Hydrogen cars blimp your ride

I think hydrogen is a hyped-up bandwagon. I'll be delighted to be proved wrong, but I don't see how hydrogen is going to help us with our energy problems. Hydrogen is not a miraculous source of energy; it's just an energy carrier, like a rechargeable battery. And it is a rather inefficient energy carrier, with a whole bunch of practical defects.

The "hydrogen economy" received support from Nature magazine in

Figure 20.24. Top: A compressed-air tram taking on air and steam in Nantes. Powering the trams of Nantes used 4.4 kg of coal (36 kWh) per vehicle-km, or 115 kWh per 100p-km, if the trams were full. [5qhvcb] Bottom: A compressed-air locomotive; weight 9.21, pressure 175 bar, power 26 kW; photo courtesy of Rüdiger Fach, Rolf-Dieter Reichert, and Frankfurter Feldbahnmuseum.

Figure 20.24. Top: A compressed-air tram taking on air and steam in Nantes. Powering the trams of Nantes used 4.4 kg of coal (36 kWh) per vehicle-km, or 115 kWh per 100p-km, if the trams were full. [5qhvcb] Bottom: A compressed-air locomotive; weight 9.21, pressure 175 bar, power 26 kW; photo courtesy of Rüdiger Fach, Rolf-Dieter Reichert, and Frankfurter Feldbahnmuseum.

Figure 20.25. The Hummer H2H: embracing the green revolution, the American way. Photo courtesy of General Motors.

a column praising California Governor Arnold Schwarzenegger for filling up a hydrogen-powered Hummer (figure 20.25). Nature's article lauded Arnold's vision of hydrogen-powered cars replacing "polluting models" with the quote "the governor is a real-life climate action hero." But the critical question that needs to be asked when such hydrogen heroism is on display is "where is the energy to come from to make the hydrogen?" Moreover, converting energy to and from hydrogen can only be done inefficiently - at least, with today's technology.

Here are some numbers.

• In the CUTE (Clean Urban Transport for Europe) project, which was intended to demonstrate the feasibility and reliability of fuel-cell buses and hydrogen technology, fuelling the hydrogen buses required between 80% and 200% more energy than the baseline diesel bus.

• Fuelling the Hydrogen 7, the hydrogen-powered car made by BMW, requires 254 kWh per 100 km - 220% more energy than an average European car.

If our task were "please stop using fossil fuels for transport, allowing yourself the assumption that infinite quantities of green electricity are available for free," then of course an energy-profligate transport solution like hydrogen might be a contender (though hydrogen faces other problems). But green electricity is not free. Indeed, getting green electricity on the scale of our current consumption is going to be very challenging. The fossil fuel challenge is an energy challenge. The climate-change problem is an energy problem. We need to focus on solutions that use less energy, not "solutions" that use more! I know of no form of land transport whose energy consumption is worse than this hydrogen car. (The only transport methods I know that are worse are jet-skis - using about 500 kWh per 100 km - and the Earthrace biodiesel-powered speed-boat, absurdly called an eco-boat, which uses 800 kWh per 100p-km.)

Hydrogen advocates may say "the BMW Hydrogen 7 is just an early prototype, and it's a luxury car with lots of muscle - the technology is going to get more efficient." Well, I hope so, because it has a lot of catching up to do. The Tesla Roadster (figure 20.22) is an early prototype too, and it's also a luxury car with lots of muscle. And it's more than ten times more energy-efficient than the Hydrogen 7! Feel free to put your money on the hydrogen horse if you want, and if it wins in the end, fine. But it seems daft to back the horse that's so far behind in the race. Just look at figure 20.23 - if I hadn't squished the top of the vertical axis, the hydrogen car would not have fitted on the page!

Yes, the Honda fuel-cell car, the FCX Clarity, does better - it rolls in at 69 kWh per 100 km - but my prediction is that after all the "zero-emissions" trumpeting is over, we'll find that hydrogen cars use just as much energy as the average fossil car of today.

Figure 20.26. BMW Hydrogen 7. Energy consumption: 254 kWh per 100 km. Photo from BMW.
Figure 20.27. The Earthrace "eco-boat." Photo by David Castor.
Figure 20.28. The Honda FCX Clarity hydrogen-powered fuel-cell sedan, with a Jamie Lee Curtis for scale. Photo courtesy of automobiles.honda.com.

Here are some other problems with hydrogen. Hydrogen is a less convenient energy storage medium than most liquid fuels, because of its bulk, whether stored as a high pressure gas or as a liquid (which requires a temperature of -253 °C). Even at a pressure of 700bar (which requires a hefty pressure vessel) its energy density (energy per unit volume) is 22% of gasoline's. The cryogenic tank of the BMW Hydrogen 7 weighs 120 kg and stores 8 kg of hydrogen. Furthermore, hydrogen gradually leaks out of any practical container. If you park your hydrogen car at the railway station with a full tank and come back a week later, you should expect to find most of the hydrogen has gone.

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