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Why do manufacturers of cars focus on electric motors and not on hydrogen engines? originally appeared on Quora: the place to gain and share knowledge, empowering people to learn from others and better understand the world.
Answer by Steve Hench, Design of Renewable Energy and Hydrogen Production Systems, on Quora:
Hydrogen will be a great fuel for cars, and even more so for long-haul transport trucks (tractor-trailer rigs).
The real reason that Hydrogen (H2) is not much considered for engines has to do with the thermodynamic efficiency of engines vs. fuel cells.
1 gallon of gasoline has an energy content of about 130 MegaJoules (MJ).
1 kg of H2 is in the same range (130–140 MJ).
At first glance, it would appear that they are pretty much equal, except that H2 costs several dollars per kg just to produce ($4.50, according to the National Renewable Energy Laboratory), which must be done using renewable energy as the original power source if we are to get any real benefit from using the H2.
However, an internal combustion engine (ICE) running on gasoline (the Otto cycle) or Hydrogen operates at thermodynamic efficiency level of around 20–25%.
On the other hand, a fuel cell that converts H2 and Oxygen into electricity to feed an electric motor operates at an efficiency level of 60% or even greater. Gasoline (or diesel) cannot be used in a fuel cell.
Putting these facts together, we see that 1 kg of H2, used in a fuel cell to power an electric motor is equal to 2.5 to 3 gallons of gasoline, and even greater for urban driving conditions.
The result is that the fuel cost per mile is equal when the price (at the pump) for 1 kg of H2 is about 3 times that of 1 gallon of gasoline.
It also means that a vehicle that would have required a 20-gallon gas tank only needs a 7-kg H2 tank, or about 1/3 of a cubic meter in volume at a relatively low pressure of 250 bar.
Lots of people like to quote the “Hindenburg effect” for the dangers of H2. Actually, H2 is far safer than gasoline in many ways, and the Department of Transportation has approved a number of containers for use by consumer-operated vehicles. In fact, Toyota has introduced its first H2-powered car, the Mirai, into selected areas of the U.S., where they have also coordinated installation of H2 refueling stations.
Ergo, if you have arguments about safety, take it to them—they’ve done their homework.
Yesterday at my neighborhood gas station in Texas the price for unleaded premium was $2.90/gallon. The H2 equivalent price would be $8.60/kg. We can easily produce H2 with wind turbines and get it to the pump and beat that price.
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