Energy from the sun
Solar energy shares many of the advantages of hydropower and wind: there is no cost for the ‘fuel,’ it is certainly inexhaustible, and there is virtually no pollution. In addition, solar energy can be used in any area of abundant sunshine, whereas hydropower is restricted to sites with appropriate water sources, and wind is best in areas where wind blows often. Solar energy can be used by any country or any region, eliminating many of the geopolitical issues concerned with unevenly distributed resources such as petroleum. The sun’s energy derives from the conversion of mass to energy
according to Einstein’s equation,
E = mc2
introduced in Chapter 9. The mass loss associated with the nuclear processes in the sun amounts to about four million tonnes per second. Since c2 is itself a huge number, the energy production per second in the sun is so large that we have no way of translating it into our normal experience. The sun radiates this energy into all directions in space. Since Earth is a tiny ‘dot’ 150 million kilometers from the sun, the fraction of the sun’s energy hitting the Earth is only one two-billionth (1/2,000,000,000th!) of the sun’s total output.