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Abstract In this work, earth-abundant CZTSSe thin film solar cells were fabricated by sulfo-selenization of the Mo/Zn/Cu/Sn/Cu metallic precursors. The influences of morphological and compositional properties of the absorbers on performance of solar cells were investigated by tuning Cu content in the films. The Raman analysis showed that absorbers consist of a kesterite CZTSSe phase with ZnSe as a minor secondary phase. X-ray photoelectron spectroscopy (XPS) analyses revealed that the surfaces are Cu depleted and Zn enriched compared with the bulk composition of the absorbers. The results indicate that during sulfo-selenization the Cu diffused into the film and the Zn towards the film surface. The performance of the solar cells initially improved with the increasing of the Cu content and then decreased. By tuning the Cu content in the absorbers, the minority-carrier life time improved from 0.8 to 1.6 ns. The power conversion efficiency increased from 5.1 to 8.03% with fine controlling of Cu composition of the CZTSSe absorbers. The diode-ideality factors are higher than 2, suggesting an increased interfacial recombination in the devices. The high ideality-factors A and low minority carrier life times may originate from surface and bulk related defects, which in turn limits the Voc and the achievable high conversion efficiency for the CZTSSe thin film solar cells.

Abstract Methane dry reforming with CO2 using FeO powder in molten salt has been investigated at various flow rates of CH4/CO2 mixed gases (CH4/CO2=1) between 50 and 400 ml/min at 1223 K in an infrared furnace. This work is carried out to determine the usefulness of this method for the chemical storage of solar energy. The CH4/CO2 mixed gases passing through the molten salt (Na2CO3/K2CO3=1) containing the FeO powder were catalytically decomposed into CO, H2 and H2O. The product gas mole ratios, CO/H2/H2O, were shown to be 3:1:1 for a high flow rate of 200 ml/min and to be CO/H2=2:1 for a low flow rate of 50 ml/min. The results were explained in terms of the kinetics of the CH4-reforming reaction and the thermodynamics of the redox process of FeO powder mixed in the molten salt; CH 4 +2FeO⇒2Fe+H 2 +CO+H 2 O Fe+CO 2 ⇒FeO+CO for a high flow rate, and FeO+CH 4 ⇒Fe+2H 2 +CO Fe+CO 2 ⇒FeO+CO for a low flow rate.

Abstract The quest for more efficient solar absorbers has resulted in the development of numerous coating techniques for the absorption panel itself. The Chrome-Black coating is an electroplated black-chrome coating on a copper substrate which combines the properties of high visible absorption (α), low infra-red emission (ϵ) and excellent temperature stability in both air and vacuum environments. Results obtained show that surfaces may be produced both with high α ϵ ratios, for example α = 87 per cent, ϵ = 3 per cent and α ϵ = 28 and with high absorption, for example α = 92 per cent, ϵ = 8 per cent and α ϵ = 11 . These results were obtained assuming an air-mass-2 spectral distribution and a 50°C black body weighting for absorption and emission respectively. All samples are known to be stable to at least 300°C. This type of coating would be expected to have good anticorrosion properties and this has been confirmed by electro-chemical oxidation and reduction testing. A comparison is made between the topography of this coating and of sputtered metal surfaces.

Abstract An improved hybrid vacuum and pressure-assisted infiltration technique was developed for the infiltration of phase change materials (PCM) into the graphite foam matrix. A single chamber with no moving part infiltration setup was designed and fabricated. Pelletized PCM was introduced to provide enough porosity for air removal using vacuum pumps with no need for transfer PCM after melting and infiltration. Simple design, the use of stainless steel, and the corrosion resistance feature of PCM provides a very cost-effective design and easily controllable process. Mixed alkali and alkaline chloride salts as PCM were infiltrated into the high porosity graphite foam to enhance the thermal conductivity of latent heat storage medium. Chloride based PCM with proven corrosion-resistant features, high energy storage density that enables storage and release of energy at nearly constant temperatures close to the melting temperature of 355 °C are used in this study, as an example. The composites of infiltrated graphite foam and chloride salt PCMs were studied using SEM, EDS microstructural analyses to determine the effectiveness of the infiltration process. An infiltration efficiency greater than 90% of the available porosity was achieved. The thermal conductivity of the infiltrated samples was analyzed using a laser Nano-flash thermal conductivity device. The thermal conductivity of the foam/PCM composite was shown to be larger by a factor greater than 40 times of pure chloride PCM (1–2 W/m-K). Low-cost infiltration with proven efficacy and repeatability of infiltrated PCM could be a breakthrough for 3rd generation of CSP plant applications with supercritical CO2 power cycles.

Abstract In this paper, we designed, simulated and analyzed high efficiency of SnS-based solar cells. This work is related to the influence of a glancing angle deposition (GLAD) technique for deposition of SnS layer, on the photovoltaic performance of SnS-based solar cells. The photovoltaic parameters have been calculated for the samples prepared at different oblique incident flux angles (α = 0°, 45°, 55°, 65°, 75°, and 85°). The best efficiency was found for the sample prepared at α = 85°. We simulated the J-V characteristics and showed how the absorber layer that prepared by GLAD technique at different incident flux angles, influence the short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF), and efficiency (η) of solar cell.

Abstract Grain boundaries (GBs) in multicrystalline silicon (mc-Si) degrade the solar cells performances. To enhance the conversion efficiency of photovoltaic cells, preferential grooving was achieved in GBs in order to reduce their area and then their highly recombination effect. For this purpose, a chemical etching method in HF/HNO3 solution was used. In this study, we show how grooved GB enables deep penetration of phosphorus and metallic contacts, which lead to a P–Al-co-gettering of undesired impurities. As a result, we observe a decrease in the recombination activity in regions close to the GBs as compared to ungrooved sample; this was investigated by the two-dimensional Light-Beam-Induced-Current (LBIC) imaging. In addition, we carried out a two dimensional representation of the Internal-Quantum-Efficiency (IQE), where images show an improvement of the electrical activity in grooved GBs.

Abstract There are instances in remote areas where heat is being wasted, e.g., in internal combustion, engines, etc. Some of this heat can be recovered to produce distilled water in solar stills. The solar still replaces the cooling tower, ponds, or radiators normally used to control the engine temperature. The diesel cooling water in such a system remains separate from the saline water in the solar still. The advantages of using such a system compared with a conventional solar still are: 1. (a) water costs are very much reduced 2. (b) the area occupied is much less, i.e., about 1 5 th 3. (c) production has much less seasonal variation 4. (d) the efficiency of the solar still is improved due to the higher operating temperatures. From experiments conducted at Highett using a Mk VI solar still fitted with a simple heat exchanger and a separate electrically-heated source of hot water to simulate the waste heat, design data are not available for application to working systems. The information required to match a solar still to a diesel's cooling requirement is: 1. (a) engine efficiency 2. (b) hourly fuel consumption 3. (c) hourly solar radiation 4. (d) hourly ambient temperatures. A by-product of this work has been the production of a “solar water heater” which costs less than that of the cheapest conventional system. This “solar” hot water system uses a heat exchanger similar to what is used to transfer the waste heat to the saline water. It is envisaged to have hot water productions approximately the same as the distilled water productions. The influence of hot water production on the output of the waste heat solar still is discussed.

Abstract In many cases, hazardous wastes are subject to thermal treatment at elevated temperatures. Some types of wastes do not have a sufficient calorific value to cover the heat demand of the high temperature process. For thermal treatment of e.g. filter residues, dusts, sulfuric acid, aluminium dross, foundry sand, or waste water, supplementary energy supply is needed. The specific energy demand ranges from 0.5 to 2.5 kWh/kg (2–10 MJ/kg). An important aim of process optimisation is the reduction of (fossil) energy consumption and exhaust gas flow. Concentrated solar energy promises advantages when applied to high energy consuming waste treatment processes with regard to substitute fossil or electric energy consumption, to reduce CO2 emissions, and exhaust gas flow. In parallel to conceptional studies, a solar-heated rotary kiln mini-plant has been designed and constructed for tests in the DLR solar furnace. The tests will give indications of boundary conditions for solar thermal treatment or conversion of selected hazardous materials.

Abstract It is cost effective to manufacture a reflective surface of a solar parabolic trough concentrator in a parabolic cylinder shape by pure bending of a flat sheet. However, the surface manufactured by such an elastic bucking is only a coarse approximation of a parabola, which is not precise enough for meeting the demand of a high quality concentrator. A novel design concept was proposed to remove this error by applying an external force on both edge of a sheet, together with two additional forces: the edge torsion force and the pressing force. The optimal position and magnitude of two additional forces were figured out among various conditions, thereby a theoretically maximal concentration ratio up to 115 was found. Prototypes and engineering realizations of this method were also presented. This method provides a very attractive approach for low cost and high efficiency solar energy solutions.