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
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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
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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.