The economic growth in many parts of the world during the past decade was sustainable because of affordable energy prices. The dependence on oil and electricity has made energy a vital component of our energy needs. In the 20th century, the population quadrupled, and our energy demand increased by 16 times. The exponential energy demand is exhaust ing our fossil fuel supply at an alarming rate. About 13 terawatts (TW) of energy is currently needed to sustain the lifestyle of 6.5 billion people worldwide. By the year 2050, we will need an additional 10 TW of clean energy to maintain
the current lifestyle [1]. To achieve this