Standardisation of fuel-cell (FC) systems is the key to kickstart their deployment in the heavy-duty (HD) sector.

FC applications have been deployed for almost every HD vehicle available, from buses to trucks, from ships to aircraft. However, these projects, including commercial deployments such as Alstom’s iLint train, rely on original equipment manufacturers (OEMs) and FC system manufacturers to engineer the complete vehicle from the ground up. The vehicle chassis and the FC system must therefore be engineered around each other, by two cooperating teams that can be located on different continents, and the resulting work is hardly reusable in the next project, much less on a competitor’s chassis.

The consequence of this situation is that HD FC vehicles have long development times, difficulties achieving economies of scale, and do not benefit from competition as FC suppliers and OEMs are bound to each other, increasing their costs and slowing their adoption. Standardisation of HD FC systems can go a long way to boost their viability in the market. In particular, it can:

• Pool all HD OEMs in a single large market for HD FCs;
• Reach MW scale with modular units, covering even more OEM sectors;
• Enable fair competition between FC suppliers, removing vendor lock-in;
• Reduce development and innovation costs for OEMs, lowering the entry threshold;
• Improve the supply chain with fewer FC models, giving higher reliability;
• Enable automation of mass production;
• Reduce total cost of ownership, which is far more important for commercial HD users than for consumers of luxury cars (e.g. Tesla).

The StasHH project is funded by the European Commission with the task to establish standards for size and interfaces (physical and digital) of HD FCs. According to StasHH’ definition, a fuel-cell module (FCM) contains the FC stack, air compressors, humidifiers and other balance-of-plant (BoP) units, but not hydrogen storage, filters and radiators; DC/DC converters can be optionally included in the FCM.

The physical size of the StasHH standard is dictated chiefly by the available dimensions in a European truck, which was identified as one of the most challenging environments to install an FCM due to the tight spaces induced by EU regulations. A European truck can install a FCM either in the diesel tank areas on either side, between the front and hind wheels, or in the engine bay. We found that a maximum height of 680 mm and a maximum width of 700 mm would be almost universally supported for the diesel tank area, with length strongly depending on the specific vehicle. Engine bay measures vary among manufacturers, but a box with measures 700 mm×1360 mm×1020 mm is acceptable to most.

StasHH defines three basic form factors with different length [1], but same width and height; assuming a unit length of 340 mm, the StasHH standard form factors are 1 in height, (slightly more than) 2 in width, and either 3, 4 or 5 in length for respectively types A, B and C.

Form factors are not tied to a specific range in power capability, as long as it is above 30 kW;  tolerances are +0/−100 mm. Optionally, units can be oriented on the side, but it is not required that units shall function in more than one nominal orientation.

Form factors can be combined by stacking multiple units: AA is for example two A volumes on top of each other, and BBB is three B volumes. Currently, industry feedback within the StasHH consortium seems to favour A and B form factors, with composites AA, BB and BBB also being popular.

StasHH’ standard defines some general areas where the physical interfaces can be located [2], but does not define in detail the position of each connector, its exact size or its shape, which are left to the manufacturers to decide; this because moving a hose by a moderate length or employing an adapter are not considered major hurdles in manufacturing, in the way modifying a chassis to make space for an FCM would be. A requirement is however that main hydraulic and pneumatic connection shall not interfere in vertical and horizontal direction, to facilitate deployment of manifolds when installing multiple FCMs.

The digital interface enables control of the FCM operation, e.g. state changes and setpoints, as well as diagnostic and fault messages and sensor information. It is preferable to build upon existing standards to the largest extent possible. Due to its prevalence in the automotive sector and present usage by several FCM suppliers, CAN bus is chosen as the low-layer protocol; the more recent CAN-FD is supported as an option. While other technologies such as FlexRay may be relevant for the automotive industry, Ethernet is the most useful for other application areas such as maritime and to be future-proof. Ethernet has the benefit of higher transmission capacity and network size, and with the development of automotive Ethernet standards it has a potential for increased use also in automotive applications. Therefore, the protocol is also implementable over Ethernet with IP and either TCP or UDP as transport protocol. The higher-level layer is implemented, as customary for HD applications, with SAE J1939. Support for fuel cell systems is being added to SAE J1939, and StasHH is defining how to use these in a way that supports interoperability while not restricting the internal implementation of FCMs.

As it is expected that several applications may employ multiple FCMs, the standard allows both hosting them all on the main CAN bus, or using a single primary FCM as gateway to the other secondary FCMs (daisy-chain). In case the DC/DC converter is not included in the FCM, the digital interface allows letting the FCM control an external DC/DC converter.

The StasHH project has built 8 prototypes of StasHH-compliant system, currently undergoing testing at the CEA laboratories in France; a final iteration of the standard and final, fully compliant designs from 7 major FCM manufacturers will be published in 2024.