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

Solar radiation is the electromagnetic energy emitted by the sun, primarily in the form of ultraviolet, visible, and infrared light. When this radiation enters the Earth's atmosphere, it undergoes several physical phenomena:

• Absorption: Atmospheric gases like ozone, water vapor, and carbon dioxide absorb specific wavelengths of solar radiation, converting them into heat. Ozone absorbs most ultraviolet radiation, while water vapor and carbon dioxide absorb infrared radiation.
• Scattering: As radiation hits air molecules, dust, and aerosols, it is redirected in various directions. Rayleigh scattering occurs with small particles (like air molecules) and is wavelength-dependent, while Mie scattering occurs with larger particles (like dust and water droplets) and is less wavelength-dependent.
• Reflection: Radiation is reflected back into space by clouds and the Earth's surface. The fraction of reflected radiation is known as the albedo.
• Transmission: The portion of radiation that passes through the atmosphere without being absorbed or scattered reaches the Earth's surface as direct radiation.

Solar radiation reaching the surface is categorized into beam (direct) and diffuse radiation. The total solar radiation on a horizontal surface (I) is the sum of these components.

Beam Radiation (I_b): This is the radiation received from the sun without having been scattered by the atmosphere. It follows a direct line from the solar disc. If I_o is the extraterrestrial radiation and θ is the angle of incidence, the beam radiation on a tilted surface is given by:

where τ_b is the atmospheric transmittance for beam radiation.

Diffuse Radiation (I_d): This is the radiation received from the sun after its direction has been changed by scattering in the atmosphere. It comes from all parts of the sky. The diffuse component on a horizontal surface is often modeled using the diffuse fraction (k) of the total global radiation (I_g):

For a tilted surface with a tilt angle β, the diffuse radiation (I_d,t) is typically estimated using the isotropic sky model:

This assumes the sky is a uniform source of diffuse radiation.