"Rotomolding is probably the choke point. It takes hours to make a liner. Blow molding takes minutes to make a liner," said Tarek Abdel-Baset, Forvia's chief engineer for hydrogen storage systems. "Most carbon fiber tanks have rotomolded liners. With a blow molded tank we can make them faster and cheaper. We still have to wrap [using carbon fiber sheets], but we have gotten rid of a lot of waste."
Forvia's blow molded tanks can hold 10,000 pounds per square inch of pressure, twice the pressure of competitors' similarly sized tanks. Stacked behind the cab of a Class 8 truck, eight tanks provide enough fuel for about 400 miles of driving range.
Although the tank has few moving parts — there's just the valve — it is one of the most complex components on a Class 8 hydrogen-powered truck.
"Moving a gas is always more complicated than moving a liquid. There are more sensors and controls, and it becomes a pretty complicated system in a hurry. It really affects the rest of the vehicle. Now the tank is an integral part of the whole propulsion system," Abdel-Baset said.
While automating the production process and switching to a blow molded inner liner has dramatically reduced costs, there is still work to be done to reduce expenses enough to turn a profit.
About 60 percent of the cost of the tank is the carbon fiber outer wrap that gives the tank the ability to contain the high-pressure hydrogen and withstand the tremendous impacts that can occur in a high-speed crash. Forvia's tanks, Abdel-Baset said, use more efficient windings of the carbon fiber wrap for strength. Forvia also recycles carbon fiber waste.
Forvia engineers are developing a hydrogen tank system that fits between frame rails. Those could be used in Class 3-6 trucks, and possibly even pickups.
Cylindrical tanks are not practical for body-on-frame vehicles.
"That's like trying to fit a cylinder into a box. There's an amount of wasted space with that. There's a big push to perfect the conformable tank," Abdel-Baset said.
He estimated that using a conformable tank that fits between frame rails would deliver 30 to 40 percent more hydrogen capacity than using cylindrical tanks in the same space.
"We have proven smaller-scale prototypes. The goal is to have it in production by 2030," Abdel-Baset said.