Direct radiation estimates from horizontal global irradiance values

J. Phys. ZV F ance 9 (1999) Di ec adia ion es ima es om ho izon al global i adiance alues V. Ruiz, F. Rosa, V. Fe nandez and M. Sil a AICIA, Escuela Supe io de lngenie os, Se illa, Camino de 10s Descub imien o s/n, 41 092 Se illa, Spain Abs ac . One o he main ac o s de e mining he economic easibili y o a sola he mal powe plan is he a ailabili y o di ec adia ion a he plan si e. Du ing las yea s, wo Cen al Recei e Powe Plan s (Solgas and Colon Sola ) ha e been p oposed in he Sou h Wes o Spain (Huel a). Fo his a ea only global sola adia ion da a a e a ailable in a his o ical ep esen a i e da abase. Based on an 11 yea s adia ion da abase ga he ed a a nea by loca ion, dis ance less han 100 km, 12 co ela ions, (one pe mon h), be ween M and Md ha e been ob ained. Sola global adia ion da a om he powe plan si e and gene a ed co ela ions ha e allowed he "cons uc ion" o a Di ec Radia ion Design yea ha has been used bo h o design he sola plan helios a ield and ecei e and o es ima e annual ene gy p oduced by he sola plan . 1. INTRODUCTION In a sola powe plan , knowledge o di ec i adiance dis ibu ion h ough a yea is necessa y o es ablish: The ene gy p oduced by he sola plan du ing a gi en pe iod o ime. The beha io o sola componen s, specially he ecei e , du ing ansien cloudy pe iods. The economic esul s o he sola sys em. In hyb id concep s o sola plan s as Solgas [I], sola and con en ional he mal ene gy a e in eg a ed in a common sys em. The de elopmen o he app op ia e ene gy in e ace, and he s udy o he ope a ion s a egy, equi e he knowledge o he sola di ec adia ion a ailabili y, and i s empo al dis ibu ion. When Solgas P ojec was p oposed, no di ec adia ion alues we e a ailable on si e. Only a 5 yea s da abase wi h alues o global mean i adiance on ho izon al su ace in 5 minu es ime s eps, was a ailable. So ha , i was necessa y o apply a p ocedu e o build up a sola di ec adia ion design yea om a ailable da a, o op imize he sola plan design. Se e al in es iga ion g oups ag ee poin ing o he exis ence o a deep ela ion be ween di use global i adia ion a io Kd , and global/ex a e es ial i adia ion quo ien , K . In he same way, a s ong dependence om he di uselex a e es ial i adia ion quo ien , KdO, can be ound on he K quo ien . Some Kd -K, , Kdo-K co ela ions o es ima e alues o di use i adia ion, om global i adia ion da a o de e mine di ec i adia ion alues, a e a ailable in li e a u e. Depending o he i adia ion in eg a ion s ep, can be g ouped in o: Hou ly co ela ions: O gills-Holland[2], Iqbal[3], Colla es[4], Liu-Jo dan[S], F u os-Ruiz[6], e c. Daily co ela ions: Colla es[4], Liu-Jo dan[5], Mune -Hawas[7], Ru h-Chan [S], F u os-Ruiz[6], e c. Mon hly co ela ions: F u os-Ruiz [6], Page[9], e c. The use o one o hese exis ing co ela ions o es ima e di ec sola i adia ion om a 5 minu es mean global i adiance on ho izon al su ace da abase, was no conside ed adequa e because: A icle published online by EDP Sciences and a ailable a h p://dx.doi.o g/10.1051/jp4:1999398 P 3-618 JOURNAL DE PHYSIQUE IV They co ela e a ios o i adia ion (ene gy) ins ead o a ios o i adiance (powe ). The in eg a ion o 5 minu es mean global i adiance alues in o hou ly, o longe i adia ion alues esul s in a loss o in o ma ion. Mos o hem we e calcula ed using measu emen s om loca ions a away om he p oposed, wi h di e en la i udes and clima es. So ha , o gene a e a di ec adia ion design yea o he sola plan si e om he egis e ed global i adiance alues, 12, (one pe mon h), mean i adiance in 5 minu es ime s eps co ela ions ha e been ob ained om an 11 yea s adia ion da abase o a nea by loca ion, less han 100 km away. 2. CORRELATIONS Md - M AND Mdo - M Using i adiance ins ead o i adia ion alues, Md- M, and MdO- M, co ela ions a e ob ained: To elabo a e he M, - Md co ela ions, he ollowing p ocedu e was applied o he 11 yea s da abase o adia ion measu es in 5 seconds ime in e al, aken by he G oup o The modynamics o he Uni e si y o Se ille: F om he o iginal da abase alues, - ime, global ho izon al i adiance Igh, di use ho izon al i adiance Idh, and di ec i adiance ID, mean i adiance alues in 5 minu es ime in e als we e calcula ed. F om heo y, ex a e es ial ho izon al i adiance IOh a he middle ime o each mean i adiance alue was calcula ed. M, , Md and MdO we e calcula ed and checked o a oid inconsis encies. The il e ed da abase sample was classi ied in o 12 mon hly subsa nples. Fo each mon h, he ela ion be ween M, and Md was analyzed di iding he [0,1] M, in e al in o 40 subin e als. Dis ibu ion o Md in each subin e al is no a no mal dis ibu ion, and is s ongly dependen o he numbe o a ailable da a inside he in e al. In ac , some imes i can be adjus ed o a modal dis ibu ion, in o he cases can be adjus ed o a bimodal dis ibu ion. Due o he o me easons, and aking in o accoun ha median alues a e e y close o modal ones, he median alue o Md and he medium alue o M, o each subin e al we e chosen as hei ep esen a i es alues. 12 Md - M, co ela ions, one pe mon h, we e calcula ed and used as speci ied in nex sec ion. M alues o e 0.8-0.85 make no sense om a physical poin o iew. Median Md alues o in e als highe han hese M, limi s ha e no been calcula ed. Figu e 1 o Figu e 12 p esen he analyzed sample, and ep esen a i e Md - M, poin o each mon hly subsample in e al. STCT 9 P 3-619 JANUARY 0 0.2 0.4 0.6 0.8 1 M Figu e I Janua y Co ela ion o e i s 23042 compu ed alues. MARCH M Fi,yu e 3 Ma ch Median Co ela ion o e s 27760 compu ed alues. MAY 0 0.2 0.4 0.6 0.8 1 M Figu e 5 May Median Co ela ion o e i s 33936 compu ed alues. FEBRUARY 0 0.2 0.4 0.6 0.8 1 M Figu e 2 Feb ua y Median Co ela ion o e i s 26994 con pu ed alues. APRIL M Figu e.4 Ap il Median Co ela ion o e i s 34433 compu ed alues. JUNE 0 0.2 0.4 0.6 0.8 1 M Figu e 6 June Median Co ela ion o e i s 31 789 compu ed alues. P 3-620 JOURNAL DE PHYSIQUE IV JULY I AUGUST SEPTEMBER I OCTOBER Figu e 7 July Median Co ela ion o e i s 18778 compu ed alues. Figu e 9 I Figu e 10 Sep embe Med an Co ela ion o e i s 24067 compu ed clues. Oc obe Median Co ela ion o e i s 24242 compu ed alues Figu e 8 Augus Median Co ela ion o e i s 23100 compu ed alues. NOVEMBER Figu e I I No embe Median Co ela ion o e i s 18447 compu ed alues DECEMBER Figu e 12 Decembe Median Co ela ion o e i s 20791 compu ed alues. STCT 9 P 3-621 3. ESTIMATION OF DIRECT IRRADIANCE VALUES FROM HORIZONTAL GLOBAL IRRADIANCE MEASUREMENTS To gene a e he mean di ec i adiance design yea om he 5 minu es da abase o global mean i adiance, he ollowing p ocedu e was applied: Calcula ion o sola ime. De e mina ion o ex a e es ial sola i adiance o he Julian day and sola ime. Calcula ion o M,. Calcula ion o Md om co ela ions p esen ed in he o me sec ion. Calcula ion o di use i adiance on ho izon al su ace, based on Md and global i adiance. Finally, ollowing exp essions we e used o calcula e Di ec I adiance: ID,^ ID = -- sen a wi h, ID,h = Di ec i adiance on ho izon al su ace. ID = Di ec i adiance Ig,h = Global i adiance on ho izon al su ace = Di use i adiance on ho izon al su ace. a = Ele a ion angle o he Sun. 4. RESULTS The quali y o di ec i adiance es ima ions om global i adiance has been checked wi h he di ec and global i adiance alues measu ed a he me eo s a ion ins alled a he plan si e. Di ec i adiance was calcula ed om global i adiance ollowing he p ocedu e desc ibed abo e. Bo h measu ed di ec i adiance and calcula ed di ec i adiance we e hen compa ed. Figu e 13 p esen s daily e olu ion o calcula ed and measu ed di ec i adiance, showing he good ag eemen exis ing be ween measu ed and es ima ed alues o di ec adia ion. Ho a Sola Figu e 13.- Measu ed and es ima ed di ec i adiance daily e olu ion. P 3-622 JOURNAL DE PHYSIQUE IV Con inuos ope a ion o he Da a Acquisi ion Sys em has pe mi ed o ge da a o di ec and global i adiance alues du ing a whole yea . 5. CONCLUSIONS Compa ison o calcula ed and es ima ed alues o di ec i adiance leads o he ollowing conclusions: Fo e y clea days, di ec i adiance alues a e app oxima ely 10% less han measu ed ones. Fo clea days, me hod es ima es co ec ly inciden di ec i adiance on si e. P ecision is no dependan o he pe iod o yea . Fo annual es ima ions, calcula ed di ec i adia ion esul s 2 % lowe han measu ed di ec i adia ion. Re e ences [l] M. Blanco and V. Ruiz. The Solgas P oyec . P oceeding o he Eu opean Con e ence and Con ac o s Mee ing. Venice, I aly. No embe , 1995. [2] J.F. O gill and K.G.T. Holland. Co ela ion equa ion o hou ly di use adia ion on a ho izon al su ace. Sola Ene gy, 19, 357-359. 1977. [3] M. Iqbal. P edic ion o hou ly di use sola adia ion om measu ed hou ly global adia ion on a ho izon al su ace. Sola Ene gy, 23 (5), 491-503. 1980. [4] M. Colla es-Pe ei a and A. Rabl. The a e age dis ibu ion o sola adia ion co ela ions be ween di use and hemisphe ical and be ween daily and hou ly insola ion alues. Sola Ene gy, 22 (2), 155-164, (1979). [5] B. Liu and R.C. Jo dan. The in e ela ionship and cha ac e is ic dis ibu ion o di ec , di use and o al sola adia ion. Sola Ene gy, 4, 1, 19. 1960. [6] Fabian F u os. Tesis Doc o al. Uni e sidad de Se illa. 1987. [7] T. Liu and N.M. Hawas. Co ela ion be ween daily di use and global adia ion o India. Ene gy Co e s, Mgm , 24 (2), 15 1-154. 1984. [8] D.W. Ru h and R.E. Chan . The ela ionship o di use adia ion o o al adia ion in Canada. Sola Ene gy, 18, 153-154. 1976. [9] J.K. Page. The es ima ion o mon hly mean alues o daily o al sho wa e adia ion on e ical and inclined su aces om sunshine eco ds o la i udes 40N-40s. P oc. U.N. Con . New Sou ces Ene gy. Pape 598,4,378-390. 1961.