Ing. Ladislava Černá, Ph.D.

The key components of photovoltaic (PV) systems are PV modules representing basic devices, which are able to operate in outdoor conditions for a long time. PV modules can be manufactured from different materials using different production technologies. The main criterion supporting or limiting the successful placement of specific technologies on the market is the price of electricity produced by PV systems. The levelized cost of energy (LCOE) method considers investment costs, operating costs, and the total energy produced during a PV system's service life. The influence of price, efficiency, and service life of PV modules on the LCOE (together with the availability of materials) sets limits for applicable technologies. Increasing the efficiency of the modules from 21% to 23% could lead to a reduction of the area-dependent part of the PV system costs by 8.7%. Extending the service life from 25 to 30 years could reduce the LCOE by about 10%. As shown in the work, wafer-based crystalline silicon technologies best meet these criteria due to their high efficiency, low costs, long service life, and the availability of materials at present. Technological innovations make it possible to increase the efficiency of the modules closer to the physical limits and to extend the service life of the modules.

Since the beginning of the solar boom, photovoltaics has expanded to a previously unsuspected extent due to a significant drop in prices. As the area for installation is limited and the occupation of agricultural land for installation is undesirable, experiments have begun with a combination of agricultural production and photovoltaics - agrophotovoltaics. However, a further reduction in the price of photovoltaic components means that even where the installation does not seem to make sense, it is possible today to build a system that finds its use. Such an example can be the installation of modules between trees of agroforestry systems, which are innovative and multifunctional farming managements aimed at adaptation of agriculture to impacts of the climate change.

There exist many photovoltaic (PV) power plants which are based on thin-film technology. Unlike PV power plant with crystalline silicon technology, the diagnostic possibilities of thin-film PV modules are limited due to seasonal effects and problematic utilization of thermography. The main problem of degradation of these PV plants is the area degradation which affects even PV power plants with transformer inverters. Although there exist measurement methods based on I–V curve measurement, these methods require specific climatic conditions (clear sky, sufficient irradiance) and time. Here, we present the novel approach to diagnose thin-film modules affected with degradation which provides quick results with low-cost equipment.

In recent years, there has been little interest from students in technical fields and the industrial sector thus suffers from a significant shortage. This shows the importance of motivating future students to study technical disciplines from an early age. Within the CTU in Prague, a very successful event is organized every year - the Children's University, where children spend a week at the university and get acquainted with the world of technology. One of the fields they come into contact with is photovoltaics. The form of teaching for children is described in the article.

Potential induced degradation (PID) is a serious threat for the photovoltaic (PV) industry. The risk of PID may increase with increasing operating voltage of PV systems. Although PID tests are currently standard tests, the expansion of floating PV power plants and installation in humid climates show that PID-free modules are still sensitive to this type of degradation. Therefore, a method that can detect PID in the initial phase before standard tests reveal it, is necessary to increase the reliability of PV systems and maintain their lifetime. One possible tool for revealing early-stage PID manifestations is impedance spectroscopy and I-V dark curves measurements. Both IS and dark current measurement methods are sensitive to cell shunt resistance (RSH), which is strongly influenced by PID before significant power loss and can act as an early stage PID detection mechanism. The paper describes the differences of the common P-type PV module parameters both during the degradation process and also during the regeneration process when diagnosed by conventional and IS and dark current measurement methods.

There exist over 2 GW of photovoltaic (PV) systems in the Czech Republic, exposed to moderate continental climate. Although there exist many PV modules defects, thanks to the generallythe same production year 2009, only some ofthem are usual at systems installed in Czech Republic. This work shows delamination failures that are frequent in moderate climate conditions. Special account istaken into edge delamination defect and its possible propagation in modules of standard construction. Combined PV panel and PV inverter failure is caused by edge delamination with water penetration and high string voltage. The electric discharge channel is created between the string of solar panels and the grounded PV panel frames. The result of the discharge channel created because of edge delamination is inverter switch-OFF and few months later total destruction of the inverter because of protective relay damage. The number of combined PV panel and PV inverter failures is increasing substantially after ninth year of operation of PV panels in moderate climate. Additional sealing of the PV panel frames by transparent polysiloxane gel reduced the number of combined PV panel and PV inverter failures very substantially.

PV modules can be manufactured using different materials by different fabrication technologies. The main criteria supporting or limiting a successful placement of particular technologies on the market is the cost of electricity produced by PV systems. The Levelized Cost of Energy (LCOE) method takes into account the investment cost, the operating costs, and the total energy produced during the system service life. The influence of price, efficiency and service life of PV modules on LCOE (together with the availability of materials) sets limits for applicable technologies.

The effect of the connection of different, shaded or damaged module on the performance of the whole string or the photovoltaic (PV) panel connected to a single inverter is very often discussed. Although there exist the means for protecting the PV system against negative influence of connecting PV modules with different parameters into one system (diodes, power optimizers), the real impact is not examined anymore. The simulation tools presume the connection of the same module type with same parameters and the differences are discussed only theoretically. The simulations performed in the SPICE program rather indicate that with less damage, one different module should not have a significant effect on the power drop, even in the theoretical case that no bypass diode is included in the string. The results of simulation as well as the measurement on the real system with modules with different parameters are presented in this work.

With effect from the end of 2018, the Energy Regulatory Office's (ERÚ) interpretative opinion allows the replacement of photovoltaic (PV) system components. These components also include PV modules. Due to the development of PV modules, it is not to be expected that modules with corresponding parameters will always be available. Thus, the question of the possibility of replacing a part of the modules in the string with modules with other parameters opens. This work deals with the issue of how such an exchange on a PV power plant will manifest itself.

PID stands for "Potential Induced Degradation", a phenomenon first described in the 1970s. Furthermore, the PID was forgotten and module manufacturers, together with photovoltaic power plant owners, started to deal with it again in the new millennium, when it started to show up strongly in larger power plants. The impact of the PID on the power plant can be very significant, due to the fact that modules can lose up to 70 % of their original performance in real conditions due to PID. In addition, some modules run faster and the power plant becomes financially loss-making. The reach of the PID module increases over time and can cause high energy losses and ultimately total module failure. There are several types of PID. Some are reversible, others are not, and for some, the principle of their origin is relatively well known, while in others it is only speculated. However, they have one thing in common, namely that the basic condition for creating a PID is a high voltage difference in the string, so it is also sometimes called High-Voltage stress. PV systems using crystalline silicon are mostly PID shunting (PID-s), where local short-circuits are generated and thus a significant reduction in performance. Thin-film modules may also suffer from a PID effect. As a rule, thin-film modules are not reversible degradation due to electrochemical corrosion of the TCO layer (transparent conductive oxide).

Currently, there is about 2 GW installed photovoltaics (PV) capacity in the Czech Republic. It represents approximately 10 million of PV modules which shall be disposed in the future. Because of the fear of future situation, the government introduced a fee for their recycling which must be paid for every PV module, either as additional fee to modules installed before 2013 paid by the operator or by the producer in the case of the currently sold modules. The fee level and reasonability of its introduction is discussed in this paper.

One of interesting technology of photovoltaic modules which can be used within an industrial scale is CdTe. These modules are indeed problematic due to Cd content, but still represent interesting alternative to standard crystalline photovoltaic modules, mainly thanks to their significantly higher energy yield. Often discussed problems connected with thin-film modules are their stability, variability of production generations and also the degradation. One of possible method which can reveal early state of degradation connected with shunts is described in this article.

Thin-film photovoltaic modules based on CdTs, CdS, and CIGS, show reversible power changes. This phenomenon is referred to in the literature as a lightsoaking effect. These reversible performance changes make repeated STC measurements very difficult to be made, especially due to the state of the module being changed when stored. In the literature, it is very often described how to achieve a steady state in laboratories that would correspond to the situation in the operation of the power plant, but the question of the rate of reversible degradation after the storage of the modules is not further described in detail, although this rate can be influenced by the temperature or the type of transparent conductive contact. The following text deals with the rate of degradation and its reversibility.

At the Czech Technical University in Prague, Faculty of Electrical Engineering, courses dealing with PV system technology form a part of both the bachelor and master study programme in Electrical Engineering and Information Technology. The courses were modified to fit better to present trends in photovoltaics. Synopsis of individual courses (both lectures and exercises) are discussed in details.

Bypass diodes are an integral part of the most of current silicon PV modules and help ensure troublefree operation of the module under different light conditions. The main function of the bypass diode is well known and is often simply explained as a protection of the module against power loss at partial shading. This article describes how to present this partial truth to students and how to help them, by using standard simulation tools and laboratory exercises, to study and understand the behavior of this part of the PV Module.

A common problem to be solved during the operation of photovoltaic (PV) power plants is early detection of PV modules defects. The common electric measurement usually doesn’t show the initial damage like less serious cracks inside the module. For these purposes is necessary to use some advanced visualization method like electroluminescence. But this requires either special equipment or the dark chamber. In this text is presented a new approach to revealing the hidden defects using impedance spectroscopy. The results of measurement are presented as well as comparison between the individual methods. There exist many diagnostic methods used for PV cells and modules diagnostics.

This article discusses the experience of the PV plant based on optimizers and analyzes annual PVP production. Subsequently, the production is compared with the SAM NEREL simulation software and the simulation output made in the PVGIS system.

There exist many method used for photovoltaic (PV) modules and systems diagnostics. One of the less conventional is impedance analysis of PV cells or modules which gives additional information about measured cell, module respectively. Due to high amount of possible sources of uncertainties and low repeatability when performed under samples irradiation, the evaluation of obtained results is relatively complicated. In this paper, the comparison of conventional methods and impedance analysis and its possible evaluation and limits are presented.

Optical absorptance spectroscopy of polycrystalline CH3NH3PbI3 films usually indicates the presence of a PbI2 phase, either as a preparation residue or due to film degradation, but gives no insight on how this may affect electrical properties. Here, we apply photocurrent spectroscopy to both perovskite solar cells and coplanar-contacted layers at various stages of degradation. In both cases, we find that the presence of a PbI2 phase restricts charge-carrier transport, suggesting that PbI2 encapsulates CH3NH3PbI3 grains. We also find that PbI2 injects holes into the CH3NH3PbI3 grains, increasing the apparent photosensitivity of PbI2.

There is about 2 GW currently installed capacity of photovoltaic sources in the Czech Republic. It represents approximately 10 million of PV modules which will be transformed into the waste in the future. Because of the fear of future situation, the government introduced a fee for their recycling that must be paid for every PV module. The fee level and rationality of its introduction is discussed in this paper.

A common problem to be solved during the operation of photovoltaic (PV) power plants is early detection of PV modules defects. Usual methods are based on both measurement of electric parameters and visualization of possible defects (thermography). The common electric measurement usually doesn’t show the initial damage like less serious cracks inside the module. For these purposes is necessary to use some advanced visualization method like electroluminescence. But this requires either special equipment or the dark chamber. In this text is presented a new approach to revealing the hidden defects using impedance spectroscopy. The results of measurement are presented as well as comparison between the individual methods.

The thin film technology of photovoltaic modules is perspective from the low cost point of view and with the respect of special, for example flexible modules. However, within a range of allowed temperature it is hard to prepare a high quality semiconductor material. On the other hand the technology can easily adopt a complex multi-layer structure, particularly a tandem structure, in which the cell with the narrower band gap is covered by the one with the wider band gap. For the characteristics and diagnostics of tandem cells it is necessary to distinguish the contributions of the component sub-cells to the total performance. One of the tasks is the determination of the component contributions to the total voltage, which is strongly influenced by the amount and spatial distribution of shunts in each sub-cell. We show that the total voltage is not a simple sum of component voltages. The experimental results are presented in this paper.

The support of renewable energy sources (RES) in European Union, especially in neighbouring Germany, means gradual revolution in energetics. Recently applied approach, where, easily said, for every produced kW coming from RES, the power from conventional source in the net was reserved, is no more sustainable. For this reason, the educational institutions must respond sufficiently flexibly for the increased demand on experts in the area of energy storage, because this is the combination of energy storage and RES (especially photovoltaics) which is in our opinion the solution of current problems. In the article, the application of PV and energy storage connection is described.

A disadvantage of thin film technology, whose production requires less material, is higher susceptibility to degradation of materials used. This degradation obviously results in a performance decrease. Some materials are more susceptible to degradation, some less, like the physical principles of degradation of some materials are known, others not. One of the main reasons for the growing popularity of thin film technology PV modules is an effort to implement photovoltaic modules into buildings or objects of daily use where mechanical flexibility and ease of manufacture are the key parameters. Re-installing growth, thin-film cells, however, also means the necessity to study degradation, which can occur in some cases and, ultimately, the diagnostics, which will allow to detect a possible defect in a timely manner.

A common problem to be solved during the operation of photovoltaic (PV) power plants is early detection of faults in PV systems. For this purpose was developed many diagnostic methods which can be applied directly at the PV system without the need of its disassembling. A very popular tool is especially the analysis of temperature distribution on the PV module - thermography, which is also a good tool for checking electrical connections (fire hazard). The problem is that there is virtually no quantification of obtained thermograms. This work provides guidance on how to reliably perform such quantification without the need of any other special device using.

The problematics of thin film PV modules degradation connected with transformerless inverters operation is relatively well known. But, there exists also the problem connected with immediate power loss, caused also by high-frequency currents, which can occur when the used inverter doesn’t have sufficient filter. In the case of new installations, these problems are solved and no more occur, but there is a large couple of already existing PV systems, where changing of all inverters is not cost effective or worse, restricted by law (loss of license and advantageous feed-in tariff). Such problems can be partially solved using additional filter with suitable characteristic. In this paper, the description and verification of such a filter is presented.

In recent years, the owners of large solar parks pay his attention to the term Potential Induced Degradation (PID). It is one of the most important influences that cause considerable loss of performance of the entire photovoltaic (PV) system. The article describes the types of PID and possible mechanisms of their formation. Particularly the effect on the crystaliline silicon modules and possible solution are described.

The efficiency of conventional PV modules is usually considered constant over the entire irradiance range. This can result in erroneous evaluation of the real efficiency of PV modules, where the values of efficiency under standard testing conditions (STC) are used for calculating. According to the real yield of systems, it shows that would be advantageous for the operator to know the efficiency not only for STC irradiance value but also weighted efficiency as in the case of inverters, where are taking into account local conditions through so called European (optionally California) efficiency.

There is described the educational system of Photovoltaics at FEE CTU in Prague in the article. The connection with praxis and interfaculty study programm Inteligent Buildings is also discussed.

There is described the system of students' projects and their themes in the article.

The article summarizes the basic properties of the PV modules from the viewpoint of thermal manifestations of defects. It outlines a new evaluation method of taken thermograms.

In the paper is described Time Domain Reflectometry method which can be used for differentiation of PV modules with same static plate values. Different AC parameters can cause dissimilar behavior in alternating fields leading to premature degradation.

The presentation summarizes the basic methods used for the diagnostics of PV modules. Attention is paid to the analysis of alternate methods and achieved unique results in the measurement of PV modules.

In the article are described possibilities of using TDR method for distinction of various generation of the same PV module type.

The article describes the current and future prospects of the photovoltaic installation in the Czech Republic and Europe.

This paper provides an analysis of the irradiance influence on photovoltaic cell efficiency in dependence on the cell construction, using the standard equivalent circuit describing solar cell. The influence of the series resistance is discussed in details and results of simulations are completed with experimental result obtained by measuring crystalline silicon solar cells and in broad intervals of irradiance and temperature and measuring different types of PV modules in a broad interval of irradiance

The article summarizes the diagnostic methods used in photovoltaics. Special emphasis is placed on explaining the difficulties related to their incorrect application and possible consequences.

There are almost 2 GW installed capacity of photovoltaic sources in Czech Republic. This situation requires more specialists in the field of photovoltaics, diagnostics especially. At the Department of Electrotechnology are many subjects focused on this problematic. With the growth of photovoltaics were these subjects enhanced by other diagnostic method and grater allowance of lessons allowed coming deeper into problematic. This article contains description of laboratory exercises and equipment used in the education.

This paper describes a model of photovoltaic module that respects the frequently neglected parameters and discusses the differences between the results obtained by this model and model used in EN 50530:2010.

The article summarizes the basic methods of diagnostics of PV modules. In addition to describing the consequences at an incorrect procedure for their application are listed. It is also one part devoted to performance guarantee and its relationship to modules aging .

For photovoltaic cells efficiency is the quality of material key ingredient. Impurities in this material create recombination centers which cut down the effective carrier charge lifetime. The method of dark current measurement, which is described in paper, can be used for dominant impurity determination.

Some results in the field of the photovoltaic systems diagnostics have been discussed in the paper. There were three areas of interest solved in this work. The first was analysis of photovoltaic power plant operation and methods of localization possible failure. The second was diagnostics of silicon solar cells using measurement of dark I-V characteristics. The third area was analysis of photovoltaic modules characterization with the aim to determine the effects of the most predominant failures that can appear by outdoor conditions influence and ageing of materials.

For photovoltaic applications, the knowledge about system behaviour in real operating conditions is desirable. Presented paper describes the dependences of all important parameters of crystalline silicon (c-Si) cell and CIS photovoltaic mini-module on both temperature and irradiance obtained using cell tester Pasan IIc.

The paper describes the basic properties of various photovoltaic modules with emphasis on automobile using possibilities and mobile applications.

The paper describes the properties of solar modules and their correlation in dependence on irradiation. Modules were measured on the flash tester PASAN Sun Simulator 3c. The properties of equipment and brief description of basic diagnostic method are also discussed.

In the text is the method of unlit photovoltaic cells described. This method is used for dominant defect energy level and effective charge carrier lifetime determination. By this method were the dominant defects of silicon crystalline solar cells determined.

The text deals with the newly established and existing workplace for the diagnostics of photovoltaic cells, and modules respectively, located at the Department of Electrotechnology FEL CVUT. There are described the properties of existing equipment - the professional cell tester PASAN IIc, LBIV and LBIC method and dark current measurement; and characteristics of the new module tester PASAN Sun Simulator IIIc to measure under the Standard Testing Conditions and low light intensity and high voltage tester HiPot Sefelec SXS560.