Operation and Control of Renewable Energy Systems

Chapter 5Solar Energy Systems

5.1 Sun as Source of Energy

Solar energy is available directly from the energy produced by the Sun and is used to produce electricity, heat and light in solar energy systems. The Sun gets its energy from the nuclear fusion occurring in its core by converting millions of tons of hydrogen into helium and converting the difference in mass into energy. The Sun is a sphere of diameter 1,400,000 km, and because of nuclear fusion in its core, its outer region comprises hot gases mostly hydrogen and helium and has a surface temperature of 600 K. These gases are confined to the Sun due to the gravitational forces acting on the Sun. At this temperature, the Sun radiates the heat and light which travels through space and reaches the Earth. The rate of energy radiated from the Sun is 3.8 × 10²³ kW. The energy received by the Earth's atmosphere is at an annual average rate of about 1.3–1.4 kW/m². Out of this energy received, a fraction is reflected by the atmosphere to the space. Still it is estimated that the maximum influx at the Earth's surface is about 1 kW/m². This amount is so large that at present rate of consumption, the total energy received in 1 h is sufficient to provide energy to the whole world for 1 year. But the problem is that not all the energy received from the Sun can be effectively used because it is thinly spread. In addition, the amount of solar energy which can be used is limited by diurnal and geographic variations and weather conditions. ...