Hydrogen Storage Tank Options: Not Everything Need Look like a Sausage

The Toyota Mirai and Nikola Tre use cylindrical tanks for their onboard H2, but Linamar’s Flexform conformable storage provides options.

February 17, 2025

Thom Cannell

Linamar said its Flexform conformable hydrogen storage system can use less material in the same storage volume while delivering anywhere from 5-25% more volumetric efficiency than conventional cylindrical tanks. (Linamar)

Since the 1860 Hippomoblie, hydrogen has been a part of powered mobility. Today, most hydrogen storage applications use cylindrical tanks, but other solutions are available. At a recent Bosch-sponsored event, SAE Media noted Linamar’s Flexform conformable storage, which the company says uses the same or less material for a given storage volume while delivering anywhere from 5-25% more volumetric efficiency than conventional cylindrical tanks within that volume. “We see space as a regular bounding box where all you're losing is this area around the corners, closer to five to 10% (loss). Where Flexform really shines and where the value proposition really is, is irregular spaces, such as between frame rails” said representatives from the Linamar engineering team.

Linamar’s packaging study for an unnamed h2 van showed “55% more hydrogen storage than they could store with cylindrical tanks.” (Thom Cannell)

Linamar’s packaging study for an unnamed hydrogen-powered van with storage between, under and around the crossmember, “achieved 55% more hydrogen storage than they could store with cylindrical tanks,” the Linamar engineers said. “Where Flexform really shines is being able to fit into multiple irregular storage spaces.”

Current Flexform configurations vary from 40-80 mm (1.6-3.2 in) in diameter and use a liner covered by a carbon fiber braid. “We then fold it into the desired shape, add fittings, apply the resin and cure it in an oven,” the engineers said. “If desired by the customer, Linamar can install the assembly into an existing enclosure.” R&D, testing and validation are performed at Detroit-based McLaren Engineering with production facilities in Guelph, Ontario. GTR-13 phase 2 certification is expected to be completed in the first quarter of 2025. Others, including Forvia, have also researched non-cylindrical H2 tanks.

There are five main types of hydrogen storage options:

Type I all-metal cylinders.
Type II load-bearing metal-lined cylinders (typically steel or aluminum alloys) with glass fiber composite overwrap and partial fiber reinforcement of the metallic cylinder.
Type III non-load-bearing metal-lined cylinders (aluminum) with a full carbon fiber composite overwrap.
Type IV non-load-bearing plastic/composite cylinders with composite overwrap interlaced with thermoplastic polymers.
Type V full composite non-lined tanks are available for storage, aerospace and fuel cell hybrid vehicles (FCEVs) in experimental stages.

Standard Type IV compressed hydrogen tanks, available above 700 bar (10,000 psi) now enable aeronautic and mobility solutions due to high pressures and low weight. For example, Hexagon Purus Type IV tanks deliver pressure levels up to 950 bar.

Type IV cylindrical tank applications: Toyota, Nikola

Hyundai’s cylindrical tank from the Nexo hydrogen fuel cell vehicle. (Sebastian Blanco)

Since 2002, Toyota has used Type 4 tanks for the Mirai-based fuel cells powering its Class 8 Kenworth T680 trucks. Toyota told SAE Media:“ Our in-house developed tanks were first demonstrated in 2005 in the Toyota FCHV. Cylindrical tanks require different packaging strategies compared to conventional liquid fuels, but we have demonstrated the ability to package tanks for light-duty, heavy-duty, and other applications. The difference in energy densities between liquid and gaseous fuels drives the packaging/design choices more so than the tank; we are closely watching the development of new and/or improved storage concepts for hydrogen.”

Nikola’s head of Fuel Cell and Hydrogen Storage, Livio Gambone, the company deploys similar Type IV, 700-bar tanks for the Tre FCV. He said that spheres might be the most efficient pressure vessel, “space limitations within the vehicle mandate that we utilize the next best thing - a cylinder. Even with larger vehicle applications such as trains, cylindrical vessels in a hexagonal packing configuration would likely still be the most efficient use of space when storing pressurized hydrogen. Gambone also mentioned how “non-cylindrical (conformable) pressure vessels have recently been accounted for in the latest standards and regulations for hydrogen fuel tanks” and that “even these so-called conformable designs rely on the basic cylindrical shape to store fuel.”

Liquid hydrogen is off to the races

Toyota Gazoo Racing powered its entry into the 2024 Fuji 24 Hour Race with oval liquid hydrogen tanks, saying this delivered over 200% range increase compared to gaseous hydrogen. “We’ve reached the point where we are now on par with cars running on gasoline. I think we were able to show that hydrogen can be just as much fun as gasoline in the field of motorsports,” said Gazoo Racing president Tomoya Takahashi.