[pgfpro]

Here is part of a paragraph from the Grolier Encyclopedia:
Electrolysis is an energy-consuming process. To obtain 2 grams of hydrogen and 16 grams of oxygen by the electrolysis of 18 grams of water, the equivalent of 68,300 calories of electrical energy must be supplied. This same quantity of energy, however, can then be recovered from the hydrogen and oxygen, either suddenly in an explosion or slowly if they are brought together in a FUEL CELL.
Two grams of Hydrogen is only 1/227 pound, so the electrical energy actually required to produce a pound of Hydrogen is therefore 68,300 * 227 or 15,500,000 calories of electrical energy! This can be converted into 18,000 watt-hours or 18 kWh. As noted below, the existing technologies to create Hydrogen by electrolysis are all around 20% efficient, which means that around 100 kWh of electricity is used up to produce a single pound of Hydrogen gas. If a house's current 15-cent per kilowatt of electricity is used, that therefore would require at least $15 of house electricity to be used up to create that single pound of hydrogen gas! We will see below that one pound of hydrogen gas contains just under half of the chemical energy of a single gallon of gasoline, so, even if everything else was perfect, more than $30 of modern house electricity would be required to simply PRODUCE an equivalent amount of Hydrogen gas to one gallon of gasoline! And then that gas would have to be ferociously compressed and all the rest.


We can say this same thing in terms of "gallons". A gallon of gasoline contains around 6 pounds, and has 126,000 Btus of energy in it. A "gallon" of hydrogen (gas) only contains around 40 Btus in it. Quite a difference! Instead of a two cubic foot gasoline tank (15 gallons) in your car, you would need a tank more than 3,000 times bigger, over 6,000 cubic feet, for the equivalent Hydrogen! That's a little more than TWO standard semi trailers (8'wide x 8'high x 45' long or 2900 cubic feet each). Pretty big gas tank!