JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III NONCONVENTIONAL POWER GENERATION Previous Question Paper (August - 2022 - R16)

A Pyranometer is an instrument used to measure total solar radiation, including both direct beam and diffuse sky radiation, on a horizontal surface. It consists of a thermopile sensor protected by a glass dome.

Working Principle: The sensor surface is coated with a black absorbing material. When solar radiation hits the sensor, it absorbs the energy and converts it into heat. This creates a temperature difference between the hot junctions (exposed to radiation) and the cold junctions (shielded or in thermal contact with the body of the instrument). According to the Seebeck effect, this temperature gradient generates a small electromotive force (voltage) proportional to the intensity of the incident solar radiation. This voltage is measured by a data logger or voltmeter and calibrated to represent the irradiance in Watts per square meter (W/m²).

Sketch description: The device features a hemispherical glass dome that allows solar radiation to pass while protecting the sensor from wind and weather. Beneath this is the black-coated thermopile sensor mounted on a base, with electrical terminals connected to a recording device.

i) Altitude angle: The angle between the sun's rays and the horizontal plane on the earth's surface.

ii) Incident angle: The angle between the sun's rays and the normal (perpendicular line) to the surface of a solar collector.

iii) Zenith angle: The angle between the sun's rays and the vertical (normal) to the horizontal plane on the earth's surface. It is the complement of the altitude angle.