Electrical performance evaluation of low‐concentrating non‐imaging photovoltaic concentrator

Second generation prototype photovoltaic facades of reduced costs incorporating devices with optically concentrating elements (PRIDE) incorporate 6 mm wide ‘Saturn’ solar cells at the absorber of the dielectric concentrator. The concentrators were made using injection moulding technique with potential to manufacture in large‐scale applications. Four different concentrator panels have been experimentally verified at outdoors to identify the non‐identical current–voltage (I–V) curves. The I–V curve, fill factor and solar to electrical conversion efficiency of four PRIDE concentrator modules have been evaluated from the 24 manufactured in the ‘IDEOCONTE’ project. The maximum solar to electrical conversion efficiency and the fill factor of the PRIDE concentrator were 9·1 and 70%, respectively. The mismatch loss of the ‘unit concentrators’ has been identified that occurred due to the lack of bonding between the concentrator unit and the solar cell and the rear glass. The average power concentration ratio of PRIDE concentrators manufactured by the improved method was 2·10 compared to a similar non‐concentrating panel and the optical efficiency of the PRIDE system was 83%. Copyright © 2008 John Wiley & Sons, Ltd.     

Rondine® PV concentrators: Field results and developments

In this work the experimental results of a new PV concentrator (named Rondine®) are presented. This concentrating module has a medium concentration level (∼25×) and employs silicon solar cells. The tests have been carried out in Italy and the energy production of a prototype module is compared with that produced from a tracking flat plate crystalline PV panel. The non‐imaging optics of the concentrator allows for larger angular acceptance with respect to many solar concentrators, giving us the possibility to employ trackers for standard PV modules. The first results of complete systems of 3·9 and 4·8 kW of peak power installed in summer 2008 are presented here. Copyright © 2009 John Wiley & Sons, Ltd.     

BICON: high concentration PV using one‐axis tracking and silicon concentrator cells

BICON is a two‐stage concentrator system developed at Fraunhofer ISE which is one‐axis tracked. The innovation of this one‐axis tracked system is that it enables a high geometrical concentration of 300 × in combination with a high optical efficiency (upto 78%) and a large acceptance angle of ± 23·5° all year through. For this, the system uses a parabolic mirror (40·4 ×) and a three dimensional second stage consisting of compound parabolic concentrators (CPCs, 7·7 ×). For the concentrator concept and particularly for an easy cell integration, rear‐line‐contacted concentrator (RLCC) cells with a maximum efficiency of 25% were developed and a hybrid mounting concept for the RLCC cells is presented. The optical performance of different CPC materials was tested and is analysed in this paper. Finally, small modules consisting of six series interconnected RLCC cells and six CPCs were integrated into the concentrator system and tested outdoor. A BICON system efficiency of 16·2% was reached at around 800 W/m² direct irradiance under realistic outdoor conditions. Copyright © 2006 John Wiley & Sons, Ltd.     

Novel high-efficiency concentrator for optical fiber communication

A novel high-efficiency concentrator based on nonimaging optics has been designed and fabricated with micromachining technique. The shape of the concentrator utilizes compound parabolic concentrator (CPC), which can concentrate the all rays that have the angles less than a critical angle &thetas;_c. The theoretical concentration efficiency was calculated by ray trace simulation considering the reflectance of the concentrator's reflective layer. The metal reflection layer of reflectance 95% was formed by gold-nickel mirror plating method in a glass hole. As a result, the concentration efficiency of the concentrator was measured as 89%     

Temperature accelerated life test on commercial concentrator III–V triple‐junction solar cells and reliability analysis as a function of the operating temperature

A temperature accelerated life test on commercial concentrator lattice‐matched GaInP/GaInAs/Ge triple‐junction solar cells has been carried out. The acceleration of the aging has been accomplished by subjecting the solar cells at temperatures markedly higher than the nominal working temperature inside a concentrator, and the nominal photo‐current condition (820 X) has been emulated by injecting current in darkness. Three tests at different temperatures have been carried out. The failure distributions across the three test temperatures have been fitted to an Arrhenius–Weibull model. An Arrhenius activation energy of 1.59 eV was determined from the fit. The reliability functions and parameters of these solar cells at two nominal working conditions (80 and 100 °C) have been obtained. In both cases, the instantaneous failure rate function monotonically increases, that is, the failures are of the wear‐out kind. We have also observed that the reliability data are very sensitive to the nominal temperature condition. In fact, at a nominal working condition of 820 X and 80 °C, assuming that the concentration module works 5 h per day, the warranty time obtained for a failure population of 5% has been 113 years. However, for a nominal working condition of 820 X and 100 °C, the warranty time obtained for a failure population of 5% has been 7 years. Therefore, in order to offer a long‐term warranty, the working temperature could be a key factor in the design of the concentration photovoltaic systems. Copyright © 2014 John Wiley & Sons, Ltd.     

Characterization of optical collectors for concentration photovoltaic applications

The design and characterization of the collector of a photovoltaic concentrator system is commonly carried out for a given receiver, the optical parameters of the collector being linked to it. This paper, which has substantial tutorial content, deals with the characterization of collectors for concentrator photovoltaic systems, independently of any receiver, and providing the necessary parameters for the design of a system. This strategy allows the parameters related to the collector and the receiver, which are usually manufactured by different industries, to be totally separated. It also allows the optical collectors coming from non‐photovoltaic industries to be evaluated. The information that the mirror and lens manufacturers should provide for a photovoltaic concentrator application can be summarized under three characteristics: overall optical efficiency; light distribution; and acceptance angle. Theory, equipment, and procedures to carry out the optical characterization of the collectors are explained. Copyright © 2003 John Wiley & Sons, Ltd.     

百花岭选矿厂磨矿分级系统自动化控制升级的设想

通过对百花岭选矿厂磨矿分级系统自动化控制的运行情况进行分析,针对磨矿负荷、磨矿浓度及返砂量不能在线测量,不能满足优化控制需求,未能发挥磨机最大效率的问题。经过查阅资料、实地考察国内一些大型新建选厂的磨矿分级系统自动化控制的使用情况,对百花岭选矿厂磨矿分级自动化控制的升级改造提出了切实可行的设计思路和方法,建议添加必要的现场仪表,通过高等数学工具提高控制的有效性,采用先进的控制算法提高控制的精度。     

Sliver solar cells for concentrator PV systems with concentration ratio below 50

This paper links together two different yet complimentary technologies: concentrator photovoltaics (CPVs) and Sliver technology. Recent research and development and commercialisation efforts in concentrator technologies have centred on high‐concentration systems, encouraged by the availability of high‐efficiency, multi‐junction III‐V cells. In contrast, little attention has been paid to the potential of systems with low‐to‐medium levels of concentration. Arguably, this is due to the absence of any suitable, low‐cost concentrator cells, readily available at a commercial scale. Sliver technology is a candidate for the supply of commercial low‐cost cells suitable for systems with concentration ratios in the range of 5–50. This can be achieved via judicious choice of cell design parameters and with only minor changes to the fabrication process suitable for 1‐sun Sliver cells. Device modelling is used to show that Sliver cells are suitable for illumination intensities up to 5 W/cm², with unavoidable emitter resistance limiting performance for higher intensities. The best cells manufactured for operation at low and medium concentration had efficiencies of 18·8% at 9 suns (above 18·6% between 5 and 15 suns) and 18·4% at 37 suns (above 18·2% between 30 and 50 suns), respectively. Incorporation of sidewall texturing and SiN anti‐reflection coatings would yield efficiencies exceeding 20% for similar cells. Concentrator Sliver cells can be produced to almost any length and are perfectly bifacial, features which add significantly to their attractiveness to concentrator system designers. The availability of cheap concentrator Sliver cells could provide opportunities for new, low‐cost concentrator systems, which in turn has the potential to provide a pathway to low‐cost solar electricity. Copyright © 2009 John Wiley & Sons, Ltd.     

全内反射型太阳能聚光模块设计与研究

设计了用于太阳能聚集的全内反射（Total-internal-reflection,TIR）聚光器并采取措施进行优化,将多个TIR聚光器进行叠加放置在光波导板组成波导聚光模块。太阳光线经TIR聚光器阵列收集后照射到光波导板上并在其内部传播,由末端的光伏电池吸收。由实验结果可知,在光波导板长度为400 mm增至4 800 mm的过程中,光学效率由88.6%降低为40.2%,而辐照度由212 W/m2增长为980 W/m2。这样根据不同需求选取不同长度的光波导板,并在保证较高的输出功率的前提下大大减少所需使用的光伏电池面积,同时TIR聚光器只需水平放置在光波导板上,避免了透镜阵列与光波导板的严格对准要求,降低了制造与装配成本。     

Experimental demonstration of high‐concentration photovoltaics on a parabolic trough using tracking secondary optics

A new approach to high‐concentration photovoltaics (HCPV) based on a parabolic trough primary concentrator is presented. The design diverges from the standard HCPV arrangement of a two‐axis tracking point‐focus concentrator, and rather employs a simpler parabolic trough primary concentrator to reduce cost. To break the 2D limit of concentration, and bring the system into the realm of HCPV, the system employs an array of rotating secondary concentrators is arranged along the focal line of the parabolic trough. The resulting line‐to‐point (LTP) focus geometry allows the system to achieve a geometric concentration of 590×, yet still maintains the advantages of having a linear trough primary concentrator, namely manufacturability, economy, and scalability. A full‐scale prototype of the system was constructed in Biasca, Switzerland. During on‐sun tests a flux concentration of 364 suns was measured at the exit of the secondary concentrator, the highest reported concentration for any parabolic‐trough‐based system. Moreover, the system reached a peak efficiency of 20.2%, the highest measured solar‐to‐DC efficiency for a parabolic trough‐based solar collector. Long‐term performance is estimated by means of a coupled optical‐electrical model validated vis‐à‐vis the experimental results. This work serves as an experimental proof‐of‐concept for high‐concentration trough‐based collectors, thereby opening new avenues for reducing the cost of HCPV systems. Copyright © 2016 John Wiley & Sons, Ltd.     

基于超材料的正多边形电磁波聚焦器设计

该文基于变换光学方法,导出了正多边形电磁聚焦器的介电常数和磁导率的分布,并用有限元分析软件COMSOL进行了证实。分别仿真了TE波和线源激励下正三边形、正四边形、正五边形和正六边形电磁聚焦器附近的电场分布和能量密度分布,并讨论了正多边形电磁聚焦器聚焦区域面积大小和电磁参数偏离理论值对其聚焦特性的影响,结果表明:聚焦区域越小,电磁聚焦越强;当超材料的电磁特性偏离理论值时,电磁聚焦特性发生变化。     

Effect of trap location and trap-assisted Auger recombination onsilicon solar cell performance

Model calculations were performed to investigate and quantify the effect of trap location and trap-assisted Auger recombination on silicon solar cell performance. Trap location has a significant influence on the lifetime behavior as a function of doping and injected carrier concentration in silicon. It Is shown in this paper that for a high quality silicon (τ=10 ms at 200 ohm-cm, no intentional doping), high resistivity (⩾200 ohm-cm) is optimum for high efficiency one sun solar cells if the lifetime limiting trap is located near midgap. However, if the trap is shallow (E_t-E_v⩽0.2 eV), the optimum resistivity shifts to about 0.2 ohm-cm. For a low quality silicon material or technology (10 μs at 200 ohm-cm, prior to intentional doping) the optimum base resistivity for one sun solar cells is found to be ~0.2 ohm-cm, regardless of the trap location. It is shown that the presence of a shallow trap can significantly degrade the performance of a concentrator cell fabricated on high-resistivity high-lifetime silicon material because of an undesirable injection level dependence in the carrier lifetime. The effect of trap assisted Auger recombination on the cell performance has also been modelled in this paper. It is found that the trap-assisted Auger recombination does not influence the one sun cell performance appreciably, but can degrade the concentrator cell performance if the trap-assisted Auger recombination coefficient value exceeds 2×10^-14 cm³/s. Therefore, it is necessary to know the starting lifetime as well as trap location in order to specify base resistivity in order to predict or achieve the best cell performance for a given one sun or concentrator cell design     

Concentration photovoltaic optical system irradiance distribution measurements and its effect on multi‐junction solar cells

This paper proposes an indoor procedure based on charge‐coupled device camera measurements to characterize the non‐uniform light patterns produced by optical systems used in concentration photovoltaic (CPV) systems. These irradiance patterns are reproduced on CPV solar cells for their characterization at concentrated irradiances by using a concentrator cell tester and placing high‐resolution masks over the cells. Measured losses based on the masks method are compared with losses in concentrator optical systems measured by using the Helios 3198 solar simulator for CPV modules. Copyright © 2011 John Wiley & Sons, Ltd.     

一种环面焦斑菲涅耳聚光器的设计与分析

在聚光光伏系统中,聚光光斑辐照度的不均匀性会降低光伏系统的光电转换效率,且会在光伏电池表面形成热斑效应,灼伤光伏电池。基于多焦点方法,设计了一种环形焦斑菲涅耳太阳能聚光镜,每环小透镜在焦平面上具有一个环面焦斑,且环面焦斑在接受面上均匀依次排列,实现均匀聚光。以口径400mm,具有200环,焦斑半径20mm,F数为0.8的圆状环面焦斑菲涅耳聚光器为实例,用TracePro模拟平行太阳光垂直照射下时的照度图,得到其理想光学效率为86.77%,光能均匀度为0.8,表明环状焦斑菲涅耳聚光器具有较高的光能利用率和照明均匀性。分析了焦斑均匀性与聚光器F数的关系,当F数一定时,焦斑均匀性随着聚光器口径的增大而逐渐降低。     

Energy payback time of the high‐concentration PV system FLATCON®

The ecological benefit and sustainability of a new energy technology and its potential to reduce CO₂ emissions depend strongly on the amount of energy embodied in the materials and production processes. The energy payback time is a measure for the amount of time that a renewable energy system has to operate until the energy involved in its complete life‐cycle is regenerated. In this paper, the energy payback time of the high‐concentration photovoltaic system FLATCON® using III–V semiconductor multi‐junction solar cells has been evaluated. Considering the energy demand for the system manufacturing, including transportation, balance of system and system losses, the energy payback time turns out to be as low as 8–10 months for a FLATCON® concentrator built in Germany and operated in Spain. The energy payback time rises slightly to 12 to 16 months for a system installed in Germany. The main energy demand in the production of such a high‐concentration photovoltaic system was found to be the zinced steel for the tracking unit. Copyright © 2005 John Wiley & Sons, Ltd.     

Development and experimental evaluation of a complete solar thermophotovoltaic system

We present a practical implementation of a solar thermophotovoltaic (TPV) system. The system presented in this paper comprises a sunlight concentrator system, a cylindrical cup‐shaped absorber/emitter (made of tungsten coated with HfO₂), and an hexagonal‐shaped water‐cooled TPV generator comprising 24 germanium TPV cells, which is surrounding the cylindrical absorber/emitter. This paper focuses on the development of shingled TPV cell arrays, the characterization of the sunlight concentrator system, the estimation of the temperature achieved by the cylindrical emitters operated under concentrated sunlight, and the evaluation of the full system performance under real outdoor irradiance conditions. From the system characterization, we have measured short‐circuit current densities up to 0.95 A/cm², electric power densities of 67 mW/cm², and a global conversion efficiency of about 0.8%. To our knowledge, this is the first overall solar‐to‐electricity efficiency reported for a complete solar thermophotovoltaic system. The very low efficiency is mainly due to the overheating of the cells (up to 120 °C) and to the high optical concentrator losses, which prevent the achievement of the optimum emitter temperature. The loss analysis shows that by improving both aspects, efficiencies above 5% could be achievable in the very short term and efficiencies above 10% could be achieved with further improvements. Copyright © 2012 John Wiley & Sons, Ltd.     

Monolithically interconnected lamellar Cu(In,Ga)Se2 micro solar cells under full white light concentration

Thin film solar cells already benefit from significant material and energy savings. By using photon management, the conversion efficiency and the power density can be enhanced further, including a reduction of material costs. In this work, micrometer‐sized Cu(In,Ga)Se₂ (CIGS) thin film solar cells were investigated under concentrated white light illumination (1–50×). The cell design is based on industrially standardized, lamellar shaped solar cells with monolithic interconnects (P‐scribe). In order to characterize the shunt and serial resistance profiles and their impact on the device performance the cell width was reduced stepwise from 1900 to 200 µm and the P1‐scribe thickness was varied between 45 and 320 µm. The results are compared to macroscopic solar cells in standard geometry and dot‐shaped microcells with ring contacts. Under concentrated white light, the maximal conversion efficiency could be increased by more than 3.8% absolute for the lamellar microcells and more than 4.8% absolute in case of dot‐shaped microcells compared to their initial values at 1 sun illumination. The power density could be raised by a factor of 51 and 70, respectively. But apparently, the optimum concentration level and the improvement in performance strongly depend on the chosen cell geometry, the used contact method and the electrical material properties. It turns out, that the widely used industrial thin film solar cell design pattern cannot simply be adapted to prepare micro‐concentrator CIGS solar modules, without significant optimization. Based on the experimental and simulated results, modifications for the cell design are proposed. Copyright © 2015 John Wiley & Sons, Ltd.     

Analysis of Channel Utilization in Traffic Concentrators

The behavior of line concentrators in a data communication system has been analyzed for different channel allocation strategies. The users (terminals) are divided into classes according to their transmission rate requirements. The different bit rate classes (BRC) can be separated by dividing the network into subnets or, alternatively, they can share one concentrator which forms outgoing channels from a common quantity of channels of a basic speed, or by splitting a high speed channel into two or more channels with lower transmission rate. The equations of state and analytical expressions for the time congestion factors have been developed for the different system models. The numerical results show that a joint concentrator arrangement requires less channel capacity than a separated concentrator system for a fixed value of the congestion probability. The results of this investigation may serve as background material for planning future data networks.     

Reliability of commercial triple junction concentrator solar cells under real climatic conditions and its influence on electricity cost

This paper proposes a methodology for assessing the concentrator solar cell reliability in a real application for a given location provided the results from accelerated life tests. We have applied this methodology for the evaluation of warranty times of commercial triple junction solar cells operating inside real concentrator modules in Golden (Colorado, USA), Madrid (Spain) and Tucson (Arizona, USA) for the period 2012–2015. Warranty times in Golden and Madrid, namely, 68 and 31 years, respectively, for the analysed period, indicate the robustness of commercial triple junction solar cells. Nevertheless, the warranty time of 15 years for Tucson suggests the need of improvement in the heat extraction of the solar cell within the concentrator module. Therefore, the influence of the location on the reliability of concentrator solar cells is huge, and it has no sense to supply general reliability values for a given concentrator product. The influence of these warranty times for the three locations on the levelised cost of electricity has been analysed. Cost of €c10–12/kWh can be achieved nowadays, while after 1 GW_p cumulative installed power, a dramatic reduction to levels of €c2–3/kWh is achievable. Copyright © 2017 John Wiley & Sons, Ltd.     

A simple ray tracer to compute the optical concentration of photovoltaic modules

In a conventional photovoltaic module, some light that falls between the solar cells is internally reflected onto the cells via the backsheet and the glass–air interface of the module; thus, a module can be considered a static concentrator. We present a simple ray tracer that computes a module's optical concentration as a function of cell separation, cell geometry, and the optical properties of the encapsulants. The ray tracer's primary simplification is to divide the module's backsheet into small pixels and, since the reflection from the backsheet is approximately Lambertian and independent of the incident angle, to sum the intensity of all rays that enter a pixel and treat them as one. The advantage of this pixel approximation is that it makes it simple to simulate curved surfaces—such as the corners of a pseudo‐square solar cell—within short computation times. The results of the simple ray tracer are shown to be consistent with those of a conventional ray tracer and an LBIC experiment. We also apply the ray tracer to a present‐day SunPower module and find that 25% of the photons that fall between the cells are internally reflected onto the cells, which results in an optical concentration of 1·024. Copyright © 2005 John Wiley & Sons, Ltd.