Most human beings equate the concept of energy with the payment of electricity and gas bills or the possibility of disruption to petroleum supplies by world conflict. Before having any knowledge of physics and chemistry, I used to think of energy in terms of other simplistic relationships. For instance, my first observations related to energy came from how plants grow. Anybody can see that plants can’t grow without exposure to sunlight. Now, it is clear to me that plants obtain the energy from the Sun to carry out the photosynthesis, which is probably the most important biological process on Earth.

        Although plants draw necessary materials from the soil and water and carbon dioxide from the air, the energy needs of the plant are filled by sunlight. In the photosynthesis process, plants change the energy in sunlight to kinds of energy that can be stored for later use by synthesizing foodstuffs. When we eat an apple, for example, the chemical substances in it react in our body and another important change occurs – energy is released. The food we eat is the fuel that our body uses to operate our muscles and to maintain proper body temperature. Thus, humans and animals use sunlight indirectly by eating the plants and other animals to survive. The plant kingdom also provides many of our needs for fibers and building materials as well as wood for fuel. Solar energy is also needed for flowing winds and water. Therefore, all the necessities in life of all organisms on earth including human beings should be met, in principle, by utilizing the available energy of the sun. Unfortunately, things are not quite so simple.

        It is true that our planet is powered, almost exclusively, by electromagnetic energy that originates from the Sun. The electromagnetic energy from the Sun that reaches the surface of the Earth is available to perform work. At this point the original energy undergoes a complex series of transformations into a series of other natural energy forms, including thermal energy. As in the process of photosynthesis, this energy from the sun is continually being used to drive the material cycle and by so doing is able to sustain and create more complex and organized materials, and possibly life itself. So, we have two sources of the ultimate natural resource, the solar and the terrestrial, and our dependence has shifted from the former toward the latter. We are no longer content to rely on natural energy resources (solar power) but consume vast quantities of fossil fuel, for example, in our quest to sustain life. One of the reason for this has been the rapid grow of the population. On the other hand, as mankind understood the laws that govern the interconversion between heat and work (See Laws of Thermodynamics) and knew about the benefits of it, new energy sources and forms became important. An obvious example of this is the electricity. Along with the benefits to our society, the use of fossil fuels has unleashed a series of problems, probably comparable to its benefits.

        Fossil fuels have been a tremendous source of stored energy, but can carry us only so far into the future. Without the convenience of fossil fuels, we can only sustain ourselves by drawing on an infinite, or renewable, energy source. Given current technology that means learning to harness the power of the Sun.

        The initial assumption about energy related to the Sun turns out to be not so simplistic after all. Indeed, Sun's radiation is and will be very important for life on Earth not only for the natural ability of the Biosphere to effectively extract energy from it, but also for the prospects of becoming the ultimate resource to power our societies.