Yesterday's posting on hydrogen elicited several interesting comments from readers. One reminded me of one of the least positive possible outcomes of a push toward hydrogen: a "hydrogen economy" based on cars with internal combustion engines (ICE) modified to burn H2. Unfortunately, the superficial advantages of this pathway could make it appear attractive to regulators, manufacturers and possibly even consumers. But from the perspective on long-term energy and environmental policy, it might be even worse than our present predicament.
First, why might this option seem so appealing? Well, a car burning H2 produces no carbon dioxide and no pollutants that a good catalytic converter can't reduce to negligible levels. Moreover, the reengineering required to produce a car like this is trivial compared to producing a practical, economical fuel cell car. It involves delivering H2 to the vehicle, preventing it from all leaking or boiling away, and getting it into the cylinders effectively. That isn't simple, but it has been done on an experimental and prototype basis since the 1930s, and several carmakers are at work on it today. So you have the makings of a non-petroleum transportation system that doesn't require us to wait for fuel cells to become cost-competitive, at least on the automotive side of the equation. What could be so bad?
The problems start with hydrogen manufacturing. As virtually any good basic article on hydrogen will point out, most hydrogen today is produced by "reforming" natural gas, stripping hydrogen off the methane molecules and producing carbon dioxide as a byproduct. So right away, we have a notional zero-emissions vehicle that actually accounts for a fair quantity of emissions upstream of the car. (This is the knock on battery cars, too.) Just as bad, about a third of the energy content of the methane is lost in the process, not counting the energy cost of compressing or liquefying the hydrogen to get it to a fuel tank.
Then look at the car itself. Although an internal combustion engine can run quite nicely on H2, the efficiency gain is modest at best. In other words, there's no way to recoup the energy lost in making the H2 from natural gas. That's the main driver behind fuel cells, which have at least the potential to be 2-3 more efficient than an ICE. The "well-to-wheels" energy balance on the total Hydrogen ICE energy chain is no better than a conventional car running on diesel, and appears worse than one running on natural gas--a much easier conversion than equipping a car to burn hydrogen. That negates its greenhouse gas emissions benefits, as well. Hybridization doesn't change the outcome, either, since any of these fuel paths can be fitted to a hybrid car.
Now, at this point an advocate of this approach would probably interject that all these negatives disappear when you factor in hydrogen generated from renewable sources, such as wind, solar power, or biomass. That's true, too, but again only superficially. At the highest level, a system relying on hydrogen ICEs will require about twice as much primary energy as one feeding fuel cell cars. Even if you dismiss the potential of fuel cells altogether, you have to look at the entire system and assess whether your green electrons are better employed displacing coal or natural gas from power plants, rather than making H2. The outcome depends on the details of the system and is fairly complex to work through.
Nor are economics a good protection against this potential wrong turn in energy policy, because if H2 is offered for sale to the public at a price that is exempt from fuel taxes, it could well appear cheaper than gasoline, particularly in a market with high fuel taxes, such as Europe. In other words, short-sighted tax policy on H2 could mask the energy and environmental drawbacks of burning H2 in an internal combustion engine.
The last argument trotted out in support of the H2 ICE is that it could provide a bridge to a hydrogen fuel cell world, breaking the chicken-and-egg hurdle facing the infrastructure. Perhaps, but the likelier outcome is that the manufacturing economics favoring the H2 ICE would trump fuel cell cars for years, and we'd end up with millions of these things on the road before it became obvious how much energy they were using, compared to other alternatives.
So how do we avoid a result like this? Perhaps it's just a further refinement of public education. It wasn't so long ago that all hydrogen carried a green halo, until folks figured out there might be such a thing as "dirty hydrogen", with dirty being entirely in the eye of the beholder--I'd argue with their inclusion of nuclear-based hydrogen. Ultimately, it comes down to policies and incentives that promote the outcomes we want, in this case dramatically improved vehicle efficiency and reduced greenhouse gas emissions, rather than favoring specific pathways with advantageous treatment. A carbon trading system with a tight cap on emissions would sort the wheat from the chaff in this area pretty quickly.