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PROSOFC Report Summary

Project ID: 325278
Funded under: FP7-JTI
Country: Austria

Periodic Report Summary 3 - PROSOFC (Production and Reliability Oriented SOFC Cell and Stack Design)

Project Context and Objectives:
On 1st of May 2013, the research project PROSOFC started under the coordination of AVL List GmbH (Austria). It is the goal of PROSOFC to significantly improve the stack robustness and cost with the focus on production and operation. The first period was based on the TOFC stack design. Due to the termination of Topsoe’s SOFC activities by the end of August 2014, SOLIDpower took over the role of the industrial stack supplier to continue the project by keeping the main targets.
PROSOFC directly contributes to the objectives of Call SP1-JTI-FCH.2012.3.2 “Improved cell and stack design and manufacturability for application specific requirements”.
* Improved electrical efficiency over the state of the art
* Better robustness, including longer lifetime
o Operation in simulated real-life environment > 4,000 hours
o Demonstration of the potential to achieve longer run times required to meet market entry requirements
* Considerable cost reductions consistent with market acceptance requirements for industrial or residential or other relevant applications
* Improved manufacturing methods in terms of yield and cost, reducing stack scrap rate to 10% by 2014 and the objective to reduce it to less than 5% by 2017
* Higher power density
In particular the PROSOFC project aims at improving the robustness, manufacturability, efficiency and cost of SOLIDpowers state-of-the-art SOFC stacks so as to reach market entry requirements. The key issues are the mechanical robustness of solid oxide fuel cells (SOFCs), and the delicate interplay between cell properties, stack design, and operating conditions of the SOFC stack.
The novelty of the project lies in combining state of the art methodologies for cost-optimal reliability-based design (COPRD) with actual production optimization. To achieve the COPRD beyond state of the art multi-physical modeling concepts must be developed and validated for significantly improved understanding of the production and operation of SOFC stacks. The model should allow a probabilistic approach to consider statistical variations in production, material and operating parameters for the optimization phase. The key to this understanding are validating experiments and models on multiple levels of the SOFC system and introduction of extensive test programs specified by the COPRD methodology.
The robustness of the new stack design will be tested in 4000h stack tests under conditions close to reality. Therefore, an accelerated test program will be developed which specifically covers the stresses coming from the operation of a stationary system (heat-up, cool-down, hot-standby, load changes, etc.).

* Probabilistic based methodology available to the SOFC technology as such
* Demonstration of improved reliability
* Demonstration of minimized cost

Project Results:
Achievements to date
* The material parameters and basic knowledge about material behaviour at elevated temperatures has been passed on to WP4.
* The amount of results regarding material characterisation is beyond expectations, both in terms of new findings and characterisations of SOFC stack materials at relevant conditions.
* The results from the segmented single cell test equipment for the close to reality tests as already successfully completed and reported in time within the 2nd reporting period were transferred to the full-scale stack CFD simulation at AVL. In particular calibration parameters for electrochemical and catalytic reactions could be implemented in the full-scale model.
* The most relevant failure models could be identified mutually in the consortium. Most failure models are developed and a stack test program was established accordingly.
* Various validation cases where optiSlang was coupled with design tools such as AVL FIRE, Fluent, gProms, matlab/Simulink were established and demonstrated the usability of this software for design optimization tasks in the SOFC industry
* Based on this outcome, the heart of the PROSOFC methodology developed in WP4 has been completed on schedule. The tasks of WP4 area very complex and are subject to the risk of unforeseen difficulties in numerical modelling. In fact, in particular the multi-physics simulation model turned out to need more time and resources than expected. However, the consortium succeeded in
(i) establishing a new and precise simulation model using meta-modelling techniques,
(ii) identifying important/unimportant variables in the simulation model based on stochastic sensitivity analysis,
(iii) setting up a complete framework for the COPRD process including statistical uncertainties of material and operational parameters.

Achievements of the whole project
Remarkable achievements were achieved in terms of efficiency, cost, gas leakage and thermal cycling. The power density meets market requirements and the scrap rate was established at a low level. The demonstration of a lifetime >20.000 h was seen to be tough, since new stack designs required shorter iteration loops which did not allow a longer lifetime demonstration. The detailed achievements are discussed in the course of the 3 midterm reports and the respective deliverable reports. To sum up it can be said that the PROSOFC project was successfully finished and has achieved the targets set in the beginning of the project.

Potential Impact:
Improved understanding of stack robustness by holistic description of failure causing root. The project demonstrated a methodology for a probabilistic based design optimization for a complex system where the final robustness of the stack design depends on manufacturing, material, conditioning, and operating parameters. This requires a systematic identification, development and simplification of physical models describing those complex dependencies for the ultimate optimization task. For example, the temperature distribution inside the stack, the stack efficiency, and its losses respectively are influenced by the area specific resistance (ASR) of the cell. As a result, the temperature distribution generates temperature gradients along the cell which generate thermomechanical stresses and thus may cause damage by cell cracking or cell delamination. The ASR on the other hand among others is depending on the porosity of the anode substrate which is consequently determined by certain production parameters and the properties of the used materials. Therefore, establishing a model describing the stack robustness (stresses) as a function of all influencing parameters (production, material, geometry, etc.) will become very complex.

Disseminate awareness for holistic stack optimization and provision of powerful methodology for the SOFC community: Most likely such an optimization task will require the collaboration of various partners to combine material characterization, production, simulation and testing. In this context, the project showed the required setup of the development team for such a task. PROSOFC certainly supports to explain and to illustrate the development roadmap for future optimization tasks. To support the development, the main methodology has been published at the ECS SOFC XV conference in order to present it to the whole SOFC community.

Identification of development potential to apply methodology for future SOFC stack design: PROSOFC combined partners enabling the demonstration of a promising approach to develop such models for stack robustness optimization. The results, however, revealed the advantages of this methodology as well as the need for further development. The project has also shown where the current limitations of this holistic approach are. The main challenge is to reduce the complexity of such models to keep the simulation time in a reasonable time frame while maintaining the required accuracy to describe the behavior for the optimization task. Since processing time of the complex simulations is still the main obstacle for a comprehensive model it became obvious that the models need to be simplified for example by homogenization. Especially, in the SOFC research community the results of this project will provide a further basis for a target oriented modeling approach.

Reduction of development cost and time to market: The consortium is convinced that systematic and automated design optimization will become more and more important in the SOFC industry once commercialization increases. The historically grown stack designs available in the SOFC industry supported by specific and isolated simulations but partly also developed by trial and error will not be commercially competitive in terms of development cost and time to market. Minor changes in stack design (e.g. geometry of manifolds, used materials, etc.) already bear a significant risk to the stack manufacturer and are connected to a number of quality assurance tests. Major changes (e.g. doubling size of cell area) will certainly require several hardware generations before the design meets the quality requirements. For such big development steps, a methodology as developed in PROSOFC will significantly reduce the hardware input and shorten development time. Furthermore, the quality of the stack design will improve as more and more dependencies can be detected and made visible beforehand which may have stayed undiscovered so far. The correct analysis of data from actual production and operation will be even more valuable since important influencing parameters can be distinguished from unimportant ones.

Apply methodology beyond stack design: The methodology is certainly not restricted to stack design only. AVL for example will further investigate the implementation of the methodology for other parts of the SOFC system development. Eventually, this approach can be used for component and system design as well as for control algorithm calibration.

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