Hydrogen tries again.
Apr 23rd 2010, 14:30 by N.V. | LOS ANGELES
HAVING soared on the promise of carbon-free motoring, the idea of the “hydrogen economy” crashed and burned when it collided with reality. Hundreds of experimental hydrogen-powered cars—once hailed as the best solution for reducing America’s dependence on foreign oil for over half its consumption—are now gathering dust in manufacturers’ parking lots.|
Hydrogen’s main attraction is that when it is “burned” in a fuel-cell or an internal-combustion engine, the only emissions are heat and a wisp of water vapour. Using hydrogen as a fuel—actually, it is more accurate to refer to it as an energy carrier, since producing hydrogen requires energy from another source—therefore has the potential to reduce emissions of greenhouse gases and other pollutants. As America has abundant supplies of coal and natural gas from which hydrogen can be made, what’s not to like about it?
Several things. First, making fuel-cells compact and cheap enough to drive an electric vehicle is far from easy. Over the past 20 years, Honda—arguably the furthest down the road—has been through at least three iterations of its fuel-cell design, and is still one or possibly two generations away from having something practical to offer the motoring public. By comparison, getting a conventional internal-combustion engine to burn hydrogen instead of petrol is relatively easy. Even so, such efforts have also come to naught.
From the beginning, the cloud hanging over the whole hydrogen enterprise has not been the power source as such, but the intractable difficulty of distributing and storing the stuff. It is not hard to see why. Hydrogen atoms are the smallest and lightest in the universe. The next heaviest element in the periodic table, the inert gas helium, is used for detecting cracks in pressure vessels and the like. Even though helium atoms are four times chunkier than hydrogen atoms, they are still small enough to find all the weak spots as they worm their way through the crystalline structure of solid steel several centimetres thick. If hydrogen were used as a crack detector (it is not because of the fire hazard), it would escape four times faster.
Devising a fuel tank to constrain hydrogen has always been a challenge. To have a useful range of 480km (300 miles) or so, an electric car using a fuel cell instead of a battery pack would require around 9kg (20 pounds) of hydrogen. Storing hydrogen as a gas or liquid in a vessel containing “reversible” crystalline metal hydrides is one way to carry it around. Another is to use high-tech pressure vessels made of carbon-fibre. Some researchers are working on sponges made of carbon nanotubes that soak up hydrogen. Whichever technology is chosen, a vessel for storing hydrogen on-board a car costs hundreds of times more than a conventional petrol tank.
Meanwhile, transporting hydrogen from its production facility has presented other difficulties. Natural-gas pipelines cannot be used because hydrogen makes the steel tubing brittle and attacks the welds. Special production processes are needed to make pipes for carrying hydrogen. For that reason, few exist. The alternative is to liquefy the hydrogen at great expense and transport it in road tankers refrigerated with liquid nitrogen. Either way, the hydrogen fuel finishes up costing way too much. And all this assumes that hydrogen can be made cheaply and without producing large amounts of carbon emissions. So far, it can’t.
Such annoying realities have an annoying way of making themselves felt. When they finally did, General Motors ditched its fleet of 100 Chevrolet Equinox fuel-cell cars after a two-year trial. Likewise, BMW withdrew its own test fleet of 100 cars with internal-combustion engines modified to run on hydrogen. The final blow was last year’s announcement by Steven Chu, America’s Nobel physics laureate turned energy secretary, that he was cancelling funding for research into hydrogen-powered vehicles generally. Ever since, carmakers have been placing their low-emission bets more on plug-in hybrids, clean diesels or pure electric vehicles.
Does that mean the hydrogen economy has been finally laid to rest? Yes, as far as motoring is concerned. But the industrial use of hydrogen—as an energy carrier that is both clean and free of foreign influence—seems to be gaining favour in business circles. Dr Chu’s policy shift that axed research on hydrogen cars simultaneously poured $1 billion of stimulus money into a clean-coal project called FutureGen that the Bush administration abandoned in 2008. Though it appears to all intents and purposes like a state-of-the-art power station, FutureGen is actually a huge hydrogen production facility in disguise.
The FutureGen project—to be built in Mattoon, Illinois, by a consortium of coal-mining companies and electric utilities in partnership with the American government—will be the world’s first coal-fuelled power station to produce near-zero emissions. The 275-megawatt demonstration plant is designed to prove the feasibility of producing electricity and hydrogen from coal, while simultaneously capturing the carbon dioxide and sequestering it in deep underground reservoirs.
If the demonstration plant works as well as hoped, the plan will be to build combined electricity and hydrogen generating stations in locations where there are geological formations containing saline water overlain by a thick caprock serving as a seal. Geological surveys show America has enough saline rock formations to store three trillion tons of carbon dioxide—enough for the next 500 years at the country’s current output from human activities.
The hydrogen produced in a fully integrated, combined-cycle plant like FutureGen promises to be 25% cheaper than today’s hydrogen. More intriguing still is the chance to produce not just pure hydrogen, but also hydrogen-rich liquids and synthetic natural gas (SNG), which can be transported cheaply using the existing network of pipelines and road tankers. Delivered to a local filling station, such liquids can be readily reformed on site into pure hydrogen for powering fuel cells. In SNG’s case, the gas can also be compressed and used to fuel cars with internal-combustion engines.
Although hydrogen’s distribution problem might then have been licked, the storage problem remains. However, it is less of a problem for fixed installations than vehicles. A number of niche markets have been identified—for instance, apartment blocks, office buildings, stores and neighbourhood wireless towers—that would pay a premium for stand-alone blocks of clean and silent power.
In late February a Silicon Valley start-up called Bloom Energy—in stealth mode over the past eight years while burning through $400m of venture capital—unveiled details of the fuel-cell powered generating “boxes” it has installed at Bank of America, Coca-Cola, eBay, Federal Express, Google and Wal-Mart and over a dozen other firms that want chunks of electrical power that are both environmentally friendly and isolated from the vagaries of the grid. Bloom’s self-contained generating units, costing around $750,000 per 100-kilowatt block, produce silent, low-emission power for less than ten cents a kilowatt-hour. Thanks to a 30% federal tax credit, that works out as much the same as a combined-cycle gas-turbine plant—but without the noise and fumes.
The current generation of Bloom boxes use natural gas, ethanol or biogas to run their fuel cells. They could have an even smaller carbon footprint if fuelled with hydrogen. The choice of fuel depends on how environmentally correct the customer wishes to be. It may be premature to report that the death of the hydrogen economy has been greatly exaggerated. But hydrogen still has too much potential as an energy medium to shuffle quietly off the scene.