J. LI, NICE America Research Inc., Mountain View, California; and A. KU and J. MCROBIE, Clear Skies Hydrogen, Mountain View, California

As of December 2021, only 53 public H₂ fueling stations (48 retail, 5 transit) were present in the U.S., concentrated in clusters around California urban centers or existing as standalone stations.¹ For the large-scale deployment of H₂ fuel cell vehicles across the U.S. to be feasible, tens of thousands more stations are needed and geographic coverage must drastically expand. This creates a “chicken-and-egg” investment problem: vehicle operators need confidence that fueling capacity will be readily available before investing in an H₂-fueled vehicle, but fuel suppliers need assurance that sufficient H₂-fueled vehicles will be deployed to justify capital investment in refueling stations. How, then, can we grow fleets and refueling stations with confidence?

This article proposes a practical path for establishing a large-scale H₂ refueling network by focusing on heavy duty vehicles—more specifically, on truck fleets—whose operational profiles favor the fast refueling times and long vehicle ranges afforded by fuel cell vehicles, and on the creation of a fueling network along long-haul trucking corridors using a new liquid H₂ (LH₂) pumping technology. Once established, such a network could provide the backbone of a larger-scale network open to both private fleet and retail consumers. 

Modular LH₂ stations as building blocks. A robust commercial infrastructure for LH₂ exists across the U.S. in support of industrial processes. While liquefaction of H₂ is energy intensive, the added costs can be offset by savings from distribution and onsite storage: H₂ is liquefied at large, centralized facilities and delivered to end users by tanker truck. Liquid tankers carry about 4 t of LH₂; by contrast, the tube trailers used to transport H₂ as a compressed gas can carry only 1 t of product at a time. For operations using a few t of H₂ per day, liquid delivery can be competitive with delivery by pipeline or onsite production. Storing H₂ onsite as a cryogenic liquid is also safer, less costly and has a smaller carbon footprint than pressurized gas storage.² 

Already a cost-competitive option for H₂ refueling stations on a small scale, LH₂ delivery is becoming increasingly attractive to larger operations. Announced investments in LH₂ supply have been accelerating over the last 3 yr, resulting in the addition of nearly 200 tpd of capacity globally, and a majority of U.S. public transit agencies operating fuel cell buses have opted for LH₂-based refueling stations.^{3, 4} Although their designs may differ in other areas, all such stations have one feature in common: the use of an LH₂ pump to deliver fuel to the dispenser. LH₂ pumps are an area of active technology development, and one recently demonstrated^4,5 new pump design could potentially enable modular refueling stations at scale.

FIG. 1. Modular refueling system based on a submergible pump (top); three configurations of a refueling system, in order of increasing size (bottom).

The modular refueling system shown in FIG. 1 uses this pump, which was adapted from LNG applications, to deliver cold, high-pressure gas to a fuel dispenser. LH₂ is drawn from the tank and pressurized by the pump. The outlet stream then flows through a vaporizer to produce high-pressure, gaseous H₂, and the temperature is adjusted using a thermally integrated circuit before delivery to the vehicle. This system operates in a “direct fill” mode in which fuel is transferred directly from the onsite storage tank to the vehicle without the need for intermediate high-pressure storage, reducing both capital cost and energy demand. The direct fill system can operate continuously as long as there is fuel in the onsite tank. Together with the pump, this represents a significantly simplified refueling process that allows modularization of the refueling station where it is used. These fueling systems are capable of delivering SAE J2601-compliant fills at 35 MPa pressure; versions capable of delivering 70 MPa fills are in development. 

Demonstration of system capabilities. A mobile trailer configuration of this technology has been operational since 2020, and separate refueling demonstrations were performed in 2021 at Stark Area Regional Transit Authority (SARTA) and SunLine Transit Agency (SunLine). FIG. 2 summarizes the results of these demonstrations.

FIG. 2. Mobile trailer refueling demonstrations at two transit agencies, SARTA and SunLine. Photo: refueling in progress at SunLine.

The SARTA demonstration. The system was deployed at SARTA, located in Canton, Ohio, from February 2021–June 2021: it operated for 4 mos following a 1-mos permitting, setup and commissioning period, and had an average specific energy demand of < 0.35 kWh/kg H₂ dispensed. The system delivered a total of 3,700 kg of H₂ to in-service fuel cell buses over 118 individual fueling events and with 100% system availability; the typical filling time for an empty bus with a 40-kg tank was 10.1 min, and the average and peak fueling rates over the course of the demonstration were 3.4 kg/min and 7.1 kg/min, respectively. The fills delivered were J2601-compliant.

The demonstration concluded with an endurance test in which 52 consecutive fills, totaling 1,322 kg of dispensed H₂, were delivered over an 11.5-hr period.⁴ 

The SunLine demonstration. The system was deployed at SunLine’s Division II facility in Thousand Palms, California, from October 2021–February 2022. As with SARTA, a 1-mos permitting, setup and commissioning period preceded operation. The system operated at Sunline for 3 mos, delivering a total of 4,838 kg of H₂ to in-service fuel cell buses over the course of 230 individual fueling events, most of them with the system in unattended mode. System availability was once again 100%, and system performance (including fill rates and specific energy use) was consistent between both demonstrations. 

When the numbers from qualification testing in 2020 and the two 2021 demonstrations are combined, the system has pumped 20 metric t of LH₂ and accumulated more than 1 yr of operating experience. This experience, and the use of a simulation trailer to mimic 60-kg, 90-kg and 120-kg fills during qualification testing, indicated that the system offers comparable performance for fuel cell trucks as for transit buses—Class 8 fuel cell trucks require between 60 kg and 120 kg per fill, and the current time standard for refueling diesel trucks is up to 30 min. 

Scalable deployment for truck fleets. Refueling stations, regardless of fuel type, are typically built at their full service capacity. In a mature ecosystem with large numbers of vehicles in service, this enables the station to immediately operate at maximum capacity; in an ecosystem where the vehicle fleet is small but growing, however, station utilization will initially be low. This makes capital recovery more difficult, forming the crux of the “chicken-and-egg” investment problem facing H₂ fuel cell vehicles today. 

A modular approach to station deployment, as illustrated in FIG. 3, avoids this problem by unlocking a staged deployment path for the transition period during which fleets are growing. Smaller, portable modules can be deployed initially while the number of fuel cell vehicles on a route is low, and then be replaced with larger, permanent stations as traffic grows. The portable nature of the smaller modules enables them to be repositioned to expand geographic coverage and bypass the cost of constructing a new module in each new location. In addition to enabling more efficient use of capital, this staged approach also provides a degree of flexibility for refueling network operators to adjust their plans if fueling demand profiles diverge from forecasts.

FIG. 3. A staged approach to network deployment using modular refueling stations (top left). The capital expenditure for conventional deployment is higher than the staged approach available from modular deployment (right and bottom).

This mix of portable and permanent stations can serve local trucking using a hub-and-spoke model: a central refueling depot will provide service at a high-volume facility such as a port; portable stations will then extend the refueling network’s range along specific routes. The refueling network can grow with the trucking fleet by repositioning portable stations and replacing them with permanent ones as previously described. Current portable stations can completely refill between 10 trucks and 20 trucks per LH₂ delivery, while the permanent stations can support between 50 fills and 100 fills between deliveries. Permanent stations can be expanded in increments of 5 t through the addition of extra modules. 

A similar strategy can be used to establish the backbone of a network along trucking corridors, with portable stations set up on highways. With proper network design and coordination, regular trucking traffic can generate enough fueling demand to support such a venture. As more fuel cell trucks are added to the fleet, the network can scale up and eventually be opened to retail customers, further improving the economics for station operators. 

All of these network strategies are made possible by combining new modular refueling technologies with the proven infrastructure surrounding LH₂ delivery. This combination enables for the creation and deployment of a direct filling design that reduces cost and allows modularity, cracking the “chicken-and-egg” problem and offering a practical, affordable way to scale H₂ fuel cell transportation.H₂T

LITERATURE CITED

1. Alternative Fuels Data Center, 2021, online: https://afdc.energy.gov/stations/states 

2. Yoo, B. H., S. Wilailak, S. H. Bae, H. R. Gye and C. J. Lee, “Comparative risk assessment of liquefied and gaseous hydrogen refueling stations,” International Journal of Hydrogen Energy, Vol. 46, 2021. 

3. Eudy, L. and M. Post. “Fuel cell buses in U.S. transit fleets: Current status 2020,” National Renewable Energy Laboratory, Golden, Colorado, 2021, online: https://www.nrel.gov/docs/fy21osti/75583.pdf 

4. Li, J., et al., “Liquid pump-enabled hydrogen refueling system for heavy duty fuel cell vehicles: Fuel cell bus refueling demonstration at Stark Area Regional Transit Authority (SARTA),” International Journal of Hydrogen Energy, Vol. 46, 2021. 

5. Li, J., et al., “Liquid pump-enabled hydrogen refueling system for heavy duty fuel cell vehicles: Pump performance and J2601-compliant fills with precooling,” International Journal of Hydrogen Energy, Vol. 46, 2021.

ANTHONY KU is Chief Technology Officer at NICE America Research, a clean energy incubator based in California. Under Dr. Ku’s leadership, NICE America has been developing and commercializing technologies in the areas of H₂ infrastructure, carbon management and energy storage. He holds a PhD from Princeton University and a BS degree from Massachusetts Institute of Technology (MIT), both in chemical engineering. 

JIMMY LI is the Director of Hydrogen Energy at NICE America Research. For the last several years, Dr. Li has led a team to develop, validate and field-demo a liquid pump-based H₂ refueling technology. He holds a PhD from Georgia Institute of Technology in mechanical engineering and has been in the H₂ industry for 28 yr. 

JORDAN MCROBIE is the Director of Business Development and Commercial Partnerships for NICE America Research and has previously worked on batteries with Sanyo Energy and Samsung SDIA, on H₂ at CAFCP and on electronics manufacturing services at Sanmina. He holds a BA degree in economics from Western University (formerly UWO) in London.