Encapsulation and backsheet adhesion metrology for photovoltaic modules

Photovoltaic modules are designed to operate for decades in terrestrial environments. However, mechanical stress, moisture, and ultraviolet radiation eventually degrade protective materials in modules, particularly their adhesion properties, eventually leading to reduced solar cell performance. Despite the significance of interfacial adhesion to module durability, currently there is no reliable technique for characterizing module adhesion properties. We present a simple and reproducible metrology for characterizing adhesion in photovoltaic modules that is grounded in fundamental concepts of beam and fracture mechanics. Using width‐tapered cantilever beam fracture specimens, interfacial adhesion was evaluated on relevant interfaces of encapsulation and backsheet structures of new and 27‐year‐old historic modules. The adhesion energy, G_c [J/m²], was calculated from the critical value of the strain energy release rate, G, using G = βP ², where β (a mechanical and geometric parameter of the fracture specimen) and P (the experimentally measured critical load) are constants. Under some circumstances where testing may result in cracking of brittle layers in the test specimen, measurement of the delamination length in addition to the critical load was necessary to determine G . Relative to new module materials, backsheet adhesion was 95% and 98% lower for historic modules that were exposed (operated in the field) and unexposed (stored on‐site, but out of direct sunlight), respectively. Encapsulation adhesion was 87–94% lower in the exposed modules and 31% lower in the unexposed module. The metrology presented here can be used to improve module materials and assess long‐term reliability. Copyright © 2016 John Wiley & Sons, Ltd.     

An ice machine adapted into an autonomous photovoltaic system without batteries using a variable‐speed drive

The adaptation of a commercially available ice machine for autonomous photovoltaic operation without batteries is presented. In this adaptation a 1040 W_p photovoltaic array directly feeds a variable‐speed drive and a 24 V_dc source. The drive runs an induction motor coupled by belt‐and‐pulley to an open reciprocating compressor, while the dc source supplies a solenoid valve and the control electronics. Motor speed and refrigerant evaporation pressure are set aiming at continuously matching system power demand to photovoltaic power availability. The resulting system is a simple integration of robust, standard, readily available parts. It produces 27 kg of ice in a clear‐sky day and has ice production costs around US$0.30/kg. Although a few machine features might be specific to Brazil, its technical and economical guidelines are applicable elsewhere. Copyright © 2010 John Wiley & Sons, Ltd.     

An anticipatory approach to quantify energetics of recycling CdTe photovoltaic systems

Rapid growth in worldwide photovoltaic (PV) systems will soon result in a massive installed base of modules, electrical systems (ES), and balance of systems (BOS) that are expected to reach their end of life after two or three decades of operation. While existing recycling technologies will likely be available for steel, copper, aluminum, and other commodity materials found in the ES and BOS, these have yet to be accounted for in studies that assess the environmental impacts of PV recycling. More problematic is the lack of research identifying strategies to improve recovery of semiconductor and other module materials and develop recycling infrastructure to minimize energy required to transport these materials. The current leader in photovoltaics recycling is First Solar, which operates facilities for processing prompt scrap, breakage, and any end‐of‐life CdTe PV modules. This paper presents a comprehensive energy assessment of recycling the entire CdTe PV system based on First Solar's processes and identifies hotspots that present opportunities to improve the energy balance of future recycling operations. The energy savings derived from recycling a CdTe PV system reduces the lifecycle energy footprint by approximately 24% of the energy required to manufacture the PV system. By contrast, recycling just the CdTe PV module without the BOS has an approximately neutral net energy impact, recovering 13.2 kg of glass, 0.007 kg of Cd, and 0.008 kg of Te per m². Hotspot analysis shows that reducing the energy required to recover unrefined semiconductor material from the module and ensuring high recovery of steel and glass from the end‐of‐life CdTe PV system will have the greatest impact on the energy benefits of recycling. Also, transportation energy depends on the energy tradeoff between (i) material recovery and recycling operations at the decentralized location, and (ii) transporting, recovering, and recycling the PV system components at a centralized location. An optimal strategy (centralized versus decentralized) is presented to minimize the net energy footprint when distance to the centralized recycling facility and the recycling energy requirements at the decentralized recycling facility are varied. Copyright © 2015 John Wiley & Sons, Ltd.     

The effect of cooling press on the encapsulation properties of crystalline photovoltaic modules: residual stress and adhesion

A high‐quality encapsulation process is crucial to ensuring the performance and long‐term reliability of photovoltaic (PV) modules. In crystalline Si technology‐based modules, poly (ethylene‐co‐vinyl acetate) (EVA) is the most widely used PV encapsulant. Its encapsulation process is usually performed in a flat‐bed vacuum bag laminator. In certain types of laminators, cooling press can be applied to the module cooling process after the module encapsulation, leading to a much higher cooling rate (~100 °C/min) than conventional natural cooling due to the application of water cooling circulation and mechanical pressure on the modules. In this work, the effect of the cooling press on the encapsulation properties of PV modules with EVA as the encapsulant are assessed on the aspects of residual stress in the modules, peeling strength between glass and EVA, and the resulting EVA gel content after encapsulation. The results show that the cooling press influences the encapsulation properties of PV modules. In particular by applying the cooling press after encapsulation, the residual normal stress in the Si solar cell in the encapsulated module after cooling can be reduced by as much as 22 ± 2 to 27 ± 3% depending on the EVA gel content, whereas the peeling strength between front glass and EVA is increased by ~ 10%. This work should help the further optimization of PV module encapsulation processes aimed at improving module encapsulation quality. Copyright © 2013 John Wiley & Sons, Ltd.     

Modeling of a concentrating photovoltaic system for optimum land use

Concentrating photovoltaic solar power plants using dual‐axis trackers are in increasing demand. In a utility‐scale photovoltaic system, both capacity factor and ground coverage ratio are widely used to characterize systems in view of the land use efficiency. Current system modeling approaches lack accurate location‐specific direct normal irradiance (DNI), miss a reliable electrical model for power optimization and conversion and are inadequate for optimizing the tracker array configuration. In this paper, a comprehensive modeling of a concentrating photovoltaic system is introduced. First, a more accurate estimation of hourly DNI is obtained by considering location‐dependent DNI and air mass changes according to the sun's elevation. Second, mismatch effects of modules are factored in. Third, various power optimization and conversion levels are taken into account for optimization with self‐shading in each module. The tracker array configuration has been optimized to maximize energy harvest by getting a maximum capacity factor for a given ground coverage ratio. Copyright © 2011 John Wiley & Sons, Ltd.     

Economic competitiveness of III–V on silicon tandem one‐sun photovoltaic solar modules in favorable future scenarios

Tandem modules combining a III–V top cell with a Si bottom cell offer the potential to increase the solar energy conversion efficiency of one‐sun photovoltaic modules beyond 25%, while fully utilizing the global investment that has been made in Si photovoltaics manufacturing. At present, the cost of III–V cells is far too high for this approach to be competitive for one‐sun terrestrial power applications. We investigated the system‐level economic benefits of both GaAs/Si and InGaP/Si tandem modules in favorable future scenarios where the cost of III–V cells is substantially reduced, perhaps to less than the cost of Si cells. We found, somewhat unexpectedly, that these tandems can reduce installed system cost only when the area‐related balance‐of‐system cost is high, such as for area‐constrained residential rooftop systems in the USA. When area‐related balance‐of‐system cost is lower, such as for utility‐scale systems, the tandem module offers no benefit. This is because a system using tandem modules is more expensive than one using single‐junction Si modules when III–V cells are expensive, and a system using tandem modules is more expensive than one using single‐junction III–V modules when III–V cells are inexpensive. Copyright © 2016 John Wiley & Sons, Ltd.     

Experimental energy yield in 1·5 × and 2 × PV concentrators with conventional modules

Low concentration devices along with standard (one sun) modules represent an attractive option to reduce the cost per kilowatt‐hour in photovoltaic installations. This paper deals with the energy gains obtained over a year by two of such devices: a 2 × V‐trough concentrator and a 1·5 × single flat mirror structure. The experiment was mounted on a two‐axis tracking system located in Arguedas (northern Spain). Due to various optical and electrical phenomena, the energy gain is notably lower than the geometrical concentration. We have conducted a theoretical analysis of these phenomena and quantified the energy loss associated with each. Daily and monthly energy gains show an influence of daylight clearness index on energy output. In view of this effect, and taking into account a possible increase in degradation of the photovoltaic modules due to high working temperatures and hot‐spots, the viability of these concentration devices is far from being clear. Copyright © 2007 John Wiley & Sons, Ltd.     

Energy,cost and LCA results of PV and hybrid PV/T solar systems

Hybrid photovoltaic/thermal (PV/T) solar systems provide a simultaneous conversion of solar radiation into electricity and heat. In these devices, the PV modules are mounted together with heat recovery units, by which a circulating fluid allows one to cool them down during their operation. An extensive study on water‐cooled PV/T solar systems has been conducted at the University of Patras, where hybrid prototypes have been experimentally studied. In this paper the electrical and thermal efficiencies are given and the annual energy output under the weather conditions of Patras is calculated for horizontal and tilted building roof installation. In addition, the costs of all system parts are included and the cost payback time is estimated. Finally, the methodology of life cycle assessment (LCA) has been applied to perform an energy and environmental assessment of the analysed system. The goal of this study, carried out at the University of Rome ‘La Sapienza’ by means of SimaPro 5·1 software, was to verify the benefits of heat recovery. The concepts and results of this work on energy performance, economic aspects and LCA results of modified PV and water‐cooled PV/T solar systems, give a clear idea of their application advantages. From the results, the most important conclusion is that PV/T systems are cost effective and of better environmental impact compared with standard PV modules. Copyright © 2005 John Wiley & Sons, Ltd.     

关于提高建筑物空调能效的技术和经济性解决方案的研究

气候变化是一个越来越重要的全球性的问题.自2013年以来,建筑行业的发展使得未来能源消耗将增加得非常快.因此,减少建筑物常规能源消耗的主要方向就是可再生能源的使用.在本文中,分析了一个位于广州市越秀区的6466 m2办公大楼的空调系统的能耗减少解决方案.文中将当前的空调系统作为参考系统,基于风机盘管提供12/7摄氏度的冷冻水,或将空气冷却器作为空气处理单元的一部分.在后一种情况,冷冻水由制冷量为190Kw的蒸气压缩式制冷机提供,其制冷剂为R22.解决方案分析了以下情况以供选择:(1)在参考系统中使用热回收换热器;(2)利用由太阳能驱动的单级溴化锂/水吸收式制冷单元代替但是蒸汽压缩式制冷机;(3)耦合上述解决方案.本文对所有这些解决方案进行了讨论和并进行了经济性分析.     

40% efficient sunlight to electricity conversion

Increasing sunlight conversion efficiency is a key driver for on‐going solar electricity cost reduction. For photovoltaic conversion, the approach most successful in increasing conversion efficiency is to split sunlight into spectral bands and direct each band to a dedicated solar cell of an appropriate energy bandgap to convert this band efficiently. In this work, we demonstrate conversion of sunlight to electricity in a solar collector with an efficiency value above 40% for the first time, using a small 287‐cm² aperture area test stand, notably equipped with commercial concentrator solar cells. We use optical band‐pass filtering to capture energy that is normally wasted by commercial GaInP/GaInAs/Ge triple junction cells and convert this normally wasted energy using a separate Si cell with higher efficiency than physically possible in the original device. The 287‐cm² aperture area sunlight‐concentrating converter demonstrating this independently confirmed efficiency is a prototype for a large photovoltaic power tower system, where sunlight is reflected from a field of sun‐tracking heliostats to a dense photovoltaic array mounted on a central tower. In such systems, improved efficiency not only reduces costs by increasing energy output for a given investment in heliostats and towers but also reduces unwanted heat generation at the central tower. Copyright © 2015 John Wiley & Sons, Ltd.     

Performance Analysis of a Thermoelectric Solar Collector Integrated with a Heat Pump

A novel heat pump system is proposed. A thermoelectric solar collector was coupled to a solar-assisted heat pump (TESC-HP) to work as an evaporator. The cooling effect of the system’s refrigerant allowed the cold side of the system’s thermoelectric modules to work at lower temperature, improving the conversion efficiency. The TESC-HP system mainly consisted of transparent glass, an air gap, an absorber plate that acted as a direct expansion-type collector/evaporator, an R-134a piston-type hermetic compressor, a water-cooled plate-type condenser, thermoelectric modules, and a water storage tank. Test results indicated that the TESC-HP has better coefficient of performance (COP) and conversion efficiency than the separate units. For the meteorological conditions in Mahasarakham, the COP of the TESC-HP system can reach 5.48 when the average temperature of 100 L of water is increased from 28°C to 40°C in 60 min with average ambient temperature of 32.5°C and average solar intensity of 815 W/m², whereas the conversion efficiency of the TE power generator was around 2.03%.     

Analysis and design of phase‐interleaving series‐connected module‐integrated converter for DC‐link ripple reduction of multi‐stage photovoltaic power systems

Recently, installation of photovoltaic power systems such as building‐integrated photovoltaic in urban area has been spotlighted in renewable energy engineering field, even at the expense of the performance degradation from partial shading. The efficiency degradation of maximum power point tracking (MPPT) performance can be compensated by a kind of power‐conditioning system architecture such as module‐integrated converters (MIC), which can handle the optimal‐operation tracking for its own photovoltaic (PV) module. In case of a MIC with series‐connected outputs, it is easy to obtain a high DC‐link voltage for multiple stage PV power conditioning applications. However, switching ripple of the DC‐link voltage also increases as number of the modules increases. In this paper, as a solution for the ripple reduction, interleaved pulse width modulation‐phase synchronizing method is applied to the PV MIC modules. The switching‐ripple analysis of the MPPT power modules were performed and compared between the cases such as phase control or not. For the implementation of the phase control among the modules, Zigbee (XBee Pro, Digi International, Minnetonka, MN, USA) wireless communications transceiver and DSP (TMS320F28335, Texas Instruments, Dallas, TX, USA) series communications interface are utilized. Hardware prototype of the double‐module boost‐type 80‐W MICs has been built to validate the DC‐link voltage ripple reduction. Copyright © 2012 John Wiley & Sons, Ltd.     

Operation of series‐connected silicon‐based photovoltaic modules under partial shading conditions

Partial shading has been recognized as a major cause of energy losses in photovoltaic (PV) power generators. Partial shading has severe effects on the electrical characteristics of the PV power generator, because it causes multiple maximum power points (MPPs) to the power‐voltage curve. Multiple maxima complicate MPP tracking, and the tracking algorithms are often unable to detect the global maximum. Considerable amount of available electrical energy may be lost, when a local MPP with low power is tracked instead of the global MPP. In this paper, the electrical characteristics of series‐connected silicon‐based PV modules under various partial shading conditions are studied by using a Matlab/Simulink simulation model. The simulation model consists of 18 series‐connected PV modules, corresponding to a single‐phase grid‐connected PV power generator. The validity of the simulation model has been verified by experimental measurements. The voltage and power characteristics of the PV power generator have been investigated under various system shading and shading strength conditions. The results can be utilized to develop new MPP tracking algorithms and in designing, for example, building integrated PV power generators. Copyright © 2011 John Wiley & Sons, Ltd.     

太阳能半导体空调制冷装置模块化实验研究

建立了以水为热交换媒介的太阳能热电模块制冷实验系统.系统配置了双位能量存储装置,用以储存昼夜温差能和太阳光电转换电能,以备无日照或日照不足时系统能够连续工作.热电制冷装置模块化,用以适应制冷功率变化较大的空间制冷,并在制冷启动与温度维持不同阶段实现较大功率的切入或撤出.制冷模块以半导体热电元件为核心,冷热端均以导热性能良好的紫铜作为热交换材料,以热容量较大的水作为冷却液和散热循环液.热交换装置采取集合散热冷却分流的集散一体化热交换系统.对制冷模块制冷性能进行了实验分析,并对制冷效果进行了模拟实验,实验结果基本达到了设计的预期.     

CuCo Hybrid Oxides as Bifunctional Electrocatalyst for Efficient Water Splitting

Solar‐driven water splitting is a promising approach for renewable energy, where the development of efficient and stable bifunctional electrocatalysts for simultaneously producing hydrogen and oxygen is still challenging. Herein, combined with the hydrogen evolution reaction (HER) activity of a copper(I) complex and oxygen evolution reaction (OER) activity of cobalt‐based oxides, a type of 1D copper‐cobalt hybrid oxide nanowires (CuCoO‐NWs) is developed via a facile two‐step growth‐conversion process toward a bifunctional water splitting catalyst. The CuCoO‐NWs exhibit excellent catalytic performances for both HER and OER in the same basic electrolyte, with optimized low onset overpotentials and high current densities. The efficient HER activity is ascribed to the formation of Cu₂O, while the activity for OER is primarily enabled by Co‐based oxides and abundant oxygen vacancies. The CuCoO‐NWs allow for the assembly of a water electrolyzer with strong alkaline media, with a current density of 10 mA cm^?2 at 1.61 V. Further combination with a commercial silicon photovoltaic allows the direct use of solar energy for spontaneous water splitting with excellent stability for over 72 h, suggesting the potential as a promising bifunctional electrocatalyst for efficient solar‐driven water splitting.     

Performance,cost and life‐cycle assessment study of hybrid PVT/AIR solar systems

An alternative and cost‐effective solution to building integrated PV systems is to use hybrid photovoltaic/thermal (PV/T) solar systems. These systems consist of PV modules with an air channel at their rear surface, where ambient air is circulating in the channel for PV cooling and the extracted heat can be used for building thermal needs. To increase the system thermal efficiency, additional glazing is necessary, but this results in the decrease of the PV module electrical output from the additional optical losses of the solar radiation. PV/T solar systems with air heat extraction have been extensively studied at the University of Patras. Prototypes in their standard form and also with low‐cost modifications have been tested, aiming to achieve improved PV/T systems. An energetic and environmental assessment for the PV and PV/T systems tested has been performed by the University of Rome ‘La Sapienza’, implementing the specific software SimaPro 5·1 regarding the life‐cycle assessment (LCA) methodology applied. In this paper electrical and thermal energy output results for PV and PV/T systems are given, focusing on their performance improvements and environmental impact, considering their construction and operation requirements. The new outcome of the study was that the glazed type PV/T systems present optimum performance regarding energy, cost and LCA results. Copyright © 2005 John Wiley & Sons, Ltd.     

YieldOpt,a model to predict the power output and energy yield for concentrating photovoltaic modules

In this work, we discuss three empirical models and introduce one more detailed model named YieldOpt. All models can be used to calculate the power output and energy yield of concentrating photovoltaic (CPV) modules under different ambient conditions. The YieldOpt model combines various modeling approaches: simple model of the atmospheric radiative transfer of sunshine for the spectral irradiance, a finite element method for thermal expansion, ray tracing for the optics, and a SPICE network model for the triple‐junction solar cell. YieldOpt uses a number of constant and variable input parameters, for example, the external quantum efficiency of the cells, the temperature‐dependent spectral optical efficiencies of the optics, the tracking accuracy, the direct normal irradiance, the aerosol optical depth, and the temperature of the lens and the solar cell. To verify the accuracy of the models, the I‐V characteristics of five CPV modules have been measured in a 10‐min interval over a period of 1 year in Freiburg, Germany. Four modules equipped with industrial‐standard lattice‐matched triple‐junction solar cells and one module equipped with metamorphic triple‐junction solar cells are investigated. The higher accuracy of YieldOpt compared with the three empirical models in predicting the power output of all five CPV modules during this period is demonstrated. The energy yield over a period of 1 year was predicted for all five CPV modules with a maximum deviation of 5% by the three empirical models and 3% by YieldOpt. Copyright © 2014 John Wiley & Sons, Ltd.     

A side‐by‐side comparison of CPV module and system performance

A side‐by‐side comparison is made between concentrator photovoltaic module and system direct current aperture efficiency data with a focus on quantifying system performance losses. The individual losses measured/calculated, when combined, are in good agreement with the total loss seen between the module and the system. Results indicate that for the given test period, the largest individual loss of 3.7% relative is due to the baseline performance difference between the individual module and the average for the 200 modules in the system. A basic empirical model is derived based on module spectral performance data and the tabulated losses between the module and the system. The model predicts instantaneous system direct current aperture efficiency with a root mean square error of 2.3% relative. Copyright © 2016 John Wiley & Sons, Ltd.     

Key parameters in determining energy generated by CPV modules

We identify the key inputs and measurement data needed for accurate energy rating of concentrator photovoltaic (CPV) modules based on field observations of multiple CPV modules. Acceptance angle is shown to correlate with the observed module‐level performance ratio (PR) for the modules studied. Using power ratings based on concentrator standard test conditions, PRs between 90% and 95% were observed during the summers with up to ~10% lower PRs during the winters. A module fabricated by Semprius showed 94% ±0.7% PR over almost 2 years with seasonal variation in PR of less than 1% showing how a module with relatively large acceptance angle may show very consistent average efficiency (calculated from the energy generated relative to the energy available), potentially simplifying energy ratings. The application of the results for translation of energy rating from one location to another is discussed, concluding that most of the translation differences may be correlated with temperature differences between sites with the largest variation happening when optical efficiency depends on temperature. Copyright © 2014 John Wiley & Sons, Ltd.     

Comparative study by simulation of photovoltaic pumping systems with stationary and polar tracking arrays

Using mathematical models for the different components of the photovoltaic pumping system: generator, inverter (if applicable), motors, pumps and piping, we have developed a computer program that, for given irradiance and temperature data, calculates the flow of water pumped at any given time. The program has been applied to study the hourly and yearly water flow pumped by a photovoltaic pumping system located in Madrid, employing centrifugal pumps powered by AC motors. The photovoltaic generator consists of, in one case, a stationary array and in the second case a polar tracking array. The hourly radiation data were estimated from the distribution of the atmospheric clearness coefficients and the monthly average daily radiation on a horizontal surface. The results of this study show that the use of a polar tracking array increases the average yearly water flow compared with the stationary array more than the corresponding increase of the incident radiation on the arrays. Copyright © 2003 John Wiley & Sons, Ltd.