@inproceedings{56174, author = {{Krauter, Stefan and Bendfeld, Jörg}}, booktitle = {{Proceedings of the 41st European Photovoltaic Solar Energy Conference}}, location = {{Wien}}, title = {{{PV Microinverters: Balcony Power Plants, Latest Efficiency Rankings, Yield Calculation for Overpowered Mini PV Systems}}}, year = {{2024}}, } @article{56929, abstract = {{The market for microinverters is growing, especially in Europe. Driven by rising electricity prices and an easing in legislation since 2024, the number of mini-photovoltaic energy systems (mini-PVs) being installed is increasing substantially. Indoor and outdoor studies of microinverters have been carried out at Paderborn University since 2014. In the indoor lab, conversion efficiencies as a function of load have been measured with high accuracy and ranked according to Euro and CEC weightings; the latest rankings from 2024 are included in this paper. In the outdoor lab, energy yields have been measured using identical and calibrated crystalline silicon PV modules; until 2020, measurements were carried out using 215 Wp modules. Because of increasing PV module power ratings, 360 Wp modules were used from 2020 until 2024. In 2024, the test modules were upgraded to 410 Wp modules, taking into account the increase from 600 W to 800 W of inverter power limits, which is suitable for simplified operation permission (“plug-in”) in many European countries within a homogenised legislation area for such mini-photovoltaic energy systems or “balcony power plants”. This legislation for simplified operation also covers overpowered mini-plants, although the maximum AC output remains limited to 800 W. Presently, yield assessments are being carried out in the outdoor lab, which will take at least a year to be valid and comparable. Kits consisting of PV modules, inverters, and mounting systems are also being evaluated. Yield rankings sometimes differ from efficiency rankings due to the use of different MPPT algorithms with different MPP approach speeds and accuracies. To accelerate yield assessment, we developed a novel, simple formula to determine energy yield for any module and inverter configuration, including overpowered systems. This is a linear approach, determined by just two coefficients, a and b, which are given for several inverters. To reduce costs, inverters will be integrated into the module frame or the module terminal box in the future.}}, author = {{Krauter, Stefan and Bendfeld, Jörg}}, issn = {{1996-1073}}, journal = {{Energies}}, number = {{22}}, publisher = {{MDPI AG}}, title = {{{Efficiency Ranking of Photovoltaic Microinverters and Energy Yield Estimations for Photovoltaic Balcony Power Plants}}}, doi = {{10.3390/en17225551}}, volume = {{17}}, year = {{2024}}, } @inproceedings{47119, author = {{Krauter, Stefan and Bendfeld, Jörg}}, booktitle = {{Proceedings of the 40th European Photovoltaik Solar Energy Conference and Exhibition}}, location = {{Lisbon, Portugal}}, title = {{{PV Microinverters: Latest Efficiency Rankings, Energy Yield Assessments, Firmware Issues}}}, year = {{2023}}, } @inproceedings{32334, abstract = {{The market for microinverters is growing, especially in Europe. Driven by the strongly rising prices for electricity, many small photovoltaic energy systems are being installed. Since monitoring for these plants is often quite costly, their yields are often not logged. Since 2014, microinverters have been studied at the University of Paderborn. The investigations are divided into indoor and outdoor tests. In the indoor area conversion efficiencies as a function of load have been measured with high accuracy and ranked according to Euro- and CEC weightings. In the outdoor laboratory, the behavior in the real world is tested. Energy yields have been measured outdoors via identical and calibrated crystalline silicon PV modules. Here, the investigations were carried out with modules of the power of 215 Wp until the year 2020. Because of the increasing module power nowadays, modules with an output of 360 Wp are now being used. To assess the influence of PV module size, two extremes have been investigated: A rather small module with 215 Wp - as it has been used 10 years ago, and a brand-new module (2021) offering 360 Wp. Both types of modules contain 60 solar cells in series connection. Appling the low-power modules, the challenge for the different micro-inverters has been during weak-light conditions, using the high-power modules, some inverters temporarily reach their power limits and yield is reduced. A method using a reference configuration of inverter & module and a linear equation resulting in the actual yield, any module & inverter configuration can be characterized by just the two coefficients.}}, author = {{Krauter, Stefan and Bendfeld, Jörg and Möller, Marius Claus}}, booktitle = {{Proceedings of the 49th IEEE Photovoltaic Specialists Conference}}, location = {{Philadelphia, PA, USA}}, title = {{{Microinverter testing update using high power modules: Efficiency, yield, and conformity to a new ”estimation formula” for variation of PV panel size}}}, year = {{2022}}, } @inproceedings{34155, author = {{Krauter, Stefan and Bendfeld, Jörg}}, booktitle = {{Proceedings of the 8th World Conference on Photovoltaik Energy Conversion}}, location = {{Milano / Italy}}, title = {{{Microinverter PV Systems: New Efficiency Rankings and Formula for Energy Yield Assessment for any PV Panel Size at different Microinverter types}}}, year = {{2022}}, } @inproceedings{24550, abstract = {{Efficiencies and energy yields of microinverters available on the market during 2014‒2021 have been measured, compared, and ranked. Conversion efficiencies as a function of load have been measured indoors with high accuracy and ranked according to Euro- and CEC weightings. Energy yields have been measured outdoors via identical and calibrated crystalline silicon PV modules of 215 Wp (until 2020) and 360 Wp (starting 2021). Inverters with two inputs have been fed by two of those modules. DC input, AC power output and energy yield of each microinverter have been recorded by individual calibrated electricity meters. CEC and EU efficiency rankings have been computed and compared. To assess the influence of PV module size, two extremes have been investigated: A rather small module with 215 Wp - as it has been used 10 years ago, and a brand-new module (2021) offering 360 Wp. Both types of modules contain 60 solar cells in series connection. Appling the low-power modules, the challenge for the different micro-inverters has been during weak-light conditions, using the high-power modules, some inverters temporarily reach their power limits and yield is reduced. A method using a reference configuration of inverter & module and a linear equation y = ax + b resulting in the actual yield, any module & inverter configuration can be characterized by just the coefficients a and b.}}, author = {{Krauter, Stefan and Bendfeld, Jörg}}, booktitle = {{Proceedings of the 38th European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC 2021)}}, isbn = {{3-936338-78-7}}, keywords = {{AC-modules, Microinverter, Power Conditioning, Efficiency, Yield, PV module size, saturation, performance}}, pages = {{659 -- 663}}, title = {{{Module-Inverters (Microinverters): Influence of Module Size on Conversion Efficiencies and Energy Yields}}}, doi = {{10.4229/EUPVSEC20212021-4CO.3.4}}, year = {{2021}}, } @inproceedings{18390, abstract = {{ Efficiencies and energy yields of microinverters available on the market during 2014‒2020 have been measured, compared, and ranked. Conversion efficiencies as a function of load have been measured indoors with high accuracy and ranked according to Euro- and CEC weightings. Energy yields have been measured outdoors via identical and calibrated crystalline silicon PV modules of 215 Wp each. Inverters with two inputs have been fed by two of those modules. DC input, AC power output and energy yield of each micro-inverter have been recorded by individual calibrated electricity meters. Apparently, some inverters have been optimized for high irradiance levels and ranked better at the CEC efficiency ranking, others performed very well also at low irradiance levels, thus ranking higher at in the EU efficiency ranking. Efficiency ranks are slightly deviating from rankings by energy yield measurements. At one inverter, a slow MPPT algorithm that barely could follow quickly changing irradiance levels is most probably responsible for this effect. Another inverter switched off for a while after operation at high power, another one failed permanently. Apparently, some inverters are been optimized to show excellent datasheet ratings for EU- or CEC- efficiency. On the other hand, two inverters (each featuring two inputs) did not show an outstanding performance at the EU- and CEC-ratings but achieved leading ranks for AC energy yields. For the customer, AC yield is a major performance indicator of a microinverter and should be included in the datasheet.}}, author = {{Krauter, Stefan and Bendfeld, Jörg}}, booktitle = {{Proceedings of the EUPVSEC 2020}}, isbn = {{ 3-936338-73-6}}, location = {{online}}, pages = {{935 -- 938}}, title = {{{Micro-Inverters: An Update of Comparison of Conversion Efficiencies and Energy Yields}}}, doi = {{10.4229/EUPVSEC20202020-4DO.7.2}}, year = {{2020}}, } @inproceedings{16857, author = {{Krauter, Stefan and Bendfeld, Jörg}}, booktitle = {{Tagungsband des 35. Symposiums für Photovoltaische Solarenergie, Kloster Banz, Bad Staffelstein (Deutschland)}}, location = {{Bad Staffelstein}}, title = {{{Einfluss der Betriebstemperatur auf den Wirkungsgrad von Modul-Wechselrichtern für PV-Netzeinspeisungen}}}, year = {{2020}}, } @inproceedings{18387, abstract = {{ During comparative measurements of different PV microinverters, two yield issues came up that could not be explored via conventional efficiency measurements, but do have a significant impact on electrical energy yield: First category of issues are either sluggish or nervously acting maximum–power–point–tracking devices, which lead to reduced energy yields. The other category of issues is thermal: As a first explanation for observed reduced energy yields, it has been assumed that the conversion efficiency degrades at higher operating temperatures. This matter has been investigated in this article: A change in conversion efficiency could not be observed for elevated operation temperatures up to 50°C, despite high-precision and repeated measurements. But it was found that some inverters temporarily interrupted (or entirely stopped) operation after long periods of running at high temperatures. Also, a reduction in potential maximum power output has been detected for those inverters. Summarizing: With a high degree of certainty it can be stated that those reported yield losses have been caused by the temporary shutdowns and power limitations of the inverters.}}, author = {{Krauter, Stefan and Bendfeld, Jörg}}, booktitle = {{Proceedings of the EU PVSEC 2020 }}, issn = {{3-936338-73-6}}, keywords = {{AC-modules, Microinverter, Power Conditioning, Thermal Performance, Ventilation, Stability, Efficiency, Yield}}, location = {{online}}, pages = {{1179 -- 1180}}, title = {{{Elevated Temperatures Affecting Efficiency, Overall Performance and Energy Yield of PV Microinverters}}}, doi = {{10.4229/EUPVSEC20202020-4AV.3.6}}, year = {{2020}}, } @inproceedings{16899, abstract = {{To compare efficiency and yield of many micro-inverters available on the world market in 2014-2020, an in- and outdoor test laboratory at the University of Paderborn has been set up. The inverters have been fed by identical and calibrated crystalline silicon PV modules of 215 Wp. To monitor accurately DC input, AC power output and energy yield, each of the micro-inverters has been equipped with a calibrated electricity meter. For micro-inverters requiring control units for grid-feeding that has been acquired also. The comparison covers efficiency-load characteristics as well as electrical energy yields. Purchase costs vary considerably between the models in comparison, sometimes inverter costs are higher than module costs, particularly if an additional grid-connection or interface device is needed for operation. The weighted conversion efficiency according to EU and CEC standards has been measured and calculated. While some inverters have been optimized for high irradiance levels, they ranked better at the CEC efficiency, others performed very well also for low irradiance levels, thus ranking higher at in the EU-efficiency tables. These results are deviating from the actual energy yield measurements, which show a slightly different ranking. At one inverter, an accurate, but very slow MPPT algorithm that barely could follow quickly changing irradiance levels could be the reason for this effect. Another inverter switched off after operation at high power output for a while. Apparently, some inverters are been optimized to show excellent EU and CEC efficiency ratings. Two of the inverters featuring two inputs did not show an exceptional performance at the EU- and CEC-ratings, but they achieved top ranks at the AC energy yield for the first years. For the customer, the AC yield is a major performance indicator of any microinverter and should be included in the datasheet.}}, author = {{Krauter, Stefan and Bendfeld, Jörg}}, booktitle = {{Proceedings of the 47th IEEE Photovoltaic Specialists Conference (PVSC 47) JUNE 15 - AUGUST 21, 2020 VIRTUAL MEETING}}, issn = {{ 0160-8371}}, keywords = {{yield, AC, micro-inverter, MPPT, CEC rating, EU efficiency, Photovoltaic, Solar}}, location = {{VIRTUAL MEETING}}, pages = {{1429--1432}}, publisher = {{IEEE}}, title = {{{Comparison of Microinverters: Update on Rankings of Conversion Efficiencies and Energy Yields}}}, doi = {{10.1109/PVSC45281.2020.9300953}}, year = {{2020}}, } @inbook{48501, abstract = {{Gathering knowledge not only of the current but also the upcoming wind speed is getting more and more important as the experience of operating and maintaining wind turbines is increasing. Not only with regards to operation and maintenance tasks such as gearbox and generator checks but moreover due to the fact that energy providers have to sell the right amount of their converted energy at the European energy markets, the knowledge of the wind and hence electrical power of the next day is of key importance. Selling more energy as has been offered is penalized as well as offering less energy as contractually promised. In addition to that the price per offered kWh decreases in case of a surplus of energy. Achieving a forecast there are various methods in computer science: fuzzy logic, linear prediction or neural networks. This paper presents current results of wind speed forecasts using recurrent neural networks (RNN) and the gradient descent method plus a backpropagation learning algorithm. Data used has been extracted from NASA's Modern Era-Retrospective analysis for Research and Applications (MERRA) which is calculated by a GEOS-5 Earth System Modeling and Data Assimilation system. The presented results show that wind speed data can be forecasted using historical data for training the RNN. Nevertheless, the current set up system lacks robustness and can be improved further with regards to accuracy.}}, author = {{Balluff, Stefan and Bendfeld, Jörg and Krauter, Stefan}}, booktitle = {{Deep Learning and Neural Networks}}, publisher = {{IGI Global}}, title = {{{Meteorological Data Forecast using RNN}}}, doi = {{10.4018/978-1-7998-0414-7.ch050}}, year = {{2019}}, } @inproceedings{6633, author = {{Bendfeld, Jörg and Balluff, Stefan and Wübbeke, Stefan and Krauter, Stefan}}, booktitle = {{Proceedings of the DEWEK 2017}}, location = {{Bremen}}, title = {{{Performance of MERRA2 Data Compared to Floating LiDAR}}}, year = {{2017}}, } @inproceedings{6634, author = {{Bendfeld, Jörg and Balluff, Stefan and Krüger, J. and Krauter, Stefan}}, booktitle = {{Proceedings of the DEWEK 2017}}, location = {{Bremen}}, title = {{{Short-term wind speed and power prediction for offshore wind farms using neural networks}}}, year = {{2017}}, } @inproceedings{6635, author = {{Bendfeld, Jörg and Krauter, Stefan}}, booktitle = {{Proceedings of the 33rd European Photovoltaic Solar Energy Conference, Amsterdam, (Niederlande), 25.-29. Sept. 2017, S. 1477–1481}}, location = {{Amsterdam}}, title = {{{Update on rankings of conversion efficiencies and energy yield of micro-inverters, including inverters for two PV modules}}}, year = {{2017}}, } @inproceedings{6636, author = {{Bendfeld, Jörg and Krauter, Stefan}}, booktitle = {{Proceedings of the 33rd European Photovoltaic Solar Energy Conference, Amsterdam, (Niederlande), 25.-29. Sept. 2017, S. 1836–1840}}, location = {{Amsterdam}}, title = {{{Long-term performance of PV micro-inverters}}}, year = {{2017}}, } @inproceedings{6641, author = {{Khatibi, Arash and Bendfeld, Jörg and Bermpohl, Wolfgang and Krauter, Stefan}}, booktitle = {{Proceedings of the 33rd European Photovoltaic Solar Energy Conference, Amsterdam, (Niederlande), 25.-29. Sept. 2017}}, location = {{Amsterdam}}, title = {{{Introduction of an Advanced Method for Testing of Battery Charge Controllers for Off-Grid PV Systems}}}, year = {{2017}}, } @inproceedings{6642, author = {{Khatibi, Arash and Bendfeld, Jörg and Bermpohl, Wolfgang and Krauter, Stefan}}, booktitle = {{Proceedings of the 33rd European Photovoltaic Solar Energy Conference, Amsterdam, (Niederlande), 25.-29. Sept. 2017}}, location = {{Amsterdam}}, title = {{{Testing and Analysis of Battery Charge Controllers for Off-Grid PV Systems}}}, year = {{2017}}, } @article{6482, author = {{Balluff, Stefan and Bendfeld, Jörg}}, issn = {{1848-9257}}, journal = {{Journal of Sustainable Development of Energy, Water and Environment Systems}}, number = {{4}}, pages = {{333--346}}, publisher = {{International Centre for Sustainable Development of Water}}, title = {{{Offshore Metocean Station for Energy Purposes}}}, doi = {{10.13044/j.sdewes.2016.04.0026}}, volume = {{4}}, year = {{2016}}, } @inproceedings{6646, author = {{Bendfeld, Jörg and Balluff, Stefan and Krauter, Stefan}}, booktitle = {{14. Symposium Energieinnovation 2016}}, location = {{Graz}}, title = {{{Einbindung von Offshore Windenergie durch innovative Prognosemodelle und Speichertechnologien}}}, year = {{2016}}, } @inproceedings{6647, author = {{Bendfeld, Jörg and Balluff, Stefan and Krauter, Stefan}}, booktitle = {{2015 International Conference on Renewable Energy Research and Applications (ICRERA)}}, isbn = {{9781479999828}}, location = {{Palermo, Italy}}, publisher = {{IEEE}}, title = {{{Green Energy from the Ocean An overview on costeffectiv and reliable measuring systems}}}, doi = {{10.1109/icrera.2015.7418439}}, year = {{2016}}, }