多晶硅太阳电池绒面反射率的研究

主要研究多晶硅片在未加缓蚀剂的酸腐蚀溶液中制绒后,绒面反射率对电池片效率的影响;用RENA制绒机自带反射仪对硅片绒面反射率进行检测,用3D显微镜对多晶硅片绒面的形貌进行观察和检测分析。实验过程中,按照工业生产的实际模型,确定了多晶硅片制绒后,绒面的最佳反射率范围是18.0%~18.5%,合理范围是18%~19%;并分析了绒面反射率影响电池片效率的原因。     

酸腐蚀多晶硅绒面光学特性的模拟研究

利用COMSOL Multiphysics 3.5a有限元软件中的RF模块对酸腐蚀前后多晶硅表面的光学特性进行数值模拟,通过求解麦克斯韦方程组和材料本构方程,获得硅片的表面电场z分量、表面磁场y分量和反射率的变化规律。结果表明:与初始硅片相比,绒面的表面电场z分量和表面磁场y分量的数值明显偏大,当波长为600nm时,绒面表面电场z分量的最大值和最小值分别为初始硅片的3.2倍和3.5倍,表面磁场y分量两个极值约为初始硅片的7.5倍;初始硅片反射率较高,绒面具有较好的陷光作用,其反射率明显偏小。通过对比实验和模拟结果可知,模拟值和试验值变化趋势基本一致,两者吻合较好,可为实际生产和试验研究提供理论指导。     

酸性添加剂对多晶硅绒面形貌的影响

采用各向同性腐蚀法制备多晶硅绒面,通常使用的腐蚀液为HNO3和HF的混合溶液,增加适量酸性添加剂,可以有效地改进制绒效果,提高多晶硅电池转换效率。文章研究了酸性添加剂在不同酸腐蚀液浓度配比条件下制备的绒面特性。研究结果表明,腐蚀液中加入酸性添加剂后,绒面表面腐蚀坑细小均匀,有效地降低了绒面反射率,减少了电池产生的漏电;当腐蚀液中HNO3/HF/酸性添加剂的浓度比为8∶1∶0.4时,所制备绒面的反射率达到最低值,为21.87%,其转换效率最高。     

酸腐蚀多晶硅表面的光反射率计算

分析了现有酸腐蚀多晶硅表面光反射率计算模型中存在的基本问题,提出了更符合酸腐蚀多晶硅表面形貌特征的光反射率计算模型,并就波长为550hm的单色光垂直照射下的光反射率随表面凹坑深度与球体半径比值H_(max)/R的变化进行了系统计算.结果表明,当H_(max)/R在0～0.29之间时是完全一次反射区,R_(total)是一恒定值.随着H_(max)/R增加,反射次数增多,反射率下降.当H_(max)/R=1时,也就是凹坑深度刚好为球半径时,反射率最低.     

化学腐蚀法制备多晶硅的绒面

为了降低光在多晶硅表面的反射,采用化学腐蚀法在其表面制备了绒面。根据反射光谱的测试结果,研究了不同多晶硅绒面的形貌特征及光学特性。在适当的腐蚀液中制备了3×3cm2、5×5cm2和10×10cm2多晶硅绒面。10×10cm2多晶硅绒面,在300～1100nm波长范围内的加权反射率的最好结果为5 2%,表面织构均匀,这一结果可以和具有双层减反射膜的多晶硅表面的反射率相比拟。     

电化学腐蚀多晶硅衬底减反射效果研究

将多晶硅片置于HF、N,N-二甲基甲酰胺(DMF)、去离子水的混合溶液中,研究电流密度、腐蚀时间对多晶硅绒面形貌以及表面反射率的影响.实验结果表明,可在多晶硅上获得平均孔径为5 ～ 20μm、深为1～ 3μm的腐蚀坑,其加权反射率达到11.3％,较处理之前降低了60％.     

单晶硅太阳电池的表面织构化

一种新型的腐蚀剂 ,磷酸钠 (Na3PO4 ·12H2 O)溶液 ,首次被用来腐蚀单晶硅太阳电池。在 70℃下 ,用 3%的磷酸钠 (Na3PO4 ·12H2 O)溶液腐蚀 2 5min就能在硅片表面形成金字塔大小均匀、覆盖率高的绒面结构 ,并且其表面反射率也很低。通过SEM观察发现 :开始时 ,随着腐蚀时间的增加 ,金字塔的密度越来越大 ,最后达到饱和 ;而且对于不同的浓度 ,温度 ,这种饱和时间不同 ;如果腐蚀时间过长 ,金字塔的顶部就会发生崩塌 ,从而导致表面发射率的升高。虽然异丙醇 (IPA)在氢氧化钠 (NaOH)溶液中会明显地改善织构化的效果 ,但是在磷酸钠 (Na3PO4 ·12H2 O)溶液中却会对织构化有很强的负面效应。最后 ,在实验的基础上对腐蚀机理进行了深入地探讨并认为 :择优腐蚀是金字塔形成的最基本的原因 ,而缺陷、PO3 -4 或HPO2 -4 和异丙醇等仅仅是促进大金字塔形成的原因。这种腐蚀剂的成本很低 ,不易污染工作环境且可重复性好 ,所以有可能用于大规模生产。     

酸腐蚀液对多晶硅表面织构的影响

通过在富HF的HF-HNO_3溶液体系中加入新的添加剂NH_3·H_2O,对多晶硅片进行了腐蚀试验研究。在溶液配比为HF:HNO_3:NH_3·H_2O:H_2O=12:1:1:4(体积比),腐蚀时间为10min时得到的效果最好,多晶硅的织构表面沟槽的密度更高、分布更均匀;在波长300～1000nm的范围内平均反射率为5.13%。能够获得低反射率的多晶硅织构表面的主要原因为:加入的NH_3·H_2O以及系统中反应生成的NH_4NO_3分解时产生的N_2O气体和NO_2~-起到关键作用。     

金刚线切割多晶硅片预处理对太阳电池电性能的影响研究

目前,在太阳电池生产过程中多采用酸性混合溶液HF-HNO_3-H_2O对硅片表面进行织构化处理,即进行制绒处理,以降低硅片表面的反射率,进而提高太阳电池的光电转换效率。对基于金刚线切割的多晶硅片进行预处理,并研究预处理对太阳电池电性能的影响。首先在硅片制绒前先对其表面进行喷砂处理(即预处理),使其表面形貌的微观结构发生变化,进而在制绒处理时得到更优的绒面结构,同时调节与太阳电池制备过程匹配的工艺参数。实验结果证实,在制绒前对金刚线切割多晶硅片进行预处理可以使太阳电池的光电转换效率得到一定提升。     

多晶硅酸腐蚀表面织构的研究

该文采用HF和HNO3为腐蚀液,在不同温度、添加剂和超声振荡3种情况下来进行多晶硅酸腐蚀表面织构实验研究,发现通过超声振荡,在单位面积上腐蚀坑密度较大.在1min、HFHNO3=121的腐蚀条件下,25℃时加Br2添加剂用超声震荡的方式得到较好的腐蚀效果.腐蚀坑的分布比较均匀,单位面积腐蚀坑较多,而且呈收缩型,这将有利于入射光的多次反射,获得较好的表面减反射效果.     

Ash-forming elements in four Scandinavian wood species. Part 1: Summer harvest

Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on 11 ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2–0.7%) was low compared to the ash content in the bark tissues (1.9–6.4%) and the foliage (2.4–7.7%). The woods’ content of ash-forming elements was consequently low; the highest contents were of Ca (410–1340 ppm) and K (200–1310), followed by Mg (70–290), Mn (15–240) and P (0–350). Present in the wood was also Si (50–190), S (50–200) and Cl (30–110). The bark tissues showed much higher element contents; Ca (4800–19,100 ppm) and K (1600–6400) were the dominating elements, followed by Mg (210–2400), P (210–1200), Mn (110–1100) and S (310–750), but the Cl contents (40–330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100–25,000 ppm), P (1600–5300) and S (1100–2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820–1360) and its needles the highest Si content (5000–11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden.     

Contents in Volume 23,2014

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Performance assessment of some ice TES systems

In this paper, a performance assessment of four main types of ice storage techniques for space cooling purposes, namely ice slurry systems, ice-on-coil systems (both internal and external melt), and encapsulated ice systems is conducted. A detailed analysis, coupled with a case study based on the literature data, follows. The ice making techniques are compared on the basis of energy and exergy performance criteria including charging, discharging and storage efficiencies, which make up the ice storage and retrieval process. Losses due to heat leakage and irreversibilities from entropy generation are included. A vapor-compression refrigeration cycle with R134a as the working fluid provides the cooling load, while the analysis is performed in both a full storage and partial storage process, with comparisons between these two. In the case of full storage, the energy efficiencies associated with the charging and discharging processes are well over 98% in all cases, while the exergy efficiencies ranged from 46% to 76% for the charging cycle and 18% to 24% for the discharging cycle. For the partial storage systems, all energy and exergy efficiencies were slightly less than that for full storage, due to the increasing effect wall heat leakage has on the decreased storage volume and load. The results show that energy analyses alone do not provide much useful insight into system behavior, since the vast majority of losses in all processes are a result of entropy generation which results from system irreversibilities.     

NEXT GENERATION ENGINEERED MATERIALS FOR ULTRA SUPERCRITICAL STEAM TURBINES

正1 ABSTRACT To reduce the effect of global warming on our climate,the levels of CO2emissions should be reduced.One way to do this is to increase the efficiency of electricity production from fossil fuels.This will in turn reduce the amount of CO2emissions for a given power output.Using US practice for efficiency calculations,then a move from a typical US plant running at 37%efficiency to a 760℃/38.5 MPa(1 400/5 580 psi)plant running at 48%efficiency would reduce CO2emissions by 170kg/MW.hr or 25%.     

Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H₂ yield. The results demonstrated that the optimal culture conditions for the highest H₂ production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m^?2 s^?1. Under these conditions, the maximal H₂ yield was 255 μmol mg^?1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H₂ yield included decreased O₂ content, enhanced algal growth, and increased H₂ase activity and starch content of the combined system.     

Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO_x) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO_x emissions. High NO_x emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO_x and CO₂ emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.     

Controls on the Karaha–Telaga Bodas geothermal reservoir,Indonesia

Karaha–Telaga Bodas is a partially vapor-dominated, fracture-controlled geothermal system located adjacent to Galunggung Volcano in western Java, Indonesia. The geothermal system consists of: (1) a caprock, ranging from several hundred to 1600 m in thickness, and characterized by a steep, conductive temperature gradient and low permeability; (2) an underlying vapor-dominated zone that extends below sea level; and (3) a deep liquid-dominated zone with measured temperatures up to 353 °C. Heat is provided by a tabular granodiorite stock encountered at about 3 km depth. A structural analysis of the geothermal system shows that the effective base of the reservoir is controlled either by the boundary between brittle and ductile deformational regimes or by the closure and collapse of fractures within volcanic rocks located above the brittle/ductile transition. The base of the caprock is determined by the distribution of initially low-permeability lithologies above the reservoir; the extent of pervasive clay alteration that has significantly reduced primary rock permeabilities; the distribution of secondary minerals deposited by descending waters; and, locally, by a downward change from a strike-slip to an extensional stress regime. Fluid-producing zones are controlled by both matrix and fracture permeabilities. High matrix permeabilities are associated with lacustrine, pyroclastic, and epiclastic deposits. Productive fractures are those showing the greatest tendency to slip and dilate under the present-day stress conditions. Although the reservoir appears to be in pressure communication across its length, fluid, and gas chemistries vary laterally, suggesting the presence of isolated convection cells.     

Exergetic evaluation of 5 biowastes-to-biofuels routes via gasification

This paper presents the exergy analysis results for the production of several biofuels, i.e., SNG (synthetic natural gas), methanol, Fischer–Tropsch fuels, hydrogen, as well as heat and electricity, from several biowastes generated in the Dutch province of Friesland, selected as one of the typical European regions. Biowastes have been classified in 5 virtual streams according to their ultimate and proximate analysis. All production chains have been modeled in Aspen Plus in order to analyze their technical performance. The common steps for all the production chains are: pre-treatment, gasification, gas cleaning, water–gas-shift reactions, catalytic reactors, final gas separation and upgrading. Optionally a gas turbine and steam turbines are used to produce heat and electricity from unconverted gas and heat removal, respectively. The results show that, in terms of mass conversion, methanol production seems to be the most efficient process for all the biowastes. SNG synthesis is preferred when exergetic efficiency is the objective parameter, but hydrogen process is more efficient when the performance is analyzed by means of the 1st Law of Thermodynamics. The main exergy losses account for the gasification section, except in the electricity and heat production chain, where the combined cycle is less efficient.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.