Ⅲ-Ⅴ族太阳电池的发展和应用系列讲座(5) 砷化镓基系Ⅲ-Ⅴ族化合物半导体太阳电池的发展和应用(5)

<正>聚光可利用相对便宜的光学系统,成百上千倍地提高照射到电池表面的太阳光强,相应增加电池的输出功率,降低光伏发电系统的成本。而且,聚光还可提高电池的效率。因为在理想情况下,在一定光强范围,电池的短路电流与光强呈正比,而开路电压随光强呈对数式增长。然而,实际的太阳电池器件具有一定等效串联     

温度和光强对聚光硅太阳电池特性的影响研究

利用恒压频闪式I-V曲线测试仪研究分析温度和光强对聚光硅电池特性参数的影响。研究发现,聚光硅电池开路电压V_(oc) 的温度系数随聚光比升高不断降低,从1倍聚光比的-1.97 m V/K降低到30倍聚光比的-1.71 m V/K,和其理论计算值吻合较好;和普通单晶硅电池开路电压V_(oc) 温度系数相比,该电池的要小,上述说明聚光硅电池在聚光下工作有利于其在较高温度下操作。聚光硅电池填充因子和效率均随温度升高而降低;由于串联电阻影响,该电池效率随聚光比的增大先增后减,适合在小于20倍聚光比下的系统中工作。可进一步优化该电池金属栅线覆盖率和阻值引起的功率损失以提高其适合应用的聚光比。     

聚光条件下太阳电池的热电特性分析

为了为进一步开发聚光光伏发电系统提供指导和依据，建立了聚光光伏发电系统的数学模型，然后对不同聚光光伏发电系统方案的热电特性进行了计算，分析了串联内阻和换热系数对系统性能的影响。结果表明，在特定的串联内阻下，太阳电池的峰值功率首先随光强的升高而直线升高，升高到一定程度后曲线变得平缓。曲线的拐点随串联内阻的降低而升高。换热系数越高，系统的性能越好，而且随着光强的升高，换热系数的影响越来越显著。     

单晶硅太阳电池在槽式聚光与普通光照条件下伏安特性的对比研究

为进一步对开发聚光热电联供系统提供依据与指导,在槽式聚光器中,设计了槽式单晶硅太阳能电池热电联供测试系统,并在太阳聚光条件下对单晶硅太阳电池进行了伏安特性的测试.测试结果表明,普通单晶硅太阳能电池在聚光10倍左右的情况下,开路电压变化不大,开路电流放大了4.1倍左右,伏安特性曲线基本满足线性关系.     

聚光硅太阳电池的室外高光强测试

本文介绍了聚光硅太阳电池室外高光强测试仪的基本结构及使用方法,并讨论了测试数据的处理方法和温度对聚光硅太阳电池高光强测试的影响。     

太阳能等照度带聚焦菲涅耳透镜研究

为了提高聚光发电时太阳电池的光电转换效率,从提高太阳电池表面会聚光强分布的均匀性入手,对传统平板型线聚焦透镜进行改进,提出一种用于聚光光伏发电的等照度带聚焦菲涅耳透镜设计方法。带聚焦菲涅耳透镜分为奇数个单元,每个单元宽度与太阳电池宽度相等,单元内所有尖劈角φ相等并将太阳辐射等宽度折射至太阳电池表面,从而实现各单元透过的太阳能等照度叠加。最大聚光比由光伏电池宽度、透镜与太阳电池间距以及透镜材料折射率决定。对带聚焦和线聚焦两种透镜聚光条件下电池表面温度分布情况进行比较分析,验证了等照度带聚焦透镜设计的可行性。     

串联电阻对不均匀铜铟镓硒电池性能的影响

由于铜铟镓硒太阳电池的不均匀性以及电池输出特性的非线性,现有表征大面积电池的加权平均效率需要进行修正以便更好反映光伏组件的效率。由于串联电阻的增加常被认为可改善电池均匀性,因此本文针对串联电阻的影响进行重点研究。本文基于太阳电池模型,假定大面积太阳电池可看作是多个小面积太阳电池单元并联而成的太阳电池单元组件。计算结果表明,并联光伏组件的效率比加权平均效率低;提高光伏组件的串联电阻能在一定程度上改善电池不均匀性,但未必能提高光电转换效率,这有赖于光伏组件的不均匀程度和其本身的串联电阻大小;当光伏组件本身的均匀性较好且串联电阻也较小时,提高光伏组件的串联电阻能提高光伏组件效率。     

聚光光伏电池的热平衡与冷却

建立了聚光条件下光伏电池的热平衡方程及电学特性模型,利用模型对电池的输出特性进行了计算,根据计算结果对传热过程中的热阻及电池的串联内阻对电池的温度、光电转换效率及电能输出功率的影响进行了分析。分析结果表明:电池温度随聚光率的增加而升高,电池效率和输出功率随聚光率的增加先增后降,并存在一个最大输出功率;电池冷却过程的热阻越小、工作温度越低,光电转换效率越高、输出功率越大;电池本身串联内阻越大,电池的效率越低、输出功率越小。根据分析结果提出,要使硅电池在聚光条件下长期高效、稳定安全的运行,必须对电池进行适当的冷却,要尽可能减小电池的串联内阻。     

晶硅电池在低倍聚光条件下短路电流变化规律分析

在对常规晶硅电池的性能测量过程中发现,在常温非聚光情况下,晶硅电池短路电流Isc与温度保持线性关系;但在高温低倍聚光情况下,短路电流Isc出现偏离线性的现象。使用双二极管的晶硅电池等效模型进行分析,简化短路电流表达式。在此基础上使用公式对Isc出现的偏离线性现象进行分析,指出并联电阻Rsh与串联电阻Rs的量级变化差别,引起Isc出现偏离线性,并据此定义了一个短路电流偏离线性系数αIsc。分析了短路电流偏离线性系数αIsc对Isc偏离线性的影响,在高温低倍聚光情况下,αIsc<1,晶硅电池的Isc出现明显下降。因此,在低倍聚光情况下,具有大并联电阻Rsh的晶硅电池,即αIsc≈1,能保证输出电流的稳定性。     

测量方式对太阳电池输出性能测试的影响

通过对二线与四线接法测试单晶硅太阳电池I-V曲线的实验结果对比,分析串联内阻对于太阳电池短路电流、开路电压、填充因子及最大输出功率测量结果的影响。结果发现串联内阻越大,太阳电池的短路电流、填充因子及最大输出功率测量结果越小,但对开路电压基本无影响。且太阳电池接收光强越大即输出电流越大时,串联内阻的影响也越大。二线法因串联内阻较大,相较四线测量方法,在光强分别为1160.69、734.61、470.15和232.14 W/m²时,最大功率降幅分别为64.73%、40.26%、22.98%、11.88%;填充因子降幅分别为64.10%、40.96%、22.22%、12.66%。表明内阻大小影响二线及四线测量结果,四线法测量方式能有效规避串联引线电阻和部分接触电阻,是较理想的测量方式。     

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.     

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%.     

Contents in Volume 23,2014

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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.     

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.     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures.     

Production of hydrogen from sewage biosolids in a continuously fed bioreactor: Effect of hydraulic retention time and sparging

Hydrogen was produced from primary sewage biosolids via mesophilic anaerobic fermentation in a continuously fed bioreactor. Prior to fermentation the sewage biosolids were heated to 70 °C for 1 h to inactivate methanogens and during fermentation a cellulose degrading enzyme was added to improve substrate availability. Hydraulic retention times (HRT) of 18, 24, 36 and 48 h were evaluated for the duration of hydrogen production. Without sparging a hydraulic retention time of 24 h resulted in the longest period of hydrogen production (3 days), during which a hydrogen yield of 21.9 L H₂ kg⁻¹ VS added to the bioreactor was achieved. Methods of preventing the decline of hydrogen production during continuous fermentation were evaluated. Of the techniques evaluated using nitrogen gas to sparge the bioreactor contents proved to be more effective than flushing just the headspace of the bioreactor. Sparging at 0.06 L L min⁻¹ successfully prevented a decline in hydrogen production and resulted in a yield of 27.0  L H₂ kg⁻¹ VS added, over a period of greater than 12 days or 12 HRT. The use of sparging also delayed the build up of acetic acid in the bioreactor, suggesting that it serves to inhibit homoacetogenesis and thus maintain hydrogen production.     

汽轮机数字电液调节系统挂闸异常的技术完善

分析了200MW汽轮机数字电液调节系统在运行中存在的挂闸异常问题,采取了相应的技术处理措施,且运行实践效果良好。     

新型高压共轨ECU升压模块的数字化开发与优化

为了提高喷油器电磁阀的响应速率,提出了一种基于CPLD(复杂可编程逻辑器件)应用于高压共轨ECU的数字升压模块。鉴于该升压电路结构参数多,其升压电压的恢复响应要求高等特征,基于Pspice建立了升压电路的仿真模型,研究了不同电路参数下升压模块的输出特性,全面优化了该升压模块的性能。结果显示,该升压模块的最大转换效率可以达90%以上。在柴油发动机上对ECU的试验表明,升压电压最大波动不超过10%,其恢复时间仅为1.3ms,功率管最大温升仅为41℃,满足整机运行范围内ECU的需求。     

Trace metal chemistry and silicification of microorganisms in geothermal sinter, Taupo Volcanic Zone, New Zealand

As part of a pilot study investigating the role of microorganisms in the immobilisation of As, Sb, B, Tl and Hg, the inorganic geochemistry of seven different active sinter deposits and their contact fluids were characterised. A comprehensive series of sequential extractions for a suite of trace elements was carried out on siliceous sinter and a mixed silica-carbonate sinter. The extractions showed whether metals were loosely exchangeable or bound to carbonate, oxide, organic or crystalline fractions. Hyperthermophilic microbial communities associated with sinters deposited from high temperature (92–94°C) fluids at a variety of geothermal sources were investigated using SEM. The rapidity and style of silicification of the hyperthermophiles can be correlated with the dissolved silica content of the fluid. Although high concentrations of Hg and Tl were found associated with the organic fraction of the sinters, there was no evidence to suggest that any of the heavy metals were associated preferentially with the hyperthermophiles at the high temperature (92–94°C) ends of the terrestrial thermal spring ecosystems studied.