Solar-driven high temperature hydrogen production via integrated spectrally split concentrated photovoltaics (SSCPV) and solar power tower

Hydrogen production can be achieved via combined concentrated photovoltaic (CPV) and concentrated solar power (CSP) in which concentrated radiation is spectrally split and then converted in a photovoltaic receiver and a thermal absorber. This study thus proposes an innovative solar process design integrating both thermal and quantum components of solar energy while providing a complete assessment of its global performance to demonstrate its practical interest. A stand-alone solar-to-hydrogen path was modeled and numerically simulated, which was both electrically and thermally supplied by a solar power generation unit to feed the electrolyzer power utilization unit with enhanced solar-to-hydrogen conversion efficiency. Following balance of plant (BoP), the heliostat field and cavity receiver were designed to match the entire system in which the receiver only intercepts a definite range of infrared wavelength while the rest is converted by separately insulated PV cells. Moreover, dichroic reflectors and optimum cutoff wavelength were applied to fulfill separate optimization and heat load reduction of each solar cell. Finally, the solid oxide electrolysis cell (SOEC) was designed to utilize the generated thermal and electrical power appropriately. In best case scenario, a solar-to-hydrogen conversion efficiency of 36.5% was achieved under 899 W/m² direct normal irradiance (DNI) and 1000 suns concentration. The solar plant outputs at this operating point were 850 g/h H₂ and 6754 g/h O₂. Further improvement in efficiency can be achieved through alignment in regard to the site location and annual insolation variation.     

基于分层分区的含DG配网故障恢复策略

为实现计及DG随机性出力的主动配电网分层分区故障恢复,建立了基于DG时段出力模型的主动配电网故障孤岛划分策略,并建立了主动配电网故障两阶段恢复模型,第一阶段综合考虑负荷的波动性和DG出力的随机性,建立考虑负荷恢复价值最优的主动配电网区域恢复方案;第二阶段利用可中断负荷建立配电网开关操作次数最优的全局优化模型,实现主动配电网故障后的故障恢复,既保证重要负荷的优化恢复,又延长了开关寿命,提高了经济性。采用改进的IEEE69节点系统进行仿真验证,验证了文中方案的有效性。     

Intelligent hybrid power generation system using new hybrid fuzzy-neural for photovoltaic system and RBFNSM for wind turbine in the grid connected mode

Photovoltaic (PV) generation is growing increasingly fast as a renewable energy source. Nevertheless, the drawback of the PV system is intermittent because of depending on weather conditions. Therefore, the wind power can be considered to assist for a stable and reliable output from the PV generation system for loads and improve the dynamic performance of the whole generation system in the grid connected mode. In this paper, a novel topology of an intelligent hybrid generation system with PV and wind turbine is presented. In order to capture the maximum power, a hybrid fuzzy-neural maximum power point tracking (MPPT) method is applied in the PV system. The average tracking efficiency of the hybrid fuzzy-neural is incremented by approximately two percentage points in comparison with the conventional methods. The pitch angle of the wind turbine is controlled by radial basis function network-sliding mode (RBFNSM). Different conditions are represented in simulation results that compare the real power values with those of the presented methods. The obtained results verify the effectiveness and superiority of the proposed method which has the advantages of robustness, fast response and good performance. Detailed mathematical model and a control approach of a three-phase grid-connected intelligent hybrid system have been proposed using Matlab/Simulink.     

Operation strategy of distributed energy storage system with multi-battery under output smoothing scenario

随着光伏发电在电网中渗透率的不断增加,光伏发电功率的不确定性和间歇性引起的光伏并网和弃电问题已引起关注。而采用"光伏+储能"的模式,却能有效缓解这一问题。在考虑储能电池容量衰退和光伏弃电率下,通过对不同光伏子阵配备的不同类型储能电池系统的运行进行仿真模拟,以消除光伏发电随机波动特性对电网的冲击为目的,研究平滑输出场景下分布式储能系统的电池的操作策略,优化储能系统中各储能电池子阵的运行。最后,采用共和地区20 MW （峰值）储能实证基地项目多电池储能系统实际案例对本模拟方法进行了验证。     

Z-源逆变器在光伏发电系统中的应用

Z-源逆变器由于采用独特的X型Z-源网络,可以利用逆变器桥臂直通状态实现升压功能,从而使单级Z-源逆变器具有与两级并网系统相类似的性能。该文论述基于Z-源逆变器的光伏并网系统在变换效率、可靠性以及成本方面的优势,提出了一种新的单级Z-源逆变器并网系统两级控制策略, 该控制策略实现了MPPT控制和逆变器并网控制,使Z-源光伏并网系统能够动态跟踪光伏电池最大功率点电压,输出电流与电网电压同相位,从而达到较高的功率因数。软件仿真和实验分析证明了该控制方法具有优良的动、静态特性,适合各种变化的天气情况。     

主动移频式孤岛检测方法的参数优化

孤岛检测是光伏系统并网必备的功能,要求既能快速检测出孤岛状态,同时又尽量减少对电网的不良影响。孤岛检测性能的好坏不仅取决于所采用的孤岛检测策略,也取决于检测策略中参数的设置是否合理,但目前的研究在参数优化的理论指导方面严重不足。该文通过对主动移频式孤岛检测方法的检测盲区进行分析,推导了带线性正反馈主动移频式(active frequency drift with positive feedback, AFDPF)孤岛检测方法的盲区大小与反馈增益间的关系,并得出特定负载下孤岛检测无盲区AFDPF反馈增益的取值范围,从而为AFDPF孤岛检测方法的参数优化提供了理论指导。     

具有最大功率点跟踪功能的双输入反激DC-DC变换器

近年来,太阳能、风能、燃料电池等绿色洁净新能源的利用越来越受到社会的关注,多输入变换器因为可以很好地整合多种能源而被广泛地应用于新能源开发中。本文采用双输入反激DC-DC变换器实现了太阳能电池和市电两种能源对负载的稳定供电,根据各种太阳能电池的特点,提出了双输入反激DC-DC变换器的控制策略,一方面使太阳能电池工作在最优状态,实现输出最大功率点跟踪,提高太阳能的利用率。另一方面当负载变化以及太阳能电池输出能量不足时可以从市电获取足够的能量以保证输出电压的稳定。最后通过仿真与实验,验证了本方案的可行性。     

Investigation of the properties of niobium pentoxide for use in dye-sensitized solar cells

This work demonstrates the obtention of Nb₂O₅ nanoparticles by the microwave-assisted hydrothermal synthesis method in a fast way and with the use of low temperatures. The heat treatment applied on the samples promotes the phase change in Nb₂O₅ from pseudohexagonal to orthorhombic as the temperature increases, with a particle size between 7.3 and 32.6 nm. The band gap of the samples decreases with increasing temperature, obtaining a minimum value of 3.04 eV at 800°C. Dye-sensitized solar cells (DSSC) were assembled using the Doctor Blade coating technique. The photovoltaic parameters of open-circuit voltage (Voc) and short-circuit current density (Jsc) were evaluated. The cells showed a photovoltaic response, demonstrating that Nb₂O₅ has a semiconductive potential. The DSSC have different characteristics regarding Jsc and Voc, showing that according to the temperature increase in the semiconductor sample, there is a decrease in the photovoltaic parameters of the cells.     

Compact spectrum splitting photovoltaic module with high efficiency

We have designed, fabricated, and tested a small, integrated photovoltaic module comprised of two separately‐contacted, high efficiency, multijunction solar cells and non‐imaging optics that both concentrate and spectrally split the incoming light. This hybrid design allows us to individually optimize the tandem cells and optical elements. The system has a measured module efficiency, including optical and packaging losses but not power combination losses, of 38.5 ± 1.9% under the AM1.5 direct terrestrial spectrum. The internal optics concentrate the light by a factor of approximately 20. We find excellent agreement between the modeled and measured performance. This is the highest confirmed conversion efficiency demonstrated for a photovoltaic module. Copyright © 2010 John Wiley & Sons, Ltd.     

Probing the growth of β‐FeSi2 nanoparticles for photovoltaic applications: a combined imaging and spectroscopy study using transmission electron microscopy

The microstructure of β‐FeSi₂ nanoparticles grown using magnetron sputtering on Si has been examined using various electron microscopy techniques. FeSi₂ nanoparticles as small as ∼4 nm are found embedded in Si after growth using co‐sputtering of FeSi₂ and Si, followed by rapid thermal annealing (RTA). The formation of nanoparticles and its variation in density with Fe content is discussed in terms of phase separation. Our study shows that the size and density of the nanoparticles as well as the extent of Fe diffusion into sputtered Si and substrate can be controlled by controlling the Fe content in the co‐sputtered film. Copyright © 2011 John Wiley & Sons, Ltd.