Quantitative electroluminescence measurements of PV devices

Electroluminescence (EL) imaging is a fast and comparatively low-cost method for spatially resolved analysis of photovoltaic (PV) devices. A Silicon CCD or InGaAs camera is used to capture the near infrared radiation, emitted from a forward biased PV device. EL images can be used to identify defects, like cracks and shunts but also to map physical parameters, like series resistance. The lack of suitable image processing routines often prevents automated and setup-independent quantitative analysis. This thesis provides a tool-set, rather than a specific solution to address this problem. Comprehensive and novel procedures to calibrate imaging systems, to evaluate image quality, to normalize images and to extract features are presented. For image quality measurement the signal-to-noise ratio (SNR) is obtained from a set of EL images. Its spatial average depends on the size of the background area within the EL image. In this work the SNR will be calculated spatially resolved and as (background independent) averaged parameter using only one EL image and no additional information of the imaging system. This thesis presents additional methods to measure image sharpness spatially resolved and introduces a new parameter to describe resolvable object size. This allows equalising images of different resolutions and of different sharpness allowing artefact-free comparison. The flat field image scales the emitted EL signal to the detected image intensity. It is often measured through imaging a homogeneous light source such as a red LCD screen in close distance to the camera lens. This measurement however only partially removes vignetting the main contributor to the flat field. This work quantifies the vignetting correction quality and introduces more sophisticated vignetting measurement methods. Especially outdoor EL imaging often includes perspective distortion of the measured PV device. This thesis presents methods to automatically detect and correct for this distortion. This also includes intensity correction due to different irradiance angles. Single-time-effects and hot pixels are image artefacts that can impair the EL image quality. They can conceivably be confused with cell defects. Their detection and removal is described in this thesis. The methods presented enable direct pixel-by-pixel comparison for EL images of the same device taken at different measurement and exposure times, even if imaged by different contractors. EL statistics correlating cell intensity to crack length and PV performance parameters are extracted from EL and dark I-V curves. This allows for spatially resolved performance measurement without the need for laborious flash tests to measure the light I-V- curve. This work aims to convince the EL community of certain calibration- and imaging routines, which will allow setup independent, automatable, standardised and therefore comparable results. Recognizing the benefits of EL imaging for quality control and failure detection, this work paves the way towards cheaper and more reliable PV generation. The code used in this work is made available to public as library and interactive graphical application for scientific image processing

Stoffliche Nutzung industrieller Abprodukte in Biogasanlagen am Beispiel Apfeltrester

Die folgende Arbeit beschreibt Potentiale und Risiken der Nutzung industrieller Abprodukte am Beispiel des Apfeltrester – einem Pressrückstand der Apfelsaftgewinnung. Dieser spielt aus finanzieller und ökologischer Sicht als Abprodukt eine steigende Rolle bei der Biogassynthese. Dabei werden die Ergebnisse des vorangegangenen Fachpraktikums vorgestellt und diskutiert. Darauf aufbauend wurden Thesen erstellt und anhand ermittelter Messwerte sowie der Literatur verifiziert. Schlussendlich werden in einer Wirtschaftlichkeitsrechnung Kosten von Bezug, Lagerung und Beschickung den Gewinnen aus der Einspeisevergütung gegenüber gestellt. Es konnte gezeigt werden, dass Apfeltrester unter Laborbedingungen nicht die befürchtete Übersäuerung des anaeroben Abbauprozesses zur Folge hatte, sondern unter vergleichbaren Erträgen mit leicht höherer Sicherheit zur Maissilage bis zu einem gewissen Anteil zu Maissilage und Stallgülle zugesetzt werden kann.:Abstract 4 Zusammenfassung 4 Abkürzungsverzeichnis 5 1 Literaturrecherche 6 1.1 Grundlagen zur Biogassynthese 6 1.1.1. Übersicht des anaeroben Abbaus organischer Substanzen 6 1.1.1 Abgrenzung zum aeroben Abbau 6 1.1.2 Ausgangsprodukte 7 1.2 Phasen der Biogasbildung 11 1.2.1 Hydrolyse 11 1.2.2 Acidogenese 12 1.2.3 Acedogenese 12 1.2.4 Methanogenese 13 1.3 Einflussfaktoren des Biogasprozesses 14 1.3.1 Temperatur 14 1.3.2 pH-Wert und Gehalt an Fettsäuren 15 1.3.3 Nährstoffversorgung und Hemmstoffe 16 1.4 Verfahrenstechnische Betriebsparameter 18 1.4.1 Faulraumbelastung 18 1.4.2 Hydraulische Verweilzeit 18 2 Material und Methoden 20 2.1 Ausgangsmaterialien 20 2.1.1 Apfeltrester der Kelterei „Sachsenobst“ 20 2.1.2 Maissilage des „LLH Eichhof“ 24 2.1.3 Stallgülle des „LLH Eichhof“ 25 2.1.4 Fermentergülle des „LLH Eichhof“ 26 2.2 Diskontinuierlicher Gärtest (Batch-Versuch) 27 2.2.1 Apparativer Aufbau 27 2.2.2 Versuchsdurchführung 29 2.3 Kontinuierlicher Gärversuch 30 2.3.1 Apparativer Aufbau 30 2.3.2 Versuchsdurchführung 31 3 Ergebnisse 38 3.1 Biogasertragsermittlung 38 3.1.1 Variante „Null“ 39 3.1.2 Cellulose als Referenz 39 3.1.3 Apfeltrester 40 3.1.4 Maissilage 41 3.2 Kontinuierlicher Versuch 42 3.2.1 Erläuterung der dargestellten Diagramme 42 3.2.2 Variante „Null“ 45 3.2.3 Variante „Mais“ 48 3.2.4 Variante „Mix“ 53 3.2.5 Variante „Trester“ 57 4 Diskussion 62 4.1 Fehlerrechnung und -diskussion 62 4.1.1 Systematische Fehler der Laborversuche 62 4.1.2 Zufällige Fehler der Laborversuche 64 4.1.3 Fehlerrahmen und Vergleichbarkeit der Ergebnisse 65 4.2 Thesen 67 4.2.1 Die Vergärung von Apfeltrester als Co-Fermentat hat nur wenig Einfluss auf Ertrag und Stabilität des Gärprozesses unter Einsatzbedingungen 67 4.2.2 Die Zugabe von Apfeltrester verdünnt das Fermentat 72 4.2.3 Weder Lagerdauer noch Konservierung des Apfeltresters beeinflussen messbar den Methanertrag 75 5 Einsatz von Apfeltrester als Co-Fermentat in BGA 76 5.1 Politische und wirtschaftliche Rahmenbedingungen 76 5.2 Technische und wirtschaftliche Annahmen 81 5.3 Vorstellung der Vergleichsfälle 86 5.3.1 Optimierung hinsichtlich diskreter Parameter des Transports 86 5.3.2 Optimierung hinsichtlich der Verteilung des Tresters 87 5.3.3 Verwertung des Gärrestes 90 6 Fazit 93 Literaturverzeichnis 95 Abbildungsverzeichnis 100 Tabellenverzeichnis 103 Eidesstattliche Erklärung 105 Anhang 106Due to the increasing ecological and financial importance of industrial waste products in the recovery of biogas the following thesis describes potentials and risks of the usage of one of these products using apple pomace – the filter cake of the apple juice production. Thereby the issues of the three-month practical course in the LHL Eichhof, a laboratory in middle Germany, are shown and discussed. As conclusion several theses are given and verified with help of the taken measurements and scientific literature. At the end an economical calculation compares the present costs of purchase, storage and processing with the proceeds of the reimbursement by the german renewable energy sources act (EEG). Against the misgiving that apple pomace could decrease the pH-value to an unacceptable level for the anaerobic decomposition process the fermentation of this product gets a comparable output even with a little more reliability compared to corn silage when added up to a defined level to corn silage and slurry.:Abstract 4 Zusammenfassung 4 Abkürzungsverzeichnis 5 1 Literaturrecherche 6 1.1 Grundlagen zur Biogassynthese 6 1.1.1. Übersicht des anaeroben Abbaus organischer Substanzen 6 1.1.1 Abgrenzung zum aeroben Abbau 6 1.1.2 Ausgangsprodukte 7 1.2 Phasen der Biogasbildung 11 1.2.1 Hydrolyse 11 1.2.2 Acidogenese 12 1.2.3 Acedogenese 12 1.2.4 Methanogenese 13 1.3 Einflussfaktoren des Biogasprozesses 14 1.3.1 Temperatur 14 1.3.2 pH-Wert und Gehalt an Fettsäuren 15 1.3.3 Nährstoffversorgung und Hemmstoffe 16 1.4 Verfahrenstechnische Betriebsparameter 18 1.4.1 Faulraumbelastung 18 1.4.2 Hydraulische Verweilzeit 18 2 Material und Methoden 20 2.1 Ausgangsmaterialien 20 2.1.1 Apfeltrester der Kelterei „Sachsenobst“ 20 2.1.2 Maissilage des „LLH Eichhof“ 24 2.1.3 Stallgülle des „LLH Eichhof“ 25 2.1.4 Fermentergülle des „LLH Eichhof“ 26 2.2 Diskontinuierlicher Gärtest (Batch-Versuch) 27 2.2.1 Apparativer Aufbau 27 2.2.2 Versuchsdurchführung 29 2.3 Kontinuierlicher Gärversuch 30 2.3.1 Apparativer Aufbau 30 2.3.2 Versuchsdurchführung 31 3 Ergebnisse 38 3.1 Biogasertragsermittlung 38 3.1.1 Variante „Null“ 39 3.1.2 Cellulose als Referenz 39 3.1.3 Apfeltrester 40 3.1.4 Maissilage 41 3.2 Kontinuierlicher Versuch 42 3.2.1 Erläuterung der dargestellten Diagramme 42 3.2.2 Variante „Null“ 45 3.2.3 Variante „Mais“ 48 3.2.4 Variante „Mix“ 53 3.2.5 Variante „Trester“ 57 4 Diskussion 62 4.1 Fehlerrechnung und -diskussion 62 4.1.1 Systematische Fehler der Laborversuche 62 4.1.2 Zufällige Fehler der Laborversuche 64 4.1.3 Fehlerrahmen und Vergleichbarkeit der Ergebnisse 65 4.2 Thesen 67 4.2.1 Die Vergärung von Apfeltrester als Co-Fermentat hat nur wenig Einfluss auf Ertrag und Stabilität des Gärprozesses unter Einsatzbedingungen 67 4.2.2 Die Zugabe von Apfeltrester verdünnt das Fermentat 72 4.2.3 Weder Lagerdauer noch Konservierung des Apfeltresters beeinflussen messbar den Methanertrag 75 5 Einsatz von Apfeltrester als Co-Fermentat in BGA 76 5.1 Politische und wirtschaftliche Rahmenbedingungen 76 5.2 Technische und wirtschaftliche Annahmen 81 5.3 Vorstellung der Vergleichsfälle 86 5.3.1 Optimierung hinsichtlich diskreter Parameter des Transports 86 5.3.2 Optimierung hinsichtlich der Verteilung des Tresters 87 5.3.3 Verwertung des Gärrestes 90 6 Fazit 93 Literaturverzeichnis 95 Abbildungsverzeichnis 100 Tabellenverzeichnis 103 Eidesstattliche Erklärung 105 Anhang 10

Speichertechnologien in Elektroautos und für Photovoltaikstrom in Hinblick auf ein autarkes Gesamtsystem

This literature research gives an overview about the various possibilities of energy storage for photovoltaics and electric vehicles. Therefore it discusses the general need for buffering and storage of renewable energy, the political setting and economic progress of electric mobility. Configurations, chemical reactions, advantages and disadvances of lead-, nickel-based-, metal-air, lithium-, high-temperature and redox-flow-batteries are discussed in concise form. A table of miscellaneous batteries sorted by their electrical and physical characteristics is attached to this document.:Abstract 4 1 Situation und Überblick zur Elektromobilität in Deutschland 5 1.1 Erneuerbare Energien als Zukunftsressource 5 1.2 Vorteile stromgetriebener Antriebe gegenüber Verbrennungsmotoren 6 1.3 Der nationale Entwicklungsplan Elektromobilität 8 2 Speicherung, Pufferung und Verfügbarkeit von Photovoltaikstrom in Bezug auf mobile und stationäre Systeme 10 2.1 Grundlagen zur Photovoltaik 10 2.1.1 Verfügbarkeit der photoelektrischen Energie 10 2.1.2 Technische Umsetzung 11 2.2 Möglichkeiten zur Speicherung regenerativer Energie 13 2.2.1 Anforderungen an Speichersysteme 14 2.2.2 Synthetische Kraftstoffe als Energiespeicher 14 2.2.3 Mechanische Energiespeicher 15 2.2.4 Elektrische Energiespeicher 16 2.2.5 Elektrochemische Energiespeicher 17 2.3 Anwendungsbeispiele für Photovoltaikstrom 19 3 Beschreibung der physikalischen und chemischen Prozesse elektrochemischer Speicher 22 3.1 Vergleichende Kennzahlen 23 3.2 Blei-Säure 26 3.3 Nickel-basiert 29 3.3.1 Nickel-Cadmium 29 3.3.2 Nickel-Metallhydrid 31 3.3.3 Nickel-Zink 33 3.4 Metall-Luft 35 3.4.1 Zink-Luft 36 3.4.2 Aluminium-Luft 37 3.4.3 Lithium-Luft 38 3.5 Lithium-Ion 39 3.5.1 Batterietypen 40 3.5.2 Aufbau und Funktion 42 3.5.3 Schaltung für Großbatterien 43 3.5.4 Forschungs- und Entwicklungslinien 44 3.6 Hochtemperaturbatterien 48 3.6.1 Natrium-Nickelchlorid 49 3.6.2 Natrium-Schwefel 50 3.7 Redox-Flow 52 3.7.1 Vanadium 53 3.7.2 Vanadium-Brom 54 3.7.3 Natrium-Polysulfid-Bromid 54 3.8 Hybrid-Flow 55 3.8.1 Zink-Brom 55 3.8.2 Cer-Zink 57 3.9 Auswertung der Vergleichsmatrix 58 4 Entwicklungstendenzen zwischen Elektromobilität und Energiewirtschaft 60 4.1 E-Energy / Smart Grid 61 4.2 Virtuelle Kraftwerke 62 4.3 Ausbau der Stromtrassen 64 4.4 Energieladesysteme 66 4.4.1 Stromtankstellen 66 4.4.2 Austausch der Energiespeicher 68 4.4.3 Induktive Energieübertragung 68 5 Zusammenfassung 69 Literaturverzeichnis: 70 Abbildungsverzeichnis 77 Tabellenverzeichnis 78 Eidesstattliche Erklärung 79 Anhang 8

Electroluminescence imaging of PV devices: single-time-effect statistics and removal

The statistics and removal of occurring specific image artefacts (i.e. single-time-effects [STE]) during qualitative analysis of EL imaging is discussed. STE are caused by single nuclear particles such as heavy ions, along with neutrons and protons with energies above 10 MeV. When charged particles cross the sensitive region of the CCD matrix, they cause effects of ionization and lead to spots only visible once after signal readout. Depending on whether STE occur in the EL image with sample excitation or in the background image without, they are visible in the corrected EL image as bright or dark spots. These can be confused conceivably with cell defects. Within this work the intensity offset due to STE as well as their occurrence over time is evaluated for multiple EL images. For the examined setup it is shown that the disruptive influence of STE is visible for measured cell voltages under 0.65 V. For this case a robust STE removal method is proposed using an additional EL image taken in series

Module scale electroluminescence of PV devices: measurements and image quality

Electroluminescence (EL) imaging is a fast and comparatively cheap method for spatially-resolved and non-destructive analysis of photovoltaic (PV) devices. To enable a quantitative use of captured images and support a common standard on EL measurements, this paper focusses on parameters defining the quality of EL images. The image quality is determined and tracked for different EL measurements during various processing steps. It is shown, that although simple post processing methods, e.g. spatial filters, can enhance the visual appearance of EL images, they do not improve the quality of the signal itself

Electroluminescence imaging of PV devices: uncertainty due to optical and perspective distortion

Electroluminescence (EL) images taken from on-field measurements often suffer from optical and perspective distortion affecting the interpretation and quantification of the images taken. Methods to correct these distortions are presented as well as a method to assess the associated uncertainties. This method uses the uncertainty of pixel position as intermediate step. The influence of pixel deflection, re-projection error and depth-of-field blur is evaluated. Three different camera systems are compared regarding tilt angle dependence. The re-projection error and the camera’s focal length are identified as major influence on the resulting uncertainty. It was shown that EL images with sufficient quality can be recovered, from images taken at high perspective misalignments with tilt angles of about 50°

Electroluminescence imaging of PV devices: camera calibration and image correction

A method for the correction of electroluminescence (EL) images of PV devices is presented. This includes a camera calibration based on focus, dark current, flat field and lens distortion as well as artefact removal, including single-time-effects and erroneous pixels. Image correction allows EL images taken with different systems or perspectives to be normalized and used for quantitative analysis. Results include an image correction of a 4x9 cell module, imaged in different perspective positions. After correction, intensity difference and positional error were found to be less than 1%, respective 2%

Spatially and spectrally resolved electroluminescence measurement system for PV characterisation

A system that combines the advantages of fast global electroluminescence (EL) measure-ments and highly detailed spectral EL meas-urements is presented. A Si camera-based EL system is used to measure the intensity of radi-ative recombination of the PV device spatially resolved over its full area. A monochromator-based system is then used to measure local-ised emission spectra at specific points of interest identified, as such as defects and cracks. The first measurement results of a mc-Si and an a-Si PV device show good agreement with reported behaviour of such devices and high-light the potential to distinguish between differ-ent defect types and reveal performance changes that would be missed using camera-based EL only

Spatially and spectrally resolved electroluminescence measurement system for photovoltaic characterisation

A system that combines the advantages of fast global electroluminescence (EL) imaging and detailed spectrally resolved EL measurements is presented. A charge-coupled device camera-based EL imaging system is used to measure the intensity of radiative recombination of the photovoltaic (PV) device spatially resolved over its full area. A monochromator-based system is utilised to measure localised emission spectra at given points of interest. Measurements of multi-crystalline and amorphous silicon PV devices demonstrate the potential to investigate radiative defects and reveal performance variations and non-uniformities. This links inhomogeneities much closer to device physics than using camera-based EL only

Electroluminescence imaging of PV devices: Advanced vignetting calibration

IEEE Electroluminescence (EL) imaging is affected by off-axis illumination together with sensor and lens imperfections. The images’ spatial intensity distribution is mainly determined by the vignetting effect. For quantitative EL imaging, its correction is essential. If neglected, intensities can vary significantly (>50%) across the image. This paper introduces and tests four vignetting measurement methods. The quantitative comparison of different methods shows that vignetting should be characterized preferably in plane by the source of the same type as the photovoltaic (PV) device to be tested. A direct PV-based measurement in short distance with spatial inhomogeneity correction is proposed for general-purpose vignetting characterization. For precise vignetting characterization, vignetting-object separation using pattern recognition is proposed. The use of non-PV light sources for vignetting characterization can cause vignetting overcorrection and can even decrease the quality of the vignetting-corrected images