Tor Oskar Sætre

• Segbefia, Oscar Kwame; Akhtar, Naureen & Sætre, Tor Oskar (2023). Moisture induced degradation in field-aged multicrystalline silicon photovoltaic modules. Solar Energy Materials and Solar Cells. ISSN 0927-0248. 258. doi: 10.1016/j.solmat.2023.112407. Fulltekst i vitenarkiv Vis sammendrag

  Moisture ingress is one of the key fault mechanisms responsible for photovoltaic (PV) devices degradation. Understanding moisture induced degradation (MID) mechanisms in field-aged PV modules is more reflective of the reality in the field. In the present work, MID products of reclaimed solar cells from 20-year-old field-aged silicon PV modules is investigated. The defective areas in the PV modules were identified using visual inspection, electroluminescence (EL), ultraviolet fluorescence (UV–F), and infrared thermal (IR-T) techniques. SEM-EDS analysis is used to elucidate the role of moisture on the observed degradation mechanisms. Degradation of the ethylene vinyl acetate (EVA) encapsulation produces acetic acid, carbon dioxide, phosphorus, sulfur, fluorine, and chlorine. Migration of metal ions under the influence of moisture ingress makes the formation of oxides, hydroxides, sulfides, phosphates, acetates, and carbonates of silver, lead, tin, copper, zinc, and aluminum feasible. Also, other competing reactions can lead to the formation of stannates of copper, silver, sodium, and zinc. Another observation is that, in the presence of MID species, Pb is preferentially corroded (to form lead acetate complexes) instead of the expected sacrificial Sn in the solder. These MID species account for different defects and fault modes that lead to parasitic resistance losses. This is witnessed by the 1.2%/year degradation in the Pmax of the PV module.

• Segbefia, Oscar Kwame; Akhtar, Naureen & Sætre, Tor Oskar (2023). Defects and fault modes of field-aged photovoltaic modules in the Nordics. Energy Reports. ISSN 2352-4847. 9, s. 3104–3119. doi: 10.1016/j.egyr.2023.01.126. Fulltekst i vitenarkiv Vis sammendrag

  PV module durability and reliability influences its efficiency and return on investment. Hence, collection of ample and credible PV module reliability data in each climatic zone becomes increasingly essential. In this work, defects and fault modes of field-aged multicrystalline silicon PV modules installed outdoors in Grimstad from 2000 to 2011 are investigated. The investigations were done using visual inspection, current–voltage characterization, temperature coefficient profiling, ultraviolet fluorescence, electroluminescence, infrared thermal imaging, and SEM-EDS analysis. Most PV modules show signs of microcracks, moisture ingress, corrosion, potential induced degradation, optical degradation, and irregular temperature sensitivities. Oxidized silver, tin, and lead were observed in the SEM-EDS results, which confirmed the remnants of moisture ingress. On average, the modules show power output of 78% and their efficiency dropped from 13% to 10%. The average temperature coefficient of efficiency of the module was found to be ca. -0.5%/°C, corresponding to an average degradation rate of 1.09 %/year over the 20 years period. However, the annual degradation rates when the modules were in the field and indoors were 0.98% and 1.33 %, respectively. It is believed that limited evaporation of activated volatile carboxylic products under indoor conditions led to the formation and accumulation of carboxylic acids, hence higher rate of degradation. Moisture induced degradation (MID) mechanisms was the root cause for the overall degradation in the PV modules’ power output, especially over the later years.

• Ibrahim, Mohammad; Sætre, Tor Oskar; Grasmo, Geir & Aune, Ragnhild (2022). Characterisation of Nickel Silicide Deposited on Steel and Nickel Substrates, World PM2022 Proceedings. European Powder Metallurgy Association. ISSN 978-1-899072-55-2.
• Ibrahim, Mohammad; Sætre, Tor Oskar & Aune, Ragnhild (2022). Laser Metal Deposition of Nickel Silicide on S355 Structural Steel, TMS 2022 151st Annual Meeting & Exhibition Supplemental Proceedings. Springer. ISSN 978-3-030-92381-5. s. 249–258. doi: 10.1007/978-3-030-92381-5_22.
• Ibrahim, Mohammad; Sætre, Tor Oskar & Aune, Ragnhild (2022). Characterization of Gas Atomized Nickel Silicide Powder for Additive Manufacturing with Varying Silicon Content, TMS 2022 151st Annual Meeting & Exhibition Supplemental Proceedings. Springer. ISSN 978-3-030-92381-5. s. 1463–1472. doi: 10.1007/978-3-030-92381-5_139.
• Tareq, Foysal Kabir; Aune, Ragnhild Elizabeth & Sætre, Tor Oskar (2022). Influence of process parameters on laser metal deposition (LMD) of inductively coupled plasma spheroidized (ICPS) NiSi32 powder, World PM2022 Proceedings. European Powder Metallurgy Association. ISSN 978-1-899072-55-2.
• Tareq, Foysal Kabir; Aune, Ragnhild Elizabeth; Grasmo, Geir; Akhtar, Naureen & Sætre, Tor Oskar (2022). Preparation and Characterization of Spherical Nickel Silicide Powder by Inductively Coupled Plasma Spheroidization for Additive Manufacturing, TMS 2022 151st Annual Meeting & Exhibition Supplemental Proceedings. Springer. ISSN 978-3-030-92381-5. s. 1488–1496. doi: 10.1007/978-3-030-92381-5_141. Fulltekst i vitenarkiv Vis sammendrag

  Metal alloy powder with spherical-shaped morphology, high flowability, and packing density is the main requirements for metal-based additive manufacturing (AM). Among metal alloys, nickel silicide is considered as a potential candidate due to its unique properties such as high melting point, good electrical conductivity, as well as high corrosion and wear resistance. However, the fabrication of spherical nickel silicide powder has proven to be a challenging task. In the present work, spherical NiSi16 alloy powders were synthesized by inductively coupled plasma spheroidization (ICPS). The influence of the feed rate on the properties of the as-prepared powder was investigated using different analytical techniques to evaluate the particle morphology, particle size distribution, oxygen content, bulk density, fluidity, and spheroidization rate. The results showed some unique advantages of the ICPS technology in the preparation of spherical nickel silicide powder that is believed to be well suited for AM.

• Segbefia, Oscar Kwame; Akhtar, Naureen & Sætre, Tor Oskar (2022). The effect of moisture ingress on titania antireflection coatings in field-aged photovoltaic modules, 978-1-7281-6117-4. IEEE conference proceedings. ISSN 978-1-7281-6117-4. s. 1237–1244. doi: 10.1109/PVSC48317.2022.9938896. Vis sammendrag

  Titanium dioxide (TiO 2 ) or titania antireflection coating (ARC) enhances photovoltaic (PV) module efficiency. Yet, degraded TiO 2 can affect the performance reliability of PV modules. In the present work, the effect of moisture ingress on the degradation of TiO 2 ARC in a field-aged multicrystalline silicon PV module is investigated. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses show degradation of the TiO 2 ARC. Disintegration of the TiO 2 nanoparticles (NPs) were also observed. The assumed Ti-O stoichiometry of the degraded TiO 2 ARC in the field-aged PV module was found to be higher than 1:2. It turned out that moisture ingress strongly influences the surface morphology and defects, crystallinity, and stoichiometry of TiO 2 ARC in the PV module during field operation. Silver and aluminium NPs migrate to and aggregate on the surfaces of the TiO 2 NPs which might likely lead to the formation of titania-metal complexes such as titania-alumina and silver-titania complexes. These degradation mechanisms affect the opto-electrical properties of the TiO 2 ARC in the PV module.

• Segbefia, Oscar Kwame & Sætre, Tor Oskar (2022). Investigation of the Temperature Sensitivity of 20-Years Old Field-Aged Photovoltaic Panels Affected by Potential Induced Degradation. Energies. ISSN 1996-1073. 15(11). doi: 10.3390/en15113865. Fulltekst i vitenarkiv Vis sammendrag

  One effect of moisture ingress on solar panels is potential induced degradation (PID). Solar panels affected by PID experience large leakage currents between the solar cells and the module’s frame, which leads to substantial power degradation. In the present work, the temperature coefficients of 3 old PV panels affected by PID were investigated. In the electroluminescence images, solar cells nearer to the edge of the modules appear darker due to ohmic shunting. IR thermal images acquired under clear sky outdoor conditions show that the majority of the warmer cells (hotspots) were located closer to the edge of the modules. The difference in cell temperature (∆T) due to PID effect ranges from 7 °C to 15 °C for the 3 field-aged modules. The average temperature coefficient of efficiency (βηm) was found to be −0.5%/°C. Also, it was observed that the temperature coefficients of open circuit voltage (βVoc = −0.4%/°C), maximum power point voltage (βVmpp = −0.5%/°C), and fill factor (βFF = −0.2%/°C), were the underlying factors for the degradation in the Pmax of the old solar panels affected by PID. This accounted for an average 1.2%/year overall degradation in the efficiency of these modules. Most notably, it was discovered that the PV modules affected by PID show negative temperature coefficients of maximum power point current (βJmpp) due to large leakage currents. This observed negative βJmpp we believe is characteristic of PV panels affected by PID.

• Segbefia, Oscar Kwame; Imenes, Anne Gerd; Burud, Ingunn & Sætre, Tor Oskar (2021). Temperature profiles of field-aged multicrystalline silicon photovoltaic modules affected by microcracks. I Angus, Rockett (Red.), 2021 IEEE 48th Photovoltaic Specialists Conference (PVSC). IEEE conference proceedings. ISSN 978-1-6654-1922-2. s. 0001–0006. doi: https:/doi.org/10.1109/PVSC43889.2021.9518939. Vis sammendrag

  In this work, the temperature sensitivities of field-aged multicrystalline silicon PV modules affected by microcracks are investigated. It is found that the temperature coefficient of efficiency of all modules has increased more than 10 times over the 20 years period, mainly due to a degradation in the temperature coefficients of fill factor. Temperature coefficient of efficiency of PV modules affected by microcracks changed from -0.44 %/ °C to -1.51 %/°C under solar irradiance conditions at 1010 - 1030 W/m 2. Inconsistent values for the Evans–Floschuetz efficiency ratio versus temperature plots for the microcrack affected modules were also observed.

• Segbefia, Oscar Kwame; Paudyal, Basant Raj; Burud, Ingunn & Sætre, Tor Oskar (2021). Temperature Coefficients of Photovoltaic Modules under Partial Shading Conditions. Proceedings of the European Photovoltaic Solar Energy Conference. ISSN 2196-100X. s. 1180–1186. doi: 10.4229/EUPVSEC20212021-5CV.2.3.
• Hariyadi, Arif; Suwarno, Suwarno; Denys, Roman Volodymyrovich; Colbe von, Jose Bellosta; Sætre, Tor Oskar & Yartys, Volodymyr (2021). Modeling of the hydrogen sorption kinetics in an AB2 laves type metal hydride alloy. Journal of Alloys and Compounds. ISSN 0925-8388. 893. doi: 10.1016/j.jallcom.2021.162135. Fulltekst i vitenarkiv
• Shyikira, Antoine de Padoue; Akhtar, Naureen; Skomedal, Gunstein; Sætre, Tor Oskar & Middleton, Peter Hugh (2021). High temperature oxidation of higher manganese silicides. Corrosion Science. ISSN 0010-938X. 185. doi: 10.1016/j.corsci.2021.109327. Fulltekst i vitenarkiv
• Segbefia, Oscar Kwame; Imenes, Anne Gerd & Sætre, Tor Oskar (2021). Moisture ingress in photovoltaic modules: A review. Solar Energy. ISSN 0038-092X. 224, s. 889–906. doi: 10.1016/j.solener.2021.06.055. Fulltekst i vitenarkiv
• Segbefia, Oscar Kwame; Imenes, Anne Gerd & Sætre, Tor Oskar (2020). Outdoor fault diagnosis of field-aged solar modules, European Photovoltaic Solar Energy Conference and Exhibition 37th EU PVSEC 2020. EU PVSEC. ISSN 3-936338-73-6.
• Berthod, Charly; Søndergaard, Sissel Tind; Strandberg, Rune; Odden, Jan Ove; Nie, Shuai & Hameiri, Ziv [Vis alle 7 forfattere av denne artikkelen] (2019). Temperature Sensitivity of Multicrystalline Silicon Solar Cells. IEEE Journal of Photovoltaics. ISSN 2156-3381. 9(4), s. 927–964. doi: 10.1109/JPHOTOV.2019.2911871. Vis sammendrag

  This paper presents an experimental investigation of the temperature coefficients of multicrystalline silicon solar cells. The aim was to determine if some cell parameters can affect positively the temperature sensitivity without detrimental impact on the efficiency. Commercial solar cells with different bulk resistivities, compensation levels, and cell architectures have been studied. We report that the base net doping, the location of the solar cell along the brick and the cell architecture have significant impacts on the temperature coefficients. Moreover, we show how the change in recombination mechanisms along the ingot height affects the temperature coefficients. The compensation level was observed to have no significant effect on the temperature coefficients. We also demonstrate why aluminum back-surface-field and passivated emitter rear contact solar cells have similar temperature sensitivities despite a better passivation and higher open-circuit voltage for the latter cell architecture. Finally, we have found that reducing the bulk resistivity can improve the solar cells’ performance in hot climates.

• Paudyal, Basant Raj; Imenes, Anne Gerd & Sætre, Tor Oskar (2018). Review of Guidelines for PV Systems Performance and Degradations Monitoring. Proceedings of the European Photovoltaic Solar Energy Conference. ISSN 2196-100X. s. 2037–2050. doi: 10.4229/35thEUPVSEC20182018-6DV.1.32. Fulltekst i vitenarkiv Vis sammendrag

  The recent growth in the PV system deployment and the higher scale of their production make it necessary to pay more attention towards the performance of those systems. System monitoring will provide the status of the systems showing possible degradations and any impending system failures. It also helps with maintaining system quality and ensuring the optimal performance of the system for its lifetime. COST Action PEARL PV aims to formulate such monitoring guidelines for the PV systems applicable for all types of PV technologies, depending upon the end use and duration of the monitoring need. The objective of the present paper is to quantify and provide a review of the guidelines and standards for monitoring of PV systems performance and degradation in practice, and also some results of preliminary work done regarding important information needed to be included in the monitoring guideline.

• Sætre, Tor Oskar (2018). Simulations of some effects on grain boundaries in solar cells. Proceedings of the European Photovoltaic Solar Energy Conference. ISSN 2196-100X. s. 107–109. doi: 10.4229/35thEUPVSEC20182018-1CV.4.9. Vis sammendrag

  Grain boundaries in solar cells can give several important effects relevant for the performance of solar cells. The grain boundaries can give both negative and positive effects on the power generation. Hence, the study of these effects is an important topic. It is in the present paper suggested that Monte Carlo simulations may be a possible tool for simulating these effects. Some preliminary results are given to demonstrate the method. It is possible to develop this simulation concept into more advanced models which can be of importance in studying several effects of grain boundaries in solar cells.

• Sætre, Tor Oskar (2016). Simulation of IQE tuning of individual cells for DC-balancing multijunction tandem cells. Conference record of the Photovoltaic Specialists Conference. ISSN 0160-8371. 2016-November, s. 350–353. doi: 10.1109/PVSC.2016.7749609.
• Berthod, Charly; Strandberg, Rune; Odden, Jan Ove & Sætre, Tor Oskar (2016). Reduced temperature sensitivity of multicrystalline silicon solar cells with low ingot resistivity. Conference record of the Photovoltaic Specialists Conference. ISSN 0160-8371. 2016-November, s. 2398–2402. doi: 10.1109/PVSC.2016.7750071.
• Sætre, Tor Oskar (2016). Simulations of the effect of the contact energy levels on a simple model of a hot carrier cell, IEEE 43rd Photovoltaic Specialists Conference 2016 (PVSC). IEEE Press. ISSN 978-1-5090-2724-8. s. 0354–0357. doi: 10.1109/PVSC.2016.7749610.
• Sætre, Tor Oskar (2015). Challenges with Balancing Excitations in Intermediate-Band Solar Cells, Photovoltaic Specialist Conference (PVSC), 2015 IEEE 42nd. IEEE conference proceedings. ISSN 978-1-4799-7944-8. doi: 10.1109/PVSC.2015.7355803. Vis sammendrag

  New insight into the potential of practical solar cells can be given through alternative modelling approaches like Monte Carlo simulations. In the present work, the performance of intermediate band solar cells was examined by this method. It is demonstrated that the balance of excitations from the valence band to the intermediate band and from the intermediate band to the conduction band is of great importance for the performance of such cells. Several cases with different distributions of photons given by ASTM standards have been employed in order to detect spectrum sensitivity. Incident photons are accounted for as they interact with the electrons in the valence band or in the intermediate band.

• Sætre, Tor Oskar (2015). Effect of Quantum Efficiency on the Performance of Multijunction Tandem Cells, Photovoltaic Specialist Conference (PVSC), 2015 IEEE 42nd. IEEE conference proceedings. ISSN 978-1-4799-7944-8. doi: 10.1109/PVSC.2015.7356110. Vis sammendrag

  New insight into the potential of practical solar cells can be given through alternative modelling approaches like Monte Carlo simulations. In the present work, the performance of three stacks of cells connected in series was examined at different levels of internal quantum efficiency. Incident photons, generated by employing the ASTM G173-03 and E490-00a data sets, are accounted for individually as they interact with the stack of cells. The values of the different bandgaps were chosen from a paper by K. Tanabe (2009), and the performance was studied based on photon dynamics.

• Berthod, Charly; Strandberg, Rune; Odden, Jan Ove & Sætre, Tor Oskar (2015). Reduction of temperature coefficients in multicrystalline silicon solar cells after light-induced degradation, Photovoltaic Specialist Conference (PVSC), 2015 IEEE 42nd. IEEE conference proceedings. ISSN 978-1-4799-7944-8. doi: 10.1109/PVSC.2015.7355753.
• Sætre, Tor Oskar (2014). Monte Carlo Generated Photon Spectra for Device Simulation, Proceedings 29th European Photovoltaic Solar Energy Conference and Exhibition. WIP Renewable Energies. ISSN 3-936338-34-5. s. 73–75. doi: 10.4229/EUPVSEC20142014-1BV.6.1.
• Tayyib, Muhammad; Odden, Jan Ove & Sætre, Tor Oskar (2014). Temperature Coefficients of Solar Cells from Elkem Solar under Varied Intensities and Selective Wavelength Regions of the AM 1.5 Spectrum, Proceedings 29th European Photovoltaic Solar Energy Conference and Exhibition. WIP Renewable Energies. ISSN 3-936338-34-5. s. 3378–3382. doi: 10.4229/EUPVSEC20142014-5DV.3.25.
• Tayyib, Muhammad; Odden, Jan Ove & Sætre, Tor Oskar (2014). Influence of Spectral Composition on the Temperature Coefficients of Solar Cells from Elkem Solar. I King, Richard R. (Red.), 40th IEEE Photovoltaic Specialists Conference, Proceedings of the. IEEE conference proceedings. ISSN 978-1-4799-4398-2. s. 2630–2634. doi: 10.1109/PVSC.2014.6925469.
• Tayyib, Muhammad; Odden, J. O.; Ramchander, N.; Prakash, M. B.; Surendra, T. S. & Muneeshwar, R. [Vis alle 9 forfattere av denne artikkelen] (2014). Two Years Performance Comparison of Elkem Solar Multicrystalline Silicon with Polysilicon in a PV Grid-Connected System. I King, Richard R. (Red.), 40th IEEE Photovoltaic Specialists Conference, Proceedings of the. IEEE conference proceedings. ISSN 978-1-4799-4398-2. s. 3230–3233. doi: 10.1109/PVSC.2014.6925623.
• Berthod, Charly; Odden, Jan Ove & Sætre, Tor Oskar (2014). Scanning electron microscopy analysis of defect clusters in multicrystalline solar grade silicon solar cells. I King, Richard R. (Red.), 40th IEEE Photovoltaic Specialists Conference, Proceedings of the. IEEE conference proceedings. ISSN 978-1-4799-4398-2. s. 2947–2950. doi: 10.1109/PVSC.2014.6925549. Vis sammendrag

  Solar cells from an identical commercial manufacturing unit have been investigated by electroluminescence to first detect the defect clusters. A further analysis has been done by scanning electron microscopy in secondary electron imaging mode to understand the propagation mechanism of defects. It appears that defect cluster boundaries can be very sharp or spread in the bulk with little apparent effect on the overall cell efficiency. And it is shown that grain boundaries act clearly as arrests to further propagation of these defects.

• Yordanov, Georgi Hristov; Sætre, Tor Oskar & Midtgård, Ole-Morten (2014). 1.6 suns at 58°20'N - the solar resource in southern Norway. I King, Richard R. (Red.), 40th IEEE Photovoltaic Specialists Conference, Proceedings of the. IEEE conference proceedings. ISSN 978-1-4799-4398-2. s. 0815–0820. doi: 10.1109/PVSC.2014.6925040. Vis sammendrag

  We measured an extreme overirradiance event of 1.6 suns at latitude 58°20'N during a solar resource assessment in southern Norway. The burst occurred when the sun showed in a narrow gap between broken, optically thin altocumulus clouds. The enhancement was most intense within 3° around the solar disk. The annual solar irradiation in the plane of an optimally tilted PV array peaked at 1.30 MWh/m2 in the year 2013, and measured 1.20 MWh/m2 in the previous two years. These values exclude irradiance below 0.05 suns but include reflections from the sea surface and terrain which have not been quantified. The long-term average predicted by the Photovoltaic Geographical Information System (PVGIS) is only 1.04 MWh/m2. 15 years of global horizontal irradiation data reveal that the PVGIS underestimates the local solar resource by at least 10%.

• Yordanov, Georgi Hristov; Midtgård, Ole-Morten; Sætre, Tor Oskar; Nielsen, Henrik Kofoed & Norum, Lars Einar (2013). Overirradiance (Cloud Enhancement) Events at High Latitudes. IEEE Journal of Photovoltaics. ISSN 2156-3381. 3(1), s. 271–277. doi: 10.1109/JPHOTOV.2012.2213581. Vis sammendrag

  Contrary to intuition, solar irradiance peaks at partially cloudy conditions. Clouds can boost sunlight by over 1.5 times, even at high latitudes. Depending on cloud velocity, the bursts last from seconds to minutes. Measuring irradiance on a tilted surface with 10-ms resolution allows for a detailed study of such events in Southern Norway, almost at sea level. All monthly maxima from April through September 2011 exceeded 1300 W/m2. The slow sensor registered an annual maximum of 1413 W/m2, while the fast sensor’s range was found insufficient. A burst reaching 1528 W/m2 was registered in June 2012. Near the Equator, bursts exceeding 1800 W/m2 have been observed. These numbers are striking since the extraterrestrial solar irradiance peaks in January at about 1400 W/m2. The phenomenon is attributed mainly to forward scattering of light in optically thin clouds (adjacent to the sun), which is much stronger for angles within 5° around the solar disk.

• Yordanov, Georgi Hristov; Sætre, Tor Oskar & Midtgård, Ole-Morten (2013). Optimal temporal resolution for detailed studies of cloud-enhanced sunlight (Overirradiance), 39th Photovoltaic Specialists Conference (PVSC), 2013 IEEE, Proceedings. IEEE conference proceedings. ISSN 978-1-4799-3299-3. s. 985–988. doi: 10.1109/PVSC.2013.6744306. Vis sammendrag

  Enhancement of sunlight by clouds can lead to irradiance peaks much exceeding the extraterrestrial levels — close to 2 suns near the Equator and at least 1.5 suns at latitudes of about 60°. Some extreme overirradiance events can last many minutes, but durations in the order of 1 second are also possible. The present paper reports the shortest bursts recorded in Southern Norway in the years 2012 and 2013. Our records of 10-millisecond resolution from 2012 show that the optimal instantaneous irradiance sampling interval is less than 0.15 s at the present test site, while the optimal averaging time is less than 0.13 s. We propose simple equations for deriving these times in an arbitrary geographical location from data recorded with very fine temporal resolution. The small values in the present coastal site are attributed to rather high cloud speeds.

• Yordanov, Georgi Hristov; Midtgård, Ole-Morten & Sætre, Tor Oskar (2013). Ideality factor behavior between the maximum power point and open circuit, 39th Photovoltaic Specialists Conference (PVSC), 2013 IEEE, Proceedings. IEEE conference proceedings. ISSN 978-1-4799-3299-3. s. 729–733. doi: 10.1109/PVSC.2013.6744254. Vis sammendrag

  The local ideality factor analysis of dark and light I-V curves has been used in the past to study various performance degradation effects in solar cells. Trapping, edge recombination and injection-level-dependent recombination are expressed as “lumps, humps and bumps” in the plots of the local ideality factor over cell voltage (m-V plots). Earlier applications of this differential technique did not correct the plots for the series resistance effect. Thus, the bumps at the higher voltages introduced by some mechanisms were more difficult to quantify. A possible solution is to analyze ISC-VOC curves, but their measurement is not always possible. We present a formula for calculation of the RS-corrected local ideality factor. The m-I plot can be more informative than the m-V plot which varies strongly with the cell temperature. We present results from several crystalline-silicon (c-Si) PV technologies showing the m-I plot behavior between the MPP and open circuit. For some of the tested modules, the ideality factor is much higher at the MPP.

• Tayyib, Muhammad; Dahl, Espen H; Odden, Jan Ove; Baggethun, P. & Sætre, Tor Oskar (2013). Microscopic Defects and Impurity Analyses of Multicrystalline Silicon Solar Cells from Different Manufacturing Routes, 39th Photovoltaic Specialists Conference (PVSC), 2013 IEEE, Proceedings. IEEE conference proceedings. ISSN 978-1-4799-3299-3. s. 1459–1464. doi: 10.1109/PVSC.2013.6744419. Vis sammendrag

  It is important to fully understand the physical behavior of solar cells made by materials from alternative process routes. Solar cells from Elkem Solar Grade Silicon and standard polysilicon have been investigated with light beam induced current and electroluminescence imaging. The low efficiency regions have been further analyzed by Scanning Electron Microscopy under different imaging modes. It was found that cell regions of low performance had undergone plastic deformations resulting in the creation of crystalline defects appearing as subgrain patterns. Similar patterns were observed in both ESS™ and standard polysilicon. Energy-dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) were used to study crystallographic orientations and impurities.

• Tayyib, Muhammad; Odden, Jan Ove; Preis, Primin & Sætre, Tor Oskar (2013). Impurity Analyses of Silicon Wafers from different Manufacturing Routes and Their Impact on LID of Finished Solar Cells, 39th Photovoltaic Specialists Conference (PVSC), 2013 IEEE, Proceedings. IEEE conference proceedings. ISSN 978-1-4799-3299-3. s. 1454–1458. doi: 10.1109/PVSC.2013.6744418. Vis sammendrag

  This abstract summarizes the measurements of impurity concentrations in directionally solidified silicon ingots from different feedstocks. The substitutional Carbon and interstitial Oxygen are measured on as-sawn wafers using FTIR. Active iron concentration is mapped on a-Si:H passivated wafers. It is observed that these impurities present in Elkem Solar Grade Silicon (ESS™) concentrations are comparable to the standard polysilicon which are in the acceptable ranges for silicon for solar industry. The measured LID of the finished solar cells is also comparable.

• Tayyib, Muhammad; Odden, Jan Ove; Ramchander, N.; Prakash, M. B.; Surendra, T. S. & Muneeshwar, R. [Vis alle 9 forfattere av denne artikkelen] (2013). Performance Assessment of a Grid-Connected mc-Si PV System made up of Silicon Material from Different Manufacturing Routes, 39th Photovoltaic Specialists Conference (PVSC), 2013 IEEE, Proceedings. IEEE conference proceedings. ISSN 978-1-4799-3299-3. s. 109–114. doi: 10.1109/PVSC.2013.6744110. Vis sammendrag

  This abstract summarises the performance of an Elkem Solar photovoltaic (PV) system installed in the Sunbelt Region (between 35° North and 35° South) in Hyderabad, India, which has been fully operational since August 2012. The PV system consists of 28 multicrystalline silicon PV modules made from the standard Siemens process and from material produced by a metallurgical route – the Elkem Solar Silicon (ESS™) process. A comparative performance study of the ESS™ modules with respect to standard polysilicon has been carried out under the various climatic and solar radiation conditions at the location. The present study suggests that the ESS™ PV modules have a slightly better performance than standard polysilicon modules as a function of solar irradiation, and thereby the total kWh generated has also been higher for the ESS™ modules.

• Beyer, Hans-Georg; Sætre, Tor Oskar & Yordanov, Georgi Hristov (2013). Using broad-band irradiance data to model the short circuit response of aSi modules, 39th Photovoltaic Specialists Conference (PVSC), 2013 IEEE, Proceedings. IEEE conference proceedings. ISSN 978-1-4799-3299-3. s. 751–753. doi: 10.1109/PVSC.2013.6744258. Vis sammendrag

  aSi modules show large variations in their response to the incoming irradiance as measured by broad-band irradiance sensors, making the check and prediction of their performance difficult when only broad-band data are available. One approach to overcome this difficulty is given by the use of detailed models to estimate the irradiance spectra from the broad-band data. Here, it is tested to what degree the detailed modeling could be substituted by a semi-empirical approach to reflect the modules response based on but the information on direct and diffuse irradiance and solar geometry. The model performance is measured by its capability to give the correct monthly mean short-circuit current together with a reasonable R2 value of the scatter of modeled and measured data. A first test of a respective model has shown reasonable results.

• Tayyib, Muhammad; Odden, Jan Ove; Hvidsten Dahl, E.; Baggethun, P. & Sætre, Tor Oskar (2013). Elkem Silicon vs Polysilicon: A Quantitative Impurity Element Analyses. I EU PVSEC, 2013 (Red.), 28th European Photovoltaic Solar Energy Conference: Proceedings. WIP. ISSN 3-936338-33-7. s. 1692–1697. doi: 10.4229/28thEUPVSEC2013-2CV.4.15.
• Tayyib, Muhammad; Odden, Jan Ove; Ramchander, N.; Prakash, M. B.; Surendra, T. S. & Muneeshwar, R. [Vis alle 9 forfattere av denne artikkelen] (2013). A Materials Perspective on one Full Year Performance of Multicrystalline Si PV Modules in a Grid-Connected System. I EU PVSEC, 2013 (Red.), 28th European Photovoltaic Solar Energy Conference: Proceedings. WIP. ISSN 3-936338-33-7. s. 4166–4170. doi: 10.4229/28thEUPVSEC2013-5BV.7.34.
• Tayyib, Muhammad; Odden, Jan Ove & Sætre, Tor Oskar (2013). Effect of Temperature and Sun Intensity on Multicrystalline Silicon Solar Cells. I EU PVSEC, 2013 (Red.), 28th European Photovoltaic Solar Energy Conference: Proceedings. WIP. ISSN 3-936338-33-7. s. 1595–1598. doi: 10.4229/28thEUPVSEC2013-2CV.3.39.
• Tayyib, Muhammad; Odden, Jan Ove & Sætre, Tor Oskar (2013). UV-induced Degradation Study of Multicrystalline Silicon Solar Cells Made from Different Silicon Materials. Energy Procedia. ISSN 1876-6102. 38, s. 626–635. doi: 10.1016/j.egypro.2013.07.326. Vis sammendrag

  The effect of ultraviolet-induced degradation (UV-ID) on solar cells made from two different solar grade materials has been compared. By using identical wafer and cell production units, effects originating in the two materials; solar grade produced by the Elkem Solar method (ESS™) was compared to standard polysilicon solar cells. Silicon wafers were selected precisely from similar positions from respective silicon bricks to process identical standard solar cells. The quantum efficiency maps at particular laser wavelengths and IV parameters of all solar cells were measured before and after UV-ID to visualize defects sites in the solar cells and to observe the extent of degradation. The experimental results indicate a general tendency that the cells made from the ESS™ material perform slightly better than standard polysilicon material.

• Yordanov, Georgi Hristov; Sætre, Tor Oskar & Midtgård, Ole-Morten (2013). Differential Analysis of PV Module I-V Curves. I EU PVSEC, 2013 (Red.), 28th European Photovoltaic Solar Energy Conference: Proceedings. WIP. ISSN 3-936338-33-7. s. 3207–3211. doi: 10.4229/28thEUPVSEC2013-4AV.5.17.
• Yordanov, Georgi Hristov; Sætre, Tor Oskar & Midtgård, Ole-Morten (2013). Overirradiance Studies Require Subsecond Resolution; Exclude Thermopile Pyranometers and Commercial Data Loggers. I EU PVSEC, 2013 (Red.), 28th European Photovoltaic Solar Energy Conference: Proceedings. WIP. ISSN 3-936338-33-7. s. 3455–3459. doi: 10.4229/28thEUPVSEC2013-4AV.6.32.
• Yordanov, Georgi Hristov; Sætre, Tor Oskar & Midtgård, Ole-Morten (2013). 100-millisecond Resolution for Accurate Overirradiance Measurements. IEEE Journal of Photovoltaics. ISSN 2156-3381. 3(4), s. 1354–1360. doi: 10.1109/JPHOTOV.2013.2264621. Vis sammendrag

  Cloud enhancement of sunlight results in peak irradiance well exceeding extraterrestrial levels, even at high latitudes. Values above 1.8 kW/m2 are possible in the equatorial regions. Recently, we detected bursts over 1.5 kW/m2 in Northern Europe at latitude close to 60◦N. Overirradiance events (intensities much higher than 1 sun) can last tens of minutes, as well as less than 1 s. They may have caused series arcing in photovoltaic modules, leading to fires and loss of property. The accurate measurement of short bursts requires sensors with response times on the order of milliseconds. The long response times of thermopile pyranometers smooth out important details of very short-lived peaks and may cause underestimations of more than 30%. However, sampling with very high resolution can result in very large data files. Thus, the question of an optimal sampling rate arises. This paper will show a method to answer this question. We propose two simple equations that relate the optimal sampling and averaging times to the second temporal derivative of irradiance at the narrowest peak. We studied records with 10-ms resolution from Southern Norway and arrived at an upper limit of 132 ms for accuracy level of 10 W/m2.

• Yordanov, Georgi Hristov; Midtgård, Ole-Morten; Odden, Jan Ove & Sætre, Tor Oskar (2012). Test of the European JRC Performance Model for c-Si PV Modules, 27th European Photovoltaic Solar Energy Conference (EU PVSEC), Frankfurt, Germany, September, 2012. WIP - Renewable Energies. ISSN 3-936338-28-0. s. 3306–3312.
• Yordanov, Georgi Hristov; Midtgård, Ole-Morten; Sætre, Tor Oskar; Nielsen, Henrik Kofoed & Norum, Lars Einar (2012). Over-Irradiance (Cloud Enhancement) Events at High Latitudes, 27th European Photovoltaic Solar Energy Conference (EU PVSEC), Frankfurt, Germany, September, 2012. WIP - Renewable Energies. ISSN 3-936338-28-0. s. 3709–3713. doi: 10.1109/pvsc-vol2.2013.6656797.
• Verma, Deepak; Tayyib, Muhammad; Sætre, Tor Oskar & Midtgård, Ole-Morten (2012). Outdoor Performance of 10 year Old a-Si and Poly-Si Modules in southern Norway conditions, 38th IEEE Photovoltaic Specialists Conference (PVSC), 2012, proceedings. IEEE conference proceedings. ISSN 978-1-4673-0064-3. s. 002368–002371. doi: 10.1109/pvsc.2012.6318074. Vis sammendrag

  The outdoor performance of 10 years modules has been measured in southern Norway conditions. For this study, Poly-Si and a-Si modules are selected and the measurements are carried out using a portable electronic load. The I-V characteristics and maximum power have been recorded for several modules of each technology. It is found that Poly-Si modules perform very well even after 10 years of span whereas some of a-Si modules have visual degradation which causes significant power losses. The experimentally outdoor monitored values of Pmp, Vmp, short circuit current (Isc) , Open circuit voltage (Voc) and efficiency for different modules are compared with manufacturer’s values.

• Yordanov, Georgi Hristov; Midtgård, Ole-Morten & Sætre, Tor Oskar (2012). PV modules with variable ideality factors, 38th IEEE Photovoltaic Specialists Conference (PVSC), 2012, proceedings. IEEE conference proceedings. ISSN 978-1-4673-0064-3. s. 002362–002367. doi: 10.1109/pvsc.2012.6318073. Vis sammendrag

  The classical single-exponential I–V curve model for crystalline-Si PV devices assumes a constant ideality factor. The model is widely applied in e.g. modeling the power output of PV systems at different irradiances and temperatures, and also in calculating the Equivalent Cell Temperature (ECT) from the open-circuit voltage. The present paper presents results from several crystalline-Si (c-Si) module types suggesting that the ideality factor may change with irradiance. The possible implications of such variability are discussed, in particular the need for a new ECT calculation procedure as well as for revision of some PV performance models.

• Verma, Deepak; Tayyib, Muhammad; Sætre, Tor Oskar & Midtgård, Ole-Morten (2012). Outdoor performance of north-facing multicrystalline modules in Southern Norway, 38th IEEE Photovoltaic Specialists Conference (PVSC), 2012, proceedings. IEEE conference proceedings. ISSN 978-1-4673-0064-3. s. 002372–002375. doi: 10.1109/pvsc.2012.6318075. Vis sammendrag

  The present paper deals with reports on an outdoor performance evaluation of multicrystalline modules facing north in Southern Norway. The relevance of this study is mainly for building integrated systems where some of the facades are in a far from optimum position. The impact of shading on the photovoltaic modules’ performance is also evaluated. A dedicated experimental set up has been created to study the PV modules performance under the above mentioned conditions. The results indicate significant power extraction from the PV modules even in the north facing direction. Effects of shadowing are also considered.

• Yordanov, Georgi Hristov; Midtgård, Ole-Morten & Sætre, Tor Oskar (2012). Equivalent cell temperature calculation for PV modules with variable ideality factors, 38th IEEE Photovoltaic Specialists Conference (PVSC), 2012, proceedings. IEEE conference proceedings. ISSN 978-1-4673-0064-3. s. 000505–000508. doi: 10.1109/pvsc.2012.6317666. Vis sammendrag

  Outdoor testing of PV modules involves monitoring their operating temperatures which have strong influence on the output power. Back-of-module sensing is associated with significant uncertainty due to temperature drop across the back encapsulation and also due to non-uniform temperature over the module's area. The international standard IEC 60904-5 defines a procedure for calculating the Equivalent Cell Temperature (ECT) of PV devices from their open-circuit voltage. This and other standards (as well as some module performance models) assume a single-exponential I–V curve model with a constant ideality factor. However, this parameter may vary with the illumination level and the operating temperature. If this variation is significant, the standard ECT calculation procedure may introduce unacceptable errors. A new equation is derived for the case when both dependencies are linear.

• Verma, Deepak; Sætre, Tor Oskar & Midtgård, Ole-Morten (2012). Review on up/down conversion materials for solar cell application, 38th IEEE Photovoltaic Specialists Conference (PVSC), 2012, proceedings. IEEE conference proceedings. ISSN 978-1-4673-0064-3. s. 002608–002613. doi: 10.1109/pvsc.2012.6318129. Vis sammendrag

  The present paper reviews the methods of photon up- and down conversion strategies for improving the efficiency of solar cells. Photons with a lower energy than the band gap will be lost in a normal solar cell. The principle of the up conversion technique is that two or more photons are converted into a photon with energy higher than the band gap energy. High energy photons will lose the energy above the band gap energy limit. Down conversion is a process where a high energy photon is converted into several lower energy photons with energies above the band gap. A description is given of the most common methods and materials for these conversions resulting in higher solar cell efficiencies.

• Yordanov, Georgi Hristov; Tayyib, Muhammad; Midtgård, Ole-Morten; Odden, Jan Ove & Sætre, Tor Oskar (2012). Test of the European Joint Research Centre performance model for c-Si PV modules, 38th IEEE Photovoltaic Specialists Conference (PVSC), 2012, proceedings. IEEE conference proceedings. ISSN 978-1-4673-0064-3. s. 002382–002387 . doi: 10.1109/pvsc.2012.6318077. Vis sammendrag

  The performance of ten c-Si PV modules is studied at different levels of illumination and module temperatures and is modeled in terms of relative efficiency with respect to Standard Testing Conditions (STC). A recently proposed model is tested in Nordic conditions for generic mono- and mc-Si devices with screen-printed cells as well as for some high-efficiency cell designs. Two of the modules are field aged. Averaged model coefficients are derived and compared to values found in the literature. Irradiance and module temperatures measured in 2011 are then used to estimate the expected annual energy yields. The measured yields equal the predicted ones within 1.6% (mean bias error −1.0%) which suggests good modeling accuracy. The annual average relative efficiency of new c-Si modules for the test site in Southern Norway is 0.95, among the highest values in Europe. It is attributed to cool ambient air and frequent windy conditions. A theoretical relationship is derived between the first coefficient of the performance model and I–V curve model parameters. Fitted and predicted values agree well for most of the tested devices. The equation may be used by module manufacturers as a quantitative guideline for designing products with superior energy yields.

• Yordanov, Georgi Hristov; Midtgård, Ole-Morten & Sætre, Tor Oskar (2012). Series resistance determination and further characterization of c-Si PV modules. Renewable Energy. ISSN 0960-1481. 46, s. 72–80. doi: 10.1016/j.renene.2012.03.012. Vis sammendrag

  This paper presents a new algorithm for determination of the series resistance of crystalline-Si PV modules from individual illuminated I-V curves. The ideality factor and the reverse saturation current are then extracted in the classic way. The approach is applied to in-situ measured data from modules based on two types of mc-Si feedstock. The results indicate that the method yields physically meaningful parameters. An improved definition of local ideality factor is suggested, resulting in m-V plots unaffected by the series resistance. In addition, m-I plots are introduced for the first time. The novel differential techniques reveal an unexpected rise of the ideality factor at open circuit by about 5%.

• Yordanov, Georgi Hristov; Midtgård, Ole-Morten; Sætre, Tor Oskar; Nielsen, Henrik Kofoed & Norum, Lars (2012). Overirradiance (Cloud Enhancement) Events at High Latitudes, 38th IEEE Photovoltaic Specialists Conference (PVSC), 2012, proceedings. IEEE conference proceedings. ISSN 978-1-4673-0064-3. doi: 10.1109/PVSC-Vol2.2013.6656797. Vis sammendrag

  Contrary to intuition, solar irradiance peaks at partially cloudy conditions. Clouds can boost sunlight by over 1.5 times, even at high latitudes. Depending on cloud velocity, the bursts last from seconds to minutes. Measuring irradiance on a tilted surface with 10-ms resolution allows for a detailed study of such events in Southern Norway, almost at sea level. All monthly maxima from April through September 2011 exceeded 1300 W/m2. The slow sensor registered an annual maximum of 1413 W/m2, while the fast sensor's range was found insufficient. A burst reaching 1528 W/m2 was registered in June 2012. Near the Equator, bursts exceeding 1800 W/m2 have been observed. These numbers are striking since the extraterrestrial solar irradiance peaks in January at about 1400 W/m2. The phenomenon is attributed mainly to forward scattering of light in optically thin clouds (adjacent to the sun), which is much stronger for angles within 5° around the solar disk.

• Tayyib, Muhammad; Sætre, Tor Oskar & Odden, Jan Ove (2012). Micro Defects and Impurity Analyses of Multicrystalline Silicon Solar Cells, 27th European Photovoltaic Solar Energy Conference (EU PVSEC), Frankfurt, Germany, September, 2012. WIP - Renewable Energies. ISSN 3-936338-28-0. s. 1384–1388. doi: 10.1109/pvsc.2013.6744419. Vis sammendrag

  It is important to fully understand the physical behavior of solar cells made by materials from alternative process routes. Solar cells from Elkem Solar Grade Silicon and standard polysilicon have been invested with light beam induced current (LBIC) and electroluminescence imaging. The low efficiency regions have been further analyzed by Scanning Electron Microscopy under different imaging modes. It was found that cell regions of low performance had undergone plastic deformations resulting in the creation of crystalline defects appearing as subgrain patterns. Similar patterns were observed in both ESS™ and standard polysilicon.

• Tayyib, Muhammad & Sætre, Tor Oskar (2012). Cyclic Straining and Stress Analyses of Multicrystaline Silicon Solar Cells, 27th European Photovoltaic Solar Energy Conference (EU PVSEC), Frankfurt, Germany, September, 2012. WIP - Renewable Energies. ISSN 3-936338-28-0. s. 1389–1393. Vis sammendrag

  Cracking of solar cells has been one of the main reasons for failure and rejection. It is therefore important to determine the mechanical properties of solar cells for evaluating the cracking root cause. Solar cells and wafers have in the present work undergone cyclic loads and fracture tests using standard mechanical testing methods; three points bend test and four points shear test. The performances of bare solar cells have been investigated by electroluminescence images and IV characteristics from sun simulator. Furthermore, the fracture strengths of the solar cells and wafers are calculated from breaking tests and the fractured cross sectional surface areas have been inspected by scanning electron microscopy.

• Tayyib, Muhammad; Theobald, Jens; Peter, Kristian; Odden, Jan Ove & Sætre, Tor Oskar (2012). Accelerated Light-Induced Defect Transformation Study of Elkem Solar Grade Silicon. Energy Procedia. ISSN 1876-6102. 27, s. 21–26. doi: 10.1016/j.egypro.2012.07.023. Vis sammendrag

  Solar cells made of silicon feedstock from a metallurgical route must qualify not only the initial efficiency, but must also be comparable to the solar cells made from reference polysilicon on the spectral response after light induced degradation. A detailed comparative study of light induced defects and its impact on cell performance is necessary for both materials. We have studied accelerated light induced degradation (ALID) defect transformation for Elkem Solar Silicon and polysilicon solar cells by selecting wafers from different positions from respective silicon bricks. Active boron-oxygen complexes and iron ions in multicrystalline silicon solar cells have been analyzed, and their impacts on the current voltage characteristics of the solar cells have been studied in detail.

• Tayyib, Muhammad; Harshavardhana Rao, Y; Ramanjaneyulu, M; Surendra, T. S.; Odden, Jan Ove & Sætre, Tor Oskar (2012). Initial light-induced degradation study of multicrystalline modules made from silicon material processed through different manufacturing routes, 38th IEEE Photovoltaic Specialists Conference (PVSC), 2012, proceedings. IEEE conference proceedings. ISSN 978-1-4673-0064-3. s. 2395–2399. doi: 10.1109/pvsc.2012.6318080. Vis sammendrag

  The paper presents results of initial light-induced degradation (LID) of multicrystalline silicon photovoltaic (PV) modules made of crystalline silicon from different manufacturing processes. The modules were installed within the Sunbelt, in Hyderabad, India. Current-voltage (I-V) characteristics are measured and infra-red (IR) images of the modules are taken at regular intervals. A relationship of the IV degradation with the IR images is discussed. Results from laboratory LID tests at room temperature are performed parallel to the outdoor degradation of PV modules. It was found that the total LID, measured on the module level, after the initial 40 hours is similar for both materials resulting in approximately 1.0% degradation of the maximum module power output. This is slightly higher than what was found in laboratory accelerated light induced degradation (ALID) tests at 120°C on the cell level [1].

• Imenes, Anne Gerd; Yordanov, Georgi Hristov; Midtgård, Ole-Morten & Sætre, Tor Oskar (2011). Development of a Test Station for Accurate in Situ I-V Curve Measurements of Photovoltaic Modules in southern Norway, 37th IEEE Photovoltaic Specialists Conference, Seattle, June 19-24, 2011. Proceedings. IEEE conference proceedings. ISSN 9781424499663. Vis sammendrag

  The development of an outdoor test station for accurate in situ I-V curve measurements of photovoltaic (PV) modules is described. The modules are installed in an open-rack configuration at the University of Agder in Southern Norway. Seven new and three aged PV modules of different type and make are being tested, including monoand multicrystalline silicon from differing manufacturing routes, triple-junction amorphous silicon, and CIS. Data acquisition is controlled with a multichannel electronic load system and LabVIEW software, recording high-resolution I-V curves at one-minute intervals. Between I-V curve sweeps, each module is operated at the maximum power point. Characteristic electrical parameters are extracted and stored together with values of module temperatures and in-plane solar irradiance, the latter recorded at subsecond resolution. The paper describes the experimental set-up in more detail, discusses some local environmental effects, and presents a sample of test results.

• Beyer, Hans-Georg; Yordanov, Georgi Hristov; Midtgård, Ole-Morten; Sætre, Tor Oskar & Imenes, Anne Gerd (2011). CONTRIBUTIONS TO THE KNOWLEDGE BASE ON PV PERFORMANCE: EVALUATION OF THE OPERATION OF PV SYSTEMS USING DIFFERENT TECHNOLOGIES INSTALLED IN SOUTHERN NORWAY, 37th IEEE Photovoltaic Specialists Conference, Seattle, June 19-24, 2011. Proceedings. IEEE conference proceedings. ISSN 9781424499663. doi: 10.1109/pvsc.2011.6186600. Vis sammendrag

  To assist in establishing an accepted knowledge base on PV-modules and systems performance using a representative range of technologies, devices have to be installed at diverse locations, covering a broad range of environmental conditions. For the example of a high latitude location, modules and systems are installed and under investigation in southern Norway (Kristiansand region) by the University of Agder in cooperation with industrial partners. This paper presents first results of the analysis of module performance. The operational behavior of the modules is used to derive a modeling scheme applicable for performance prediction. This use is demonstrated by giving the expected annual performance of different module technologies for a set of sites in southern Norway.

• Verma, Deepak; Midtgård, Ole-Morten & Sætre, Tor Oskar (2011). Review of photovoltaic status in European (EU) perspective, 37th IEEE Photovoltaic Specialists Conference, Seattle, June 19-24, 2011. Proceedings. IEEE conference proceedings. ISSN 9781424499663. doi: 10.1109/pvsc.2011.6186641.
• Verma, Deepak; Midtgård, Ole-Morten & Sætre, Tor Oskar (2011). A Report on Efficient Hybrid Solar Cells. I Ossenbrink, H.; Jäger-Waldau, A. & Helm, P. (Red.), 26th European Photovoltaic Solar Energy Conference, Proceedings of the International Conference held in Hamburg, Germany 5 - 9 September 2011. WIP. ISSN 3-936338-27-2. s. 580–586.
• Sætre, Tor Oskar; Midtgård, Ole-Morten & Yordanov, Georgi Hristov (2011). A new analytical solar cell I-V curve model. Renewable Energy. ISSN 0960-1481. 36(8), s. 2171–2176. doi: 10.1016/j.renene.2011.01.012. Vis sammendrag

  A simple mathematical equation that can represent empirical IeV curves of individual solar cells, systems of solar cells and modules has been found. The basic model is determined by four parameters: the open circuit voltage, the short circuit current and two shape parameters. With the four parameters determined, the complete currentevoltage curve, the fill factor and the maximum power point are given by simple analytical functions. The model is valid both in the positive and the negative (dark condition) voltage range. Several simple examples demonstrate some of the potential of the model. Due to its mathematical simplicity, it is suggested that the model will be suitable for analytical modeling of complex systems.

• Nge, Chee Lim; Midtgård, Ole-Morten; Yordanov, Georgi Hristov; Norum, Lars Einar & Sætre, Tor Oskar (2010). A New maximum power point tracking approach for partial shading conditionsance, 25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion. WIP. ISSN 3-936338-26-4. s. 4475–4478.
• Nge, Chee Lim; Midtgård, Ole-Morten; Sætre, Tor Oskar & Norum, Lars Einar (2010). Energy management for Grid-Connected PV system with storage battery, 25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion. WIP. ISSN 3-936338-26-4. s. 4688–4691.
• Yordanov, Georgi Hristov; Midtgård, Ole-Morten; Sætre, Tor Oskar; Odden, Jan Ove; Buseth, Torfinn & Imenes, Anne Gerd [Vis alle 8 forfattere av denne artikkelen] (2010). Compensated SoG-Si from a Metallurgical Route: High Latitude Outdoor Performance, 25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion. WIP. ISSN 3-936338-26-4. s. 4289–4293. Vis sammendrag

  We compare the outdoor performance of two polycrystalline-Si PV modules of identical design, but with cells based on different types of solar-grade Silicon (SoG-Si). The cells of one of the modules are made of Si feedstock purified in the conventional chemical route, whereas the other module has cells based on solar Si produced from a pyrometallurgical route. Electrical and electronic parameters of the modules are extracted from measured current-voltage data and compared. The two modules perform similarly in the Nordic conditions at which they have been tested. Only minor differences are found between their electrical parameters. Analysis of the electronic parameters related to p-n junction quality reveals the general similarity of the two materials, but also indicate subtle differences.

• Sætre, Tor Oskar; Yordanov, Georgi Hristov; Midtgård, Ole-Morten & Odden, Jan Ove (2010). A THEORETICAL STUDY OF THE EFFECT OF DEGRADATION CAUSED BY DIFFUSION OVER A 30-YEAR LIFESPAN IN c-Si PV DEVICES. Conference record of the Photovoltaic Specialists Conference. ISSN 0160-8371. s. 1732–1736. Vis sammendrag

  An important issue for the crystalline Si wafer based PV industry is the performance of the cells over a life span of 25 to 30 years. The present paper discusses the main sources of degradation with focus on the diffusion of elements in a wafer over a 30- year period which may result in semiconductor device degradation. The possibility of carrying out accelerated tests at elevated temperatures as a method of testing individual cells is discussed with the aid of diffusion models.

• Dahl, Espen Hvidsten; Osinniy, v.; Larsen, Arne Nylandsted; Tronstad, Ragnar; Middleton, Peter Hugh & Sætre, Tor Oskar [Vis alle 7 forfattere av denne artikkelen] (2010). IRON IMPURITIES IN WAFERS BASED ON DIFFERENT So-G SILICON FEEDSTOCK. Conference record of the Photovoltaic Specialists Conference. ISSN 0160-8371. s. 1571–1575. Vis sammendrag

  Iron is the dominant impurity in multicrystalline solar grade silicon (SoG-Si) produced by the Elkem Solar metallurgical method, and can be found in concentrations as large as 1014 -1015 atoms cm-3. The aim of the present investigation has been to reveal the chemical nature of iron and iron precipitates in Elkem Solar Silicon® (ESS?). The experimental approach which is used to characterize iron and its precipitates is based on a combination of several experimental techniques, such as microwave photoconductivity decay, secondary ion mass spectrometry, x-ray fluorescence, and transmission electron microscopy, which produce mutually complementary information. Wafers from two different Elkem Solar multicrystalline p-type feedstock, Elkem 1(simplified Elkem Solar process) and Elkem 2 (early plant start-up test production) where examined and compared to a reference multicrystalline p-type silicon from an external source. The average minority carrier lifetime of Elkem 1, 2.1 ?s was significantly low compared to 28 ?s for both Elkem 2 and reference. Fe-B pair concentration was higher in Elkem 1, and there is also suggested that Fe-Al and Fe-O pair concentrations were higher in Elkem 1. F-Al-O concentrations in clusters are higher in low minority carrier lifetime areas compared to high lifetime areas. Cluster containing these elements seems to have strong recombination strength. The concentration of clusters is higher in low lifetime areas. Clusters located in high lifetime areas are on the other hand much larger suggesting that the total content of Fe, Al and O to a higher degree should be located in the clusters and less as interstitial iron and iron precipitates. These forms of impurities can together make a large contribution to minority carrier lifetime and partly explain the low lifetime found in Elkem 1 wafers.

• Yordanov, Georgi Hristov; Midtgård, Ole-Morten & Sætre, Tor Oskar (2010). Two Diode Model Revisited: Parameters Extraction from Semi-log Plots of I-V Data. Conference record of the Photovoltaic Specialists Conference. ISSN 0160-8371. s. 4156–4163. Vis sammendrag

  This paper presents an improved method to extract physically meaningful parameters from outdoor I-V data of polycrystalline-Si PV modules. The two-diode model of a PV cell is adapted for modules. A novel algorithm is devised to estimate the series resistance from I-V data sets. The ideality factor and the reverse saturation current of the diffusion diodes are then calculated from partially linear semi-logarithmic plots. The complexity and ambiguity typical for non-linear curve fitting are thus avoided. The method is applied to outdoor I-V curves from polycrystalline-Si modules, and preliminary results are presented. A new definition of the local ideality factor is introduced. It compensates for the series-resistance effect at higher voltages, such that a constant ideality factor is obtained for polycrystalline-Si modules in this range of voltages.

• Verma, Deepak; Dutta, V; Midtgård, Ole-Morten & Sætre, Tor Oskar (2010). TiO2 Nanoparticles Mixed P3HT Hybrid Absorbing Layer. Conference record of the Photovoltaic Specialists Conference. ISSN 0160-8371. s. 806–809. Vis sammendrag

  Hybrid absorber layers had been deposited using spin coating technique using surfactant free TiO2 nanoparticles dispersed in P3HT poly (3hexylthiophene). 1HNMR spectra have confirmed the chemical attachment between TiO2 nanoparticles and P3HT. Photoluminescence (PL) measurement confirms the PL quenching for the hybrid layer which is a measure of the degree of dispersion of nanoparticles in the P3HT matrix and also confirms that the required dissociation of excitons is taking place. Charge transfer is further confirmed with the help of cyclic voltammetry

• Midtgård, Ole-Morten; Sætre, Tor Oskar; Yordanov, Georgi; Imenes, Anne Gerd & Nge, Chee Lim (2010). A qualitative examination of performance and energy yield of photovoltaic modules in southern Norway. Renewable Energy. ISSN 0960-1481. 35(6), s. 1266–1274. doi: 10.1016/j.renene.2009.12.002. Vis sammendrag

  Three different, commercially available photovoltaic modules have been monitored outdoors in the town of Grimstad, Norway. The present paper describes the experimental setup that was implemented, in particular details of the low-cost electronic loads. Results compare measured performance with manufacturer's data, and temperature measurements enable a comparison with performance at standard test condition temperature. Overall, the monocrystalline module performed best both regarding maximum efficiency and overall energy production, whereas the module based on triple junction amorphous silicon technology had the worst performance considering these criteria. The gross numbers of energy yield corresponding to measurements over a whole year show that photovoltaic technology could become a viable alternative also in a Northern country like Norway.

• Grigoriev, Sergey A.; Millet, Pierre; Dzhus, K.A.; Middleton, Hugh; Sætre, Tor Oskar & Fateev, Vladimir (2010). Design and characterization of bi-functional electrocatalytic layers for application in PEM unitized regenerative fuel cells. International Journal of Hydrogen Energy. ISSN 0360-3199. 35(10), s. 5070–5076. doi: 10.1016/j.ijhydene.2009.08.081. Vis sammendrag

  Results concerning the development and characterization of bi-functional electrocatalytic layers for application in unitized regenerative fuel cells (URFCs) based on proton exchange membrane (PEM) technology are reported. Carbon-supported hydrophobic (10 wt.% of PTFE) Pt catalysts (40 wt.% of Pt), and Pt and Jr black powders of large specific areas have been synthesized. Their structure, morphology and electrochemical properties have been investigated using SEM, TEM, XRD analysis, and by measurements of polarization curves and cyclic voltammograms. Current-voltage curves have been recorded during water electrolysis and H-2/O-2 fuel cell experiments to evaluate their performances at the lab-scale (7 cm(2) active area). Results show that, among various Pt-Ir compositions, the best URFC current-voltage performances are obtained with anodic electrocatalytic structures made of two adjacent porous layers, a first one made of Jr (50 wt.%) in direct contact with the polymer membrane and a second one made of Pt (50 wt.%) coated over the first one. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

• Yordanov, Georgi Hristov; Midtgård, Ole-Morten & Sætre, Tor Oskar (2010). EXTRACTING PARAMETERS FROM SEMI-LOG PLOTS OF POLYCRYSTALLINE SILICON PV MODULES OUTDOOR I-V DATA: DOUBLE-EXPONENTIAL MODEL REVISITED. Conference record of the Photovoltaic Specialists Conference. ISSN 0160-8371.
• Yordanov, Georgi Hristov; Midtgård, Ole-Morten & Sætre, Tor Oskar (2010). Two-diode model revisited : parameters extraction form semi-log plots of I-V data, 25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion. WIP. ISSN 3-936338-26-4. s. 4156–4163.
• Yordanov, Georgi Hristov; Midtgård, Ole-Morten & Sætre, Tor Oskar (2010). Extracting parameters from semi-log plots of polycrystalline silicon PVmoduls outdoor I-V data : double-exponential model revisited. I IEEE, IEEE (Red.), 35th IEEE Photovoltaic Specialists Conference Honolulu, HI June 20-25, 2010. IEEE Press. ISSN 978-1-4244-5891-2. s. 002756–002761.
• Nge, Chee Lim; Midtgård, Ole-Morten & Sætre, Tor Oskar (2009). A Comparative Simulation Analysis of Maximum Power Point Tracking Approaches. I Andersen, Hadle Oftedal ; Ljung, Per Erik & Ståhl, Eva-Britta (Red.), Nordisk lyrikktrafikk. Modernisme i nordisk lyrikk 3. Helsinki University Press (HUP). ISSN 978-952-10-6003-8. s. 120–142. Vis sammendrag

  The occurrence of multiple local maxima due to partial shading conditions poses a serious challenge to MPPT techniques. This paper compares the popular real-time MPPT algorithm with the scanning approach using PSPICE simulation. The MPPT methods are compared at dynamic partial shading conditions. The compromises between real-time and scanning methods are investigated. It is shown that the scanning approach is able to search for global MPPs but incurs power loss during the scanning period. A new strategy that reduces the scanning period by skipping parts of the voltage range is presented in this paper.

• Nge, Chee Lim; Midtgård, Ole-Morten; Norum, Lars E. & Sætre, Tor Oskar (2009). Power Loss Analysis for Single Phase Grid-Connected PV Inverters, Proceedings of INTELEC 09-31st International Telecommunications Conference. IEEE conference proceedings. ISSN 9781424424900. Vis sammendrag

  This paper presents a method for power loss analysis applied on single-phase grid-connected PV inverter. The often neglected current ripple effects are included in power device switching and conduction losses. The relationships amongst component losses, output inductance, switching frequency and dc-link voltage are investigated. It is shown that current ripple effect is important to power loss analysis due to varying irradiation. The closed form solutions of component losses are proposed and verified with SPICE simulation results.

• Nge, Chee Lim; Yordanov, Georgi Hristov; Midtgård, Ole-Morten; Sætre, Tor Oskar & Norum, Lars Einar (2009). A Comparative Simulation Analysis of Maximum Power Point Tracking Approaches. I 2009, EUPVSEC (Red.), 24th European Photovoltaic Solar Energy Conference and Exhibition Proceedings. EUPVSEC. ISSN 3-936338-25-6.
• Nge, Chee Lim; Midtgård, Ole-Morten; Norum, Lars Einar & Sætre, Tor Oskar (2009). Power Loss Analysis for Single Phase Grid-Connected PV Inverters. I Hur, Jin (Red.), INTELEC 09-31st International Telecommunications Energy Conference. IEEE - INTELEC. ISSN 978-1-4244-2491-7.

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• Paudyal, Basant Raj; Imenes, Anne Gerd & Sætre, Tor Oskar (2018). Review of Guidelines for PV Systems Performance and Degradations Monitoring. Vis sammendrag

  The recent growth in the PV system deployment and the higher scale of their production make it necessary to pay more attention towards the performance of those systems. System monitoring will provide the status of the systems showing possible degradations and any impending system failures. It also helps with maintaining system quality and ensuring the optimal performance of the system for its lifetime. COST Action PEARL PV aims to formulate such monitoring guidelines for the PV systems applicable for all types of PV technologies, depending upon the end use and duration of the monitoring need. The objective of the present paper is to quantify and provide a review of the guidelines and standards for monitoring of PV systems performance and degradation in practice, and also some results of preliminary work done regarding important information needed to be included in the monitoring guideline.

• Shyikira, Antoine de Padoue; Skomedal, Gunstein; Middleton, Hugh P. & Sætre, Tor Oskar (2018). High Temperature Oxidation of Higher Manganese silicide and Alloys.
• Sætre, Tor Oskar (2017). A Simple Monte Carlo Model of a Hot Carrier Cell.
• Sætre, Tor Oskar (2016). Monte Carlo simuleringer av solceller.
• Berthod, Charly; Strandberg, Rune; Odden, Jan Ove & Sætre, Tor Oskar (2016). Reduced Temperature Sensitivity of Multicrystalline Silicon Solar Cells with Low Ingot Resistivity.
• Berthod, Charly; Strandberg, Rune; Odden, Jan Ove & Sætre, Tor Oskar (2015). Reduction of Temperature Coefficients in Multicrystalline Silicon Solar Cells after Light-Induced Degradation.
• Sætre, Tor Oskar (2015). Challenges with Balancing Excitations in Intermediate-Band Solar Cells.
• Sætre, Tor Oskar (2015). Effect of Quantum Efficiency on the Performance of Multijunction Tandem Cells.
• Yordanov, Georgi Hristov; Sætre, Tor Oskar & Midtgård, Ole-Morten (2015). Extreme overirradiance events in Norway: 1.6 suns measured close to 60°N. Solar Energy. ISSN 0038-092X. 115, s. 68–73. doi: 10.1016/j.solener.2015.02.020. Vis sammendrag

  We report the most extreme overirradiance event of 1.6 kW/m^2 measured so far in Grimstad, southern Norway (latitude 58°20’), at altitude of only about 60 m a.s.l. Images of the sky conditions taken with a wide-dynamic-range camera suggest that this is not the ultimate value for our location, but that extremes as high as 1.7 kW/m^2 may be possible. The phenomenon was caused by strong forward scattering of sunlight within 3° around the solar disk in thin, broken altocumulus clouds. The normalized spectrum of sunlight during such extreme events is very similar to the normalized clear-sky spectrum measured at Air Mass 1.4 and irradiance of 1.0 kW/m^2. We suggest that the values exceeding 1.8 kW/m^2 reported in the literature for a few equatorial regions do not represent the theoretical global maximum, and extremes of at least 2.0 kW/m^2 (two suns) may be possible at latitudes within ±30° around the Equator, even at sea level.

• Sætre, Tor Oskar (2014). Monte Carlo Generated Photon Spectra for Device Simulation.
• Tveit, Per & Sætre, Tor Oskar (2012). Interview: Per Tveit.
• Tayyib, Muhammad; Sætre, Tor Oskar; Midtgård, Ole-Morten & Odden, Jan Ove (2011). LIGHT AND HEAT INDUCED DEGRADATION STUDY OF ELKEM SOLAR SILICON SOLAR CELLS. I Ossenbrink, H.; Jäger-Waldau, A. & Helm, P. (Red.), 26th European Photovoltaic Solar Energy Conference, Proceedings of the International Conference held in Hamburg, Germany 5 - 9 September 2011. WIP. ISSN 3-936338-27-2. s. 1503 –1506. Vis sammendrag

  Multicrystalline solar cells of two different silicon production routes have been tested by light and heat induced degradation. Solar cells made of standard poly silicon cells have been experimentally compared to cells produced with the Elkem Solar Silicon (ESS) material. Initially, the two types of cells performed similarly, with efficiencies of about 16%. The experiments demonstrate a high potential of such methods for studying accelerated degradation phenomena. However, since the number of cells examined is limited, major conclusions cannot be drawn from the present results.

• Tayyib, Muhammad; Sætre, Tor Oskar; Midtgård, Ole-Morten & Odden, Jan Ove (2011). Analysis of Some Effects of Possible Device Degradation over a 30 Year Lifespan. I Ossenbrink, H.; Jäger-Waldau, A. & Helm, P. (Red.), 26th European Photovoltaic Solar Energy Conference, Proceedings of the International Conference held in Hamburg, Germany 5 - 9 September 2011. WIP. ISSN 3-936338-27-2. s. 1437–1441. Vis sammendrag

  An important issue for the crystalline Si wafer based PV industry is the performance of the cells over a life span of 25 to 30 years. The present paper discusses the main sources of degradation with focus on the diffusion of elements in a wafer over a 30-year period, which may result in semiconductor device degradation. Some experimental results of accelerated tests are presented. It has been shown that the variations of the performance of solar cells as manufactured vary considerably, and that a large statistical sample is necessary in order to obtain good conclusions from such experiments.

• Nge, Chee Lim; Midtgård, Ole-Morten; Sætre, Tor Oskar & Norum, Lars Einar (2010). Energy Management for Grid-Connected PV System With Storage Battery.
• Nge, Chee Lim; Midtgård, Ole-Morten; Yordanov, Georgi Hristov; Norum, Lars Einar & Sætre, Tor Oskar (2010). A New Maximum Power Point Tracking Approach for Partial Shading Conditions.
• Yordanov, Georgi Hristov; Midtgård, Ole-Morten & Sætre, Tor Oskar (2010). Extracting Parameters from Semi-Log Plots of Polycrystalline Silicon PV Moduls Outdoor I-V Data: Double-Exponential Model Revisited.
• Nge, Chee Lim; Yordanov, Georgi Hristov; Midtgård, Ole-Morten; Sætre, Tor Oskar & Norum, Lars Einar (2009). A Comparativ Simulation Analysis of Maximum Power Point Tracking Approaches.
• Grigoriev, Sergey; Fateev, Vladimir; Middleton, Peter Hugh; Sætre, Tor Oskar & Millet, Pierre (2008). A comparative evaluation of palladium and platinum nanoparticles as catalysts in proton exchange membrane electrochemical cells. ?. 1(4), s. 343–354. Vis sammendrag

  Abstract: The goal of the present study is the development and comparative characterisation of carbon-supported and nanostructured Pd- and Pt-based electrocatalysts for hydrogen oxidation in Proton Exchange Membrane (PEM) H2/O2(air) fuel cells and proton reduction in PEM water electrolysers. Catalysts have been synthesised in a solution using a combined impregnation/reduction polyol method. They have been characterised using X-ray Diffraction (XRD) analysis, Transmission Electron Microscopy (TEM), Thermogravimetric Analysis (TGA) and cyclic voltammetry. NanoPt, nanoPd and nanoPt-Pd catalysts deposited onto a carbon carrier have been used to prepare Membrane-Electrode Assemblies (MEAs) which, in turn, have been tested in PEM fuel cell and water electrolysis configuration. Using Pt0.5Pd0.5 (40 wt% on Vulcan XC-72) as a catalyst at the anodic side of a fuel cell, a typical cell voltage of 0.7 V was obtained at a current density of ca. 1.1 A cm¿2. Using Pd (40 wt% on Vulcan XC-72) as a catalyst at the cathodic side of an electrolysis cell, a typical voltage of 1.70 V was obtained at a current density of 1 A cm¿2. The electrochemical performances of the MEAs containing nanoPd-Vulcan were found similar to those obtained with nanoPt-Vulcan, either in fuel cell mode or electrolysis mode of operation. Palladium can, therefore, be used as an alternative catalyst for the hydrogen electrode in PEM electrochemical cells.

• Midtgård, Ole-Morten & Sætre, Tor Oskar (2008). A COMPARATIVE SIMULATION STUDY OF TWO-TERMINAL MULTIJUNCTION CELLS VERSUS CONNECTED INDIVIDUAL CELLS IN A SPECTRUM SPLITTING SCHEME. ?. s. 253–256. Vis sammendrag

  High efficiency PV devices are more complicated also from a system point of view than devices based on single band gap PN junctions. This makes modeling and simulation an important issue. The present paper presents two approaches; one is based on circuit models that are solved numerically whereas the other is analytical. Comparative simulations on hypothetical cells show that the maximum power of a composite mulitijunction device can never reach the sum of the power levels of the individual junctions at their optimum performance (spectrum splitting). The two modeling approaches complement each other, and may be used for analyzing larger systems.

• Grigoriev, Sergey; Ilyukhina, L.I.; Middleton, Hugh; Sætre, Tor Oskar; Chernyshova, O.V. & Fateev, Vladimir (2007). Comparative evaluation of palladium and platinum nanoparticles as catalysts in PEM electrochemical cells. Vis sammendrag

  The goal of the present study is development and characterization of nanostructured carbon-supported Pd-based electrocatalysts for hydrogen oxidation and proton reduction in proton exchange membrane (PEM) fuel cells and electrolysers. The catalysts were synthesized in a liquid phase using simultaneous sorption/reduction technique. For catalysts characterization cyclic voltammetry, SEM, TEM, XRD and TGA have been applied. Using the synthesized Pt, Pd and Pt-Pd catalyst, membrane-electrode assemblies (MEAs) for PEM fuel cell and electrolysers have been prepared and successfully tested. For instance, in a fuel cell with catalyst Pd40/Vulcan-XC72 on a hydrogen electrode at a voltage of 0,7 V, a current density of 0,7 A/cm2 was realized. The typical voltage of PEM electrolysis cell with this catalyst on the cathode was ca. 1,75 V at a current density of 1 A/cm2. In general, the electrochemical performances of the MEAs containing the Pd electrocatalysts on carbon carrier on hydrogen electrode were comparable to that of the MEAs including the Pt-based electrocatalysts

• Tayyib, Muhammad; Sætre, Tor Oskar & Midtgård, Ole-Morten (2015). Degradation and Performance Studies of Elkem Solar Grade Silicon in Comparison to the Reference Polysilicon. Universitetet i Agder. ISSN 1504-9272.

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