Bunker Mulligan "Let us endeavor so to live that when we come to die even the undertaker will be sorry." ~Mark Twain

August 17, 2004

Fuel Cells

Filed under: Engineering — Bunker @ 1:12 pm

I know, they are the answer to our quest for renewable free energy that won’t pollute the planet. A new announcement that the technology is maturing takes the world by storm. SDB often answers these issues, but he is taking a pass because he’s tired of hearing about the new revolution. I can’t speak of the technology the researchers are studying, but the implication is that they are some form of exotic battery. I guess the term “fuel cell” is key to getting research grants.

Some of you children out there are too young to remember when nuclear energy was going to produce free electricity for everyone in the US. Checked your electric bill lately? Nuclear energy is relatively cheap, but the regulation and safety requirements drive the cost up. And the fact that we aren’t going to build any with new technology any time soon means that source is going away. And quickly.

Okay, students. Where do we get hydrogen for these fuel cells? There, in the back. No, it doesn’t grow on trees. Next? No, it doesn’t come out of a faucet. And you? Correct! It comes from water!

Ah, but a water molecule is a combination of hydrogen and oxygen atoms. When a fuel cell uses hydrogen to create energy, it does this by burning the hydrogen in an oxygen environment. The byproduct is water.

Where did that energy come from? Well, there are all kinds of energy in the world–chemical, potential, kinetic, electrical, thermal. The energy in hydrogen is chemical, converted to thermal, then to electrical. Once used, it has no more energy to offer. It has joined with another little hydrogen atom and a larger oxygen atom to become water.

Wow, you say. That’s a great cycle! We start with water, get some electricity, and end up with water again. Can’t get any cleaner or cheaper than that!

Ah, but somehow the water must first be converted to hydrogen and oxygen so that the fuel cell can recombine them back into water while generating the heat energy we need. There must be an energy balance. Energy out equals energy in minus inefficiency. So, in a perfect fuel cell, the energy inherent to the hydrogen is perfectly converted to electricity. Well, except for the energy absorbed in the recombination process. So, I guess there never can be a perfect fuel cell.

I’ve walked all around the real issue trying not to state what is obvious to engineers, and what should be obvious to others. Maybe I should point it out to those of you without any technical background. Some form of energy must be used to convert the water molecules to hydrogen and oxygen atoms Our energy balance comes into play once again. Energy out (hydrogen) equals energy in (power required to split the water molecule into hydrogen and oxygen atoms) minus inefficiency. Perhaps we’ll use electricity to do the converting. If both processes are absolutely perfect, we will create enough electricity in the whole process to equal the amount of electricity we used to create the hydrogen in the first place. No net gain. We burned oil or coal to create electricity to create hydrogen to create clean electricity.

Let me help you understand this in another way. If I want to heat water, is it more efficient to light a gas fire under a pot or set it on an electric range? The gas flame directly heats the water. Electricity must be created by first heating water into steam, using the energy in that steam to drive a turbine which rotates a generator to produce electricity. That electrical energy is then transported by wire to your house where it is converted to thermal energy to heat the water. That’s heating water to heat water. Kinda like using electricity to create electricity.

Fuel cells serve a very specific purpose. Space travel. They provide electricity with drinking water as a byproduct. Cost is not the issue in space travel. Size and weight are.

Fuel cells are not an alternate energy source.


  1. Whenever I see these stories about some great new source of energy, I always feel a tinge of worry: do these people know something that I don’t know, something that justifies all their excitement?

    I long for the day when the answer to that question might be yes, but so far the answer has always been no: you cannot “create” energy (somebody ought to put this in a law form; maybe they could give it a catchy name like, say, The First Law of Thermodynamics).

    Too bad most journalists never took hard science. A guy in a labcoat could tell them that he can run cars on human excrement and they’d believe every word.

    Comment by John Rogers — August 17, 2004 @ 1:59 pm

  2. Remember the stories about fuel cells powering everything from our homes and cars to pocket flashlights? I liked the idea of non-polluting energry until I wondered where all of the Hydrogen comes from. The amount of electricity used to create Hydrogen is huge.

    Well at least we have solar and wind power. Oh, wait. To get the amount of energy equivalent to what one gas station contains in fossil fuels would required windmills and solar cells covering the state of New Jersey.

    If the eco-idiots and the media-morons had their way, we would all be driving horse drawn carriages, reading by candle light, and warming our houses with peat fires.

    If only we could find a way to harness energy from idiocy. It’s limitless and self generating.

    Comment by Cerberus — August 17, 2004 @ 10:46 pm

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