A recent online poll asked whether people should pay an additional tax to drive their gas guzzling vehicles – or as I call them, mini-tanks. The results showed that 60% thought it was a terrific idea that would “encourage the shift toward more efficient cars”. That got me thinking about hydrogen fuel cells and their touted efficiency and place as so-called green fuel-of-choice.
Then it hit me – hydrogen fuel cells are in fact not efficient or green when you consider their footprint over their life cycle (also known as “well to wheel” for cars). In fact, a careful analysis shows just the opposite—hydrogen fuel cells are far less efficient than conventional gasoline-based engines, and require much more energy to even make this hydrogen “usable”. Let’s see why…
Hydrogen does make an emission-less fuel cycle possible, but there’s a catch: hydrogen must be extracted from biomass or by electrolysis of water using …electricity! The statistics below are drawn from simple mathematical analysis using the known BTU of energy per barrel of oil, the energy needed to run a car, and process efficiencies for gasoline- and hydrogen-powered cars:
- Gasoline-powered cars in 2007 had an energy efficiency of about 25%, well to wheel.
- Hydrogen-powered cars, where the hydrogen is extracted by electrolysis, has an efficiency of about 12%–less than half that of gasoline-powered vehicles.
Why the pronounced difference? After all, isn’t hydrogen supposed to be a “green” fuel? In theory, hydrogen is a clean fuel. It’s the extraction of hydrogen that makes it dirty. Here’s why:
- Electrolysis, used to extract hydrogen, is a 70% efficient process.
- Within the fuel cell itself, some of that energy is converted into non-usable water vapour, and the potential energy yield drops by another 15%.
- The best fuel cell we have is also about 70% efficient, lowering the potential energy yield by another 30%.
- Because hydrogen is a gas, it takes up 3107 times the space of its gasoline equivalent. The energy needed in compressing it to fit in a tank is huge and further reduces the potential energy yield by another 27.4%
- The U.S. relies on its supply of coal and coal-fired stations, which run at only 40% efficiency, to produce the electricity needed to extract the hydrogen.
Taking all the factors into consideration, it takes twice the energy that was used for gasoline-powered cars and one third that of the entire energy consumption of the U.S. to produce the hydrogen used in cars. Not to mention the little fact of increased CO2 emissions of about 270% from the coal-powered plants to produce hydrogen.
Even if we were to scrap the coal-fired stations, and go for renewable resources to muster up the huge energy (think 1.53 trillion kwh) needed to fuel this hydrogen production “process”, we wouldn’t be able to achieve it. It would take the entire area of the U.S. covered with solar panels to make a dent in the amount of energy needed to produce hydrogen for its cars. In such high numbers, wind power and solar would show the carbon payback and GHG contribution from the manufacturing process to be counterproductive and extremely high.
So there you have it—half the efficiency of gasoline-powered cars, and much higher carbon footprint once life cycle considerations are taken into account. I guess it’s back to skateboards for everyone!
If you’re interested in reading a more in-depth analysis of the numbers presented above, the New Atlantic Journal of Technology & Society has a great article titled, The Hydrogen Hoax.