JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Tech III Year NON-CONVENTIONAL POWER GENERATION Previous Question Paper (October - 2020 - R16)

A concentrated collector is a solar thermal device designed to increase the intensity of solar radiation on a receiver by using optical elements such as mirrors or lenses. The working principle involves collecting solar energy over a large aperture area and focusing it onto a significantly smaller absorber area, which increases the flux density and allows for the attainment of much higher temperatures compared to flat-plate collectors.

The system consists of a reflector (parabolic or cylindrical mirror) that tracks the sun, a receiver (absorber tube) placed at the focal point, and a heat transfer fluid circulating through the receiver. As parallel solar rays strike the curved surface of the reflector, they are reflected and converged at the focal line or point. The concentrated energy heats the fluid flowing through the receiver to high temperatures, which is then used for power generation or industrial processes. The concentration ratio is defined as the ratio of the aperture area to the absorber area.

The solar radiation received on a tilted surface differs from that on a horizontal surface because the angle of incidence of the sun's rays changes with the tilt angle and orientation. The total solar radiation on a tilted surface is the sum of three components: beam radiation, diffuse radiation, and reflected radiation from the ground.

The beam radiation on a tilted surface is calculated by multiplying the beam radiation on a horizontal surface by the ratio of the cosine of the angle of incidence on the tilted surface to the cosine of the zenith angle. As the tilt angle increases toward the equator, the surface becomes more perpendicular to the sun's rays, generally increasing the beam component during winter months.

The diffuse component is influenced by the view factor between the surface and the sky. A surface tilted at an angle beta sees less of the sky than a horizontal surface, reducing the diffuse radiation received from the sky dome. Conversely, the reflected component accounts for the radiation reflected from the ground onto the tilted surface, which increases as the tilt angle increases, depending on the ground albedo. Optimal tilt angles are typically chosen based on the latitude and the seasonal requirements of the application to maximize the annual or seasonal solar energy collection.