Solar Insolation





Solar Radiation


Solar Declination Angle

Dec. 21/22

Jun. 21/22
The earth is a sphere (360o) that rotates 15o with respect to the sun each hour. During the day rotation causes the sun to rise and set in the sky. Each hour the angle (H) that the solar radiation is striking the surface changes. These changes in solar radiation contribute to cyclic daily changes in weather.

Hour Angle
The Zenith Angle (Z) is the angle from the observers zenith point to the suns’ position in the sky. In order to calculate the zenith angle latitude, solar declination angle and hour angle must be considered.

Zenith Angle
The solar constant is the average amount of energy striking one square meter (perpendicular to the suns’ rays) each second at the top of the earths’ atmosphere. The satellite measured solar constant is 1366 W/m2. Of this energy reaching the top of the atmosphere as much as 70% can be absorbed & reflected by the atmosphere. Solar insolation is the amount of energy received by the sun at the earths’ surface. On a clear day ~1000 W/m2 reaches a surface perpendicular to the incoming radiation. This energy varies due to the angle of the incoming radiation and again cloud cover.