Ing. Tomáš Finsterle, Ph.D.

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.

Transition metal oxides are materials combining properties of electrical conductivity, optical transparency, and catalytical function. They are widely used in applications including solar cells, flat panel displays, and detectors. In particular, high work function oxides such as MoO3, WO3, and V2O5 have become popular. In many applications, low deposition temperatures are required, leading to amorphous structure. In this study, thin films of amorphous MoOX, WOX, and VOX were prepared by pulsed laser deposition, and their optical properties and work function were determined. Samples of polycrystalline ZnO were also prepared for comparison. Substrate temperature was varied in the range of 25 °C–100 °C and oxygen pressure was varied in the range of 10–20 Pa during the process. Effect of pressure during sample cool-down and chamber venting was also observed.. Optical characterization was based on photothermal deflection spectroscopy, which is a non-contact and non-destructive method for measuring directly absorptance spectra with sensitivity down to 10–4. Absorptance in the band gap serves as an indication of the presence of defects such as oxygen vacancies or metallic phases. Our optimized films achieved a sub-bandgap absorption coefficient as low as 103 cm−1 for MoOX, VOX, and 102 cm−1 in the case of the WOX. From the gradient of the absorption edge, Urbach energy was obtained, evaluating disorder in the semiconductor material. The work function of each material was obtained by Kelvin probe, and a slight correlation with Urbach energy was found. X-ray photoelectron spectroscopy indicated successful stochiometric transfer mainly for the lowest pressure and highest temperature samples.

The method of detecting deep defects in photovoltaic materials by Fourier-Transform Photocurrent Spectroscopy is reviewed. As new materials appear, a prediction of potentially achievable open-circuit voltage is highly desirable. From thermodynamics, a prediction can be made based on the radiative limit, neglecting non-radiative recombination and carrier transport effects. Beyond this, more accurate analysis has to be done. We analyzed a series of hydrogenated amorphous silicon solar cells of different thicknesses at different states of light soaking. Combining empirical results with optical, electrical and thermodynamic simulations, we provide a predictive model of the open-circuit voltage for a given defect density and absorber thickness. We observed that, rather than defect density or thickness, it is the total number of defects, that matters. Alternatively, including defect absorption into the thermodynamic radiative limit gives also useful upper bound to the open-circuit voltage.

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.

The easy and fast detection of drug content and concentration levels is demanded in biological research as well as in clinical practice. Here we study on microscopic level how nanodiamonds and gold nanoparticles interact with a multifunctional drug molecule directly on a biosensor surface. The sensors are made of interdigitated Au electrodes coated by 5 nm hydrogenated or oxidized nanodiamonds and further combined with Au colloidal nanoparticles (size 20 nm) providing nanoscale composite (spacing 100 nm). Atomic force microscopy is employed to measure local tip-surface adhesion forces and surface topography. AFM adhesion maps show that the drug binds to all types of nanoparticles and the adhesion is also significantly influenced by the substrates on which the nanoparticles are deposited. Role of local AFM tip interaction with nanostructured surface is also discussed.

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).

Celkový instalovaný elektrický výkon z fotovoltaických zdrojů v České republice v současné době dosahuje hodnoty cca 2 GW. To představuje přibližně 10 milionů fotovoltaických (PV) modulů, které bude potřeba v budoucnu zlikvidovat. Protože má vláda z budoucí situace obavy, zavedla poplatek za jejich recyklaci, který musí být placen za každý PV modul buď provozovatelem (moduly instalované před rokem 2013), nebo výrobcem modulu (v současnosti prodávané moduly). Velikost poplatku a oprávněnost jeho zavedení jsou témata tohoto článku.

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.

We show that two-terminal multijunction cells interconnected by tunnel junctions are fairly immune to individual local shunts, thanks to the shunt quenching. Interestingly, they may still suffer from global shunts. We revise the paradigm of a multijunction cell as a simple serial connection of component cells. This paradigm remains valid only for multijunction cells with laterally conductive interlayers. Instead, a new equivalent circuit is proposed and verified by measurement and simulations. As a main approach, selective illumination is applied and the voltage is measured at the end terminals. The global shunt is seen as a shift from logarithmic to linear intensity response. The presence of tunnel junction is important for an optimum configuration of tandem structures such as metal-halide perovskite with crystalline silicon solar cell.

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.

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.

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.

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.

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.

V posledních letech upírají majitelé velkých solárních parků svou pozornost k termínu Potential Induced Degradation (potenciálem indukovaná degradace, PID). Jedná se o jeden z nejvýznamnějších vlivů, který způsobuje citelnou ztrátu výkonnosti celého fotovoltaického (PV) systému. V článku jsou popsány druhy PID a také možné mechanizmy jejich vzniku. Pozornost je věnována zejména vlivu PID na moduly z krystalického křemíku a možnosti řešení.

S poklesem ceny fotovoltaických komponent, zejména modulů, došlo k masivnímu nárůstu fotovoltaických instalací i v místech, kde není příliš vysoká úroveň ozáření. Zatímco u používaných invertorů je běžně uváděným údajem Evropská, popřípadě Kalifornská účinnost zohledňující lokální klimatické podmínky v místě instalace, u fotovoltaických modulů podobný údaj chybí. Ve výpočtech teoretické výtěžnosti je pak použita konstantní hodnota účinnosti, která může hodnotu předpokládané výtěžnosti výrazně zkreslit.