What level of efficiency can be achieved?
Electricity is consumed to split water into hydrogen and oxygen.
This hydrogen is then used to generate electricity .
There is a net loss. How bad is it?
Imagine if all the cars in the world ran on hydrogen fuel cells. How many nuclear power pants would it take to produce the electricity to split the water to handle that kind of volume?
There are over 600 million motor vehicles in the world today. If present trends continue, the number of cars on Earth will double in the next 30 years. (
http://hypertextbook.com/facts/2001/...Stasenko.shtml)
To keep it simple, assume each vehicle is driven 15,000 miles each year.
Any electricity from the grid that is used to generate this hydrogen means that the equivalent electricity is not available for other purposes, like dvd players and televisions, unless more electrical generating plants are constructed (solar, hydro, dino oil, nucleur, wind, water, etc.)
Energy is never free.
On edit:
600 million cars, times 15 thousand miles per year, devided by 30 miles per gallon equals 300,000,000,000 gallons of gas per year.
Unless I did the math incorrectly.