Hydrogen is not an energy source but an energy carrier, which means that its potential role has similarities with that of electricity. Both hydrogen and electricity can be produced by various energy sources and technologies. Both are versatile and can be used in many different applications. No greenhouse gases, particulates, sulphur oxides or ground level ozone are produced from the use of either hydrogen or electricity. If the hydrogen is used in a fuel cell, it emits nothing but water.

     Hydrogen contains more energy per unit of mass than natural gas or gasoline, making it attractive as a transport fuel. However, hydrogen is the lightest element and so has a low energy density per unit of volume.