Solar 602m6g

Solar Radiation Measuring instruments

Classification 1.

Pyrheliometer: It is the solar radiation measuring instrument which collimates the radiation to determine the beam intensity as a function of incident angle. 1. 2. 3.

2.

Pyranometer: It is the solar radiation measuring instrument which measure the total hemispherical solar radiation. 1. 2. 3. 4. 5.

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3.

Angstrom Pyrheliometer Abbot Silver disc Pyrheliometer Eppley Pyrheliometer

Eppley Pyranometer Yellot Solarimeter (Photo Voltraic Solar Cell) Moll – Gorczyheski solarimeter Bimetallic Actiono graphs of Rabitzsch type Velochme pyranometer Thermoelectric pyranometer

Sun shine Recorder

Pyrheliometer   

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Measures Beam Radiation Sensor disc is located at the base of a tube whose axis is aligned with the direction of the sun’s rays. Diffused radiation is essentially blocked from the sensor surface. A collimator tube is installed over the sensor with circular cone angle 50 . Works on “Thermopile effect” Sun tracking system is necessary. Problems with instruments: 

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Imprecision in tracking mechanism Imprecision in measurement due to aperture angle and circular solar contributions

Eppley Pyreheliometer

Angstrom Compensation Pyrheliometer

Contd.. A thin blackened shaded manganin strip is heated electrically until it is at the same temp. as a similar strip which is exposed to solar radiation.  Thermocouples on the back of strips measure the temperature of the strips.  One strip exposed to the Sun.  One strip heated by an electric current until it is the same temperature as the strip exposed to the sun.  When balanced, the energy absorbed by strip from Sun is equal to the energy absorbed by strip from electric current.  Accuracy: ±1.0 to 1.5%  Energy H of direct radiation is calculated by means of formula HDN = Ki2 =R / Wα HDN = Direct radiation incident on a n area normal to sun’s rays R = resistance per unit length of the absorbing strip i = heating current in amperes, W = the mean width of absorbing strip, α = absorbing co – efficient of the absorbing strip 

Abbot Silver disk Pyrheliometer 

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Consists of a blackened silver disk positioned at the lower end of a tube with diaphragm to limit the whole aperture to 5.7 0 . A mercury in the glass thermometer is used to measure the temperature at the disk. A shutter made of three polished metal leaves is provided at the upper end of the tube to allow solar radiation to fall on the disk at regular intervals and the corresponding changes in temperature of disk are measured. A thermometer stem is bent through 90 so that it lies along the tube to minimize its exposure to the sun. Very good stability Widely used for calibrating pyranometer.

Eppley Pyrheliometer 

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Sensitive element is a temperature compensated 15 junction bismuth silver thermopile mounted at the base of a brass tube with limiting diaphragms of which subtend an angle of 5.7. The tube is filled with dry air and is sealed with a crystal quartz window which is removable. Stable instrument Used as a sub standard.

Pyranometer 

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Measures total or global radiation over a hemispheric field of view. If a shading ring is attached the beam radiation is prevented from falling on the instrument sensor. Sun radiation fall on black surface Cold junction is located in such a place where it doesn’t receive the radiation e.m.f. proportional to solar radiation is generated. + 2 % accuracy

Eppley pyranometer

Yellot Solarimeter ( Photovoltaic Solar Cell) 

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Silicon cell are used. Silicon solar cell have the property that their light current is a linear function of the incident solar radiation.

Sunshine Recorder 

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The duration of bright sunshine is measured by means of sunshine recorder. Sun’s rays are focused by a glass sphere to point in a card strip held in a groove in a spherical bowl mounted concentrically with the sphere. Whenever there is sunshine image formed is intense enough to burn the spot on the card strip. With the sun images moves along the strip during the day. Burnt space whose length is proportional to the duration of sunshine.

Sunshine recorder