"If you were to ask a layman which is the most important resource among food, energy and water, the answer is likely to be "food." As a matter of fact, humans can survive longer without food and energy than without water. However, humans depend on the sun as the primary source of energy that assures our survival on this planet. Furthermore, the civilized world is highly dependent on energy for comfortable living and mobility. This suggests that energy is a very important requirement. The fact is we need all of them and their interrelationship is discussed below (1)"--