As the "hydrogen highway" vision takes form through incremental technology advancements and demonstrations on many levels, much of the glory is captured by hydrogen fuel cell vehicles. It's true that they're marvels of technology and are deserving of this attention. As shared in Green Car Journal's Summer 2005 issue ("Hydrogen/Where We Are on the Drive to the Future"), automakers have come a long way and these vehicles are so good, they make it seem effortless to drive on this most environmentally positive fuel. But that's far from the case.
The vehicles are truly million dollar machines, using hand-built or limited production componentry handsomely packaged within normal-looking sedans, minivans, and SUVs. They drive seamlessly, for the most part, assuring us that the mission of bringing hydrogen vehicles to the highway can be accomplished. Still, there's a lot of work ahead to make this vision workable - costs must come down, fuel cell durability must improve, and challenges that go beyond the vehicles themselves must be met. Creating hydrogen economically is one of them, as is developing a widespread refueling infrastructure. Storing hydrogen is yet another significant technical challenge, and that's what this story is about, although a car once again appears to be the star.
This story begins and ends with Stanford Ovshinsky, an inventor of rarified stature who, many decades ago, made discoveries involving amorphous and disordered materials that created a whole new area of materials science. He was recognized with a Time Magazine "Heroes of the Planet Award" because of this work and how it led to many breakthrough applications, including his patented nickel-metal-hydride batteries (he and the company he founded, Rochester Hills, Michigan-based Energy Conversion Devices, hold the patents). As it turns out, this work has also led to the ability to store hydrogen in solid form at low pressure, a technology being developed by ECD business unit Ovonic Hydrogen Systems.
This is no small thing. Before we can buy a hydrogen-fueled vehicle in the showroom, some big technical hurdles need to be overcome in the lab, and one of the biggest is hydrogen storage. A hydrogen vehicle's range depends directly on how efficiently this fuel can be converted to motive power and, more fundamentally, how much fuel can be stored on-board. Range will be especially important in the early years of hydrogen vehicle commercialization since a refueling infrastructure will still be in its infancy.
Automakers have been grappling with the issue for a long time. Liquid hydrogen, championed most visibly by BMW, is attractive because a much greater amount of liquid hydrogen can be stored in a given tank size than gaseous hydrogen. This translates to greater range. However, the downside is that hydrogen must be stored at -423 degrees F to keep it in liquid form, and getting it down to this temperature requires a lot of energy and special fueling equipment.
Most automakers use gaseous hydrogen in their developmental fuel cell and hydrogen internal combustion vehicles because of this. However, gaseous storage also has its challenges. Current 5,000 psi (pounds per square inch) hydrogen cylinders simply don't hold enough fuel for a decent driving range.
That has prompted many automakers to explore a new generation of even higher 10,000 psi hydrogen storage cylinders, which require additional changes to support this high pressure including 10,000 psi-capable lines, fittings, and dispensing equipment.
Then there's the approach offered by Ovonic Hydrogen Systems' solid hydrogen storage, a concept so clever and intriguing it seems improbable... yet it works. A tank containing powdered metal alloys is filled with hydrogen at a relatively low 1,500 psi. Removing heat during the process causes the metal to absorb hydrogen like a sponge, and a new material called a metal hydride is created. Hydrogen stored in solid form like this is in a safer state and can be stored within a tank at a lower 250 psi. On-board systems determine when hydrogen is needed by an engine or fuel cell, providing heat to reverse the process so gaseous hydrogen is released from the hydride and into the fuel system. In an interesting phenomenon, a greater volume of hydrogen can be stored in the same size cylinder with metal alloy than without it, a consideration that provides better driving range.
Several years ago, Green Car Journal drove a 2002 Toyota Prius hybrid equipped with such a system. Operating as a hydrogen hybrid vehicle, it produced near-zero emissions and drove seamlessly. Ovonic Hydrogen Systems has now gone one better by offering several second-generation Prius hybrids equipped with a similar system to showcase its solid metal hydrogen storage. Some of these vehicles will operate as part of a hydrogen hybrid demonstration fleet at Southern California's South Coast Air Quality Management District in Diamond Bar, California, a program that will prove the viability of hydrogen hybrids in everyday use.
Beyond the solid hydrogen storage, other modifications to these vehicles include vents and leak detectors to ensure safe operation, as well as hydrogen-compatible fuel lines, an engine management computer that operates new gaseous fuel injectors, and a variety of sensors. A turbocharger is used to compensate for the lower engine output that comes with combusting hydrogen.
All this technology is wrapped within sharp-looking demonstration vehicles that promise to forward the company's solid hydrogen storage message in a very high-profile way. These high-tech cars also demonstrate that hydrogen internal combustion could represent a more readily-achievable interim step toward the hydrogen highway as more complex and expensive fuel cell vehicles evolve in coming years. With potentially larger numbers of more affordable internal combustion hydrogen vehicles on the road, there's also more incentive for building the hydrogen refueling infrastructure that will be needed for those fuel cell vehicles in the future.
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