Hydrogen as a Fuel

I started this blog for the purpose of collecting and evaluating opinions about the future roles hydrogen might play in the global energy economy.

Basics first.

Energy density

Hydrogen is one of a number of forms in which energy can be stored. Practical alternatives to hydrogen include gasoline, propane, natural gas aka methane (in either liquid or compressed form), and batteries. Less practical alternatives include TNT, dynamite, and C-4, which can store a great deal of energy that is however hard to release at a usable rate.

The hydrogen atom consists of one proton and one electron. This makes it by far the lightest of all elements in the periodic table, so light in fact as to make comparisons of gravimetric (by-weight) energy density meaningless.  Hence I’ll stick to volumetric energy, in units of megajoules per liter (MJ/L).

To make hydrogen storage practical it needs to be compressed, typically to a pressure between 35 and 70 MPa (5,000 to 10,000 psi). The latter is standard for the so-called hydrogen highway and is therefore what I’ll assume here.

The first five entries in the following table are from Wikipedia

Coal 35 MJ/L
Gasoline 32.4 MJ/L
Propane 25.3 MJ/L
Wood 13 MJ/L
Hydrogen 5.6 MJ/L
Panasonic NCR18650B battery 2.56 MJ/L (6800 of these cells used in the Tesla Model S)
Tesla Model S battery 0.77 MJ/L (based on 85 kWh/(84″x48″x6″))
Tesla 400 kWh battery 0.22 MJ/L.
Tesla 10 kWh Powerwall 0.18 MJ/L
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