System memory effects in the sizing of stand‐alone PV systems

Models based on daily energy balance (or long‐term models) have been widely used as a tool in the stand‐alone photovoltaic (PV) system sizing, mainly with the purpose of obtaining analytical expressions of the relation between the generator size and the storage capacity of the battery. The system can then be designed to meet the reliability requirements of the specific case. However, such models represent the complex operation of a stand‐alone system in an oversimplified way. There is little research so far on the reliability and improvement of such models. Validation and possible modification of a long‐term system model requires comparison of the simulated state of charge (SOC) of the battery with that obtained from an experimental system. In this work, experimental data from a 6‐month operation of a basic stand‐alone PV system have been analysed and compared with modelling results. One obvious improvement that could be applied to the long‐term system model is to account for a charging efficiency of the battery, and this possibility is examined in the present work. However, comparison with the modelling results shows that the data cannot be fitted by simply taking into account battery inefficiency. A method to account for system memory effects in the increase of the battery SOC, imposed by the operation of the regulator, is necessary to accurately model the macroscopic diurnal charging/discharging process. Copyright © 2012 John Wiley & Sons, Ltd.     

Impact of distributed power electronics on the lifetime and reliability of PV systems

This paper quantifies the impact of distributed power electronics in photovoltaic (PV) systems in terms of end‐of‐life energy‐capture performance and reliability. The analysis is based on simulations of PV installations over system lifetime at various degradation rates. It is shown how module‐level or submodule‐level power converters can mitigate variations in cell degradation over time, effectively increasing the system lifespan by 5–10 years compared with the nominal 25‐year lifetime. An important aspect typically overlooked when characterizing such improvements is the reliability of distributed power electronics, as power converter failures may not only diminish energy yield improvements but also adversely affect the overall system operation. Failure models are developed, and power electronics reliability is taken into account in this work, in order to provide a more comprehensive view of the opportunities and limitations offered by distributed power electronics in PV systems. It is shown how a differential power‐processing approach achieves the best mismatch mitigation performance and the least susceptibility to converter faults. Copyright © 2017 John Wiley & Sons, Ltd.     

Exploiting existing dams for solar PV system installations

Recognizing the issues of land shortage and growing concerns for protecting natural lands, installers and project developers, with the help of scientists and engineers, continuously try to locate alternative spots for photovoltaic (PV) system installations. In the present paper a novel approach is suggested and analysed: installing solar PV systems on the downstream face of existing dams. This approach provides advantages that could favour even large‐scale systems with a capacity of several MWp. First, produced energy could cover water reservoirs' needs supporting energy‐intensive processes as water pumping and treatment in a sustainable manner. Moreover, energy provision to inhabited areas near the dams and the subsequent creation of independent mini grids could mitigate energy poverty. In the case of hydroelectric dams, the so‐created hybrid system (PV‐hydro) could become notably efficient, because the intermittent solar energy would be counterbalanced by the flexibility of hydropower. Finally, we found a notable number of existing water reservoirs in Africa that are either under‐utilized or non‐powered. That unexploited energy potential can also be amplified by PV‐system installation. The analysis included data collection from various sources. Datasets have been cross‐checked and extended in the newly created GIS‐based model, enabling the selection of the most suitable sites in South Africa, taken as case studies. Following their identification, the selected dams have been analysed using the PVGIS tool in order to estimate the annual energy production. The results have been very encouraging, indicating that PV systems on the face of dams are an advantageous option for renewable energy production. © 2015 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.     

Optimal sizing and life cycle assessment of residential photovoltaic energy systems with battery storage

This paper presents the optimal sizing and life cycle assessment of residential photovoltaic (PV) energy systems. The system consists of PV modules as the main power producer, and lead–acid batteries as the medium of electricity storage, and other essential devices such as an inverter. Five‐parameter analytic PV cell model is used to calculate the energy production from the modules. Electrical needs for a family living under normal conditions of comfort are modelled and used within simulation of the system performance, with an average daily load of approximately 9·0 kWh. The system's performance simulations are carried out with typical yearly solar radiation and ambient temperature data from five different sites in Turkey. The typical years are selected from a total of 6 years data for each site. The life cycle cost of the PV system is analysed for various system configurations for a 20‐year system life. The role of the batteries in PV energy systems are analysed in terms of the cost and power loss. The system performance is analysed as a function of various parameters such as energy production and cost. It is shown that these change substantially for different system configurations and locations. The life cycle assessment of the energy system described was also carried out to determine the environmental impact. It was found that, with the conservative European average electricity mix, energy pay back time (EPBT) is 6·2 years and CO₂ pay back time is 4·6 years for the given system. Copyright © 2007 John Wiley & Sons, Ltd.     

An analysis of reliability in the early stages of photovoltaic systems in Japan

In order to disseminate Photovoltaic (PV) technologies into the energy network, the cost down is not only important, but also improving the performance of the PV system is significant issues. Long‐term reliability is one of the most important issues in terms of PV system performance. Previous researches were mainly focused on the reliability of PV modules, but the PV system is composed of a power conditioner, wiring, junction box, and so on. To improve the reliability of PV systems, it is important to accumulate trouble cases focused on all components of PV system. In this paper, we aim at evaluation of the reliability for the PV system on the early stages of PV system's lifetime by using large number of Japanese PV systems' data from the field Test in Japan. New Energy and Industrial Technology Development Organization has been running the “Field test project in Japan” from 1992. In this project, PV system users have cooperated with the collection of monitoring data and reported on the information of maintenance and certain failures of PV systems for 4 years after installation of PV system. Using those reports each year of installation, we evaluated reliability of PV systems by means of parameters such as Mean Time Between Failure, Mean Time To Repair, and the suspension time of PV system. As a result, the main trouble of PV systems was related power conditioner, and a few trouble of PV module was caused by typhoon. Moreover, the trend of the failure rate before FY 2000 of installation was demonstrated as the trend of initial failure in “bathtub curve;” however, the trend of its after FY 2001 of installation was indicated as the accidental failure in “bathtub curve.” Further, the operator simply forgot to restart the power conditioner after maintenance or suspensions of PV system in many trouble cases, and the user did not notice that it had been suspended for a while. These trouble cases can be avoidable easily through the effective alarm such as error message of power conditioner systems with monitoring systems. Thereby, monitoring with the evaluation method of PV systems is one of the important technologies due to the long‐term reliability and stable operation. Copyright © 2010 John Wiley & Sons, Ltd.     

Operational performance of grid‐connected PV systems on buildings in Germany

This paper presents operational performance results of grid‐connected PV systems in Germany, as collected and elaborated for the Photovoltaic Power Systems Programme (PVPS) of the International Energy Agency (IEA). Performance ratios obtained from 235 PV installations in Germany and from 133 PV plants in other countries are compared and discussed. For Germany, a significant rise in PV system performance and reliability was observed for new PV installations due to higher component efficiencies (e.g., inverter) and increased availabilities. There is a lack of long‐term experience in performance and reliability of PV systems, owing to the absence of monitoring programmes. As an outcome of IEA PVPS collaborative work, Task 2 provides reliable and worldwide monitoring performance data and results (www.task2.org). Technical and operational data is available for system planning and comparison, for teaching and training purposes as well as for future developments of financing schemes (e.g., feed‐in‐tariffs) in order to stimulate the PV market. Copyright © 2004 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.     

On the role of solar photovoltaics in global energy transition scenarios

The global energy system has to be transformed towards high levels of sustainability in order to comply with the COP21 agreement. Solar photovoltaic (PV) offers excellent characteristics to play a major role in this energy transition. The key objective of this work is to investigate the role of PV in the global energy transition based on respective scenarios and a newly introduced energy transition model developed by the authors. A progressive group of energy transition scenarios present results of a fast growth of installed PV capacities and a high energy supply share of solar energy to the total primary energy demand in the world in the decades to come. These progressive energy transition scenarios can be confirmed. For the very first time, a full hourly modelling for an entire year is performed for the world, subdivided in 145 sub‐regions, which is required to reflect the intermittent character of the future energy system. The model derives total installed solar PV capacity requirements of 7.1–9.1 TWp for the electricity sector (as of the year 2015) and 27.4 TWp for the entire energy system in the mid‐term. The long‐term capacity is expected to be 42 TWp and, because of the ongoing cost reduction of PV and battery technologies, this value is found to be the lower limit for the installed capacities. Solar PV electricity is expected to be the largest, least cost and most relevant source of energy in the mid‐term to long‐term for the global energy supply. Copyright © 2017 John Wiley & Sons, Ltd.     

Analysis of degradation mechanisms of crystalline silicon PV modules after 12 years of operation in Southern Europe

The long‐term reliability of photovoltaic modules is crucial to ensure the technical and economic viability of PV as a successful energy source. The analysis of degradation mechanisms of PV modules is key to ensure current lifetimes exceeding 25 years. This paper presents the results of the investigations carried out on the degradation mechanisms of a crystalline silicon PV installation of 2 kWp after 12 years of exposure in Málaga, Spain. The analysis was conducted by visual inspection, infrared thermography and electrical performance evaluation. By visual inspection, the most relevant defects in the modules were identified and ranked according to their frequency. The electrical performance was assessed by comparing the characteristic parameters of the individual modules, obtained by outdoor measurements at the start and end of the exposure period. The correlation of the visual defects and the shifts in the electrical parameters was analysed. The results presented show that glass weathering, delamination at the cell‐EVA interface and oxidation of the antireflective coating and the cell metallization grid were the most frequently occurring defects found. The total peak power loss, including the initial light induced degradation, was 11.5%, which corresponded almost totally to a loss in short‐circuit current. Copyright © 2011 John Wiley & Sons, Ltd.     

Technical and economic analysis of grid‐connected PV systems by means of simulation

Research on monitored grid‐connected PV systems can lead to an improved performance of PV systems. This view is based on monitoring results from PV systems in Western Europe which lag behind the expected values. However, current methods for analysing these systems do not allow to investigate the potential system efficiency improvement on the basis of field experience. Hence, we have developed a method for analysing monitored grid‐connected PV systems which meets this need. In this method the common technical approach to analysing PV systems is broadened with an economic assessment. First an energy loss analysis of the PV system is made using its monitored data. In our analysis the energy loss effects in the PV system are split up by simulation. This provides a profound insight into the actual performance of the system. Next, measures to enhance the performance of the system are identified. The costs involved to improve the performance are analysed. Finally, the cost‐effectiveness of the potential improvements is calculated. In this paper we will present our method TEAMS. Although we will not formulate strict rules, we will provide a well‐defined frame and structure for the application of the TEAMS method. It is shown that applying TEAMS contributes to improved transparency in the evaluation of monitored grid‐connected PV systems. Copyright © 1999 John Wiley & Sons, Ltd.     

Compressive‐shear adhesion characterization of polyvinyl‐butyral and ethylene‐vinyl acetate at different curing times before and after exposure to damp‐heat conditions

Photovoltaic (PV) module efficiency and reliability are two factors that have an important impact on the final cost of the PV electricity production. It is widely accepted that a good adhesion between the encapsulant and the different substrates of a PV module is needed to ensure long‐term reliability. Several testing procedures exist that use a metric derived from the force at interface failure to characterize the adhesion. It has, however, not been demonstrated that those metrics relate directly to the interfacial adhesion (defined as the surface energy density needed to break interfacial bonds), and the obtained results usually relate to an apparent adhesion strength. In this work, we describe a new design for compressive‐shear testing of polymer layers bonded to rigid substrates. We use it to characterize real interfacial adhesion of ethylene‐vinyl acetate (EVA) and polyvinyl‐butyral (PVB) to a glass substrate before and after degradation in damp‐heat. Our results show that a peak‐force based metric is unable to capture the evolution of adhesion through degradation, and a new metric based on the elastic strain energy of the encapsulant is proposed. Moreover, we show that PVB adhesion to glass is much more affected by damp‐heat exposure where polymer saturation takes place, in comparison with the adhesion of EVA to glass. The presented characterization protocol is a powerful tool that can help in assessing the reliability of an encapsulant facing specific degradation conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

铁路5G-R基站太阳能供电架构及应用

针对铁路5G专用移动通信(5G-R)系统基站布置密集、单体功耗高的特点,结合铁路无线通信的需求,研究采用太阳能(PV)为5G-R系统基站的射频拉远单元(RRU)设备供电的方案。对比分析5G-R系统RRU设备日用电规律及太阳能电池日发电规律,确定了采用太阳能结合储能与外电源的供电体系,通过比较几种太阳能电池与外电源组合供电架构的经济性与可靠性,推荐采用直流侧切换的供电架构,并进一步提出了采用直流侧智能配电的太阳能供电方案。本研究在保证5G-R系统运行安全可靠的同时,通过采用太阳能供电方式降低了铁路5G-R系统对外电源的需求。     

Optimal sizing of photovoltaic‐hydro power plant

The work presents a technological concept of energetically independent and ecologically sustainable system of electric energy production by joint operation of photovoltaic (PV) and hydro electric (HE) power plant as a unique technological system of solar hydroelectric (SHE) power plant. The sustainability of such system is based exclusively on the solar energy input, as the renewable and pure energy resource, and the use of hydro energy, due to the possibility of its continuous production of energy and its well‐known flexibility in covering the consumers' needs. For the purpose of connecting all relevant values into one integral SHE system, a mathematical model was developed for selecting the optimal size of the PV power plant as the key element for estimating the technological feasibility of the overall solution. The model was tested on electric energy supply from the island of Vis in Croatia. The obtained power of the PV power plant was 41 MW_p which corresponds to collector field of approximately 25 ha, while the estimated related storage was 20 hm³. The results show that the subject model describes the SHE very well and that the proposed concept of joint operation of PV and HE power plants is real and possible. The application of such sustainable SHE systems could significantly increase PV industry worldwide, i.e. the share of solar energy in energy balances of numerous countries. Proposed hybrid simulation‐dynamic programming model is suitable to optimize PV plant in accordance with system characteristics. Copyright © 2009 John Wiley & Sons, Ltd.     

Development of a Methodology for Improving Photovoltaic Inverter Reliability

In evaluating the energy-generation potential of a photovoltaic (PV) energy system, the system is usually assumed to work without interruptions over its entire life. PV energy systems are fairly reliable, but as any complex system, they may fail. In PV systems, the inverter is responsible for the majority of failures, and most inverter failures are blamed on the aluminum electrolytic capacitors typically used in the dc bus. This paper investigates the effects of common failure modes on the reliability of PV inverters and suggests a model framework for decomposing the inverter into subsystems for more detailed study. The challenges of statistical analysis based on small data sets are discussed, and simulations are performed to illustrate the proposed model using a simple decomposition into subsystems of the inverter used in the 342-kW PV system at the Georgia Tech Aquatic Center.     

Environmental life cycle assessment of roof‐integrated flexible amorphous silicon/nanocrystalline silicon solar cell laminate

This paper presents an environmental life cycle assessment of a roof‐integrated flexible solar cell laminate with tandem solar cells composed of amorphous silicon/nanocrystalline silicon (a‐Si/nc‐Si). The a‐Si/nc‐Si cells are considered to have 10% conversion efficiency. Their expected service life is 20 years. The production scale considered is 100 MW_p per year. A comparison of the a‐Si/nc‐Si photovoltaic (PV) system with the roof‐mounted multicrystalline silicon (multi‐Si) PV system is also presented. For both PV systems, application in the Netherlands with an annual insolation of 1000 kWh/m² is considered. We found that the overall damage scores of the a‐Si/nc‐Si PV system and the multi‐Si PV system are 0.012 and 0.010 Ecopoints/kWh, respectively. For both PV systems, the impacts due to climate change, human toxicity, particulate matter formation, and fossil resources depletion together contribute to 96% of the overall damage scores. Each of both PV systems has a cumulative primary energy demand of 1.4 MJ/kWh. The cumulative primary energy demand of the a‐Si/nc‐Si PV system has an uncertainty of up to 41%. For the a‐Si/nc‐Si PV system, an energy payback time of 2.3 years is derived. The construction for roof integration, the silicon deposition, and etching are found to be the largest contributors to the primary energy demand of the a‐Si/nc‐Si PV system, whereas encapsulation and the construction for roof integration are the largest contributors to its impact on climate change. Copyright © 2012 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.     

Hybrid Cd‐free CIGS solar cell/TEG device with ZnO nanowires

A green energy device with a CuInGaSe₂ (CIGS) photovoltaic (PV) cell covered with a passive light‐trapping structure (ZnO nanowires (NWs)) and connected to an active energy‐harvesting device (thermoelectric generator (TEG)) is presented. The efficiency of the ZnO NWs/CIGS PV device obtained using a deposition temperature of 550 °C and Cd‐free processes reaches 16.5%. The series‐connected CIGS PV cell with a TEG had a record‐high efficiency of 22% at a cool‐side temperature (T_c) below 5 °C. The open‐circuit voltage (V_oc) of the hybrid CIGS PV/TEG device was increased from 0.64 to 0.85 V. This technology has potential for high‐efficiency energy‐harvesting applications. Copyright © 2014 John Wiley & Sons, Ltd.     

A Methodology for Photovoltaic System Reliability & Economic Analysis

This paper describes the approach and progress on a 1981 study of photovoltaic (PV) system reliability being conducted by Battelle-Columbus for Sandia Laboratories as part of DOE's PV Systems Definition Project. Initially, the study is concerned with the functional modeling of reliability and maintenance of a PV system. We begin with relatively general, but simple, system level reliability models that can be expanded to more detailed, lower-level forms as input data justify. Corrective maintenance is Included to permit estimates of system availability. The output of these models will be coupled with life-cycle energy cost models and applied to PV system designs.     

A novel power benefit prediction approach for two‐axis sun‐tracking type photovoltaic systems based on semiconductor theory

Photovoltaic (PV) systems incorporated with sun‐tracking technology have been proposed and verified to effectively increase the power harvest. However, the actual power generated from a PV module has not been investigated and compared with that analyzed from theoretical models of the PV material. This study proposes a novel method for estimating the power benefit harvested by a two‐axis sun‐tracking type (STT) PV system. The method is based on semiconductor theory and the dynamic characteristics, including maximum power point tracking of PV modules that can be integrated with the database of annual solar incidences to predict the power harvested by any STT PV system. The increment of annual energy provided by an STT PV system installed at any arbitrary latitude, compared with that by a fixed‐type system, can be accurately estimated using the proposed method. To verify the feasibility and precision performance of this method, a fixed‐type and a two‐axis STT PV system were installed at 24.92° north latitude in northern Taiwan and tested through long‐term experiments. The experimental results show that the energy increments estimated by the theoretical model and actual measurement are 19.39% and 16.74%, respectively. The results demonstrate that the proposed method is capable of predicting the power benefit harvested by an STT PV system with high accuracy. Using our method, a PV system installer can evaluate beforehand the economic benefits of different types of PV systems while taking different construction locations into consideration, thereby obtaining a better installation strategy for PV systems. Copyright © 2012 John Wiley & Sons, Ltd.