Application-Oriented Design and Field Trial of the Eneramic® Power Generator
In the above applications frequent start-stop cycles are required, thus the system and the stack are consistently being optimized regarding thermal and redox stability. The compact SOFC-battery hybrid system is powered by a planar SOFC stack. The current stack design consists of 40 cells with 90µm electrolyte stabilized cells of partly stabilized zirconia (3YSZ) simply sandwiched between Crofer® interconnects and printed layers of sealing glass. The design process for a reliable and cycleable stack involved the minimization of thermal mismatch within the stack assembly, a design of redox stable anodes as well as the optimization of the start-up procedure to reduce thermal stress. Different thermal heating rates up to 20 K/min have been imposed on the planar stack either in a furnace or an insulated hotbox environment. Today eneramic®stacks sustain more than 110 system cycles without cell fractures at a power degradation below 0.3% per cycle in lab tests. The results of thermo- and redox-cyclization of stacks and complete systems are emphasized and discussed in detail. Besides it was found by quality analysis of different commercial electrolytes that especially the quality of the 3YSZ material itself has a predominant effect on the robustness and cycleability in later operation. Current possibilities for quality tests were insufficient and expensive whereof a noncontact inspection process for planar ceramics is under development at IKTS’ material diagnostics branch. The measurement system is based on the optical coherence tomography (OCT). This quality inspection is capable to identify structural defects like fractures in ceramic electrolytes and reject them from MEA production at the earliest.
The prototypes have repeatedly shown a high degree of maturity in the laboratory scale. The long-term robustness of the insulated core module including SOFC stack and gas processing module (GPU) highlights the achieved power degradation of only 0.5% per 1,000 hrs. This ongoing propane fuelled test is currently operated for more than 14,000 hrs at full nominal power in a test bench. The ultra-compact gas processing module of the eneramic® system is built of brazed Crofer®sheet metal and ceramic components and combines CPOx-reformer, catalytic afterburner and cathode air preheater. Although operated at elevated temperatures up to 900°C in the burner the multilayer sheet metal assembly shows gas-tight behavior under aggressive redox atmosphere and no breakaway degradation.
To demonstrate the progressive technology level and to push commercialization a field trial phase has begun in 2014. For this purpose, a manual pilot scale production was established at IKTS. Currently the 3rd generation of eneramic®prototypes is tested under real-life applications in the field of cathode corrosion protection and mobile LED-boards for traffic road signs. In such long-run applications it was shown that the LPG-powered fuel cell system is superior to conventional battery-only powered solutions as is automatically charges the battery as long as fuel is available and thereby reduces the service costs. The results of these ongoing outdoor tests of several thousand hours are described.
The Fraunhofer patented eneramic® technology is developed with financial support by the Fraunhofer Future Foundation. A spin-off from IKTS in cooperation with industrial partners is in preparation to bring the technology into market.