CHAPTER 2 - SOLAR RADIATION

Abstract

This chapter provides an overview on solar radiation. The availability of solar energy in any location in the world can be studied by two methods. The first involves measurements from a radiation monitoring network and the second is based on the use of physical formulae and constants. Solar constant is a term used to define the rate at which solar radiation is received outside the earth's atmosphere, at the earth's mean distance from the sun, by a unit surface perpendicular to the solar beam. The spectral distribution of direct solar radiation is altered as it passes through the atmosphere by absorption and scattering. The amount of energy absorbed depends on the length of path in which the solar beam traverses. A common method of describing relative energy levels is the air mass, which is the ratio of the actual length the solar beam traverses relative to the depth of the atmosphere with the sun in its zenith position. The chapter also highlights the data from a radiation measurement network. It is difficult to obtain reliable solar radiation data. The most reliable data is associated with the main meteorological stations, but these are often widely dispersed and a considerable distance from the location of any potential application.