Characteristics of solar radiation

TLDR: The solar constant is defined as the energy received from the sun on unit area exposed normally to the sun's rays at the average sun-earth distance in the absence of the earth's atmosphere as mentioned in this paper.

Abstract: Publisher Summary This chapter discusses the characteristics of solar radiation. The most important parameter in the survey of solar radiation measurement is the energy received outside the earth's atmosphere. This parameter has a degree of constancy when compared to that received on the ground. Therefore, it is called the solar constant. It is defined as the energy received from the sun on unit area exposed normally to the sun's rays at the average sun–earth distance in the absence of the earth's atmosphere. The 1970 ISES Congress in Melbourne accepted the value of 1353 W/m 2 for the solar constant with an error of about ± 1.5%. The variability of solar energy incident on a collector surface on the ground is considerably greater than that of the extraterrestrial solar energy. On a clear sunshine day, the energy increases from zero at sunrise to a maximum at solar noon and decreases to zero at sunset. At any moment, clouds may intercept the sun and decrease the energy to a low value because of the diffuse radiation.