiency & permeate flux improved by 9.9 % & 30.2 %, eSTEC reduced by 5.7 %. [ABSTRACT FROM AUTHOR]

Direct absorption parabolic trough solar collector (DAPTSC) using nanofluid absorber has been demonstrated as an efficient technology for exploiting solar energy at high temperature. However, most mono nanofluids are unable to achieve broadband absorption and hybrid nanofluids are unstable at high temperature. In this work, the mono nanofluid and optical glass combined absorption is proposed for the DAPTSC. In which the absorption glass (HB850) and an outer glass tubes form an annular space for indium-tin-oxide (ITO)/Therminol VP-1 nanofluid flowing. Monte Carlo Ray-Tracing and Finite Volume Method (MCRT-FVM) coupled model is developed and validated for system investigation. The results show that the novel collector with the combined absorber exhibits obvious enhancement in thermal performance compared to Therminol VP-1 or ITO/Therminol VP-1 nanofluid. The DAPTSC with concentric annular tube (CAT) has a significantly superior thermal performance to that of the single tube collector, with 45.91 % higher achievable temperature gain and 1.15 % more achievable exergy efficiency. Finally, an eccentric annular tube (EAT) is proposed for further improvement. To quantify the performance improvement of the DAPTSC with EAT, a comparison has been made to that of a DAPTSC with CAT. The results indicate that EAT configuration shows 1.96 % enhancement in the exergy efficiency. [ABSTRACT FROM AUTHOR]

• The efficient conversion of full-spectrum solar energy to hydrogen is achieved. • Blended nanofluid is optimized for the cascading full-spectrum utilization. • The potential of blended nanofluid in hydrogen production system is verified. • The solar-to-hydrogen efficiency of the proposed system could reach up to 44.75 %. The integration of photovoltaic (PV) water electrolysis and medium-temperature thermochemical reactions with nanofluid filters presents a promising prospect for efficiently converting the complete spectrum of solar energy into hydrogen. However, the behavior of nanofluid in hydrogen production systems has yet to be thoroughly investigated in previous studies. In this regard, the current study introduces an innovative approach by incorporating Ag@SiO 2 -Au blended nanofluid filters into a concentrating photovoltaic/thermal (CPV/T) system. The system is further coupled with a proton exchange membrane (PEM) electrolyzer and a methanol steam reforming (MSR) system. The nanofluid filter is optimized to properly disintegrate the incident sunlight to drive PEM and MSR systems. This synergistic design enables the efficient sequential utilization of the complete solar spectrum, culminating in the storage of solar energy in the form of hydrogen. A comprehensive investigation is conducted by establishing models of CPV/T, PEM and MSR to examine the performance of the integrated system. The results demonstrate the significant promise of the blended nanofluid in facilitating a solar-driven hydrogen production system across the entire spectrum. Through optimization of nanofluid, the optimum nanofluid exhibits the capacity to maintain the system electrical efficiency at a minimum of 7.23%. This underscores the effective harnessing of high-grade solar energy. Based on GaAs solar cell, the solar-to-hydrogen efficiency (44.75%) of the system is impressive, in which 34.46% is the efficiency of solar energy electricity to hydrogen, and the efficiency of solar heat to hydrogen is 49.75%. It exhibits high conversion efficiency of sunlight to hydrogen when compared with analogous hydrogen production systems. These outcomes firmly establish the potential of blended nanofluid filters within hydrogen production systems, offering a feasible pathway toward achieving comprehensive solar-driven hydrogen production. [ABSTRACT FROM AUTHOR]

The membrane distillation (MD) systems integrated with photovoltaic/thermal (PV/T) collectors can hardly obtain large permeate flux and favorable electrical performance simultaneously. Therefore, an innovative hybrid nanofluid filtered concentrating PV/T (CPV/T)-direct contact membrane distillation (DCMD) system is proposed. The novelty is that Ag/saline water nanofluid acts as a multifunctional fluid capable of absorbing solar spectrum, which cannot be efficiently utilized by solar cells, and converting it into heat to directly produce water in DCMD. Mathematical models of both nanofluid filtered CPV/T and DCMD are established to evaluate the system performance. Results indicated that nearly 70% of solar radiation is converted into useful energy by the nanofluid filtered CPV/T device. Besides, detailed parametric studies are performed to explore how the system performance is affected by the operation and design parameters. It is found that Ag/saline water nanofluid can be heated to 353 K for desalination, at which, the DCMD module can produce 26.4 kg m−2 h−1 of fresh water. Meanwhile, the electrical efficiency of the system is 12.2% and the equivalent system thermal efficiency can reach a maximum of 71.3%. Furthermore, we demonstrate that the use of Ag/saline water nanofluid as feed stream can mitigate the temperature polarization and improve DCMD performance. • Nanofluid filtered CPV/T-direct contact membrane distillation system is proposed. • Ag/saline water nanofluid acts as a multifunctional fluid in the hybrid system. • Simultaneously produce 26.4 kg m−2 h−1 of fresh water and 608 W of electricity. • Electrical efficiency of 12.2% & equivalent thermal efficiency of 71.3% obtained. • Temperature polarization and membrane distillation performance are improved. [ABSTRACT FROM AUTHOR]

One main challenge facing nanofluid filters in PV/T systems is their long-term dispersion stability. This work studies the stability of the Ag@SiO 2 nanoparticles suspended in propylene glycol (PG)-based fluids for use as optical filters. These nanofluid filters are subjected to high temperature heating test and thermal cycling test to analyze their thermal stability and identify appropriate base fluids. The results of UV–Vis spectroscopy and visual inspection show that both the most concentrated Ag@SiO 2 /PG + water nanofluid and Ag@SiO 2 /PG nanofluid exhibit excellent thermal stability when heated to 95 °C and 120 °C, respectively and no agglomeration is observed for exposure to thermal cycling test. A theoretical model with the measured transmittance of the identified Ag@SiO 2 nanofluids as the input is introduced to evaluate performance of the nanofluid filtered PV/T system by varying the nanoparticles concentration, optical path-length and concentration ratio. The results indicate that Ag@SiO 2 /PG + water filter and Ag@SiO 2 /PG filter for PV/T systems using silicon cells show the capability to increase the economic value of more than 30% at optimum nanoparticles concentration of 12.7 mg/L and optical path-length of 35 mm and 40 mm, respectively, when the concentration ratio varies from 1 to 30 suns. • Stability of Ag@SiO 2 nanoparticles in PG-based fluids as optical filters is studied. • High temperature heating and thermal cycling tests are designed for the nanofluids. • PG + water & PG based nanofluids show good thermal stability heated to 95 °C and 120 °C. • No agglomeration of PG + water & PG based nanofluids found exposure to thermal cycles. • Using 12.7 mg/L nanofluids yields market value increase more than 30% at 1–30 suns. [ABSTRACT FROM AUTHOR]

Several researchers have demonstrated that plasmonic nanofluids based filters can potentially enhance hybrid solar photovoltaic/thermal (PV/T) systems performance. In this work, we report a facile process for achieving silica-coated silver (Ag) nanoparticles using dimethylamine (DMA) as a basic solvent to induce tetraethyl orthosilicate (TEOS) hydrolysis. Then, the prepared Ag@SiO 2 nanoparticles which have a controllable silica shell thickness are suspended in propylene glycol-CoSO 4 hybrid fluid. Finally, the characteristics of the PV/T system filtered by the Ag@SiO 2 /CoSO 4 -PG nanofluids are evaluated based on the indoor test and photo-thermal conversion model. The results show that the nanoparticles prepared under optimized conditions, i.e., pH value of 8–9, water: ethanol volume ratio of 1:4, temperature of 25 °C, TEOS volume of 0.05 mL, and reaction time of 12 h, exhibit an absorption peak at 474 nm. Further, this study reveals that Ag@SiO 2 /CoSO 4 -PG nanofluid filter with concentration of 25.4 mg/L gives a reasonable spectral match with silicon concentrator solar cell according to the measured optical transmittance and the calculated filtering efficiency of 39.3%. The use of 25.4 mg/L Ag@SiO 2 /CoSO 4 -PG nanofluid filter produces a higher total efficiency of 63.3% and yields economic value enhancement of 67.8% compared to the PV only system when worth factor (w) is 3. • A facile process for achieving silica-coated silver (Ag) nanoparticles is proposed. • Ag@SiO 2 particles prepared at optimized conditions shows absorption peak at 474 nm. • Adding Ag@SiO 2 particles & CoSO 4 to PG causes increase in the filtering efficiency. • Ag@SiO 2 /CoSO 4 -PG nanofluid (25.4 mg/L) gives good spectral match with silicon cell. • Using 25.4 mg/L nanofluid yields total η of 63.3% & market value increase of 67.8%. [ABSTRACT FROM AUTHOR]

In this paper, the optical absorption properties and photo-thermal conversion characteristics of GO-water nanofluids were experimentally studied and compared. With the increase of GO mass fraction or the decrease of GO sheet size, the optical absorption capacity of nanofluids can be enhanced, and a thin layer of nanofluid can absorb most of the solar irradiation. As for a direct absorption solar collector (DASC), the temperature rise increased with the irradiation angle at the reverse-irradiation mode because of the natural convection induced temperature uniformity improvement. There existed optimal GO concentrations with respect to the maximum temperature rises of GO nanofluids, and the optimal value is GO sheet size dependent. For GO sheet sizes of 50–200 nm, 200–500 nm and >500 nm, the optimal mass fractions are 150, 180 and 220 ppm, respectively, and the corresponding temperature rises were increased by 9.2 °C (28.2%), 7.9 °C (24.1%), and 6.9 °C (21.0%) as compared with that of water at the reverse irradiation angle of 45°. A 3D numerical simulation was performed to understand the irradiation angle induced natural convection contribution to the photo-thermal conversion performance, and an agreement was achieved with the experiment. [ABSTRACT FROM AUTHOR]

Summary: In this paper, an experimental study was performed to investigate the photothermal conversion properties of CuO‐H2O nanofluid‐based volumetric receiver mainly considering the effects of nanoparticle (NP) concentration, irradiation time, and receiver depth. First, stable aqueous suspensions of CuO with NPs having average diameter close to 10 nm were produced by the precursor transformation method. The spectral transmittances of CuO‐H2O nanofluids decrease with increasing the NP concentration (0.01‐0.25 wt%) at wavelengths of 200 to 1350 nm. The photothermal conversion performance of CuO‐H2O nanofluids is sensitive to the receiver depth, irradiation time, and NP concentration. The higher NP concentration causes stronger optical absorption in the upper part and reduces the temperature at the bottom accordingly. The temperature difference between CuO‐H2O nanofluid and distilled water increased initially and then decreased with the increase of penetration depth, and there existed an optimal depth of 1 cm with respect to the best photothermal conversion performance. The receiver efficiency decreased with increasing the light irradiation time, and an efficiency improvement up to 30.4% was achieved for the 0.25 wt% nanofluid at the optimal depth of 1 cm as compared with water. This work shows that volumetric receivers provide a potential alternative for solar thermal energy utilization versus surface‐based absorber especially under concentrated solar radiation. [ABSTRACT FROM AUTHOR]