The Toyota Mirai fuel-cell electric vehicle is so far a niche vehicle, but that hasn’t stopped Toyota from dreaming big — really big. Project Portal is a proof of concept semi truck that runs on a scaled-up version of the Mirai’s powertrain.

The Mirai is an four-door car, though, with a maximum weight of two tons. The proof of concept vehicle needs to haul 80,000 pounds, the combined gross vehicle weight of a big rig. So how many times do you have to scale the Mirai system to create that kind of power? Twice, according to Tak Yakoo, a senior executive engineer at Toyota.

“A semi is 36 tons, 18 times the size of a Mirai,” Yakoo said in a phone interview. “But we only use twice as much fuel cell and a relatively small battery.” The battery modules are flexible, so you can add more for a huge truck or fewer for a little passenger car or SUV. The scalability of the Mirai system is the point of the exercise, Yakoo said.

“Cars have so many different sizes of engines — 1.4L, 2.0L, 3.5L, etc.,” Yakoo said. “This is one standard fuel cell system with only a change of battery module size. That’s the dramatic change.” The system in the vehicle shown today at the Port of Los Angeles creates 670 hp and 1,325 lb-ft of torque, enough to move a full tractor-trailer and keep it moving down the highway.

For this concept, the engineers simply removed the components related to the diesel drive train and replaced them with the hydrogen fuel cell system. Taking out the diesel engine “leaves a huge space,” Yakoo said with a laugh. “Using that, we brought in the power electric controlling system, the fuel cells, the electric motor, and the fuel tank.” The tank did have to be fitted behind the cab for this demonstration vehicle.

This is only the beginning of Project Portal, a feasibility study in the use of zero-emissions vehicles for heavy duty. Toyota will begin working on the study along with the Port of Los Angeles’s Clean Air Action Plan this summer.

Toyota isn’t the only company working on emissions-free long-haul trucks. Nikola Motor Company has the Nikola One concept, and Elon Musk announced via tweet that Tesla will introduce a heavy-duty truck later this year.

It’s a tough nut to crack, though. “There are many unknown engineering things we need to explore,” Yakoo said. “We may not even know what is the sticking point or bottleneck” in these early stages of the project. “We are sure right now that I am seeing a fuel cell truck moving with 80,000 pounds of freight.”

Toyota’s overall goal is to produce one fuel cell system to rule them all, no matter the size. As Yakoo said at the end of our interview, “Scalability. That’s our dream — and my dream — to make it happen.”