Periodic Reporting for period 3 - Giantleap (Giantleap Improves Automation of Non-polluting Transportation with Lifetime Extension of Automotive PEM fuel cells)
Reporting period: 2019-05-01 to 2019-10-31
While battery buses are being deployed in several cities across Europe, the cost of batteries and their limited range pose serious economical and technical limits.
Fuel-cell buses running on hydrogen have in fact been tested in Europe for more than a decade, and are able to store 10 to 20 times more energy in hydrogen tanks than in the same weight of batteries. However, fuel cells are still more expensive than batteries per installed kW, and the more complicated balance-of-plant system required in such buses (valves, compressors, humidifiers, etc.) has proven to be unreliable in previous demonstrations.
The Giantleap project improved availability and reliability of fuel-cell systems for buses by developing diagnostic and prognostic systems for automotive fuel cells and their ancillary components, integrating this knowledge in an advanced control system, and testing and evaluating the improvement in performance.
Since it is expected that the largest reduction in fuel-cell cost will occur in the car-sized segment, due to the larger size of the market compared to buses, Giantleap assumed that buses will use car-derived fuel cells, which are significantly cheaper but have a shorter life: therefore, it will be necessary to change fuel cells at least once during the life of the bus.
This is easily done if the fuel cell system is not integrated within the bus, but rather in its own range extender, which is mounted on the back of the bus. This approach fits well with a fleet of battery buses, which can be equipped with range extenders when required and thereby have their range increased. The ability to rapidly swap a malfunctioning fuel-cell system is another advantage, and the battery of the bus provides a redundant power source that can at least bring the bus back to the depot so a new range extender can be attached in case of malfunctions.
The Giantleap project built such a range extender and tested it on the road (operational environment, TRL7) and assessed its effect on the reliability of hydrogen-battery buses.
The higher reliability of the complete system, its flexibility and (as fuel cells become mass produced) its competitive price will allow the bus and coach sector to transition to zero-emission operation, improving air quality in our cities and reducing greenhouse gas emissions.
We developed a dynamic diagnostic method that exploits control theory's relay feedback to measure key parameters to estimate the state of health of a fuel cell without any additional expensive equipment, and tested on full-size stacks. We studied the previously observed phenomenon of rejuvenation, where some degradation can be recovered when shutting down the cell in a particular way; we have now a much better understanding of how this phenomenon behaves and under which conditions it occurs.
We developed model-based prognostic methods that allowed us to estimate with confidence the lifetime of fuel cell stacks, based on the method of Energetic Macroscopic Representation.
Fuel-cell stacks were produced in both laboratory scale and in full size; the overall system was first extensively tested first in a laboratory and then implemented in a trailer prototype.
We noticed that it was especially difficult to find data on balance-of-plant components of a fuel-cell system, such as compressors, humidifiers etc. At the same time these components are the most common cause of failures in FC systems, whereas fuel cells themselves are quite reliable. We decided therefore to generate this data ourselves, and make it available for the public; the experimental campaign was concluded and the data has been made openly available.
Through close cooperation among the industrial partners, the hydrogen range extender was designed and built, and was tested on the public roads in the area of Eindhoven.
The fuel-cell system proved itself to be very robust, and impressed Bosch' engineers: while they were used to construction of about 5 prototypes for ICE engines, under the assumption that 2 or 3 would crash under testing, both Giantleap test systems passed the testing phase unscathed, showing no significant consequences in case of some minor accidents (e.g. a malfunctioning cooling loop).
An analysis of data generated for long-term testing of air compressors showed that automotive-derived compressors often have a different behaviour when coupled with fuel cells: during transients, they often cross the surge line in the compressor diagram, causing accelerated wear. This explains the all-too-common phenomenon of failing compressors in FC systems, which has often given a bad reputation to fuel cells themselves for low reliability. Bosch found a solution by implementing a bypass valve, though the real solution would be compressors developed specifically for fuel cells.
Giantleap's results show that fuel cell technology has the potential to be not just as reliable, but in fact significantly more robust than internal combustion engines, assuming the system is done right. Giantleap produced many public reports, and more importantly public data, that will help researchers and industry to further develop more reliable FC systems in all domains, not just for buses.