Fraunhofer-Allianz Energie c/o Fraunhofer-Institut für Solare Energiesysteme ISE

Heidenhofstr. 2, 79110 Freiburg

Hall map

Energy Storage Europe 2018 hall map (Hall 8b): stand B39

Fairground map

Energy Storage Europe 2018 fairground map: Hall 8b


Simone Ringelstein

Geschäftsführung | Fraunhofer-Allianz Energie

c/o Fraunhofer-Institut für Solare Energiesysteme ISE Heidenhofstr. 2
79110 Freiburg

+49 761 4588-5077

+49 761 4588-9077


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  • 11  Research and Education, Trade Publishers, Associations/Organisations
  • 11.01  Research Institutes and Projects

Our products

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.

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Product category: 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.

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Product category: Research Institutes and Projects

APV-RESOLA – Agrophotovoltaic - A Contribution to Resource-Efficient Land Use

The costs of ground-mounted PV systems continue to fall. Experts forecast that in about five to eight years, such PV installations will become cost-effective even without the financial support of the Renewable Energy Act (EEG). Decreasing costs spurn on new types of business models for land use and as a result new challenges arise. Increased competition for land use, for example, can cause the rental price for land to rise. The innovation group APV-RESOLA is therefore developing and investigating a new type of PV system that ensures the coexistence of agriculture use and electricity production on the same piece of land.

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About us

Company details

The Fraunhofer Energy Alliance offers research and development
services in the fields of renewable energy, storage technologies,
energy efficiency, digitization and analysis of the energy system as
well as components and concepts for plants, buildings and districts.
Besides small and medium-sized enterprises, industrial companies, political organizations and institutions also get solutions from one source. With more than 2,000 employees it is one of the largest energy research groups in Europe.

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