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 that uses optical elements, such as mirrors or lenses, to focus solar radiation from a large aperture area onto a smaller receiver area. By increasing the flux density of solar energy, it achieves significantly higher temperatures than flat-plate collectors, making it suitable for power generation.

The working principle involves two main components: the reflector (concentrator) and the receiver. The reflector captures direct beam radiation over a wide area and reflects it toward a focal point or line. The receiver, which contains a heat transfer fluid, is placed at this focus to absorb the concentrated energy. The concentration ratio is defined as the ratio of the aperture area to the receiver area. Common types include parabolic troughs, parabolic dishes, and central receivers (heliostats).

Sketch Description: The sketch should show a parabolic reflective surface with parallel incident solar rays striking the surface and converging at a single point or line where a pipe (receiver) is located. The receiver pipe carries the working fluid, which gains thermal energy as it passes through the high-intensity focal zone.

Solar radiation incident on a tilted surface differs from that on a horizontal surface because the angle of incidence changes the effective aperture area and the intensity of the intercepted rays. The total radiation on a tilted surface is the sum of beam, diffuse, and reflected components.

The beam radiation on a tilted surface is calculated by multiplying the beam radiation on a horizontal surface by a geometric factor, R_b, which is the ratio of the cosine of the angle of incidence on the tilted surface to the cosine of the zenith angle. The formula is:

Where θ is the angle of incidence and θ_z is the zenith angle. As the tilt angle increases, the surface may become more perpendicular to the sun's rays during specific seasons, increasing the beam component. However, the diffuse radiation component is affected by the view factor between the surface and the sky, typically modeled using the isotropic sky assumption, which reduces the diffuse contribution as the tilt increases. Additionally, the reflected component from the ground increases with the tilt angle, depending on the ground albedo. Proper orientation and tilt angle optimization are essential to maximize the annual energy collection for specific geographical locations.