Solar Radiation & Its Measurement-1

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SOLAR RADIATION & ITS SOLAR RADIATION & ITS MEASUREMENT MEASUREMENT CHAPTER 2 CHAPTER 2 BY BY DR.A.M.SURENDRA KUMAR DR.A.M.SURENDRA KUMAR 10/28/22 1 DR.A.M.SURENDRA KUMAR
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SOLAR RADIATION & ITS MEASUREMENT CHAPTER 2 BYDR.A.M.SURENDRA KUMAR 10/30/20121DR.A.M.SURENDRA KUMAR OUTLINE Properties of Radiations: Solar constantSolar Radiation at the Earths surface Sun at Zenith Solar Radiation Geometry Altitude angle Zenith Angle Solar Azimuth angle Local Solar time Solar Radiation measurement Pyranometer Pyrheliometer Estimationof Average solar Radiation Solar Radiation on Tilted surface 10/30/2012DR.A.M.SURENDRA KUMAR2 INTRODUCTION Solar energy -Received in the form of Radiation Converted Directly /indirectly- Heat& electricity. Drawbacks: 1. Intermittent& variable manner in which arrivesat the earths surface 2.Large area required to collect the energy Radiated as electromagnetic waves Electromagnetic waves- Wave length range from0.2 to 4.0 micrometer Consist of1. Ultraviolet radiation 8% 2. Visible light- 46% 3.Infrared Radiation -46% 10/30/2012DR.A.M.SURENDRA KUMAR3 10/30/2012DR.A.M.SURENDRA KUMAR4 SOLAR CONSTANT 10/30/2012DR.A.M.SURENDRA KUMAR5 SOLAR CONSTANT [Isc]The rate at which solar energy arrives at the top of the atmosphere. This is the amount of energy received in unit time on a unit area perpendicular to the suns direction at the mean distance of the earth from the sun. According to NASA ,Isc = 1353 W/m2 = 116.5langleys/hr. = 1165 kcal/m2/hr 10/30/2012DR.A.M.SURENDRA KUMAR6 Thedistance between the earth & the Sun varies a little through the year. Theearthisclosesttothesuninthesummerand farthest away in the winter. Thisvariationinthedistanceproducesanearlysinusoidalvariationintheintensityofsolarradiation,Ithat reaches the earth. This can be approximated by the equation where nis the day of the year 10/30/2012DR.A.M.SURENDRA KUMAR7 365nx360cos 0.033 1+ =scII 10/30/2012DR.A.M.SURENDRA KUMAR8 10/30/2012DR.A.M.SURENDRA KUMAR9 The air massAM= 1 when the sun is at the zenith i.e. directly over head (Sun at Zenith : Positionof the sun directly over head) AM =2when zenith angle is 600AM=sec when AM > 3 10/30/2012DR.A.M.SURENDRA KUMAR10 10/30/2012DR.A.M.SURENDRA KUMAR11 10/30/2012DR.A.M.SURENDRA KUMAR12 10/30/2012DR.A.M.SURENDRA KUMAR13 10/30/2012DR.A.M.SURENDRA KUMAR14 10/30/2012DR.A.M.SURENDRA KUMAR15 10/30/2012DR.A.M.SURENDRA KUMAR16 10/30/2012DR.A.M.SURENDRA KUMAR17 10/30/2012DR.A.M.SURENDRA KUMAR18 10/30/2012DR.A.M.SURENDRA KUMAR19 10/30/2012DR.A.M.SURENDRA KUMAR20 ZENITH ANGLE Z It is the complementary angle of suns altitude angle. It is a vertical angle between the suns rays and a line perpendicular to the horizontal plane through the point. i.e. the angle between the beam from the sun and the vertical. 10/30/2012DR.A.M.SURENDRA KUMAR21 =2tuZ 10/30/2012DR.A.M.SURENDRA KUMAR22 10/30/2012DR.A.M.SURENDRA KUMAR23 (Altitude angle) Azimuth angle(s) It isthe horizontal anglemeasured from north to the horizontal projection of the suns rays 10/30/2012 DR.A.M.SURENDRA KUMAR 25 10/30/2012DR.A.M.SURENDRA KUMAR26 10/30/2012DR.A.M.SURENDRA KUMAR27 10/30/2012DR.A.M.SURENDRA KUMAR28 10/30/2012DR.A.M.SURENDRA KUMAR29 LOCAL SOLAR TIME 10/30/2012DR.A.M.SURENDRA KUMAR30 TheLocalSolarTime(LST)isbasedonthedefinition ofnoonatagivenlocationasbeingtheinstantwhen the Sun is at its highest position (greatest altitude above the horizon) in the sky. 10/30/2012DR.A.M.SURENDRA KUMAR31 10/30/2012DR.A.M.SURENDRA KUMAR32 TheEquationofTime(EoT)isan empiricalequationthatfactorsinthe eccentricity of the Earths elliptical orbit and the tilt of the Earths axis. 10/30/2012DR.A.M.SURENDRA KUMAR34 LST= ST 4( ST LONGITUDE L O C) + EOT Where LST = Local solar Time ST = Standard Time LOC = Longitude of Location EOT =Equation of Time correction The negative sign is applicable for the eastern Hemisphere 10/30/2012DR.A.M.SURENDRA KUMAR35 HOUR ANGLE (e) The hour angle e is the angle through which the earth must turn to bring the meridian of a point directly in line with the suns rays. eequivalent to 150 per hour It is measured from noon based on the LST It is positive in the morning and negative in the afternoon. e = 15( 12 LST) 10/30/2012DR.A.M.SURENDRA KUMAR36 DAY LENGTH Since 150 of the hour angle are equivalent to 1 hour, The Day length td ( in hours) td =(2 e)/15 = where |is the latitude of location o is the declination angle

10/30/2012DR.A.M.SURENDRA KUMAR37 ( ) c tan tan cos1521|AVERAGE SOLAR RADIATION According to Angstrom, the monthly average horizontal solar radiation is given by Where a & b are constants depending upon the location n is the average daily hrs. of bright sunshine N = td is the max. daily hrs of bright sun shine for the same period (((

||.|

\|+ =Nnb H0a Hav N= td = daily length =( ) c tan tan cos1521| 10/30/2012DR.A.M.SURENDRA KUMAR40 10/30/2012DR.A.M.SURENDRA KUMAR41 10/30/2012DR.A.M.SURENDRA KUMAR42 10/30/2012DR.A.M.SURENDRA KUMAR43