Former US president Bill Clinton speaks at 'The National Clean Energy Summit' at the Cox Pavillion in Las Vegas, Nevada - (08/18/08).

"Energy is at the heart of the three greatest challenges U.S. faces today," Clinton said.

"Cost for ordinary Americans are soaring for energy, for food, for healthcare. Increasingly they have financed those costs with flats waged through debt which has contributed, we all know, to the home mortgage crisis and many other debt crunches I think are still going to come at us in waves over the next couple of years."