Solar Radiation Research Paper

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Chapter 1. Introduction to solar radiation

1.1 Introduction

As sun is an important source of energy, it is useful to study solar radiations that are emitted by the sun. There are both positive and negative effects of the solar radiation. Sun’s solar radiation spectrum resembles to black body with a temperature of 5800K. As distance between sun and earth is large, only a part of radiation reaches the earth’s surface.

1.2 Solar radiation

The electromagnetic radiations emitted by the sun are across most of the electromagnetic spectrum. Solar radiation includes ultraviolet, infrared, X-ray, visible light and radio waves. These radiations in increasing order of wavelengths are :-
• Ultraviolet C – The spectrum of Ultraviolet C is in the range
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1 AU = 1.496 × 1011 m. It includes all types of radiation. The value of solar constant as measured by the satellite was 1.3608 kW/m2 with a variation of 0.0005 kW/m2. The extraterrestrial flux on any day can be calculated by :- I’ext = Isc ( 1 + 0.0033 cos 360n/365 )

Where n is day of the year and Isc is known as solar illuminance constant whose magnitude is 128 × 103 lx. [2]*
Chapter 2. Solar radiation at the surface of the earth

2.1 Solar radiation at the earth’s surface

• The diameter of the sun is 1.39 × 106 km while that of the earth is 1.27 × 104 km. The mean distance between them is 1.49 ×108 km. Because of this large distance, the sun subtends a very small angle at the earth’s surface of about 32 minutes. Hence, the radiation received at the earth’s surface from the sun is almost
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The detectors which are used for solar radiation instrumentation are of four basic types 1) Photovoltaic 2) Thermoelectric 3) Thermomechanical 4) Calorimetric. Out of these, the first two detectors are most commonly used.

• Photoelectric detectors – Photoelectric detectors measure solar radiation by measuring short circuit current with the help of silicon solar cells. They are simple in construction and they do not require clear domes or convection suppressing devices. They are insensitive to tilt as output is not affected by natural convection. Its main disadvantage is that it cannot measure radiation with wavelengths greater than the band gap of photovoltaic detectors.

• Thermoelectric detectors – Thermoelectric detectors use a thermopile which consists of a series of thermocouple junctions. Thermopile generates a voltage proportional to the temperature difference between hot and cold junctions which in turn is proportional to the incident solar radiation. A radial differential thermopile is used in a pyranometer where hot junction is coated with velvet black and cold junction is coated with white barium sulphate
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