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Silica-based antireflection coatings (ARCs) used in photovoltaic (PV) modules often encounter soiling problems, which has been recognized as one of the most serious problems degrading the power output of PV modules. In this work, four kinds of silica-based ARCs were prepared to investigate the effects of surface morphology and chemistry on their anti-soiling properties under Ningbo’s climate. To reveal the influences of surface morphology, hollow silica nanoparticle (HSN)- and solid silica nanoparticle (SSN)-based ARCs were prepared and compared. To understand the surface chemical effects, we comparatively studied the soiling behavior of hydrophilic and hydrophobic HSN ARCs postmodified with methyl and fluorinated groups (named CH3-HSN and F-HSN, respectively). After half-year field tests, we found that the HSN ARCs with a rougher surface exhibited better anti-soiling performance than the SSN ARCs. On the other hand, the hydrophilic ARCs showed better soiling resistance than the hydrophobic controls because of the role of rain cleaning in the soiling mitigation of the hydrophilic samples installed at a moderate tilt angle under a typical coastal climate. Comparing the hydrophobic samples modified with methyl and fluorinated groups, the former was superior to the latter in both laboratory and outdoor tests because of the larger adhesion force between contaminants and the surface in the fluorinated-HSN ARCs. These findings provide constructive guidance for the applications of silica-based ARCs in PV modules installed in coastal areas, which is the key to maximizing the power output of PV modules in practice.

Nowadays, casted multicrystalline silicon is the most important material in photovoltaic industry. In order to reduce the cost of silicon ingots, the recycle of silicon ingot tailings is explored. In this paper, the secondary utilization of silicon block tailings with a thickness of 25 mm, matched with process of diamond wire saw machine was studied. The comparative analysis on technical parameters of bottom red zone and wafers generated by virgin crushed polycrystalline silicon feedstock and secondary utilized tailings was discussed. The result shows that recycle of tailing seeds is feasible. The above-mentioned tailings of diamond wire saw ingots shall be with a thickness of 25 mm. The bottom red zone of area paved by tailings is 2 mm longer than that in area paved by virgin crushed polycrystalline silicon feedstock. But the difference of cell conversion efficiency is negligible, 0.01% lower. Consequently, it is feasible to recycle high-efficiency multicrystalline ingots tailings, which push forward further cost reduction of high-efficiency multicrystalline ingots.

Single-layer antireflection (SLAR) coatings have been applied in crystalline silicon solar modules for a decade, which evolved from open-pore silica at an early stage into closed-pore structures nowadays in industry. For improving photovoltaic and aesthetic characteristics of solar modules, not only AR properties but also color neutrality of AR coatings need to be intensively studied. In this work, the double-layer antireflection (DLAR) coatings were designed and their residual color was studied by comparing with conventional SLAR and DLAR coatings under both normal and oblique incidences. According to the design, we fabricated the mesoporous DLAR coatings, which exhibited a high average transmittance of Tave = 99.02% at visible wavelengths from 380 nm to 780 nm and a low chroma value of C = 3.35. Applying the mesoporous DLAR coatings to the crystalline silicon mini-modules, the power conversion efficiency was increased by 2.40% on average in relative terms. Besides the power output gain, durable DLAR coatings with neutral color are of great significance for not only imparting a natural and sheer-black appearance to photovoltaic modules without unwanted blueish color, but also finding practical applications in consumer electronics, building glazing, and display windows.

Wax deposition during crude oil transmission can cause a series of negative effects and lead to problems associated with pipeline safety. A considerable number of previous works have investigated the wax deposition mechanism, inhibition technology, and remediation methods. However, studies on the shearing mechanism of wax deposition have focused largely on the characterization of this phenomena. The role of the shearing mechanism on wax deposition has not been completely clarified. This mechanism can be divided into the shearing dispersion effect caused by radial migration of wax particles and the shearing stripping effect caused by hydrodynamic scouring. From the perspective of energy analysis, a novel wax deposition model was proposed that considered the flow parameters of waxy crude oil in pipelines instead of its rheological parameters. Considering the two effects of shearing dispersion and shearing stripping coexist, with either one of them being the dominant mechanism, a shearing dispersion flux model and a shearing stripping model were established. Furthermore, a quantitative method to distinguish between the roles of shearing dispersion and shearing stripping in wax deposition was developed. The results indicated that the shearing mechanism can contribute an average of approximately 10% and a maximum of nearly 30% to the wax deposition process. With an increase in the oil flow rate, the effect of the shearing mechanism on wax deposition is enhanced, and its contribution was demonstrated to be negative, shear stripping was observed to be the dominant mechanism. A critical flow rate was observed when the dominant effect changes. When the oil flow rate is lower than the critical flow rate, the shearing dispersion effect is the dominant effect, its contribution rate increases with an increase in the oil flow temperature. When the oil flow rate is higher than the critical flow rate, the shearing stripping effect is the dominant effect, its contribution rate increases with an increase in the oil flow temperature. This understanding can be used to design operational parameters of the actual crude oil pipelines and address the potential flow assurance problems. The results of this study are of great significance for understanding the wax deposition theory of crude oil and accelerating the development of petroleum industry pipelines.

The seed assisted growth technology has been used to fabricate the high performance multicrystalline silicon (mc-Si) for photovoltaic application nowadays, which can effectively control the dislocation density by forming uniform and small grains. In this work, we have systematically investigated the effect and mechanism of silicon wafer flakes as the seeds for mc-Si growth. Silicon flakes were put on the crucible bottom as nucleation agents by two different settings, i.e., orderly stacking without interspace and intentionally piling up with interspace. It was found that the numerous small and uniform grains with diameter of ~ 0.5 mm were homogenously formed in the intentionally piled up wafer flake seed layer since the liquid silicon drops flew down and solidified in the interspaces during the melting of polysilicon feedstocks. These small self-formed grains served as new seeds, which were better than orderly stacked wafer flakes as seeds. Minority carrier lifetime and photoluminescence mappings have shown that the initial dislocation density of grains with smaller sizes based on the piled silicon flake seeds was much lower than those without seeds or stacked silicon flake seeds, and meanwhile the dislocation propagation was suppressed by means of smaller grain sizes due to the denser grain boundaries. As a result, the corresponding average conversion efficiency of Al-BSF processed solar cells from the mc-Si assisted by piled silicon flakes as seeds was absolutely 0.29% higher than those without seeds and 0.17% higher to those assisted by stacked silicon flakes.

The high performance multicrystalline (HPMC) silicon material with the feature of small and uniform grains has already been widely adopted in photovoltaic industry nowadays. However, the HPMC silicon ingots still suffer a comparatively lower minority carrier lifetime at the ingot edges induced by Fe in-diffusion. Here, we have engineered the grain boundaries (GBs) to control the low carrier lifetime zone at the HPMC silicon ingot edges, based on the grain nucleation enhanced by silicon powder coating at the crucible walls. The resultant GBs with high density paralleling to the crucible walls can getter Fe impurity, and meanwhile become the barriers for Fe diffusion. Therefore, the detrimental effect of interstitial Fe impurity on the carrier lifetime of edge wafers is sufficiently reduced and the performance of corresponding solar cells is improved. The solar cells have a narrower distribution in the performance, which is beneficial for the stability and durability of solar cells and modules. This growth concept using GBs to control the behaviors of Fe diffused from the crucible walls is interesting for photovoltaic application.

The casting method is a low-cost technique to fabricate photovoltaic monocrystalline silicon wafers. The development of cast monocrystalline silicon (CM-Si) materials requires high quality and low cost. To further reduce CM-Si's cost, a large-scale recycled seed has become a focused topic. This work compared new seeds and a large-scale recycled seed in the same growth so that the experimental errors in the growth environment were eliminated. Detailed characterizations on defect distribution and performances have shown that seed recycling will generate extra initial defects. However, it becomes influential for solar cell performance only when defect concentration reaches a certain level. Finally, a related defect propagation mechanism was revealed for manufacturers to optimize industrial growth strategies.

Fractures not only control the distribution of oil and gas reservoirs, but also are key points in the research of oil and gas reservoir development programmes. The tectonic fractures in the Lower Cambrian shale reservoirs in the Feng'gang No. 3 block are effective reservoir spaces for hydrocarbon accumulation, and these fractures are controlled by palaeotectonic stress fields. Therefore, quantitatively predicting the development and distribution of tectonic fractures in the Lower Cambrian shale reservoir is important for the exploration and exploitation of shale gas in the Feng'gang No. 3 block. In the present study, a reasonable geological, mechanical and mathematical model of the study area was established based on the faults systems interpreted from seismic data, fracture characteristics from drilling data, uniaxial and triaxial compression tests and experiments on the acoustic emissions (AE) of rocks. Then, a three-dimensional (3-D) finite element method is applied to simulate the palaeotectonic stress field with the superposition of the Yanshan and Himalayan movements and used to predict the fracture distribution. The simulation results indicate that the maximum principal stress value within the study area ranged from 269.97 MPa to 281.18 MPa, the minimum principal stress ranged from 58.29 MPa to 79.64 MPa, and the shear stress value ranged from 91.05 MPa to 106.21 MPa. The palaeotectonic stress field is controlled by the fault zone locations. The fracture development zones are mainly controlled by the tectonic stress fields and are located around the faults, at the end of the fault zones, at the inflection point and at the intersection of the fault zones.

This paper focused on studying an octagonal thermal field to improve the quality of multi-crystalline silicon ingot. A global numerical model was adopted to investigate the effects of the modified furnace on the temperature distribution and temperature gradients distribution during the directional solidification process. The numerical results indicated that a more uniform temperature distribution and lower temperature gradients were obtained in the modified furnace. Meanwhile, the experimental ingot was obtained by using the modified furnace. Experimental tests of minority carrier lifetime distribution, dislocation clusters, and the average conversion efficiency for the conventional ingot and the modified octagonal ingot were carried out. The results indicated that the modified octagonal silicon ingot could achieve lower defect density, especially near the crucible wall. Therefore, the average conversion efficiency of the modified octagonal ingot was improved by 0.12% compared with the conventional ingot. Furthermore, the mechanism and control of ingot side dislocation multiplication were discussed.

Shale rock formations often contain calcite, which is a mineral that plays an important role in the failure of shale and in fracturing the reservoir volume. This study uses digital images to characterise the mesoscopic-scale non-uniformity of shale resulting from the shape, size and distribution of calcite in the shale. The geometry of the calcite is mapped to a finite element mesh based on the meso-scale structure of the rock. The numerical failure analysis model RFPA2D-DIP, which can accurately represent the meso-scale structure of shale, is used to simulate uniaxial compression. The influence of the meso-scale structure on the compressive strength and the failure process under various loading conditions are studied. The simulation results show that the meso-scale structure has an important influence on the compressive strength and the ultimate failure mode of samples loaded in various directions α . Furthermore, the results show that the compressive strength varies significantly with the direction of the load, indicating anisotropy. Depending on the direction, the failure mode can take the form of an inverted V ( α =0°, 30°, 45°), an inverted Z ( α =15°), a line ( α =75°), or a V ( α =60°, 90°). The spatial distribution of the acoustic emissions (AE) we observed is similar to those observed in macroscopic failure modes. The fractal dimension (D) of the shale fractures under various loading conditions is calculated using the box-counting method. The fractal dimension is an effective indicator of the failure mode. The value of D corresponding to the various failure modes is as follows: for the inverted Z the maximum value is 1.688016, for the line the minimum value is 1.481904, and for both the inverted V and the V, the value is between 1.688016 and 1.481904. Therefore, the failure mode is more complex for larger values of D.

The preparation of multicrystalline silicon ingots with different boron-gallium doping ratio was studied in this work. The resistivity distribution, minority carrier lifetime, photoelectric conversion efficiency and light-induced degradation ratio were analyzed and compared. The results showed that with the increase of gallium doping ratio, the minority carrier lifetime of ingot and the conversion efficiency of silicon wafers were both decreased, at the same time the light-induced degradation ratio was decreased obviously, but it was not proportional to gallium concentration, By comparing the impurities concentration, it was preliminarily inferred that the impurities of copper and iron may also affect the light-induced degradation. Based on the performance of resistivity, conversion efficiency and light-induced degradation, the optimal gallium-doped ratio of multicrystalline ingots was between 20 and 25%.

A composite nucleant with Si powder as the main component was introduced to prepare high-performance multicrystalline (HPM) silicon ingot in this work. The effect of different sizes of Si powder on the ingot performance was investigated and compared with the conventional HPM silicon ingot which seeded from poly-Si particles. It is proved that the composite nucleant with Si powder of large particle size (D50 = 355 μm) can induce small and uniform grains, showing uniform minority carrier lifetime distribution and low dislocation cluster area ratio. Meanwhile, the length of red zone at the ingot bottom is significantly shorter than conventional HPM silicon ingot, which significantly increases the yield of the ingot. The ingot grown with suitable composite nucleant can achieve high cell efficiency and the solar cells have low light-induced degradation (LID) value due to low interstitial oxygen concentration which are comparable to the conventional HPM silicon ingot.

The impact of constitutional supercooling (CS) on the grain structure of cast multicrystalline silicon (mc-Si) materials was investigated. Indium impurity was chosen as the CS dopant because of its low equilibrium segregation coefficient so that CS effect could be obtained at relatively low doping concentration. Industrial indium (In) doped G2 and boron-indium (B–In) co-doped G5 seed-assisted multicrystalline silicon (mc-Si) ingots were fabricated and characterized. Self-nucleated grains and epitaxial grains could be obtained, respectively, as the result of tuning the doping amount of indium. Constitutional-supercooling-related defects (CSD) were found in the co-doped ingot and could suppress the growth and propagation of dislocation-type defects. As a result, the overall deleterious defect density of B–In co-doped mc-Si wafers was well reduced compared to that of referential B-doped wafers, and the average solar cell performance of B–In co-doped ingots was obviously enhanced.

In the situation that the modular multilevel converter (MMC) needs to maintain a good current control performance within a wide scope of operations such as the intermittent new energy grid connection and electric locomotive, etc, this paper starts from the output current slope generated after the output voltage and system voltage of MMC converter are jointly acted on the equivalent coupling reactance to analyze the mathematic relation among the current error, output voltage and other correlatives and propose the MMC current hysteresis control method based on output current slope. This method is characterized by simple algorithm, definite physical significance, high output accuracy, small output current ripple, fast dynamic response and strong robustness, etc. Finally, the effectiveness and feasibility of this method is verified by the physical controller — RTDC close-loop real-time simulation experiment.