The latest news from academia, regulators
research labs and other things of interest
Posted: January 28, 2008
Fuel-cell cars race to reality
(Nanowerk News) For those who dream of a cleaner, greener future thanks to nonpolluting technologies, recent auto shows have showcased some ideas. The biggest conglomeration was at the December 2006 Los Angeles Auto Show, where green machines were a dominant theme. The January Detroit auto show was more low-key on the green front, but there were a couple of intriguing, well-developed concepts on display there as well.
At the Los Angeles show there were three fuel-cell-powered SUVs--the Chevrolet Equinox Fuel Cell, Ford Explorer Fuel Cell, and Nissan X-Trail Fuel Cell concepts--and one fuel-cell sedan, the second-generation Honda FCX. Taking a different route altogether, BMW showed the Hydrogen 7, a luxury 7 Series sedan that can burn hydrogen or gasoline interchangeably in its conventional V12 engine.
In Detroit, Ford showed its Airstream minivan concept and GM unveiled the sporty-looking Chevrolet Volt. Both are essentially electric vehicles with onboard charging from some other power source, be it a small gasoline or diesel engine, or a hydrogen fuel cell. (A typical gasoline-electric hybrid car uses an electric motor, powered by a high-voltage battery pack, to assist the gasoline engine.)
As shown, the Volt had a small gasoline engine as its onboard charger. The Airstream used a hydrogen fuel cell.
How does a fuel-cell car work? A fuel-cell car is an electric vehicle that generates its own power from hydrogen-fed fuel cells. That power can then go directly to an electric motor or charge a battery pack. The only "tailpipe" emissions from a fuel-cell electric car are water and water vapor.
The fuel cell is a device that turns the chemical energy in a fuel directly into electricity. A single cell consists of a sandwich of two metallic plates with a plastic membrane between them. Hydrogen is fed to one side of the cell, where a catalyst coating helps break it into protons and electrons. The electrons stream off as an electric charge while the protons migrate through the membrane to the other plate, where they combine with atmospheric oxygen to make water. Numerous cells are packed together into a "stack" that can generate enough voltage to power a vehicle or some other electric device.
What's new here? Automakers have been showing fuel-cell vehicles in various stages of development for more than 10 years. But this latest crop takes us a step closer to reality with vehicles that behave like "normal" cars by being able to sustain highway speeds, start up in freezing weather, and cruise hundreds of miles between hydrogen fill-ups. (Refueling with hydrogen is a much slower process than a gasoline fill-up.)
Manufacturers claim those vehicles have cruising ranges of hundreds of miles: almost 200 miles for the Chevy Equinox, more than 311 miles for the X-Trail, and up to 350 for the Ford Explorer and Honda FCX.
Over the last few years the fuel-cell stack at the heart of the technology has become much smaller and also more powerful. For example, the fuel cell from the latest X-Trail concept vehicle is reportedly 60 percent smaller but 40 percent more powerful than the version shown on a 2003 X-Trail concept. And it now makes the equivalent of 120 horsepower. The fuel-cell stack in the new FCX sedan is only about the size of a briefcase and powers a 127-hp motor. Increasing power while decreasing the stack's size makes it possible to fit a hydrogen power unit in a conventional vehicle while minimizing the interior space it takes up.
Another trend in the development of fuel-cell vehicles is the use of a powerful backup battery. In the Honda FCX and Nissan X-Trail, the electric motor draws power from the fuel cell but a compact lithium-ion backup battery provides an extra boost of acceleration when needed. Regenerative braking--capturing energy from slowing the car down--charges the battery. The fuel cell aids recharging, as well.
The Ford Airstream and Chevrolet Volt take a different tack. They're known as "series hybrids." They are essentially made to be electric cars powered by a battery, although the ideal battery doesn't exist yet. Onboard charging of that battery could come from a gasoline or diesel engine--or a hydrogen fuel cell--whatever is most feasible. But the gas engine, fuel cell, or whatever only recharges the main battery, it doesn't move the vehicle. Also, those two are "plug-in" hybrids, meaning that you can plug the car into household current to charge the main battery. That way, it will run farther without the need to tap into the gasoline, diesel, or hydrogen supply as often.
Right now lithium-ion batteries are the favored cutting-edge battery technology because they can store much more electricity in a smaller space than other currently available battery types can.
What do fuel-cell vehicles cost? Don't ask. The carmakers don't like to say what it costs to make a fuel-cell car. With tens of millions invested in development and only a few cars produced, the costs per car are currently astronomical. Estimates of $1 million per car are common. Honda has estimated that it might get the retail cost of a fuel-cell car down to $84,000 by 2018 if all goes well.
Even excluding development costs, manufacturing costs are very high because the individual components--motors, fuel-cell stacks, batteries--are made in small volumes with expensive materials. Those costs could come down a lot if the technologies were standardized and mass produced. So far, though, the rapid pace of change has inhibited manufacturers from committing to any current design.
Road blocks to fuel-cells going mainstream. The elephant in the corner in any discussion of fuel-cell cars is the lack of a hydrogen fuel distribution infrastructure. Hydrogen is the most abundant element in the universe, but that doesn't make it inexpensive to produce, store, or deliver. In nature, it's often combined with other elements, such as carbon or oxygen Therefore it takes a lot of energy to separate, compress, liquefy and store hydrogen for later use.
The least-expensive method for producing hydrogen is to strip it from natural gas, a process that releases carbon dioxide. But if the driving force behind a hydrogen economy is to reduce greenhouse gases and dependency on fossil fuels, then natural gas and other hydrocarbons aren't the best source for hydrogen fuel. Renewable and nuclear energy can be used to make hydrogen without generating carbon dioxide.
Hydrogen proponents like to point to the electrolysis of water as another (and inexhaustible) hydrogen source. Despite the promise, there are problems with that approach. For example, electrolysis consumes a lot of electricity to free up hydrogen that then has to undergo expensive processing and transport, only to be turned back into electricity via the fuel cell. By one estimate you've wasted three quarters of the energy that was initially available just to get it to the car. And right now, the least-costly electricity comes from fossil-fuel-burning power plants.
It's not easy being green. For the generation of energy to be as environmentally benign as its intended use in transportation, we might need to look at renewable sources such as solar and wind power to reclaim hydrogen from water. Right now, though, the cost per kilowatt for "green" electricity is higher--sometimes much higher--than for electricity generated by conventional nuclear, gas, coal, and oil-fired plants.
Technology challenges lie ahead for the fuel and the vehicles. Automakers are working to accommodate alternatives to gasoline, as they're preparing for the long-term possibility that this planet might run out of petroleum that is cost-effective to extract and refine.
Advancements in battery design and the new science of nanotechnology might enable feasible new choices for the future. Fast-charging advanced batteries could eliminate the need to use hydrogen as a passenger-car fuel, but so far, that type of battery has been as elusive as inexpensive fuel cells.
THE BOTTOM LINE
As we have seen on the auto show circuit this year, recent strides have made what was once science fiction into a potential reality. It seems likely that we'll see a lot more hybrids and plug-in hybrids that rely more heavily on electricity by 2020 and beyond, but whether they'll use mobile hydrogen fuel cells remains an open question.