Photonics in photovoltaic systems

This paper gives an overview on photonics for photovoltaic systems. Starting from the spectral and angular distribution of the electromagnetic radiation from the sun, many important optical approaches how to improve the efficiency of solar cells are presented and discussed. Topics include antireflective coatings, various light trapping structures, refractive, reflective and fluorescent concentrators, and components for spectral management. The theoretical background is shortly described and examples of the experimental and also of the commercial realisation are given

Combining Query Rewriting and Knowledge Graph Embeddings for Complex Query Answering

The field of complex query answering using Knowledge Graphs (KGs) has seen substantial advancements in recent years, primarily through the utilization of Knowledge Graph Embeddings (KGEs). However, these methodologies often stumble when faced with intricate query structures that involve multiple entities and relationships. This thesis primarily investigates the potential of integrating query rewriting techniques into the KGE query answering process to improve performance in such situations. Guided by a TBox, a schema that describes the concepts and relationships in the data from Description Logics, query rewriting translates a query into a union of rewritten queries that can potentially widen the prediction scope for KGEs. The thesis uses the PerfectRef algorithm for facilitating query rewriting, aiming to maximize the scope of query response and enhance prediction capabilities. Two distinct datasets were employed in the study: The Family Dataset, a subset of Wikidata, and DBPedia15k, a subset of DBPedia. The effectiveness of the proposed methodology was evaluated against these datasets using different KGE models, in our case TransE, DistMult, BoxE, RotatE, and CompGCN. The results demonstrate a notable improvement in complex query answering when query rewriting is used for both The Family dataset and DBPedia15k. Furthermore, the amalgamation of query rewriting and KGE predictions yielded a performance boost for The Family dataset. However, the same was not observed for DBPedia15k, likely due to discrepancies and errors present within DBPedia15k compared to the Full DBPedia KG used for validation in our framework. This research suggests that query rewriting, as a pre-processing step for KGE prediction, can enhance the performance of complex query answering, mainly when the dataset is not fully entailed. This study provides important insights into the potential and limitations of integrating query rewriting with KGEs. It may serve as a guidepost for future research to improve the complex query answering when a TBox is available.Masteroppgave i informatikkINF399MAMN-PROGMAMN-IN

Bandgap Optimization of Photovoltaic Tandem Cells Based on Spectra Collected over a Full Year

Spectral data collected every minute at the test station in Grimstad, Norway, are used to investigate the impact of spectral variation on tandem cells. The results are displayed as efficiency maps which are compared to equivalent maps for the air mass 1.5 global (AM1.5G) reference spectrum. Most of the maps are calculated for ideal cells and will thus serve as benchmarks for what can possibly be achieved under real conditions, but the impact of non-radiative recombination is also included. It is found that there is generally good agreement between the efficiency under the AM1.5G spectrum and the efficiency found using the collected spectra. The main difference is that a slight blueshift in the real spectra favors larger bandgaps. Seasonal efficiency maps and maps for different types of conditions are also presented. The largest deviation from the reference spectrum is found for the three darkest months of the year. Optimizing the bandgaps for this period may increase seasonal production by several percent, albeit with a significant accompanying reduction in annual production. For June, the sunniest month, as well as for cloudy and lowlight conditions, it is found that the optimal bandgaps are slightly larger than those found for the AM1.5G.publishedVersio

AUSTRALIA AND BRAZIL: A DIALOGUE ON CITIZENSHIP EDUCATIONAL IN THE SCHOOL CURRICULA

The debate on citizenship education has impacted the area of education in several aspects, mainly in the introduction of changes in school curricula. Therefore, it is timely to identify, analyse and discuss the implications that such changes have had on curricula. The present study was carried out to understand the contents, skills, attitudes and values the Australian Curriculum and the Brazilian Curriculum have incorporated to develop citizenship education. This qualitative research highlights the relevance attributed to citizenship in the curriculum of several countries and in the proposals of international organizations. Therefore, it explains the main features of the curricula in focus. Finally, the results are discussed

Analysis of spectral irradiance distribution for PV applications at high latitude

Submitted version.© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The spectral distribution of global tilted irradiance measured in Grimstad, Norway, is analyzed in terms of the average photon energy (APE) blue fraction (BF) and useful fraction (UF). The results based on eight months of recorded data show a general shift of the APE, BF, and UF values to higher values than reference AM1.5G spectrum, with 1.63 eV, 0.45, and 0.88 being the average indices, respectively. The statistical coefficient of variation (CV) is used to determine the variation of indices. The CV for APE, BF, and UF are calculated to be 20.1%, 26.1%, and 25.7%, respectively confirming the earlier findings on APE being a more accurate index for the quantification of spectral distribution. Also, the spectral indices were classified in terms of sky conditions using the clearness index and CV. The results show a higher variation of indices in the cloudy sky conditions compared to clear and partially sunny sky conditions.submittedVersio

Investigating the fit of a model for students’ understanding of fractions in a Norwegian context

To capture the complexity of students’ understanding of fractions, a model linking part-whole to the subconstructs ratio, operator, quotient and measure has been proposed. We ask if this model is compatible with students’ achievements in a Norwegian context. Responses from 638 students were analysed using structural equation modelling (SEM), and a good fit of the model was obtained after removing the ratio subconstruct. In particular, part-whole is seen to be important for operator, quotient and measure. Using qualitative analysis of interviews, we found reasoning associated with ratio, with a weak link to the part-whole subconstruct

Investigation of temperature coefficients of PV modules through field measured data

Varying broadband irradiance and temperature are generally known as the major factors influencing the performance of PV modules, but studies have also shown the substantial impact of spectral variations. In this work, a simple and efficient method to calculate the temperature coefficient using long term data is demonstrated. Temperature coefficients of PV modules are estimated from long term performance data following IEC 60891 standard with additional spectral correction, and are compared against the datasheet values. Significant improvement of correlation coefficient from −0.89 to −0.97 is observed during the regression for maximum power temperature coefficient of two poly-crystalline modules, after spectral correction by spectral factor (SF). Also, the standard deviation of yearly estimated values of these coefficients reduced from 5–7 % to 1–2 %. In another setup involving spectral measurements and various PV technologies, the annual mean of 1.62 eV for average photon energy in 350–1700 nm range, suggests a general blue shift of the spectrum. Higher averages than reference values of useful fraction (UF) for c-Si, CIGS and HIT technologies also validate the blue shift of spectrum. Results show SF produces maximum power temperature coefficients closer to the datasheet values compared to UF, suggesting better applicability of SF as an index for spectral correction. The coefficient values were found closer to STC values and the results from Mann and Kendall test, employed to detect any underlying monotonic trend in the development of temperature coefficients over eight years, showed no increasing or decreasing trend and hence no degradation of temperature coefficients for the long-term exposed PV modules.publishedVersio

Integration of hydrogels in microfabrication processes for bioelectronic medicine: Progress and outlook

Recent research aiming at the development of electroceuticals for the treatment of medical conditions such as degenerative diseases, cardiac arrhythmia and chronic pain, has given rise to microfabricated implanted bioelectronic devices capable of interacting with host biological tissues in synergistic modalities. Owing to their multimodal affinity to biological tissues, hydrogels have emerged as promising interface materials for bioelectronic devices. Here, we review the state-of-the-art and forefront in the techniques used by research groups for the integration of hydrogels into the microfabrication processes of bioelectronic devices, and present the manufacturability challenges to unlock their further clinical deployment.publishedVersio

Uniqueness verification of blue fraction as a parameter of spectral irradiance quantification

Author's accepted version.The spectral distribution of global irradiance is measured in the optimal tilt (45° south) plane of array for the calender year 2020 in Grimstad, Norway. In this work the spectral distribution is quantified in terms of the Blue Fraction (BF). The uniqueness of BF has been tested and reported using the same methodology used for uniqueness verification of average photon energy (APE). The results show that the coefficient of correlation between the APE and BF was 0.98, meaning a possible bijective relation between these two parameters whereby both indicate a similar spectrum. The percentage contribution of integrated irradiance (Rc) was calculated for 25 nm wavelength bins for the BF region 350-650 nm. Spectra are grouped by their BF value in steps of 0.02, each group containing measurements falling within ±0.01 of the central value. The corresponding standard deviation (SD) varied from 0.05% to 0.21% for the spectra denoted by BF values from 0.44 to 0.60. The coefficient of variation (CV) was found as high as 12% for the wavelengths below 450 nm while it remained relatively low from 450-650 nm, meaning a low dispersion of Rc values around the mean value. The results indicate that the uniquenss of BF can be statistically confirmed for the measured wavelength range.Uniqueness verification of blue fraction as a parameter of spectral irradiance quantificationacceptedVersio