There’s an interesting reason why hydrogen fuel cells could be a better power source for vehicles than lithium-ion batteries and it’s rooted in basic physics. Hydrogen has a far greater energy density or unity per volume than lithium-ion batteries.
Energy density is the amount of potential power stored in a particular area. It’s also the big drawback to lithium ion batteries. A present generation rechargeable lithium-ion battery has an energy density of .9-2.63 mega joules per kilogram. That means each kilogram of lithium ion battery is capable of storing around .252 to .7364 kilowatt hours of electricity.
That’s why present generation electric cars are so heavy. They have to carry several hundred kilograms of lithium ion batteries in order to stay on the road. It also shows us why auto industry people like Toyota’s chief of automotive operations Bob Carter are so enthusiastic about hydrogen fuel cells.
Fuel Cells have a Greater Energy Density than Lithium Ion
Such fuel cells use a chemical reaction to turn hydrogen gas directly into electricity. That eliminates combustion which eliminates pollution. Instead of greenhouse gases, a fuel cell vehicle (FCV) puts out a cloud of water vapor which makes this a green technology (at least on a local level).
They also run on a fuel that theoretically has a greater energy density than lithium ion batteries. A liter of compressed hydrogen gas has an energy density of 5.6 mega joules the equivalent of 1.568 kilowatt hours of electricity. It should be noted here that at least some of this power might be lost in the process the fuel cell uses to generate electricity so real world power levels might be less. Although theoretically fuel cells might deliver more power because they are more efficient than engines.
It also brings us to the big problem facing non-internal combustion engine vehicles which is what both fuel cells and lithium ion powered vehicles are. These power sources simply deliver far less energy density than fossil fuels.
Fuel cells are also far more efficient than engines at least on paper. A hydrogen fuel cell is around 80% efficient that means it uses around 80% of the energy it produces. A present generation gasoline engine in contrast is around 30% efficient.
Gasoline and Diesel are still better fuels than Hydrogen or Lithium-Ion
Gasoline and diesel fuel each have an energy density of 36 mega joules a liter – the equivalent of 10.08 kilowatt hours. That means a few gallons or liters of gasoline or diesel fuel can provide as much or more power than several hundred pounds of lithium ion batteries. It also means that a few gallons of gasoline or diesel fuel will provide as much power as 20 or 30 gallons of hydrogen gas.
The energy density of gasoline explains why your old Toyota Corolla can run a lot farther on a tank of petrol than your neighbor’s shiny new Tesla can run on a charge. Petroleum products are simply a far superior source of energy to present generation batteries.
Compressed natural gas or propane also offers a lot more energy density than hydrogen gas or lithium ion batteries. A liter of compressed natural gas or propane offers an energy density of 26 mega joules – the equivalent of 7.28 kilowatt hours of electricity. That means a dozen gallons of natural gas or propane will deliver as much power as several hundred pounds of lithium ion batteries or 30 or 40 gallons of hydrogen gas.
Natural gas and propane powered cars and trucks present a real challenge to electrics and fuel cell vehicles because those fuels offer less pollution with higher energy density. Elon Musk has recognized this part of the reason why he’s going deep into debt to build Tesla’s Giga Factory is to increase the energy density of his vehicles.
Fuel Cells Need more Energy Density
The energy density figures make one thing very clear, if electric cars or fuel cell driven vehicles are ever to become a serious alternative to gasoline, diesel or gas powered automobiles their energy density will have to be greatly increased.
One solution might be to create fuel cells that run off of a more energy dense fuel such as gasoline, natural gas or diesel fuel. Researchers at the University of Maryland’s Energy Research Center are working on a gasoline-powered fuel cell designed to be used in cars. That could create a non-polluting gasoline powered car. The current plan is to use it in hybrids but if it works the technology could simply be adapted for a straight FCV an electric drive car that runs on electricity made from gasoline.
There’s another big advantage to gasoline powered fuel cells, a driver could fill the tank of a gasoline powered FCV at any existing gas pump. That means no special infrastructure would have to be built for them. Current estimates are that it will cost $4 to $5 million to build special filling stations for hydrogen FCV cars.
Another solution would be to use natural gas or propane powered fuel cells. Those too could fill up at existing stations or in the case of natural gas powered vehicles from the natural gas line that already runs into most American and Canadian homes.
The bottom line is that both fuel cell powered vehicles and electric vehicles are going to need a lot of improvement before they reach the average driveway. If they cannot deliver a respectable level of energy density they’ll never be anything but toys for wealthy eco geeks.