Zero-emission buses are today very interesting for many municipalities and authorities in light of the increasing scepticism towards diesel's emissions of local pollution and greenhouse gases.
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.
