This page last updated on 01/26/2019.

Copyright © 2001-2019 by Russ Meyer

Tonight I read an article on Bush's proposal for hydrogen powered cars.  The scientific ignorance of the article is breathtaking.  It tends to cast the issues in a political light.  That is a tedious trend in mainstream media when they attempt to articulate scientific and technical issues.  It's like, "We know hydrogen powered cars are being held down by Bush and his oilman cronies!"  Yeah, right...gee, do ya think basic science and economics might have something to do with it...naaahhhh, couldn't be!

A Few Opening Remarks

The purpose of this article is to compare the efficiency of a hydrogen powered car to a conventional gasoline powered car.  However, before getting started, I'd like to devote a few paragraphs to combating some hideous misconceptions promulgated by the technologically ignorant media.

I frequently hear politicians, homemakers, even fellow engineers extolling hydrogen power as the savior of the modern world.  The truth is, there is no such thing as "hydrogen power."  Hydrogen is an energy storage medium.  It does not generate energy.  The energy stored in hydrogen has to come from somewhere else.  You cannot just go out and mine hydrogen, process it, and put it in your car.  Hydrogen has to be produced somehow.  For example, most people are familiar with the production of hydrogen by electrolysis of water.  It's true that the hydrogen itself came from the water, but it took electrical energy to break the chemical bond it had with oxygen.  A fraction of the electrical energy used to conduct the electrolysis has become locked as potential energy in the chemical configuration of gaseous hydrogen and oxygen.  When you burn that hydrogen, you are recombining it with oxygen and extracting that fraction of stored energy.  So, hydrogen is not a source of energy...it's just a way to store energy for a while; like a battery.  The energy in hydrogen has to come from somewhere else.

Now that I've made that point so emphatically, let me take it right back.  Actually, we can and do "mine" hydrogen.  Know how?  By mining coal, pumping oil, and piping natural gas.  These are substances that contain stored solar energy in chemical configurations, namely hydrogenated carbon compounds, through the metabolic action of plants.  In a sense, it's just like hydrogen that has been liberated from water via electrolysis.  A fraction of the energy of the sun has become locked up as potential energy in the chemical configuration of hydrocarbons.  These fossil fuels are just a storage medium for solar energy.  When burned, they release years of absorbed solar radiation in just a few minutes.

The point of all this is that hydrogen does not address energy needs in any way at all.  The only thing that can be said for hydrogen is that it provides a means to store and release energy that does not involve a carbon cycle.  In particular it avoids environmental problems with carbon monoxide and carbon dioxide.  Environmental concerns are the only possible justification for pursuing hydrogen vehicles.  Even if we could wave a magic wand and change every vehicle on the planet to use hydrogen, it wouldn't address the energy production problem.  How we choose to produce energy might still involve fossil fuels (like coal fired power plants) and the attendant carbon dioxide problem.  At the moment, the only known way to escape fossil fuels with present technology is nuclear fission.

If you were going to embark today on a crusade to stop most carbon dioxide emissions and simultaneously ensure the energy independence of the United States, there would be but one practical approach:

• Energy Storage - batteries, hydrogen, and perhaps a few synthetic hydrocarbon compounds for specialized applications
• Energy Production - nuclear fission accompanied by a modicum of fossil fuels (again for special applications)

Maybe that is exactly the groundwork the Bush administration is laying now.

Now then...back to the main topic; how does the efficiency of a hydrogen powered vehicle compare to a gasoline powered vehicle?

Hydrogen Verses Gasoline

Let's find out how much energy it takes to make a trip in a gasoline powered car verses a hydrogen powered one.  First some assumptions; these assumptions basically fix the required amount of kinetic energy to make the trip:

• The cars travel the same distance over the same route.
• The cars weigh the same.
• The cars travel the same speed.
• The cars have the same rolling friction and aerodynamic drag characteristics.

  To calculate the amount of fuel energy needed to move the cars that distance, we'll make a few more assumptions:

• Conversion efficiency of gasoline to kinetic energy in a modern car engine is 25%.
• Conversion efficiency of electrical energy to kinetic energy in an electric motor is 65%.
• Conversion efficiency of hydrogen to electricity in a fuel cell is 50%.

Now let:

E_g = gasoline fuel energy needed to make the trip
E_h = hydrogen fuel energy needed to make the trip
E_k = total kinetic energy required for the trip

So, the fuel energy required by the gasoline car will be:

energy from fuel * gas engine efficiency = kinetic energy for trip

Expressed as an equation it would be:

E_g * 0.25 = E_k

The fuel energy required by the hydrogen powered car will be:

(energy from fuel * fuel cell efficiency) * electric motor efficiency = kinetic energy for trip

Expressed as an equation it would be:

(E_h * 0.50) * 0.65 = E_k            ...or in other words...
E_h * 0.33 = E_k

Since the cars need the same amount of kinetic energy to make the trip, E_k is the same for both.  We can use that to find the energy ratio between the two vehicles:

E_h * 0.33 = E_g * 0.25
(0.33/0.25) * E_h = E_g
1.3 * E_h = E_g

This means the gasoline powered vehicle will take about 30% more fuel energy to move the same distance as a hydrogen powered car.  The hydrogen powered car converts the fuel energy into kinetic energy in two steps, but the combined efficiency of those two steps is a bit greater than that of a gasoline engine.  The gasoline powered car converts fuel energy to kinetic energy in one step.  Here's a comparative graphic.  I tried to draw the width of the arrows to scale.  They show proportionally where the energy is going.

Energy Flow of a Gasoline Powered Vehicle - One Step Conversion

• The initial cost of the vehicle incurs a penalty since the associated technology is not yet mature.

• A big penalty will be incurred in the initial cost of the vehicle until the effects of mass production are felt.

• We don't really have an economical way to produce vast quantities of hydrogen fuel.  Using wind and solar power to do it is definitely not the way; at least economically speaking.  Cracking hydrogen from fossil fuels is attractive, but might result in consuming more fossil fuel than we are using today...it depends on the efficiency of the cracking process.  (By the way, the most efficient way known of producing hydrogen in quantity is mixing natural gas with high pressure steam.)  Liberating hydrogen from fossil fuels might create as much carbon dioxide waste as just burning the stuff in a regular gasoline engine...negating any hoped for environmental benefit.  Using nuclear power to liberate hydrogen by electrolysis of water is an excellent choice technically and economically, but has too much political baggage.  The technology can do it...all you'd have to do is decide you're not afraid of nuclear power.

• There is no infrastructure in place to distribute hydrogen fuel.  The present fossil fuel distribution system evolved over a hundred years and cost billions of (todays) dollars.  That cost was amortized over an entire century.  Trying to replace it would be a daunting economic proposition.

Many problems with hydrogen powered cars can be fixed by just using batteries instead of a hydrogen fuel cell.  Batteries are 80-90% efficient at storing and releasing energy compared with 50% for a fuel cell.  The only problem is that they weigh a lot and that detracts from the efficiency and utility of the vehicle.  Still, maybe it would make more sense to put effort into improving battery technology.  One objection to using batteries is that they take hours to charge.  Maybe you could use interchangeable battery packs.  You'd pull into a service station, swap out the whole battery pack, and get back on the road.  A more difficult problem with batteries is their energy density.  For the space they take up and how much they weigh, they don't provide much energy.  To drive a mini-van 350 miles at 60 mph using present state-of-the-art battery technology, all the space behind the two front seats would have to be packed with batteries.  What a bummer!  Gasoline cars handle this task with aplomb because the energy density of the fuel is so much better.

Check out this article on hydrogen powered cars.  It provides a good overview of the related technical and economic factors.  Also, for an excellent overview of the issue, take a look at this article.  Here is a fabulous, short video that does a thorough treatment of the efficiency issues for hydrogen powered cars.

Gee, I wonder why you don't see hydrogen fuel cell powered vehicles all over the road.  Must be a conspiracy between Bush and his oilman cronies.  Yeah right.  Uhhh...maybe it has more to do with the fact that it doesn't make any economic sense at all...do ya think?