The big problem is big numbers. The world uses some 320 billion kilowatt-hours of energy a day. It's equal to about 22 bulbs burning nonstop for every person on the planet. No wonder the sparkle is seen from space. Hoffert's team estimates that within the next century humanity could use three times that much. Fossil fuels have met the growing demand because they pack millions of years of the sun's energy into a compact form, but we will not find their like again.