Shots Across The Bow

Fuel cells and other myths

There's a little discussion on fuel cells going over at SKBubba's house, and I wanted to add my two cents worth. I put an abbreviated version of this in the comments section over there.

There is a tendency for people to see fuel cells as the solution to all our energy problems.

"It burns hydrogen, not oil, and produces clean water as it's only emission. How wonderful! We are saved from pollution and the Middle East at the same time!"

Unfortunately, while the above is true, it only represents half the story. There is a little known flaw in this panacea that dooms it to marginal success, if not abject failure. Come with me while we explore...

The Dark Side of the Fuel Cell (Cue the spooky music.)

Our story begins with the laws of thermodynamics. Unlike election campaign laws, these laws are inflexible and cannot be ignored, no mater how much politicians might hope. Breaking them is out of the question, as is bending them, except at the quantum level, but we don't want to go there.

Trust me, we don't.

The first law says that energy and matter can neither be created, nor destroyed, only altered. In essense, you can't get something for nothing, despite what the late night infomercials tell you. The second law says that in any closed system, energy tends to decrease, while disorder tends to increase. In short, you'll never get outt what you put in. Except when you dig a hole For some reason, you always have more dirt than when you started...but I digress. These two laws are iron clad. Unbreakable. Mother nature enforces them with utmost strictness, and you know what a mother she can be.

So, let's see how those laws apply to our happy little fuel cell.

First, hydrogen doesn't play nice. Where oil plays hide and seek, once you find it, it comes along quietly to the refinery. Hydrogen, on the other hand, has to be dragged kicking and screaming away from oxygen, cause they really get along very well. It takes a lot of energy to rip the two of them apart. Just picture two teenagers in the back row of the movie theater necking. While chewing gum. And wearing braces.

Got it?

OK, so now we have separated the hydrogen, and filled up our happy little fuel cell. All is right with the world now, right? So we drive down the road, and our car, instead of burning petroleum as fuel, burns hydrogen.

This brings us to the second part of our tragic tale. Burning is another word for oxygenation, or the addition of oxygen. What we are doing is allowing our teenagers to get back together again. In the process, the hydrogen and oxygen give off energy. How much energy you ask? (OK you didn't ask, but this post would end abruptly if I didn't ask for you.)

Here's where mother nature's cops step in and ruin the party. Law one says that the most energy we can extract from oxygenating (burning) hydrogen is the same amount we used separating them in the first place. Breaking even is the best we can hope for. Law two tells us that we can't even break even, that we will lose energy with each transformation.

Yes, there's a hand in the back?

"If law one says we can't destroy energy, where does this lost energy go?"

Good question, I'm glad you asked. The lost energy is radiated away in the form of heat and light, which are useless to us in this application.

The picture gets even worse when you figure in the efficiencies of the fuel cell, which runs around 83% for the ideal fuel cell.

Finally, hydrogen has a nasty tendancy to oxidize at a highly accelerated rate. In the lab, we call this an explosion. Think Hindenberg. Now picture every car on the interstate at rush hour being the equivalent of a Ford Pinto. Every fender bender would be a potential conflagration.

In essence, we haven't reduced our energy demands at all. In fact we have increased them, so how has that reduced our dependence on foreing oil?

The sad answer is that is hasn't. Fuel cells alone do not provide an answer to our energy problems. So why are we working on them?

Well, fuel cells do have some significant advantages over internal combustion.

• They produce a clean exhaust, heat and pure water.
  
• The conversion from chemical to electrical energy (fuel cell) is significantly (about two times) more efficient than from chemical to thermal (internal combustion), which translates into better mileage. Unfortunately, the increased production costs associated with manufacturing both the cell and the fuel more than offset this advantage.
  
• A fuel cell coupled with small solar panels makes a good, clean back up power supply in stationary applications, ie office buildings.

So, while fuel cells are nice, they don't really buy us much in terms of reducing or dependency on oil. The bottom line is we need a new fuel source, one which is clean, cheap, dependable, and plentiful. The folks arguing for alternative fuels have yet to provide one which meets all of those needs. Solar conversion would be nice, but the efifciencies of solar cells makes the cost per kW prohibitive. Nuclear would work, but I don't see us exploring that path with any real enthusiasm. Hydroelectric would be nice, but unless we put turbines on every creek and waterfall, there just isn't enough to go around.

Assuming that we do crack the provlem of a cheap energy source, there is still the problem of distribution of the hydrogen. Either we lay hundreds of thousands of miles of pipes, or we transport the hydrogen via tankers, with the attendant risk of explosions. Since hydrogen production needs an abundant source of water, we can't spread out our power plants like we do now. Nor can each house have it's own fuel generation station, like some dreamers have proposed. I see another hand in the back...

"Why can't every house have a solar converter, hooked to a fuel cell for it's main power supply?"

You haven't been paying attention. This is the same ring around the rosie we dismissed earlier. OK, hook solar panels on your roof to a fuel cell in your basement. Use the solar energy to produce the electricity needed to crack the water into hydrogen and oxygen. Then oxidize the hydrogen in your fuel cell, and where are you? Even further behind than when you started. You converted sunlight into electricity(minus efficiency and thermo losses) then spent that electricity(minus efficiency and thermo losses) to crack the water, then got back the same energy during oxidation, minus efficiency and thermodynamic losses. You'd be better off skipping the fuel cell, and using simple solar conversion. Fewer losses that way.

Now as mentioned above, a solar/fuel cell combo makes an excellent back up power supply for a building. It's much cleaner, more efficient and significantly cheaper than batteries. However, it still comes up short as a primary power source.

So, what have we learned today?

Fuel cells run on hydrogen which does not exist in large reserves like oil, but must be manufactured.
Hydrogen is tricky to work with and tends to explode at the worst possible time.
Fuel cells, like every heat engine, consume more power than they put out.
Fuel cells alone will not reduce our dependence on foreign oil. In fact, it will increase it in the short run.
We still have to develop some alternative to oil power in order to make fuel cells a viable alternative to the IC engine.

And I have entirely too much time on my hands.....

Posted by Rich at November 14, 2002 5:37 PM