JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III NON-CONVENTIONAL ENERGY SOURCES Previous Question Paper (August - 2022 - R18)

Solar radiation is classified based on its interaction with the Earth's atmosphere. Extraterrestrial radiation is the solar radiation received at the outer edge of the Earth's atmosphere. It is characterized by a nearly constant intensity known as the solar constant, approximately 1367 W/m², and consists of a spectrum ranging from ultraviolet to infrared. Because there is no atmosphere to scatter or absorb the rays, the intensity is independent of weather conditions or time of day, varying only slightly due to the Earth's elliptical orbit around the sun.

Terrestrial radiation is the radiation that reaches the Earth's surface after passing through the atmosphere. During this transit, the radiation is significantly altered by absorption (by ozone, water vapor, and carbon dioxide) and scattering (by dust and air molecules). Consequently, terrestrial radiation is composed of two components: beam radiation (direct radiation received from the sun without scattering) and diffuse radiation (scattered radiation reaching the surface from all parts of the sky). The total terrestrial radiation is the sum of these two components, and its intensity is significantly lower than extraterrestrial radiation, varying based on geographical location, atmospheric clarity, and cloud cover.

Instruments used to measure solar radiation are broadly classified into two categories: pyranometers, which measure total (beam plus diffuse) solar radiation on a horizontal surface, and pyrheliometers, which measure only the direct beam radiation at normal incidence. Additionally, sunshine recorders are used to measure the duration of bright sunshine.

The Campbell-Stokes sunshine recorder is the standard instrument for measuring sunshine duration. It consists of a solid glass sphere mounted in a metallic bowl. The sphere acts as a lens, focusing the sun's rays onto a specially treated card held in a groove in the bowl. As the sun moves, the focused beam burns a trace on the card. The length of the charred track corresponds to the duration of bright sunshine. The bowl is adjustable for different latitudes to ensure the focal point remains on the card throughout the year. The total length of the burnt portions on the card, calibrated against time markings, provides the total hours of bright sunshine for the day.