7. Solar Energy

At an average rotational radius around the Sun of 1.49*10¹¹ m and with an average radius of 6,378 km, the planet Earth receives solar radiation power of approximately 1.73*10¹⁴ kW, a quantity that surpasses by far all the power requirements of the Earth’s inhabitants. This continuously received power, which is called incident solar radiation and shortened to insolation , integrates to a total energy of 5.46*10²¹ MJ per year, or more than 100 million times the total energy used by earthlings in a year. This tremendous amount of energy is abundant, free of charge, almost uniformly distributed and available to all nations and inhabitants of the planet. However, only a very small fraction of the incident solar radiation is used by the Earth’s population. Passive solar heating systems provide with space heating and hot water a low fraction of the buildings, primarily in OECD countries, while thermal solar power plants and photovoltaic cells provide a small fraction of the electricity consumed. Despite its low utilization at present, and because of the enormous amounts of power reaching the Earth, solar energy is a prime alternative energy source and has the potential to supply a very high fraction, if not all, of the power used by the Earth’s population. This chapter starts with a short exposition on the amount of solar energy available and continues with the exposition of the two main families of systems that are currently used for power production from solar energy: solar thermal systems and photovoltaic systems. Photovoltaic solar cells and solar thermal systems utilize the solar energy in entirely different ways and are examined separately. Emphasis is given on the electric power production by solar energy as well as the current and proposed systems used for electric power production. A brief mention of the passive heating systems and the environmental effects of solar energy utilization are also included in the chapter.