Developing solar cells with recycled materials and household chemicals for drinking water chlorination by communities with limited resources

Ferric tannate-sensitized n-(ZnO, SnO₂)/Cu photoelectrochemical cells were constructed for drinking water chlorination using recycled waste materials and household chemicals and utilising Fe²⁺–Fe³⁺ and Cu²⁺–Cu redox couples for charge transfer. The solar cells, which were constructed in recycled clear plastic tubing and drinking straws in a home environment, produced an open-circuit voltages of 0.4–0.6 V and a short-circuit current densities of 1–2.5 mA cm^?2. Chlorine was produced at a rate of 4 mg h^?1 from a 1% salt solution using an array of cells with a combined voltage of 5 V and a current of 200 mA. This study has demonstrated that it is possible to construct viable solar cells for drinking water chlorination using waste materials and readily available chemicals. Further studies are needed to determine how practicable this would be in regions with drinking water quality and sanitation problems.     

Development of micromorph tandem solar cells on flexible low-cost plastic substrates

We report on the development of fully flexible microcrystalline and micromorph tandem solar cells directly on low-cost substrates like poly-ethylen-terephtalate (PET) and poly-ethylen-naphtalate (PEN). The cells are deposited in nip or nip/nip configuration on the plastic substrate coated with a highly reflecting Ag–ZnO back contact. Light trapping is achieved by combining a periodically textured substrate and a diffusing ZnO front contact. Single-junction microcrystalline cells with a stable efficiency of 8.7% are achieved with an i-layer thickness of 1.2 μm. In tandem devices we obtain an efficiency of 10.9% (initial) with an open circuit voltage of 1.35 V and a fill factor (FF) of 71.5%. These cells are slightly top limited with 11.26 and 11.46 mA/cm² in the amorphous (270 nm thick) and the microcrystalline (1.2 μm thick) sub-cells, respectively. We introduce an intermediate reflector (IR) between the bottom and the top cell because it allows increasing the top cell current without compromising the stability by a thicker absorber. The IRs consist of either an ex-situ ZnO or a low refractive index P-doped silicon–oxygen compound deposited in-situ with a plasma process that is fully compatible with solar cell processing. We demonstrate significant current improvement (up to 8% relative) using both kinds of IRs.     

Anthocyanins and betalains as light-harvesting pigments for dye-sensitized solar cells

We present the photoelectrochemical properties of dye-sensitized solar cells using natural pigments containing betalains and anthocyanins as sensitizers. The dyes extracted from grape, mulberry, blackberry, red Sicilian orange, Sicilian prickly pear, eggplant and radicchio have shown a monochromatic incident photon to current efficiency (IPCE) ranging from 40% to 69%. Short circuit photocurrent densities (J_sc) up to 8.8 mA/cm², and open circuit voltage (V_oc) ranging from 316 to 419 mV, were obtained from these natural dyes under 100 mW/cm² (AM 1.5) simulated sunlight. The best solar conversion efficiency of 2.06% was achieved with Sicilian prickly pear fruits extract. The influence of pH and co-absorbers on natural sensitizers, were investigated and discussed.     

Enhancement of pool-boiling heat transfer using nanostructured surfaces on aluminum and copper

Enhanced pool-boiling critical heat fluxes (CHF) at reduced wall superheat on nanostructured substrates are reported. Nanostructured surfaces were realized using a low temperature process, microreactor-assisted-nanomaterial-deposition. Using this technique we deposited ZnO nanostructures on Al and Cu substrates. We observed pool-boiling CHF of 82.5 W/cm² with water as fluid for ZnO on Al versus a CHF of 23.2 W/cm² on bare Al surface with a wall superheat reduction of 25–38 °C. These CHF values on ZnO surfaces correspond to a heat transfer coefficient of ～23,000 W/m² K. We discuss our data and compare the behavior with conventional boiling theory.     

A novel Al and Y codoped ZnO/n-Si heterojunction solar cells fabricated by pulsed laser deposition

Al and Y codoped ZnO (AZOY) transparent conducting oxide (TCO) thin films were first deposited on n-Si substrates by pulsed laser deposition (PLD) to form AZOY/n-Si heterojunction solar cells. However, the properties of the AZOY emitter layers are critical to the performance of AZOY/n-Si heterojunction solar cells. To estimate the properties of AZOY thin films, films deposited on glass substrates with various substrate temperatures (T_s) were analyzed. Based on the experimental results, optimal electrical properties (resistivity of 2.8 ± 0.14 × 10^?4 Ω cm, carrier mobility of 27.5 ± 0.55 cm²/Vs, and carrier concentration of 8.0 ± 0.24 × 10²⁰ cm^?3) of the AZOY thin films can be achieved at a T_s of 400 °C, and a high optical transmittance of AZOY is estimated to be >80% (with glass substrate) in the visible region under the same T_s. For the AZOY/n-Si heterojunction solar cells, the AZOY thin films acted not only as an emitter layer material, but also as an anti-reflected coating thin film. Thus, a notably high short-circuit current density (J_sc) of 31.51 ± 0.186 mA/cm² was achieved for the AZOY/n-Si heterojunction solar cells. Under an AM1.5 illumination condition, the conversion efficiency of the cells is estimated at only approximately 4% (a very low open-circuit voltage (V_oc) of 0.24 ± 0.001 V and a fill factor (FF) of 0.51 ± 0.011) without any optimization of the device structure.     

Numerical investigation on heat transfer and friction factor characteristics of laminar and turbulent flow in an elliptic annulus utilizing nanofluid

In this paper, a numerical investigation on heat transfer performance and flow fields of different nanofluids flows through elliptic annulus in a laminar and turbulent flow regimes. The three-dimensional continuity, Navier–Stokes and energy equations are solved by using finite volume method (FVM) and the SIMPLE algorithm scheme is applied to examine the effects of laminar and turbulent flow on heat transfer characteristics. This study evaluates the effects of four different types of nanoparticles, Al₂O₃, CuO, SiO₂ and ZnO, with different volume fractions (0.5–4%) and diameters (25–80 nm) under constant heat flux boundary condition using water as a base fluid were used. The Reynolds number of laminar flow was in the range of 200 ≤ Re ≤ 1500, while for turbulent flow it was in the range of 4000 ≤ Re ≤ 10,000. The results have shown that SiO₂–water nanofluid has the highest Nusselt number, followed by ZnO–water, CuO–water, Al₂O₃–water, and lastly pure water. The Nusselt number for all cases increases with the volume fraction but it decreases with the rise in the diameter of nanoparticles. In all configurations, the Nusselt number increases with Reynolds number. It is found that the glycerine–SiO₂ shows the best heat transfer enhancement compared with other tested base fluids.     

An improved dynamic test method for solar collectors

A comprehensive improvement of the mathematical model for the so called transfer function method is presented in this study. This improved transfer function method can estimate the traditional solar collector parameters such as zero loss coefficient and heat loss coefficient. Two new collector parameters t and m_fC_f are obtained. t is a time scale parameter which can indicate the heat transfer ability of the solar collector. m_fC_f can be used to calculate the fluid volume content in the solar collector or to validate the regression process by comparing it to the physical fluid volume content if known. Experiments were carried out under dynamic test conditions and then test data were processed using multi-linear regression method to get collector parameters with statistic analysis. A comparison of the collector parameters obtained from the improved transfer function (ITF) method and the quasi-dynamic test (QDT) method is carried out. The results show that the improved transfer function method can accurately obtain reasonable collector parameters. The influence of different averaging time intervals is investigated. Based on the investigation it is recommended to use on line calculation if applicable for the second-order differential term with 6–9 min as the best averaging time interval. The measured and predicted collector power output of the solar collector are compared during a test of 13 days continuously both for the ITF method and the QDT method. The maximum and averaging error is 53.87 W/m² and 5.22 W/m² respectively of the ITF method while 64.13 W/m² and 6.22 W/m² of the QDT method. Scatter and relative error distribution of the measured power output versus the predicted power output is also plotted for the two methods. No matter in either error analysis or scatter distribution, the ITF method is more accurate than the QDT method in predicting the power output of a solar collector.In conclusion, all the results show that the improved transfer function method can accurately and robustly estimate solar collector parameters and predict solar collector thermal performance under dynamic test conditions.     

Elimination of pesticides and their formulation products from drinking water using thin film continuous photoreactor under solar radiation

There is an urgent need for the development of inexpensive, but reliable and efficient photocatalyst which can work under solar radiation for drinking water application. Hence the treatment options to be tried out for drinking water contaminated with pesticides and their formulation products should be cost effective and affordable. In this study, we developed a cheap and efficient photocatalyst and continuous photoreactor for the removal of pesticides from drinking water under solar radiation. Continuous photodegradation experiments were carried out with synthetically prepared commercial grade methyl parathion (Folidon 50% E.C.), dichlorvos (DDVP 70% E.C.), and analytical grade lindane. Photodegradation of mixed pesticide was carried out using both Degussa P-25 TiO₂ and N-doped TiO₂ with identical mass concentrations (50 μg/L) of all the three pesticides under UV, visible and solar radiation. Continuous reactor was operated for more than 24 h (6 h each on 4 days) for mixed pesticide degradation. N-doped TiO₂ showed 100% degradation for all the three pesticide under solar radiation. Photodegradation of mixed pesticide showed methyl parathion, dichlorvos and lindane were degrading simultaneously. However, the rate of reaction was completely different from single pesticide degradation. N-doped TiO₂ showed higher photocatalytic activity under solar radiation compared to UV and visible light. GC–MS analysis of mixed pesticide degradation showed more than 16 peaks in the middle of the reaction. Among these peaks, three intermediates such as hexachloro-benzene and para-nitrophenol and dichlorovinyl-O-methyl phosphate were identified in the middle of the reaction. However, at the end of the reaction (reactor outlet) none of the intermediates were observed.     

TiO2–Au plasmonic nanocomposite for enhanced dye-sensitized solar cell (DSSC) performance

Anatase TiO₂ nanoparticles dressed with gold nanoparticles were synthesized by hydrothermal process by using mixed precursor and controlled conditions. Diffused Reflectance Spectra (DRS) reveal that in addition to the expected TiO₂ interband absorption below 360 nm gold surface plasmon feature occurs near 564 nm. It is shown that the dye sensitized solar cells made using TiO₂–Au plasmonic nanocomposite yield superior performance with conversion efficiency (CE) of ～6% (no light harvesting), current density (J_SC) of ～13.2 mA/cm², open circuit voltage (V_oc) of ～0.74 V and fill factor (FF) 0.61; considerably better than that with only TiO₂ nanoparticles (CE ～ 5%, J_SC ～ 12.6 mA/cm², V_oc ～ 0.70 V, FF ～ 0.56).     

Year round test of a solar adsorption ice maker in Kunming,China

A solar adsorption ice maker with activated carbon–methanol adsorption pair was developed for a practical application. Its main features include utilization of a water cooled condenser and removing all valves in the refrigerant circuit except the one that is necessary for refrigerant charging. Year round performance tests of the solar ice maker were performed in Kunming, Yunnan Province, China. Test results show that the COP (coefficient of performance) of the solar ice maker is about 0.083–0.127, and its daily ice production varies within the range of 3.2–6.5 kg/m² under the climatic conditions of daily solar radiation on the surface of the adsorbent bed being about 15–23 MJ/m² and the daily average ambient temperature being within 7.7–21.1 °C. The suitable daily solar radiation under which the solar ice maker can run effectively in Kunming is above 16 MJ/m².     

Solid-phase crystallization of amorphous silicon on ZnO:Al for thin-film solar cells

The suitability of ZnO:Al thin films for polycrystalline silicon (poly-Si) thin-film solar cell fabrication was investigated. The electrical and optical properties of 700 -nm-thick ZnO:Al films on glass were analyzed after typical annealing steps occurring during poly-Si film preparation. If the ZnO:Al layer is covered by a 30 nm thin silicon film, the initial sheet resistance of ZnO:Al drops from 4.2 to 2.2 Ω after 22 h annealing at 600 °C and only slightly increases for a 200 s heat treatment at 900 °C. A thin-film solar cell concept consisting of poly-Si films on ZnO:Al coated glass is introduced. First solar cell results will be presented using absorber layers either prepared by solid-phase crystallization (SPC) or by direct deposition at 600 °C.     

Transient analysis of modified cuboid solar integrated-collector-storage system

A novel solar water heating system, modified cuboid solar integrated-collector-storage (ICS) system with transparent insulation material (TIM) has been designed and developed, which combines collection and storage in a single unit and minimizes the nocturnal heat losses. A comprehensive study has been carried out to evaluate the heat transfer characteristics inside the enclosure of the system to enhance the collection and storage of solar energy. The transient behavior of the modified-cuboid solar integrated-collector-storage system is investigated numerically to evolve optimum configuration. The optimum design for the system is obtained by carrying out a numerical parametric study with different geometry parameters like the depth of the cuboid (d = 2, 5, 8, and 12 cm), and inclination angles (10°, 20°, 30°, and 50°). The inside heat transfer coefficient of the ICS system, stratification factor and water temperature distribution inside the enclosure have been predicted by numerical simulation. Average heat transfer coefficient at the bottom surface of absorber plate is 20% higher for depth of 12 cm as compared to the 2 cm depth of cuboid section, after 2 h of heating. The stratification factor also increases from 0.02 to 0.065 as depth of the system increases from 2 cm to 12 cm. There is a marginal effect of inclination angles of the system on the convection in the enclosure. As the inclination angle increases from 10° to 50°, the average heat transfer coefficient increases from 90 W/m² K to 115 W/m² K. But the stratification factor is comparatively high for lower inclination angles. With the optimum design parameters, a field experimental set-up was built and the numerical model was validated for efficient heat collection and storage in a modified cuboid ICS system. The model is in good agreement with the experimental results.     

Fabrication and characterisations of n-CdS/p-PbS heterojunction solar cells using microwave-assisted chemical bath deposition

n-CdS/p-PbS heterojunction solar cells were prepared via microwave-assisted chemical bath deposition method. A cadmium sulfide (CdS) window layer (340 nm thickness) was deposited on an indium tin oxide (ITO) glass. A lead sulfide (PbS) absorber layer (985–1380 nm thickness) with different molar concentrations (0.02, 0.05, 0.075, and 0.1 M) was then grown on ITO/CdS to fabricate a p–n junction. The effects of changing molar concentration of the absorber layer on structural and optical properties of the corresponding PbS thin films and solar cells were investigated. The optical band gap of the films decreased as the molarity increased. The photovoltaic properties (J–V characteristics, short circuit current, open circuit voltage, fill factor, and efficiency) of the CdS/PbS heterostructure cells were examined under 30 mW/cm² solar radiation. Interestingly, changing molar concentration improved the photovoltaic cells performances, the solar cell exhibited its highest efficiency (1.68%) at 0.1 M molar concentration.     

Symmetric redox supercapacitor with conducting polyaniline electrodes

Polyaniline doped with HCl (Pani-HCl) and LiPF₆ (Pani-LiPF₆) are prepared and used as the active electrode material of symmetric redox supercapacitors. The system using Et₄NBF₄ as an electrolyte solution has lower internal resistance and larger specific discharge capacitance, and thus, it is suitable for use in a polyaniline redox supercapacitor. The capacitance of Pani-HCl decreases during ∼400 cycles and then becomes constant at ∼40 F g⁻¹. On the other hand, the polyaniline electrode doped with lithium salt like LiPF₆ shows a specific discharge capacitance of ∼107 F g⁻¹ initially and ∼84 F g⁻¹ at 9000 cycles.     

Optimizing rainwater harvesting systems as an innovative approach to saving energy in hilly communities

Rapid urbanization is increasing the amount of hilly communities around many large cities; therefore, saving water pumping energy deserves significant priority. This work proposes optimized rooftop rainwater harvesting systems (RRWHSs) and provides an energy-saving approach for hilly communities. The most cost-effective rainwater tank volumes for different dwelling types are calculated using marginal analysis. The case study at Hua-Chan Community in northern Taiwan indicates that the optimum rainwater tank volumes range from 5 m³ to 10 m³ according to the type of dwelling. The results also reveal that rainwater harvesting becomes economically feasible when both energy and water savings are addressed together. Furthermore, the cost of unit energy saving from RRWHSs is lower than that from solar PV systems. Hence, RRWHSs provide not only water savings, but also as an alternative renewable energy-saving approach to address the water–energy dilemma caused by the ever-growing hilly communities.     

Effect of solid volume fraction and tilt angle in a quarter circular solar thermal collectors filled with CNT–water nanofluid

Solar thermal collectors have significant importance due to its wide use in solar thermal technology. Augmentation of heat transfer is a key challenge for solar thermal technology. A quarter circular solar thermal collectors is investigated throughout the paper introducing carbon nanotube (CNT)–water nanofluid in the cavity. Tilt angle of this type of collector plays a vital role and heat transfer can be maximized for a particular tilt angle and solid volume fraction of the nanofluid. Galerkin weighted residual of FEM has been applied for the numerical solution of the problem. Grid independency test and code validation have been assessed for the accuracy of numerical solution. In this paper a wide range of solid volume fraction (δ = 0 to δ = 0.12) and tilt angle (ϕ = 0 to ϕ = 60°) has been investigated for Rayleigh number (Ra = 10⁵–10⁸) with varying dimensionless times. It has been found that both solid volume fraction and tilt angle play vital roles for the augmentation of heat transfer and a good heat transfer characteristic can be obtained by compromising between these two parameters. The results are shown using streamline, isotherm contour and related graph and chart.     

A study of calcium zincate as negative electrode materials for secondary batteries

The properties of calcium zincate as negative electrode materials for secondary batteries were examined by powder microelectrode, cyclic voltammetry, charge–discharge cycle measurements and X-ray diffraction (XRD) analysis. The results show that the cycleability of calcium zincate is obviously superior to that of ZnO and that of the mixture of ZnO and Ca(OH)₂ (the molar ratio of Zn:Ca=2:1). Calcium zincate forms zinc metal during the charging and exhibits an initial discharge capacity 230 mAh g⁻¹. With the discharge cut-off voltage of 1.0 V, the discharge capacity of the experimental Zn/NiOOH cell does not decay much during 500 cycles, exhibiting good prospect for practical use.     

Homogeneous p+ emitter diffused using boron tribromide for record 16.4% screen-printed large area n-type mc-Si solar cell

A record efficiency of 16.4% (156.25 cm²) has been achieved for an n-type wafer-based (hereafter, “n-based”) mc-Si solar cell. A horizontal quartz tube furnace with an industry-compatible scale is employed for forming a p⁺-emitter using boron tribromide (BBr₃) as the boron source, in which system less contamination is confirmed than in other options of boron diffusion. A significantly homogeneous emitter is achieved with the standard deviation of 1.5 Ω/sq. n-Based mc-Si solar cells are fabricated with phosphorus-diffused BSF, SiN deposition, and fire-through screen-printed contacts. The properties of the best cell are; η: 16.4%, V_oc: 607 mV, J_sc: 35.2 mA/cm², and FF: 76.7%.     

An improved preparation of 1-methyl-3-propylimidazolium iodide and its application in dye-sensitized solar cells

In this paper, we reported an improved preparation of 1-methyl-3-propylimidazolium iodide (MPII), which was the alkylation reaction of n-propyl iodide and 1-methylimidazole under solvent-free conditions by Teflon-lined, stainless autoclaves. It was shown that the resulting MPII was high pure, the conversion rate of 1-methylimidazole was close to 100% and the procedure was simple and eco-friendly. Moreover, the apparent diffusion coefficients of triiodide and iodide in the mixture with different ratios of MPII and 3-methoxypropionitrile were demonstrated by cyclic voltammetry using a Pt ultramicroelectrode. The dye-sensitized solar cells with the electrolyte, which was composed of 0.13 M I₂, 0.10 M LiI, 0.50 M 4-tert-butylpyrdine in the mixture of 3-methoxypropionitrile and MPII (weight ratio 0.65:1), gave short circuit photocurrent density of 14.82 mA/cm², open-circuit voltage of 0.69 V, and fill factor of 0.66, corresponding to the photoelectric conversion efficiency of 6.73% at the illumination (AM 1.5, 100 mW/cm²).     

Optimization of lead- and cadmium-free front contact silver paste formulation to achieve high fill factors for industrial screen-printed Si solar cells

Screen-printed n⁺–p–p⁺ solar cells were fabricated on Cz single crystalline Si material, with a 45 Ω/sq emitter and PECVD SiNx antireflective coating with a thickness of 700 Å, using different Ag pastes and commercial leaded reference paste (CN33-462, Ferro Corp.). Ag and Al contacts were co-fired using a mass-production line equipped with mesh belt conveyer furnace systems (Centrotherm thermal solution GmbH & Co. KG). The average results for single crystalline Si solar cells (156 cm²) are: I_sc=5.043 A, V_oc=0.621 V, R_s=0.0087 Ω, R_sh=15.3 Ω, FF=0.773, and E_ff=16.45%. R_sh and fill factor values of fabricated cells were slightly higher when compared with the commercial leaded Ag paste, although cells were fabricated by metallizing the lead-free silver pastes. For the lead-free Ag paste used in this study, the line pattern continuity is retained with improved edge definition in sharp contrast to that of reference Ag paste. Average value of R_s was also equivalent approximately to that of the leaded Ag paste.