Friday, May 08, 2009

The Hydrogen Myth

Over a good number of years, Americans have heard promises of the coming hydrogen energy economy, with too-good-to-be-true suggestions that once the technology has been perfected, all our energy problems will be solved. Indeed, then-president George W. Bush said in 2003 that "the first car driven by a child born today could be powered by hydrogen, and pollution-free." But as Bush's dad might have put it, "not gonna happen."

Pollution free? Well, kind of, in a dishonest sort of way. It is true that, in a car powered by a hydrogen fuel cell, the only thing that comes out the "tailpipe" is water. (The hydrogen chemically combines with oxygen to produce good ol' H2O as the byproduct of energy generation.) Hey, we can live with a little water dripping on the road.

The promise of a perfectly clean energy "source" is like candy to a scientifically naive populace. All that's needed, one assumes, is to engage America's can-do determination to make the technology practical. Then we kiss OPEC goodbye.

But not so fast. There are certainly various technical and logistical challenges to overcome before hydrogen actually powers our vehicles, but the biggest problem is more fundamental. Unlike oil, hydrogen is not an energy "source" at all; it is merely an energy storage medium*.

Hydrogen is extraordinarily abundant in the universe and on earth, but it doesn't exist in a form that's directly usable. For example, the oceans contain hydrogen at massive scale: each molecule of water consists of two hydrogen atoms and one oxygen atom. Water molecules can be split, through electrolysis, to liberate the hydrogen from the oxygen. But the splitting requires energy to break the water molecule apart; electrolysis simply passes an electric current through water to accomplish that.

Electrolysis of water is just the mirror image of what happens in a fuel cell. In electrolysis we produce hydrogen and oxygen from water and electricity; in a fuel cell we produce electricity and water from hydrogen and oxygen. The recombination of hydrogen and oxygen in the fuel cell produces energy, which powers our vehicle. And it produces water, which drips out the tailpipe.

The problem, then, is that "making" hydrogen requires energy (and at least as much energy as the hydrogen will ultimately contribute to powering our vehicle), which is why hydrogen is not itself a source of energy. You still need a source of energy to make the hydrogen, and our energy sources remain as they have been: coal, oil, gas, nuclear, and some renewables such as wind and solar. Hydrogen changes none of that. Making hydrogen is analogous to charging a battery. We charge a battery with electrical energy, and that energy is stored in the battery for later use. Similarly, we make hydrogen with electrical energy, and that energy is stored in the hydrogen for later use.

If our principal problem is a shortage of energy, then hydrogen is not an answer. And it isn't even clean: While a hydrogen powered car does not itself pollute, the electrical power plants that produce the electricity that produces the hydrogen pollute a lot. Most of our electricity is still generated by burning coal.

At the present stage of humanity's development, our most dangerous pollutant appears to be carbon dioxide, because it is implicated in global warming. Those coal fired power plants produce carbon dioxide in abundance, along with more conventional pollutants. Interestingly, hydrogen can also be produced by chemically separating hydrogen from hydrocarbon fuels (such as oil and gas), but in so doing the fuels' carbon is released to the atmosphere as carbon dioxide, just as if it had been burned. There are, apparently and still, no free lunches.

It isn't completely surprising, then, that Energy Secretary Steven Chu has just announced that the U.S. government will no longer fund research for vehicle-based hydrogen fuel cells. Government funding for other non-vehicle fuel cell applications will continue. The government has apparently concluded that fuel cells will provide no meaningful benefit in our vehicle fleet for the foreseeable future. That's just an acknowledgment, it seems to me, that hydrogen doesn't actually solve any of our pressing energy problems.

It's also an acknowledgment that other technologies that are more deployable (and, indeed, which are already being deployed) make more sense, at least for now. The most prominent example of such technologies is electric vehicles that use energy stored in batteries instead of energy stored in hydrogen. As would hydrogen powered vehicles, such vehicles still present substantial challenges to our energy infrastructure: the supply, transmissibility, and environmental impact of the electricity they require will be a huge issue for a long time to come.

* Yes, I know: Oil, like hydrogen, is itself an energy storage medium. But it is storage that is already "full" of energy, which can be exploited at a relatively low energy cost. Hydrogen, when bound in a water molecule, is "empty" storage. We can therefore consider oil but not water to be an energy source. Like all fossil fuels, oil is actually a concentrated form of solar energy. The solar energy was captured in plants through photosynthesis eons ago, and compacted by geological forces into the highly concentrated store of energy we now enjoy.

Copyright (C) 2009 James Michael Brennan, All Rights Reserved