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.     

Failure analysis on lattice matched GaInP/Ga(In)As/Ge commercial concentrator solar cells after temperature accelerated life tests

Accelerated life tests are frequently used to provide reliability information in a moderate period of time (weeks or months), and after that, a failure analysis is compulsory to detect the failure origins. In this paper, a failure analysis has been carried out after a temperature accelerated life test on lattice matched GaInP/Ga(In)As/Ge triple junction commercial solar cells. Solar cells were forward biased in darkness inside three climatic chambers in order to emulate the photo‐generated current under nominal working conditions (a concentration level of 820 suns). After the accelerated aging test, a characterization of the resulting cells by means of quantum efficiency, dark and illumination I–V curves, electroluminescence, scanning electron microscope, energy dispersive X‐ray, scanning transmission electron microscope and X‐ray photoelectron spectroscopy has been carried out. Current is identified as the cause of degradation while temperature just dominates the accelerating factor of the aging test. Current promotes the front metal damage produced by the chemical evolution of the electroplating impurities together with those of the tab soldering process. Semiconductor structure does not seem to be responsible of any failure. Therefore, this kind of lattice matched GaInP/Ga(In)As/Ge triple junction solar cells, that as of 2016, are the workhorse of CPV technology, exhibits as a very robust device if the front metal connection is properly accomplished. Copyright © 2016 John Wiley & Sons, Ltd.     

Evaluation of the reliability of high concentrator GaAs solar cells by means of temperature accelerated aging tests

Evaluating the reliability, warranty period, and power degradation of high concentration solar cells is crucial to introducing this new technology to the market. The reliability of high concentration GaAs solar cells, as measured in temperature accelerated life tests, is described in this paper. GaAs cells were tested under high thermal accelerated conditions that emulated operation under 700 or 1050 suns over a period exceeding 10 000 h. Progressive power degradation was observed, although no catastrophic failures occurred. An Arrhenius activation energy of 1.02 eV was determined from these tests. The solar cell reliability [R(t)] under working conditions of 65°C was evaluated for different failure limits (1–10% power loss). From this reliability function, the mean time to failure and the warranty time were evaluated. Solar cell temperature appeared to be the primary determinant of reliability and warranty period, with concentration being the secondary determinant. A 30‐year warranty for these 1 mm²‐sized GaAs cells (manufactured according to a light emitting diode‐like approach) may be offered for both cell concentrations (700 and 1050 suns) if the solar cell is operated at a working temperature of 65°C. Copyright © 2012 John Wiley & Sons, Ltd.     

单轴菲涅尔反射聚光CPV/T系统的分析与研究

基于TracePro光路分析软件,对菲涅尔反射聚光系统进行了模拟,发现反射聚光后在光伏电池上的光强分布均匀。在不同追踪精度的情况下,接收器上接收的能量分析表明追踪精度在±3°以内时,可以将辐射能量的70%聚集到接收器上。采用主动追踪算法定位太阳位置,考虑赤经因素对追踪精度的影响,修正算法后追踪误差小于1°。太阳能电-热综合利用CPV/T系统有效解决了聚光后电池升温的问题,验证了菲涅尔反射聚光电-热综合利用的可行性。     

聚光光伏电池及系统的研究现状

首先总结了国内外在聚光光伏发电方面的权威研究机构及公司情况,介绍了目前聚光光伏发电技术及系统的最新研究进展情况及存在的技术难点;其次综述了近几年国内外在聚光太阳电池方面的最新研究进展,并介绍了聚光光伏中的冷却问题;最后对聚光光伏发电技术的发展前景进行了展望。     

Performance of a concentrated photovoltaic energy system with static linear Fresnel lenses

A new type of greenhouse with linear Fresnel lenses in the cover performing as a concentrated photovoltaic (CPV) system is presented. The CPV system retains all direct solar radiation, while diffuse solar radiation passes through and enters into the greenhouse cultivation system. The removal of all direct radiation will block up to 77% of the solar energy from entering the greenhouse in summer, reducing the required cooling capacity by about a factor 4. This drastically reduce the need for cooling in the summer and reduce the use of screens or lime coating to reflect or block radiation.All of the direct radiation is concentrated by a factor of 25 on a photovoltaic/thermal (PV/T) module and converted to electrical and thermal (hot water) energy. The PV/T module is kept in position by a tracking system based on two electric motors and steel cables. The energy consumption of the tracking system, ca. 0.51 W m⁻², is less than 2% of the generated electric power yield. A peak power of 38 W m⁻² electrical output was measured at 792 W m⁻² incoming radiation and a peak power of 170 W m⁻² thermal output was measured at 630 W m⁻² incoming radiation of. Incoming direct radiation resulted in a thermal yield of 56% and an electric yield of 11%: a combined efficiency of 67%. The annual electrical energy production of the prototype system is estimated to be 29 kW h m⁻² and the thermal yield at 518 MJ m⁻². The collected thermal energy can be stored and used for winter heating. The generated electrical energy can be supplied to the grid, extra cooling with a pad and fan system and/or a desalination system. The obtained results show a promising system for the lighting and temperature control of a greenhouse system and building roofs, providing simultaneous electricity and heat. It is shown that the energy contribution is sufficient for the heating demand of well-isolated greenhouses located in north European countries.     

Effect of a hybrid jet impingement/micro-channel cooling device on the performance of densely packed PV cells under high concentration

This paper studies in deep the performance of a new hybrid jet impingement/micro-channel cooling scheme for densely packed PV cells under high concentration. The device combines a slot jet impingement with a non-uniform distribution of micro-channels. The Net PV output of the concentrator system, defined as the PV output less the pumping power, and its temperature uniformity are analyzed. The hybrid cooling scheme offers a minimum thermal resistance coefficient of 2.18 × 10⁻⁵ K m²/W with a pressure drop lower than in micro-channel devices. This characteristic involves that the Net PV Output of the PV receiver is higher when cooled by the hybrid design than when cooled by the micro-channel one. The chance to modify, at the design stage, the internal geometry of the hybrid cooling scheme allows improving the temperature uniformity of the PV receiver through the adequate distribution of the local heat removal capacity.     

聚光光伏的发展

简要总结了聚光光伏(CPV)的原理、优势以及不同技术路线的特色.对于聚光光伏科技和产业的历史及现状以及所面临的机遇和挑战进行了必要的阐述,论述了发展聚光光伏对我国光伏产业的重要意义,展望了聚光光伏未来的发展方向,并对此提出了一些发展建议.     

Investigations on the temperature dependence of CPV modules equipped with triple‐junction solar cells

This paper deals with the temperature impact on the IV curve of concentrator photovoltaic (CPV) modules equipped with III–V triple‐junction solar cells. The electrical parameters of three FLATCON^® type CPV modules are investigated using a sun simulator, where the module temperatures are varied by heating with infrared (IR) bulbs. It is found that all electrical parameters vary linearly to a change of temperature. The open circuit voltages and the fill factors (FFs) of the CPV modules decrease with increasing temperature. The relative decrease in open circuit voltage of the CPV modules is similar to the value of individual triple‐junction solar cells. In contrast, the short circuit current temperature coefficients are found to be different. The experimental results can be explained by considering thermal expansion effects in the module and temperature dependencies of the optical efficiencies of the Fresnel lenses. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental performance of a Fresnel-transmission PVT concentrator for building-façade integration

A building-façade integrated concentrating photovoltaic-thermal system has been designed, constructed and experimentally characterised. Comparative performances with a non-concentration reference unit have been conducted to analyse the differential outputs. The concentrating system consists of double-side reflective strips which concentrate the incident beam towards a static photovoltaic-thermal receiver. The reflectors are placed vertically at the façade and track the sun by rotating axially. The concentrating reflector outperforms the reference one in both, thermal and electrical power. The thermal output of the concentration module almost doubles the reference one and the electrical power registered is more than 4.5 times in the case of the concentrating configuration.