measurement of global solar radiation on inclined surfaces...

• • • I"dia,. J. .lId. GtJOph!J" ( lU7-l). 25. 2. 29,')..300 551. 521. I: 551. 5i6 Measurement of global solar radiation on inclined surfaces of any orientation under overcast sky condition 11. P. GARG·, K. R. RAO and R. S. PAL C.., lJral Buildi"fl Re seard« lt18titute, H oorkee (Received 13 SeptembeJ- 1972) ABSTRAaI'. La Ulili paper some of total 801ar radiation On surfacl'l di fferent i.neli o n ation. made at Roorkce under o\"ena'l't 8ky cond ition. arc presen t ed wi th the meaaurlll J{ Tile obeervetlone indicate th at th e eeeum ptto u o( Isot ropy of the sky radia tion und er UVCt('.8 8 t 81;:y condlt tcne with altrostretua typo of clouds is 1I0t [uetifled, It is shown tha t th e total received a surface of eny iucltuation ve rtee con eldera bly with th o or ientation r(,"Pf'C1 to. the for ,. given Bolar altitude. Th e ra ti o of t ctal eolar rediett on On an inclined plane of any aaimuthal onen tet tcn with respect to the sun , t o t ha t On a hori z.on tal plane 'is found to be fairlY inde pendent of BOla r al titude . It ia also observed that the albedo of t he ground with green grese varies from 20 to 24 per cent. diffuse ra diat ion forms a high percentage of the total radi ati on and Oms plays an important rule. The total radiat ion received on any day, by an incli ned plane is depend ent on t he cloudiness, the utnuspheri c tur bidity and th e albedo of t he ground. Unfort unately in tropics not much measured data is ava ilable on cloudiness per cent. Jf such data based on measurements spread over long periods are available, the esti mation of total solar radiation on a horizonta l surface cnn he mude to a fair degree of accu racy. However, in case of vettica l and inclined surfaces, knowledge of the distribution of diffuse radiation over the sky vau lt is also J)(.'C'C88aI')"• Various assumptions are made for tlu.' comp uta - tion of total solar radiation on inclined surfaces for a cloudless sky. In the formula propo-ed by Mo,"e and Czarnecki (1958) it is assumed that the diffuse radiation is conccutruu d aroun d the sun and treated as directional radiation. Wh erea s Liu an d J ord an (1961) hav e ass umed the diffuse radiation as uniformly distributed e ver the whole sky, which implies that radi ation flux 0 11 II vertical surface will he one-ha lf'of that on a horizontal surface, Norris (1966) iu Austru lia I Ill H shown, based on actuul measurement - of solar rad iat ion made on an inclined surface (GO degrees to the horizontal ) faeinl( north, that errors upto 22 per cent and 30 per cent result hy using the formula suggested It)' Liu and Jordan and )l ol'RC and Czameek i respect ively; still higher errors were found under cloudy sky eondi- lion s. Kcndratye v and Manolvu (1960) sllgge. t th at for ' 111 overea-t sky an uzimuthal i. otropy " P rcs- nt Il,ldm ",,: {Antl 'lll .ll' hl Zl 'nl' HI'tI('ll n "h Iuetltuu-, ,l u dhp lll", 295

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Page 1: Measurement of global solar radiation on inclined surfaces ...metnet.imd.gov.in/mausamdocs/525214.pdf · Measurement of global solar radiation on inclined surfaces of any orientation

•

I"dia,. J . .lId. GtJOph!J" ( lU7-l). 25. 2. 29,')..300

551. 521. I: 551. 5i6

Measurement of global solar radiation on inclined surfacesof any orientation under overcast sky condition

11. P. GARG·, K. R. RAO and R. S. PAL

C..,lJral Buildi"fl Researd« lt18titute, Hoorkee

(Received 13 SeptembeJ- 1972)

ABSTRAaI'. La Ulili paper some ob~rvati( 'nlt of total 801ar radiation On Bl~ped surfacl'l u~ di fferent i.neli o

nation. made at Roorkce under o\"ena'l't 8ky cond ition. arc presen ted al~ng. with the meaaurlllJ{ t C-'Cbl! '~U (' .Tile obeervetlone indicate th at th e eeeum ptto u o( Isot ropy of the sky radiation und er UVCt('.8 8t 81;:y condlt tcnewith altrostretua typo of cloud s is 1I0t [uetifled, It is shown tha t th e total radiati~l received b~ a surface of enyiucltuation ve rtee coneldera bly with th o or ientation wil~ r(,"Pf'C1 to.the B~ln for ,. given Bolar alti t ude . Th e ra ti oof tctal eolar redietton On an inclined plane of any aaimu thal onentet tcn with respec t to the sun , t o tha t On ahoriz.ontal plane 'is found t o be fairlY inde penden t of BOla r al titude. It ia also observed that the albedo of t heground with green grese varies from 20 to 24 per cent.

diffuse radiation forms a high percentage of thetotal radi ation and Oms plays an important rule.

The total radiat ion received on any day, by aninclined plane is dependent on t he cloudiness,the utnuspheric turbidity and th e albedo of t heground. Unfortunately in tropics not much measured data is ava ilable on cloudiness per cent . Jfsuch data based on measur ements spread over longperiods are available, th e estimation of total sola rradiat ion on a horizontal surface cnn he mude to afair degree of accu racy . However , in case of vettica land inclined surfaces, knowledge of the distributionof di ffuse radiation over the sky vau lt is a lsoJ)(.'C'C88aI')"•

Various assumptions are made for tlu.' computa tion of tota l solar radiation on inclined surfacesfor a cloudless sky. In the formula propo-ed byMo,"e and Czarneck i (1958) it is assumed thatthe diffuse radiation is lar~ely conccutruu d aroun dth e sun and treated as directional radiation.Whereas Liu and Jordan (1961) have ass umed thediffuse radiation as uniformly distributed e verthe whole sky, which implies that radi ationflux 0 11 II vertical surface will he one-half'of thaton a horizontal surface, Norris (1966) iu Austru liaI IllH shown, based on actuul measurement- ofsolar radiation made on an inclined surface(GO degrees to the horizontal ) faeinl( north, thaterrors upto 22 per cent and 30 per cent resulthy using the formula suggested It)' Liu and Jordanand )lol'RC and Czameek i respect ively; st illhigher errors were found und er cloudy sky eondilions. Kcndratyev and Manolvu (1960) sllgge. tth at for '111 overea-t sky an uzimuthal i. otropy

" Prcs- nt Il,ldm",,: Ph ,\' si ci~ l . {Antl'lll .ll' hl Zl'nl' HI'tI('ll n "h Iuet lt uu-, ,lud hplll",

295