Spectral network based on component cells under the SOPHIA European project

In the frame of the European project SOPHIA, a spectral network based on component (also called isotypes) cells has been created. Among the members of this project, several spectral sensors based on component cells and collimating tubes, so-called spectroheliometers, were installed in the last years, allowing the collection of minute-resolution spectral data useful for CPV systems characterization across Europe. The use of spectroheliometers has been proved useful to establish the necessary spectral conditions to perform power rating of CPV modules and systems. If enough data in a given period of time is collected, ideally a year, it is possible to characterize spectrally the place where measurements are taken, in the same way that hours of annual irradiation can be estimated using a pyrheliometer

NGCPV: a new generation of concentrator photovoltaic cells, modules and systems

Starting on June 2011, NGCPV is the first project funded jointly between the European Commission (EC) and the New Energy and Industrial Technology Development Organization (NEDO) of Japan to research on new generation concentration photovoltaics (CPV). The Project, through a collaborative research between seven European and nine Japanese leading research centers in the field of CPV, aims at lowering the cost of the CPVproduced photovoltaic kWh down to 5 ?cents. The main objective of the project is to improve the present concentrator cell, module and system efficiency, as well as developing advanced characterization tools for CPV components and systems. As particular targets, the project aims at achieving a cell efficiency of at least 45% and a CPV module with an efficiency greater than 35%. This paper describes the R&D activities that are being carried out within the NGCPV project and summarizes some of the most relevant results that have already been attained, for instance: the manufacturing of a 44.4% world record efficiency triple junction solar cell (by Sharp Corp.) and the installation of a 50 kWp experimental CPV plant in Spain, which will be used to obtain accurate forecasts of the energy produced at system level

The e-learning platform of the FP7-SOPHIA Project: obtanied results and perspective for its future exploitation

FP7-SOPHIA, the European PV Research Infrastructure project coordinated by CEA-INES ended on 31st of January 2015. The project focused on strengthening and optimising the research capabilities of outstanding European Research Infrastructures by pulling together numerous scientists and researchers of more than 48 relevant Research Infrastructures to share a common vision and to conduct efficient and coordinated research work in the field of PV technologies. SOPHi@Webinar is the internal e-learning platform that has organized a set of online courses/seminaries/guest lectures in parallel to more conventional training initiatives held physically. It has also been opened to non-SOPHIA members

Analysis of the performance of multi-junction solar cells under realistic operating conditions

With this work important contributions on the area of the characterization and calibration of multi-junction solar cells under standard testing conditions and under concentration, as well as for a better understanding and for the modeling of concentrator systems, were made.In the frame of this work a flash based measurement set-up was built up. In this way, the calibration opportunities of the calibration laboratory at Fraunhofer ISE could be extended, by developing a routine for the reduction of measurement uncertainty for the calibration of multi-junction solar cells under concentration. The ISE CalLab is thus, besides NREL in the USA, the only institution being able to perform calibrated measurements of multi-junction cells under concentration. However, a prerequisite for the calibration under concentration is the calibration at standard testing conditions and the verification of the cell s linearity, for which a method based on the spectral response measurement, was proposed. With the help of this method, effects, indicting a non-linearity, could firstly be observed, however not finally be explained. In this context the work performed here corresponds to pioneer work and further works have to concentrate on this topic. Concerning the calibration under concentration, the effect of the use of a poorly matched spectrum, was quantified. The effect of reduction in fill factor under concentration with excess current of the top cell could be reproduced. For the first time in this work a possible explanation for this effect could be given, basing on a carrier transfer from the top to the middle subcell by radiative recombination.Another main topic of the work is the temperature dependence of the IV parameters of III-V solar cells. Starting from a theoretical consideration and based on the up to now most detailed measurement campaign worldwide, a set of temperature coefficients was generated, which is essential for the modeling of concentrator systems. The unexpected effect of a decrease in EQE of the top cell with increasing temperature could be explained by the increasing absorption in the window layer. All in all a contribution towards a better understanding of the temperature dependence of III-V solar cells could be made. Especially the data sets of the temperature coefficients of dual- and triple-junction solar cells under concentration are unique up to now.Besides the indoor calibration of concentrator solar cells also outdoor measurements of concentrator modules were one focus of this work. Thereto a set-up for the continuous measurement of concentrator modules has been designed. As a start, the irradiation resource for concentrator modules has been discussed in detail. It turned out, that only for very sunny locations a concentrator module will have a higher irradiation resource available in comparison to a fixed mounted flat plate module. Nevertheless, analysis of long term measurement data showed, that even for Freiburg (which is not a preferable location for concentrator PV) a FLATCON module of the first generation delivers a yearly sum of energy, which is comparable to standard flat plate modules. For sunny locations and application of FLATCON modules with higher efficiency that are available now, this ratio will be shifted in favor of the concentrator modules.Starting from the analysis of the measurements of a FLATCON module on one certain day, the difficulty of the dependence of the module parameters on the incident spectrum was illustrated - a simple correlation of module performance with meteorological data is not possible. With the aid of measured direct sun spectra it could be shown that if such spectral data is available, a correlation of the module s short circuit current with the solar spectrum can be established. Topic of future works will be amongst other things the definition of a simple measurement method in order to assess the parameter "spectrum".Finally a method has been presented, with which the heating of the solar cells in a concentrator module can be determined, based on indoor measurements of the solar cells. It could be shown that although only passive cooling is used, the temperature of the solar cells does not necessarily have to be drastically above the temperature of flat plate modules. Using the data on temperature dependence of multi-junction cells, it could be shown, that the temperature related losses in a FLATCON module is smaller by a factor of two compared to standard flat plate modules

Component cell-based restriction of spectral conditions and the impact on CPV module power rating

One approach to consider the prevailing spectral conditions when performing CPV module power ratings according to the standard IEC 62670‐3 is based on spectral matching ratios (SMRs) determined by the means of component cell sensors. In this work, an uncertainty analysis of the SMR approach is performed based on a dataset of spectral irradiances created with SMARTS2. Using these illumination spectra, the respective efficiencies of multijunction solar cells with different cell architectures are calculated. These efficiencies were used to analyze the influence of different component cell sensors and SMR filtering methods. The 3 main findings of this work are as follows. First, component cells based on the lattice‐matched triple‐junction (LM3J) cell are suitable for restricting spectral conditions and are qualified for the standardized power rating of CPV modules—even if the CPV module is using multijunction cells other than LM3J. Second, a filtering of all 3 SMRs with ±3.0% of unity results in the worst case scenario in an underestimation of −1.7% and overestimation of +2.4% compared to AM1.5d efficiency. Third, there is no benefit in matching the component cells to the module cell in respect to the measurement uncertainty

Pushing Energy Yield with Concentrating Photovoltaics

A 4J CPV module achieving 41.4 % efficiency at CSTC is presented in this paper. The high efficiency is enabled through the combination of high quality achromatic full-glass lenses with high efficiency 4J solar cells. This module has been built to demonstrate the potential of CPV module technology when improving the efficiency of the optical elements as well as the solar cell performance by integrating more junctions. The characteristics of the full-glass lens module are compared to a conventional Fresnel lens module. High efficiency is one of the keys to increase the energy yield of CPV power plants and to make the technology more competitive. Another aspect is the use of diffuse, scattered and albedo light resources which is typically not converted in high-concentration PV modules. Hybrid CPV modules combine high concentration PV with a flat-plate technology like silicon to push the energy yield even further. In this work, we present latest developments of our EyeCon hybrid module technology at Fraunhofer ISE and demonstrate the potential of a bifacial submodule (136 cm2) consisting of one silicon solar cell on which six concentrator cells are mounted. The technology has significant potential to extend the application area where CPV technology can compete with conventional flat plate PV

Analysis of the output of two isotype cell sets compared to a precision spectroradiometer

Spectrally resolved measurements of the solar irradiation are needed to assess the outdoor performance of concentrator photovoltaic (CPV) technologies that employ GaAs based multi-junction cells. One coarse technique for obtaining such data – without the need to operate a full spectroradiometer system – is to measure the current output of different junctions of multi-junction cells. Specially prepared component or ‘isotype’ cells having the same optical characteristic as the whole multi-junction device but with the electrical characteristics of one single sub-cell are commonly used for this purpose. Although this provides a convenient way to measure the solar spectrum appropriate for CPV technologies that use such cells, the present literature lacks detailed comparisons of these sensors against high quality spectroradiometer systems[1]. In this work we evaluate two different sets of isotype sensors and compare with data from an OL750 spectroradiometer.JRC.F.7-Renewables and Energy Efficienc

Worldwide Energy Harvesting Potential of Hybrid CPV/PV Technology

Hybridization of multi-junction concentrator photovoltaics with single-junction flat plate solar cells (CPV/PV) can deliver the highest power output per module area of any PV technology. Conversion efficiencies up to 34.2% have been published under the AM1.5g spectrum at standard test conditions for the EyeCon module which combines Fresnel lenses and III-V four-junction solar cells with bifacial c-Si. We investigate here its energy yield and compare it to conventional CPV as well as flat plate PV. The advantage of the hybrid CPV/PV module is that it converts direct sunlight with the most advanced multi-junction cell technology, while accessing diffuse, lens-scattered and back side irradiance with a Si cell that also serves as the heat distributor for the concentrator cells. This article quantifies that hybrid bifacial CPV/PV modules are expected to generate a 25 - 35% higher energy yield with respect to their closest competitor in regions with a diffuse irradiance fraction around 50%. Additionally, the relative cost of electricity generated by hybrid CPV/PV technology was calculated worldwide under certain economic assumptions. Therefore, this article gives clear guidance towards establishing competitive business cases for the technology

BOL and EOL Characterization of Azur 3G Lilt Solar Cells for ESA Juice Mission

In the present paper, we describe the results of electrical characterization of AZUR SPACE triple-junction solar cells at a sun light intensity of 3.7% AM0 and temperatures down to −150°C. At these conditions, which are relevant for the anticipated ESA JUICE mission, the cell efficiency reaches 33.5 % at BOL. Special attention has been paid to the establishing of an in-situ characterization procedure for defining EOL cell characteristics after electron and proton irradiation at low temperature low intensity condition. It was shown that solar cells irradiated at low temperature exhibit a strong recovery effect within short time after stopping the irradiation whereas the absolute value of the recovery depends on the irradiation fluence and particle type. Further on, it was demonstrated that the degradation of the maximum power, Pmp, is much stronger than the degradation of Isc and Voc values. Experimentally defined remaining factors for electron and proton irradiation and the quantification of the observed recovery effects allow a realistic prediction of the solar cell performance at JUICE mission conditions and are essential for the planned solar cell qualification activities