High performance a-Si solar cells and new fabrication methods for a-Si solar cells

The super chamber, a separated UHV reaction-chamber system has been developed. A conversion efficiency of 11.7% was obtained for an a-Si solar cell using a high-quality i-layer deposited by the super chamber, and a p-layer fabricated by a photo-CVD method.As a new material, amorphous superlattice-structure films were fabricated by the photo-CVD method for the first time. Superlattice structure p-layer a-Si solar cells were fabricated, and a conversion efficiency of 10.5% was obtained.For the fabrication of integrated type a-Si solar cell modules, a laser pattering method was investigated. A thermal analysis of the multilayer structure was done. It was confirmed that selective scribing for a-Si, TCO and metal film is possible by controlling the laser power density. Recently developed a-Si solar power generation systems and a-Si solar cell roofing tiles are also described.     

Performance and Exergy Analyses of a Solar Assisted Heat Pump with Seasonal Heat Storage and Grey Water Heat Recovery Unit

The main research objective of this paper was to compare exergy performance of three different heat pump (HP)-based systems and one natural gas (NG)-based system for the production of heating and cooling energy in a single-house dwelling. The study considered systems based on: 1. A NG and auxiliary cooling unit; 2. Solely HP, 3. HP with additional seasonal heat storage (SHS) and a solar thermal collector (STC); 4. HP with SHS, a STC and a grey water (GW) recovery unit. The assessment of exergy efficiencies for each case was based on the transient systems simulation program TRNSYS, which was used for the simulation of energy use for space heating and cooling of the building, sanitary hot water production, and the thermal response of the seasonal heat storage and solar thermal system. The results show that an enormous waste of exergy is observed by the system based on an NG boiler (with annual overall exergy efficiency of 0.11) in comparison to the most efficient systems, based on HP water–water with a seasonal heat storage and solar thermal collector with the efficiency of 0.47. The same system with an added GW unit exhibits lower water temperatures, resulting in the exergy efficiency of 0.43. The other three systems, based on air–, water–, and ground–water HPs, show significantly lower annual source water temperatures (10.9, 11.0, 11.0, respectively) compared to systems with SHS and SHS + GW, with temperatures of 28.8 and 19.3 K, respectively.     

太阳能光伏-温差发电驱动的新型冰箱模型设计与热力学分析

结合太阳能电池温度特性和温差发电特点,设计了一套新的太阳能光伏发电-温差发电驱动的冰箱模型,该模型包括太阳能光伏电池、半导体温差发电模块、电源控制系统等.根据负载用电需求,做出了光伏发电系统的设计方案.采用热力学基本理论,对该模型进行了工作效率及 火 用 效率的分析.结果发现:能效比COP达到了2.73(一般 冰箱COP为2左右), 火 用 效率也达到42.5%.同时,该系统模型环境效益明显,可以减排CO₂ 1394.2 kg,SO₂     

Size dependence of efficiency at maximum power of heat engine

We perform a molecular dynamics computer simulation of a heat engine model to study how the engine size difference affects its performance. Upon tactically increasing the size of the model anisotropically, we determine that there exists an optimum size at which the model attains the maximum power for the shortest working period. This optimum size locates between the ballistic heat transport region and the diffusive heat transport one. We also study the size dependence of the efficiency at the maximum power. Interestingly, we find that the efficiency at the maximum power around the optimum size attains a value that has been proposed as a universal upper bound, and it even begins to exceed the bound as the size further increases. We explain this behavior of the efficiency at maximum power by using a linear response theory for the heat engine operating under a finite working period, which naturally extends the low-dissipation Carnot cycle model [M. Esposito, R. Kawai, K. Lindenberg, C. Van den Broeck, Phys. Rev. Lett. 105, 150603 (2010)]. The theory also shows that the efficiency at the maximum power under an extreme condition may reach the Carnot efficiency in principle.     

太阳能热发电聚光系统的研究进展

概述了太阳能热发电技术的发展状况,介绍了用于太阳能热发电的5种聚光系统,包括槽式、碟式、塔式、线性菲涅耳式以及地面接收式。详细阐述了这些聚光系统的光学结构、聚光原理以及聚光器件的设计方法和制作工艺,指出了不同聚光系统在聚光过程中的优缺点。文中的讨论可为太阳能热发电聚光系统的设计提供参考。     

Beam quality considerations of high power Nd:YAG lasers

High power Nd:YAG lasers with fiber optic beam delivery have introduced new capabilities for material processing applications. Here, we present the stable resonator design for high power Nd:YAG lasers to optimize beam quality for fiber optic transmission. Dependence of beam parameters on position and dioptric power of thermal lens has been investigated and optimized to achieve efficient fiber optic beam delivery. With the optimum resonator configuration, an efficient fiber optic beam delivery over the entire operating range of input power has been achieved. The results of stable resonator design with good beam quality and output power have been presented.     

两级透射-反射聚光分频电热联产系统设计和分析

在传统聚光条件下的太阳能光伏发电系统中,由于太阳光中存在所有波段的光子,而其中只有一部分能够被太阳电池用来发电,其余的部分进入太阳电池之后非但不会被用于发电,反而会变成热量使太阳电池升温,从而使电池光电转换效率下降．本文设计了一种聚光且具有分频功能的太阳能电热联产系统,利用线聚焦菲涅尔透镜和光谱选择性透过涂层改善太阳电池表面的入射光环境,在聚光的同时将不利于光伏发电的太阳光波段反射并加以收集利用．分析结果表明,与相同条件下传统的只进行聚光的光伏系统相比,两级透射一反射聚光分频电热联产系统具有更高的太阳能利用效率．     

太阳能制冷系统的优化分析

太阳能制冷系统的优化分析陈金灿，严子浚（厦门大学物理系厦门３６１００５）关键词：制冷系统，太阳能集热器，优化分析一、引言确定太阳能热力循环系统集热器的最佳工作温度，一直是集热器优化设计中的一个重要问题［１－４］。特别是应用有限时间热力学理论来研究这个...     

太阳能光伏热水系统的能量梯级利用

为了实现太阳能光伏发电系统中用于冷却太阳能电池的低品位热能利用,本文提出了太阳能光伏热水系统。通过对单体光伏光热系统(PV/T)的实验研究表明,在单体PV/T放置角度为30°,流量为200 L/h时,集热效率可达到最大值65.6%,系统的平均发电效率为14.3%,瞬时综合效率最大为83%,达到了能量的梯级利用。     

太阳能热发电聚光系统的研究进展

概述了太阳能热发电技术的发展状况,介绍了用于太阳能热发电的5种聚光系统,包括槽式、碟式、塔式、线性菲涅耳式以及地面接收式。详细阐述了这些聚光系统的光学结构、聚光原理以及聚光器件的设计方法和制作工艺,指出了不同聚光系统在聚光过程中的优缺点。文中的讨论可为太阳能热发电聚光系统的设计提供参考。     

新型低熔点熔盐黏度的实验研究

熔盐因其具有广泛的使用温度范围,低蒸气压,大热容量,低黏度,良好的稳定性,低成本等诸多特性已成为聚光太阳能热发电中颇有潜力的传热蓄热介质。准确的熔盐热物性对于太阳能发电过程中介质的传热蓄热性能有重要影响。其中熔盐黏度作为重要的热物性之一,对于提高传热效率和降低流动阻力具有决定作用。本文利用研制的高温黏度测量仪对水和HITEC盐的黏度温度特性进行了实验研究,实验结果与文献数据具有较好的一致性,证明了该高温熔盐黏度仪的可靠性。为了降低混合熔盐的熔点,改进其热物性能,本文对Solar Salt进行改性研究,得到两种新型低熔点混合熔盐,并测定得到了黏度温度特性曲线。结果表明,改性后的高温熔融盐黏度有所降低,有利于降低太阳能热发电熔盐传热管路系统的阻力和成本。     

Efficient implementation of multiple drive-in steps in thermal diffusion of phosphorus for PERC solar cells

N-type phosphorus diffusion in silicon using phosphorus oxychloride, POCl₃, has been widely used in the production of p-type silicon solar cells. The thermal diffusion process in a furnace generally involves two steps: pre-deposition and drive-in. The phosphorous doping by thermal diffusion often shows high surface concentrations, leading to an increase in charge recombination, which should be inhibited in order to fabricate high efficiency silicon solar cells. In this study, we investigate the influence of 3 drive-in steps at sequentially increasing temperatures during the POCl₃ diffusion on the emitter performance. As a result, it was found that the kink region was made shorter while maintaining surface concentration for a good metal contact without losing its passivation quality. This result is attributed to the higher active dopant concentration of the 3 drive-in step samples, leading to a lower series resistance and higher fill factor in the PERC solar cells. The results show that slight changes in the PSG process conditions can contribute to the improvement of high efficiency solar cells.     

电动汽车锂离子电池热管理系统研究进展

锂离子电池作为电动汽车最广泛使用的动力源,对工作温度高度敏感,为保证其高性能和安全运行,电池热管理系统必不可少.本文综述了近年来锂离子电池热管理系统的研究进展.首先讨论了由高低温环境和电池温度不均匀引起的临界热问题.在此基础上,对设计原则和现有的电池热管理系统进行了广泛的介绍和阐述.然后进一步分析了用于未来电池热管理系统的热电器件和内部加热方法等新兴技术.分析表明,被动和主动冷却/加热方法的组合有望满足苛刻的热要求,特别是在功率波动剧烈的动态条件下.此外,电池在变工况下所输出的电流、电压等均不相同,因此建议对电动汽车动力电池进行动态性能实时管理,从而延长电池使用寿命。     

Modeling and Performance Optimization of an Irreversible Two-Stage Combined Thermal Brownian Heat Engine

Based on finite time thermodynamics, an irreversible combined thermal Brownian heat engine model is established in this paper. The model consists of two thermal Brownian heat engines which are operating in tandem with thermal contact with three heat reservoirs. The rates of heat transfer are finite between the heat engine and the reservoir. Considering the heat leakage and the losses caused by kinetic energy change of particles, the formulas of steady current, power output and efficiency are derived. The power output and efficiency of combined heat engine are smaller than that of single heat engine operating between reservoirs with same temperatures. When the potential filed is free from external load, the effects of asymmetry of the potential, barrier height and heat leakage on the performance of the combined heat engine are analyzed. When the potential field is free from external load, the effects of basic design parameters on the performance of the combined heat engine are analyzed. The optimal power and efficiency are obtained by optimizing the barrier heights of two heat engines. The optimal working regions are obtained. There is optimal temperature ratio which maximize the overall power output or efficiency. When the potential filed is subjected to external load, effect of external load is analyzed. The steady current decreases versus external load; the power output and efficiency are monotonically increasing versus external load.     

平板集热太阳热电器件建模及结构优化

太阳能热电转换是光伏效应外另一种直接将太阳辐射转变为电能的途径, 近年来已经成为太阳能利用的热点之一. 本文以Bi₂Te₃材料为基础构建平板集热太阳热电器件模型, 采用有限元法分析AM1.5辐射条件下器件温度分布情况, 并结合基于温度的物性参数计算集热比、热臂截面积与长度变化等因素对器件的开路电压、 最大输出功率及转化效率的影响. 研究发现: 集热比与热臂长度的变化对器件性能有显著影响, 热臂截面积的变化对器件转化效率影响相对较弱; 在这一模型中, 平板集热太阳热电器件的转化效率达到1.56%.     

Solar energy conversion with fluorescent collectors

A new principle for solar energy conversion is proposed and evaluated theoretically. Collection and concentration of direct and diffuse radiation is possible by the use of a stack of transparent sheets of material doped with fluorescent dyes. High efficiency of light collection can be achieved by light guiding and special design of collectors. The optical path length in a triangular collector is computed. In combination with solar cells this type of collector offers the advantage of separating the various fractions of light and converting them with solar cells with different bandgaps. Theoretical conversion efficiency under optimum conditions is 32% for a system with four semiconductors. Thermal energy conversion offers several advantages over conventional collectors: High temperature and efficiency even under weak illumination, separation of heat transport and radiation collection, low thermal mass. Thermal efficiency is computed to be between 42% and 60%. Very attractive appear hybrid systems for generation of thermal and electric energy. An estimate of the economics of electricity generation shows that due to the concentration costs can be much lower than possible today. With the use of only silicon cells the breakeven point of $0.5/W is almost reached. Practical difficulties to be solved are: Synthesis of dyes with stringent requirements, identification of plastic materials with high transparency and development of solar cells with higher bandgaps.     

Solar-assisted liquid metal MHD power generation: A state of the art study

The research and development of LMMHD energy conversion (EC) systems which started in the 1960s has already come a long way and is heading towards commercialization. Design and development of such systems has to deal with a number of questions relating to single- and two-phase flows of molten metals, including different patterns of two-phase flow, interphase, phenomena, heat transfer, performance of LMMHD components and compatibility of liquid metals with other fluids and with confinement materials. Liquid metal MHD (LMMHD) power conversion systems proposed many years ago are gaining increasing attention in their various proposed modes, consisting of single-phase or two-phase fluid flow for a wide range of heat sources, e.g. solar energy, waste heat, nuclear energy, etc.Liquid metal MHD (LMMHD) power systems have been recently proposed for direct electrical energy conversion of low grade thermal sources of energy, like solar energy. Solar-powered LMMHD power generation systems are very attractive regarding efficiency and cost per unit of installed power. Theoretical and experimental investigations carried out in the various aspects of these systems are presented. A state of the art review of activities in the solar-powered LMMHD power systems field which have taken place so far is described here.     

立式集热板太阳能热气流电站系统研究

设计了一种立式集热板式太阳能热气流电站,分析了该系统的最大输出功率及能量转换率。数学模型考虑了系统尺寸、太阳辐射及环境条件对系统最大输出功率的影响。结果表明系统最大输出功率不仅是烟囱高度的函数,同时与太阳辐射及环境参数有很大关系。受结构限制,在太阳辐射强度为1000 W/m~2、烟囱高度为100m时,本系统能量转换率约为0.2%,在设计上可考虑采用多条集热式烟囱通道并联方式来增加集热面积,以达到提高系统最大输出功率的目的。     

Temperature dependence of GaSb and AlGaSb solar cells

Sb-based alloys offer great potential for photovoltaic and thermophotovoltaic applications. In this paper, we study the performance of Al_xGa_1-xSb (x = 0, 0.15, and 0.50) single-junction solar cells over a temperature range of 25–250 °C. The dark current-voltage, one-sun current-voltage, and external quantum efficiency measurements were acquired at different temperatures. Correlations between experimental and numerical results are made to draw conclusions about the thermal behavior of the cells. It is shown that, while the bandgaps decrease linearly with temperature leading to the reduction of open-circuit voltages, the short-circuit current densities decrease with non-linear trends. The temperature-dependent dark current densities were extracted by fitting the dark current-voltage curves to single- and double-diode models to give an insight into the effect of intrinsic carrier concentration (n_i) on the cell performance. We find that the n_i has a significant impact on temperature-dependent cell performance. These findings could lay a groundwork for the future Sb-based photovoltaic systems that operate at high temperatures.