From The Economist's Babbage blog:
A COUPLE of dozen electric cars with fuel cells under the bonnet (in
place of the more usual flat-pack of batteries beneath the floor) have
been zipping around your correspondent’s neighbourhood for the past few
years. Most are FCX Clarity models from Honda, all in the same rich
crimson colour. A couple of others are silver F-Cell station wagons made
by Mercedes-Benz. These experimental vehicles are leased to selected
users for trial periods while their manufacturers see how the
hydrogen-fuelled cars survive the cut and thrust of Los Angeles'
traffic.
So far, most seem to have acquitted themselves rather
well. Meanwhile, their drivers can feel rightly smug about the only
emission from the exhaust pipes being water vapour. Another plus is that
the fuel-cell vehicles are largely free of the “range anxiety” that
plagues battery-powered electric cars, such as the Nissan Leaf. Both the
Honda and the Mercedes have ranges not that far short of comparable
petrol cars—ie, 190 to 240 miles (300 to 380km).
Sooner or later,
though, they have to return to one of only five hydrogen-refuelling
stations open to the public in the greater Los Angeles area. But once
there, their tanks can be refilled in minutes, rather than the hours
needed to recharge a battery car.
And there’s the rub. Given
further refinement, plus economies of scale, fuel-cell vehicles ought to
be an attractive alternative to present-day motoring, if only
hydrogen-refuelling facilities were more common. As it is, outlets are
fewer and farther between than charging stations for electric vehicles
or even pumps for compressed natural gas.
Apart from the usual
chicken-and-egg problem, the plant and equipment needed for producing,
distributing and storing hydrogen is hugely expensive. Unlike the
industrial hydrogen used to make ammonia fertiliser, or for converting
heavy oil fractions into petrol, the hydrogen needed for fuel cells must
be 99.999% pure. That rules out all the cheaper ways of making it,
other than electrolysis of water.
There are problems on the
distribution side, too. Because hydrogen has the smallest molecule of
all, it leaks through practically everything. In particular, it
embrittles steel and causes corrosion, hastening crack propagation in
the process. Pipelines and storage tanks have to be specially lined at
additional cost.
Unlike fossil fuels such as petrol or diesel,
hydrogen is not a source of energy in its own right. It is merely a
means for storing electricity generated in a power station and
delivering it to the motor driving the wheels of an electric vehicle—in
much the same way as a battery works. And as free hydrogen does not
occur in useful quantities in nature, it has to be made by using
electricity to crack water into its constituent elements.
In
California, despite the many solar installations and wind farms, the
electricity coming out of the plug is neither green nor clean, being
derived predominantly (ie, 62%) from fossil fuel. During cheap-rate
periods at night—when electric vehicles tend to be recharged and
electrolysis plants are running flat out—most of California’s
electricity is imported from coal-fired power stations out of state.
Thus, like electric vehicles, hydrogen cars contribute their share of
greenhouse gases as well.
Certainly, moving the emissions from
the vehicle’s exhaust pipe to the power station makes it easier to
control the pollution. So, the question becomes whether there is a more
efficient way of packaging electricity for use in vehicles, other than
charging batteries or making hydrogen by electrolysis of water?
A
growing body of opinion seems to think liquid air is the answer (or,
more specifically, the nitrogen component that makes up 78% of air). It
is not exactly a new idea. Air was first liquefied in 1883, using
essentially the same process as today—ie, compressing it to 200
atmospheres, cooling it to -190ºC, and then letting it suddenly expand
and condense. The process turns 1,000 litres of transparent gas into 1.4
litres of light blue liquid....MORE
