Product category: Research Institutes and Projects
1 MWh Redox Flow Grid-Connected Storage
To develop a scalable electricity storage unit with an electric power of 100 kWel and a capacity of 1 MWhel, we are working on the stack and system development and the management of redox flow batteries at Fraunhofer ISE. By applying simulation-supported analysis and design of redox flow batteries, we identify optimisation potential at the cell and stack level and use this to further develop the design. Within the “1 MWh Redox-Flow Netzspeicher” project on grid-connected storage, we have developed an optimised cell stack with a power of 5 kWel for use in mini-grid systems or gridconnected storage systems. Cycling efficiency values of above 80% have been achieved at the stack level. Current research is concentrating on further increasing the power and energy density and reducing the production costs of a 5kWel cell stack.
Fundamental questions for optimisation are answered at the cell level by multiphysical modelling. In this way, we gain deeper understanding of the relevant processes and loss mechanisms. Specific measurements in situ of single cells and ex situ measurements of the electrode, membrane and electrolyte enable the charging and discharging processes to be characterized and the identification of material parameters as an essential data base for modelling and simulation. A fully automated test stand with detailed test log procedures was developed for experimental work on single cells. It is available for comprehensive materials characterization.
This year, the development and test operation of a 5 kWel cell stack was successfully completed. This power class is very suitable for investigating and optimising system-relevant process parameters. Based on the experience gained during this developmental work, we are optimising the stack design further and pursuing alternative cell concepts to increase the power density and reduce the production costs.
Based on the promising results of the development work at the materials, stack and system levels, a grid-connected, redox flow battery system with a power of 5kWel and a capacity of 20 kWh was constructed and taken into operation. Operating data from a field test are currently being recorded and analysed.
Product category: Testing, Research Institutes and Projects
20plµs - Modeling of Aluminum Alloying Processes for Silicon Solar Cells
The silicon solar cells currently dominating the PV market feature a metal contact made of alloyed aluminum on the backside. To further reduce the recombination losses of such backside contacts and thus to increase the cell efficiency, a better understanding of the formation and effect of these contact structures is important. The model for description of the Al alloying process developed at Fraunhofer ISE now allows the prediction of the electric quality of such contacts taking into account different influencing factors during their production. When transferring the model into the cell production, the process parameters then can be respectively adjusted for Al alloys to achieve best-possible contact formation.
In the current silicon solar cell production, the backside metal contact is produced by default using screen-printing of an aluminum-containing paste. Here, the aluminum is alloyed into the silicon surface in a short high-temperature firing step, and the contact is formed. A several microns deep Al-doped p+ region is generated in the silicon crystal, which is referred to as Al back surface field (BSF, Fig. 1). In the case of Al-BSF solar cells, such contacts are full-area. In the case of PERC (Passivated Emitter and Rear Cell) solar cells, they are local (dot/line-shaped). The alloying process model that was developed at Fraunhofer ISE is based on the binary Al-Si phase diagram and describes the mechanisms during aluminum alloying in silicon quantitatively. The composition of the Al-Si melt that is formed on the surface of the Si wafer during alloying, as well as Si recrystallization on this Si surface are modeled. Different influencing factors, such as the temperature during contact formation, the amount of paste applied, and additional doping substances such as boron in the paste are considered. Using the model, the doping profiles of the Al-B-doped p+ regions can be precisely calculated (Fig. 2). The structural setup and the electric quality of these contacts can be predicted. With that, a basis for the detailed optimization of Al alloyed contacts has been established that can contribute significantly to further performance increases of Al-BSF and PERC solar cells, which currently dominate the market worldwide.
Fraunhofer ISE has been developing thermochemical processes for over 15 years. We continually strive to make these processes increasingly more efficient, while reducing the carbon dioxide and exhaust gas emissions at the same time. With our innovative solutions in process technology, we help to bring on the success of the energy transformation.
Our work centers around investigations on heterogeneous catalytic material transformations in the liquid and the gaseous phase. We synthesize and characterize catalysts and, among other things, can rapidly and precisely analyze their performance at our mini-plant according to our clients wishes. We both design and operate test stands, if need be automated, in order to analyze the solid, liquid and gaseous products using state-of-the-art analytics. In order to optimize the thermochemical processes, we use the following simulation programs: CHEMCAD® for process simulations, Matlab/Simulink ® for dynamic simulations, etc., Ansys® for CFD simulations and Umberto® for life cycle assessments (LCA) and life cycle costs (LCC).
We hold patented technologies, developed in-house, for residue-free vaporization of liquid fuels and pyrolysis of many different energy carriers, biomass conversion and sustainable synthesis of fuels and chemicals from carbon dioxide and hydrogen (Power-to-Liquid). We would be glad to offer you more details about these processes upon request.
With a staff of 1150, the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, Germany is the largest solar energy research institute in Europe. Fraunhofer ISE is committed to promoting sustainable, economic, safe and socially just energy supply systems based on renewable energies. Its research provides the technological foundations for supplying energy efficiently and on an environmentally sound basis in industrialized, threshold and developing countries throughout the world. Focusing on energy efficiency, energy conversion, energy distribution and energy storage, the Institute develops materials, components, systems and processes in five business areas and offers accredited testing facilities and other expert lab services to clients. The Institute is a member of the Fraunhofer-Gesellschaft, Europes largest application-oriented research organization.