129the energy-density of compressed-air energy-stores is only about 11–28Wh per kg. The theoretical limit, assuming
perfect isothermal compression: if 1 m3 of ambient air is slowly compressed into a 5-litre container at 200 bar, the
potential energy stored is 0.16 kWh in 1.2 kg of air. In practice, a 5-litre container appropriate for this sort of pressure
weighs about 7.5 kg if made from steel or 2 kg using kevlar or carbon fibre, and the overall energy density achieved
would be about 11–28 Wh per kg. The theoretical energy density is the same, whatever the volume of the container.
130Arnold Schwarzenegger ... filling up a hydrogen-powered Hummer. Nature 438, 24 November 2005. I’m not saying
that hydrogen will never be useful for transportation; but I would hope that such a distinguished journal as Nature
would address the hydrogen bandwagon with some critical thought, not only euphoria.
Hydrogen and fuel cells are not the way to go. The decision by the Bush administration and the State of California to follow the hydrogen highway is the single worst decision of the past few years.James Woolsey, Chairman of the Advisory Board of the US Clean Fuels Foundation, 27th November 2007.
In September 2008, The Economist wrote “Almost nobody disputes that ... eventually most cars will be powered by
On the other hand, to hear more from advocates of hydrogen-based transport, see the Rocky Mountain Institute’s
pages about the “HyperCar” www.rmi.org/hypercar/.
–In the Clean Urban Transport for Europe project the overall energy required to power the hydrogen buses was between
80% and 200% greater than that of the baseline diesel bus. Source: CUTE (2006); Binder et al. (2006).
–Fuelling the hydrogen-powered car made by BMW requires three times more energy than an average car. Half of the
boot of the BMW “Hydrogen 7” car is taken up by its 170-litre hydrogen tank, which holds 8 kg of hydrogen, giving
a range of 200 km on hydrogen [news.bbc.co.uk/1/hi/business/6154212.stm]. The calorific value of hydrogen is
39 kWh per kg, and the best-practice energy cost of making hydrogen is 63 kWh per kg (made up of 52 kWh of natural
gas and 11 kWh of electricity) (CUTE, 2006). So filling up the 8 kg tank has an energy cost of at least 508 kWh; and if
that tank indeed delivers 200 km, then the energy cost is 254 kWh per 100 km.
The Hydrogen 7 and its hydrogen-fuel-cell cousins are, in many ways, simply flashy distractions.David Talbot, MIT Technology Review
Honda’s fuel-cell car, the FCX Clarity, weighs 1625 kg, stores 4.1 kg of hydrogen at a pressure of 345 bar, and is said to
have a range of 280 miles, consuming 57 miles of road per kg of hydrogen (91 km per kg) in a standard mix of driving
conditions [ ], [ ]. Using the cost for creating hydrogen mentioned above, assuming natural gas is used as
the main energy source, this car has a transport cost of 69 kWh per 100 km.
Honda might be able to kid journalists into thinking that hydrogen cars are “zero emission” but unfortunately they can’t fool the climate.Merrick Godhaven
132A lithium-ion battery is 3% lithium. Source: Fisher et al. (2006).
–Lithium specialist R. Keith Evans says “concerns regarding lithium availability ... are unfounded.” – Evans (2008).
133Two Dutch-built liners known as “The Economy Twins.” www.ssmaritime.com/rijndam-maasdam.htm.
134Transrapid magnetic levitation train. www.transrapid.de.