[ My comment: The only reason natural gas has come up as a transportation fuel at all is the false belief that there is 100 years of natural gas (even this article does, but natural gas may last far less for reasons explained in articles here).
Although this article focuses on cars, the same critique applies to heavy-duty trucks as well, which need even bigger, heavier tanks.
Alice Friedemann www.energyskeptic.com author of “When Trucks Stop Running: Energy and the Future of Transportation”, 2015, Springer and “Crunch! Whole Grain Artisan Chips and Crackers”. Podcasts: KunstlerCast 253, KunstlerCast278, Peak Prosperity]
Service, R. F. October 31, 2014. Stepping on the gas. Science Vol. 346, Issue 6209, pp. 538-541
At a conference on natural gas-powered vehicles Dane Boysen, head of a natural gas vehicle research program at the U.S. Department of Energy’s Advanced Research Projects Agency-Energy, said what industry stalwarts don’t want to hear:
“Honestly, natural gas is not that great of a transportation fuel.” In fact, he adds, “it’s a stupid fuel.”
This is because of the low energy density of natural gas. A liter of gasoline will propel a typical car more than 10,000 meters down the road; a liter of natural gas just 13 meters. Even when natural gas is chilled or jammed into a high-pressure tank—at a high cost of both energy and money—it still can’t match gasoline’s range.
Nevertheless, Boysen’s ARPAE project, called Methane Opportunities for Vehicular Energy (MOVE), is in the middle of spending $30 million over 5 years to jump-start the development of natural gas-powered cars and light-duty trucks which now burn over 60% of oil used in transportation.
But as Stephen Yborra, who directs market development for NGVAmerica, puts it, “there are an awful lot of hurdles to overcome.” Honda, for example, already makes a natural gas version of its Civic sedan. But it has sold only 2,000 of them in the United States, compared with more than 1.5 million gasoline-powered cars a year. Major improvements in fuel tanks, pumps, and infrastructure will be needed before natural gas vehicles rule the road.
One by one, Boysen ticks off formidable technical challenges and the efforts engineers are making to solve them.
GAS TANK MATERIALS. The biggest problem goes back to the meager energy density of natural gas. At ambient temperature and pressure, it’s a mere 40,000 joules per liter, slightly more than 1/1000th that of gasoline. To carry enough fuel, a car needs an oversized fuel tank, which eats into its cargo space. As a result, Honda’s natural gas Civic has less than half the trunk volume of its gasoline counterpart. “Drivers hate this because they can’t pick up people at the airport,” Boysen says.
The fuel tanks also have to be pressurized—another source of headaches. Today’s tanks compress gas to 250 bar, about 250 times atmospheric pressure. To handle the stresses, tanks must be made either from thick metal—which makes them heavy—or from lighter but expensive carbon fiber. Current tanks add an average of $3500 to the cost of natural gas vehicles.
- GAS TANK SHAPES. Spongelike fuel storage at modest pressures might free engineers to build tanks in shapes other than the now-standard high-pressure cylinder. That’s critical, because in a car, a cylinder occupies a box as big as its largest dimension, wasting a lot of space. For heavy-duty trucks and buses, which don’t have tight space constraints, an awkward tank shape is less of a problem. But it’s a killer for passenger cars.
- GASSING UP. One challenge is the time it takes to fill up. Gasoline pumps can supply as much as 10 gallons (38 liters) of fuel per minute, an energy transfer rate equivalent to 20 megawatts of power. Today’s CNG systems can fill the equivalent of a 15-gallon (57-liter) tank in 5 minutes. But they are expensive and primarily service trucks and specialized fleets.
Many advocates of natural gas cars dream of a low-pressure compressor that could be used for home refueling, as roughly half of U.S. homes—some 60 million—already have a natural gas line. If cars could be refueled at home, consumers would tolerate slower filling rates, as they do with electric vehicles. One such compressor is already on the market, Boysen notes. But it costs $5500.
- But with so few vehicles on the road, compressor manufacturers have been unwilling to invest in new technologies. As a result, says Bradley Zigler, a combustion researcher at the National Renewable Energy Laboratory in Golden, Colorado, “right now there is a valley of death between research progress and commercially available technologies.
- INFRASTRUCTURE, INFRASTRUCTURE, INFRASTRUCTURE. Even if engineers do it all—come up with a cheap space-age crystal to hold gas in a low-pressure tank, a more efficient natural gas–burning engine to reduce the demand for a large tank, and a cheap new compressor—that still might not be enough. For drivers to gamble tens of thousands of dollars on a new kind of car, analysts say, they’ll need all of these technologies to be widely available at the same time. “It has to be in a box,” Youssef says. “To me, that’s the biggest hurdle. I’m afraid we’re not there yet.”
- Even then, Boysen notes, natural gas vehicles would face competition from a more-than-viable alternative: the gasoline- and diesel-powered cars that now make up 93% of passenger vehicles on the road. Drivers will need to be convinced that a natural gas car will work at least as well as current cars do. They will need to know they can buy fuel wherever and whenever they want. And they will need a nationwide network of mechanics and parts suppliers to fix things when they break. Gasoline-powered and electric cars already cover the whole menu, but would-be competitors have far to go.
This suite of demands is particularly acute for truly novel technologies, such as hydrogen-powered fuel cell vehicles. The lack of an existing fueling infrastructure for those cars makes it far less likely that drivers will embrace them. But the fact that such challenges are also proving daunting to natural gas-powered cars, with their sizable fuel cost advantage, underscores just how difficult it is to transform the way we drive. For Boysen and his colleagues, the allure of natural gas is stronger than ever. But they know reality can be unkind to even the most appealing technologies.