This document discusses solar thermal power and provides an overview of solar radiation topics including: 1. The sun is an abundant source of energy that can be harnessed using solar thermal technologies. 2. It describes the solar resource and measurements of solar radiation, including quality control of data and methods to estimate radiation values. 3. It lists typical contents like the solar spectrum, relationships between the sun and earth, and databases/tools for working with solar radiation data.

1. SOLAR THERMAL POWER!
GEEN 4830 – ECEN 5007!
2. Solar Resource!
Manuel A. Silva Pérez
!
silva@esi.us.es !

2. Contents
} The sun as energy source
} Sun‐Earth relationships
} Solar radiation measurements
} Quality control of solar radiation data
} Solar radiation estimation
} From meteorological data
} Models for the estimation of the beam component
} From Satellite images
} Databases and tools
} Typical Meteorological Years
1
GEEN 4830 – ECEN 5007

3. El
espectro
electromagné0co
The
electromagne.c
spectrum
is
a
con.nuum
of
all
electromagne.c
waves
arranged
according
to
frequency
and
wavelength.
Energy
=
h·∙f
Planck’s
constant
h
=
6.62·∙10-­‐34
J·∙s
3·∙106
GHz
E
N
E
R
G
Y
2
GEEN 4830 – ECEN 5007

4. The
electromagne0c
spectrum
Bands
adopted
by
the
Interna.onal
Commission
on
Illumina.on
(Commission
Interna.onal
de
l'Eclairage,
CIE)
UV,
visible
e
IR
3
!m
(3000
nm)
0.3
!m
(300
nm)
Shortwave
solar
radia.on
Longwave
solar
radia.on
UV
C
UV
B
UV
A
Visible
IR
A
IR
B
IR
C
100
280
315
400
760
1400
3000
106
λ
(nm)
3·∙106
7.5·∙105
105
300
3
f
(GHz)
GEEN 4830 – ECEN 5007

5. Black
body
A
black
body
is
an
ideal
object
that
absorbs
100%
of
the
radia.on
that
hits
it.
It
also
emits
the
maximum
radia.on
at
all
wavelengths
and
all
direc.ons
at
a
given
temperature.
The
spectral
(
or
monochroma.c)
p
)
emissive
power
of
a
black
body.
ebλ
is
the
energy
emited
per
.me
and
area
units
at
each
wavelength,
and
it
is
a
func.on
of
temperature
C1
Planck’s
equa.on
ebλ = 5
λ ⋅e [ C2 / λT
]
−1
(W·∙m-­‐2
·∙μm-­‐1)
λ → µm T→K
C1 = 3.7427 ⋅108 W ⋅ m-2µm4 C2 = 1.4388 ⋅104 µm ⋅ K
4
GEEN 4830 – ECEN 5007

6. Black
body
radia0on
For
a
black
body,
as
the
temperature
increases:
ebλ
8
-­‐ The
emissive
power
10
increases
for
every
7
10
wavelength
Potencia emisiva espectral (Wm µm )
-1
6
10
-2
-­‐
The
rela.ve
amount
of
5
10
energy
emifed
at
short
4
10
wavelengths
increases
3
10 5777 K
2500 K
2
1000 K
-­‐
The
posi.on
of
the
10
maximum
emissive
1
10 300 K
power
is
displaced
to
0
10
shorter
wavelengths
0 5 10
λ (µm)
15 20
5
GEEN 4830 – ECEN 5007

7. Black
body
radia0on
Stefan-­‐Boltzmann’s
Law
The
total
emissive
power
is
the
radia.on
emifed
by
the
black
body
at
all
wavelengths,
and
is
given
by:
λ =∞ C1
eb = λ =∞
∫λ =0 ebλ dλ = ∫ dλ eb = σT 4 (W·∙m-­‐2)
λ =0 λ
5
[ ]
⋅ eC2 / λT − 1
Stefan-­‐Boltzman’s
constant
σ
=
5.6866·∙10-­‐8
W·∙m-­‐2K-­‐4
Wien’s
Law
The
wavelengths
corresponding
to
the
2897.8
maximum
emifed
power
is
inversely
λmax = (μm)
T
propor.onal
to
temperature
6
GEEN 4830 – ECEN 5007

8. Irradiance; spectral irradiance
The
irradiance
(at
a
point
of
a
surface)
is
the
radiant
power
of
all
wavelengths
incident
from
all
upward
direc.ons
on
a
small
element
of
surface
containing
the
point
under
considera.on
divided
by
the
area
of
the
element.
SI
unit
is
W·∙m-­‐2.
The
spectral
irradiance
is
the
irradiance
at
a
given
wavelength
per
unit
wavelength
interval.
The
SI
unit
is
W
m–3,
but
a
commonly
used
unit
is
W
m–2
μm–1.
⋅ ⎛ remit ⎞
2
I 0nλ = ebλ ⎜ ⎟
⎝ r ⎠
remit
7
GEEN 4830 – ECEN 5007

9. 8
GEEN 4830 – ECEN 5007

10. Solar Spectrum. Solar constant
Solar Constant Total Radiative flux (at all wavelengths)
⋅ 2500 inciding on a surface perpendicular to
I 0 nλ the sun rays at a distance of 1 AU
(W·∙m-­‐2
·∙!m-­‐1)
2000
GSC (W·∙m-­‐2)
1500 NASA 1353
WRC 1367
1000
GSC =
4921
kJ·∙m-­‐2·∙h-­‐1
500
GSC =
0.082
MJ·∙m-­‐2·∙min-­‐1
0
λ
(μm)
0,0 0,5 1,0 1,5 2,0 2,5 3,0
hfp://rredc.nrel.gov/solar/spectra/am0/
9
GEEN 4830 – ECEN 5007

11. The Sun as a blackbody
2500
Visible
2000 http://mesola.obspm.fr/solar_spect.php
UV
IR
⋅
I 0 nλ 1500 Extraterrestrial solar spectrum
(W·∙m-­‐2
·∙μm-­‐1)
1000
Black
body
@
5777
K
Size
of
the
Sun
@
1
AU
500
0
λ
(μm)
0,0 0,5 1,0 1,5 2,0 2,5 3,0
hfp://rredc.nrel.gov/solar/standards/am0/wehrli1985.new.html
10
GEEN 4830 – ECEN 5007

12. ¡The Sun is a high quality energy source!
⎛ Tamb ⎞
⎟ = QSun ⎛1 −
300K ⎞
⎜1 −
W = QSun ⎜ ⎟ ⎜ ⎟
⎝ TSun ⎠ ⎝ 5777 K ⎠
} Aprox. 95% of the extraterrrestrial solar radiation can be converted
to work
11
GEEN 4830 – ECEN 5007

13. Extraterrestrial solar radiation
On a normal surface
! "r %
2
I 0n = GSC $ 0 ' = GSC E0
# r&
On a horizontal surface
! !
I 0 = I 0n cos! z
! "r %
2
I 0 = GSC $ 0 ' cos! z = GSC E0 cos! z
# r&
12
GEEN 4830 – ECEN 5007

14. Average solar irradiance on the Earth
GSC = 1367 W·m-2
Earth
radius
=
6740
km.
The
The
energy
received
on
1
day
is
intercepted
solar
radia.on
is
distributed
on
an
area
4πR2
propor.onal
to
πR2
The
average
solar
irradiance
on
the
top
of
the
atmosphere
is
342
W·∙m-­‐2
13
GEEN 4830 – ECEN 5007

15. 14
GEEN 4830 – ECEN 5007

16. Interac.on
between
solar
radia.on
and
atmospheric
components
Rayleigh
Mie diffusion
diffusion
Beam Diffuse
irradiance
irradiance
Beam
irradiance
Albedo
irradiance
15
GEEN 4830 – ECEN 5007

17. Interac.on
between
solar
radia.on
and
the
Earth’s
atmosphere
(Clear
Day)
100%
1
Reflec0on
to
Absorp0on
space
%
%
Air
molecules
0.1
a
10
8
5
Dust,
aerosols
1
to
5
Diffuse
%
0.5
to
10
Moisture
2
to
10
Beam
11%
to
23%
83%
to
56%
5%
a
15%
16
GEEN 4830 – ECEN 5007

18. Scafering
(change
in
direc.on
per
air
molecules)
1
0.9
Coef. transmisión escaterin
0.8
0.7
Atmosphere
0.6 θz
0.5 θz=20º
0.4 z = 0 m.
0.3 Earth
0.2
0.1
0
0.3 1.3 2.3 3.3
Longitud onda (micras)
17
GEEN 4830 – ECEN 5007

19. Absorp.on
by
ozone
1
0.9
0.8
Coef. transmisión ozono
0.7
0.6 Atmosphere
θz
0.5
0.4
0.3
Earth
0.2
θz=20º
0.1 Lo=0.2
0
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Longitud de onda (micras)
18
GEEN 4830 – ECEN 5007

20. Lo
=
Ozone
layer
thickness
(cm)
0.5 Enero
Espesor capa ozono (cm)
Febrero
0.45 Marzo
0.4 Abril
Mayo
0.35
Junio
0.3 Julio
Agosto
0.25
Septiembre
0.2 Octubre
-90 -70 -50 -30 -10 10 30 50 70 90
Noviembre
Norte
Latitud (º) Sur
Diciembre
19
GEEN 4830 – ECEN 5007

21. Absorp.on
by
gases
(CO2,
O2)
1
Coef. transmisión por mezcla de gases
0.9
0.8
Atmosphere
0.7 θz
0.6
0.5
0.4 Earth
0.3 θz=20º
0.2 z
=
0
m.
0.1
0
0.3 0.8 1.3 1.8 2.3 2.8 3.3 3.8
Longitud de onda (micras)
20
GEEN 4830 – ECEN 5007

22. Absorp.on
by
water
molecules
1
Coef. transmisión por absorción del
0.9
0.8
θz=20º
0.7 Atmosphere
T=25ºC
vapor de agua
0.6
θz
0.5 RH=50%
0.4
0.3
Earth
0.2
0.1
0
0.3 0.8 1.3 1.8 2.3 2.8 3.3 3.8
Longitud de onda (micras)
21
GEEN 4830 – ECEN 5007

23. Absorp.on
and
diffusion
by
aerosols
1
Coeficiente transmisión aerosoles
0.9
0.8
Atmosphere
0.7 θz
0.6
τa(total
afenua.on)
θz=20º
0.5
α=1.3
τas(difussion)
β=0.15
Earth
0.4
τaa(absorp.on)
0.3
0.2
0.1
0
0.3 0.8 1.3 1.8 2.3 2.8 3.3 3.8
Longitud de onda (micras)
22
GEEN 4830 – ECEN 5007

24. Solar
radia.on
on
the
Earth’s
surface
2000
O3
nd
=
94
Extraterrestre
5777 K θz=20º
1500
O2
z
=
0
m.
In
Idh α=1.3
β=0.15
W/m 2·µm
IT
Ts=25ºC
1000
RH=50%
H2O
Lo
=
0.3
CO2
500 H2O
0
0,3 1,3 2,3 3,3
Longitud de onda (micras)
23
GEEN 4830 – ECEN 5007

25. CHARACTERISTICS
OF
SOLAR
RADIATION
Cycles
Solar
energy
reaches
the
earth
in
a
discon.nuous
form,
resul.ng
in
different
cycles:
} Daily
cycle:
} accounts
for
50%
of
the
total
availability
of
daily
hours.
} Another
effect
of
the
daily
cycle
is
the
modula.on
of
the
received
energy
throughout
the
day.
} Seasonal
cycle:
} modula.on
of
the
received
energy
throughout
the
year.
24
GEEN 4830 – ECEN 5007

26. SOLAR
RADIATION
CHARACTERISTICS
Low
density
} The
maximum
possible
amount
of
solar
radia.on
received
by
the
surface
of
the
atmosphere
at
1
AU
is
1367
W/m2
} Large
surfaces
are
needed
to
achieve
high
power
outputs.
} To
increase
the
density
concentra.on
should
be
used.
} Only
the
direct
component
of
solar
radia.on
can
be
concentrated.
25
GEEN 4830 – ECEN 5007

27. SOLAR
RADIATION
CHARACTERISTICS
Dependence
on
geography
(la0tude)
} Under
clear
sky
condi.ons:
the
solar
radia.on
depends
mainly
on
the
la.tude.
} La.tude
effect
is
equivalent
to
the
modifica.on
of
the
angle
of
incidence
of
solar
radia.on.
} For
the
modula.on
of
the
received
energy
the
following
can
be
used:
} Solar
tracker
} Tilted
Plane
} The
inclina.on
of
the
recep.on
plane
means:
}
Modifica.on
of
the
la.tude
effect
} Modifica.on
of
the
annual
distribu.on.
26
GEEN 4830 – ECEN 5007

28. SOLAR
RADIATION
CHARACTERISTICS
Random
character
} Solar
radia.on
on
the
Earth's
surface
is
modulated
by
clima.c
condi.ons.
} Clear
sky
condi.ons
are
not
common.
} The
la.tude
indicates
a
maximum
range,
but
the
energy
received
is
determined
by
local
clima.c
condi.ons.
27
GEEN 4830 – ECEN 5007

29. SUN-­‐EARTH
RELATIONSHIPS
Sun-­‐Earth
distance
} The earth revolves around the Sun in an elliptical orbit, with the Sun
in one of its foci.
} The amount of solar radiation incoming to the Earth is inversely
proportional to the square of the Sun – Earth distance.
} The distance is measured in astronomical units (AU) equivalent to
the mean Sun ‐ Earth distance.
28
GEEN 4830 – ECEN 5007

30. SUN-­‐EARTH
RELATIONSHIPS
Declina0on
} Eclip.c
plane
(ECLP):
the
plane
of
Earth's
revolu.on
around
the
Sun
} Equatorial
plane
(EQUP):
the
plane
containing
the
equator
} The
Polar
axis
is
.lted
23.5o
with
respect
to
the
normal
to
the
ECLP.
w ECLP
and
EQUP
cross
in
the
equinoxes
and
the
distance
is
maximum
in
the
sols.ces.
w The
angle
in
a
specific
moment
between
both
planes
is
called
DECLINATION
29
GEEN 4830 – ECEN 5007

31. SUN-­‐EARTH
RELATIONSHIPS
Rela0ve
posi0on
sun-­‐horizontal
surface
w
w
w
‐ ␣
w
30
GEEN 4830 – ECEN 5007

32. SUN-­‐EARTH
RELATIONSHIPS
Rela.ve
posi.on
Sun
-­‐
inclined
surface
} Considering
a
south
orienta.on,
the
diagram
shows
how
a
surface
inclined
β
in
a
la.tude
φ
is
similar
to
a
horizontal
surface
in
a
la.tude
φ-­‐β.
31
GEEN 4830 – ECEN 5007

33. EXTRATERRESTRIAL
SOLAR
RADIATION
Hourly
radia.on
over
horizontal
surface
} The
extraterrestrial
radia.on
on
a
normal
surface
(perpendicular
to
the
Sun´s
rays)
is
expressed
as:
I 0 n = I sc (ro r ) = I sc E0
2
w For
an
horizontal
surface
I 0 = I sc E0 cosθ z
32
GEEN 4830 – ECEN 5007

34. SOLAR
RADIATION
ON
THE
EARTH
SURFACE
Direct
solar
radia.on
(beam)
} Is
the
radia.on
coming
directly
from
the
Sun
disk.
} It
has
a
direc.onal
character
and
can
be
concentrated.
} Accounts
for
approx.
90%
of
the
solar
radia.on
on
clear
sky
days,
and
can
be
null
in
cloud
covered
days.
} As
a
direc.onal
component,
the
contribu.on
on
a
surface
is
the
perpendicular
projec.on
over
this
surface:
beam
radia.on
is
the
radia.on
on
a
plane
perpendicular
to
the
sun´s
rays.
I
=
B
cos
θ
It
can
be
maximized
with
solar
trackers.
33
GEEN 4830 – ECEN 5007

35. SOLAR
RADIATION
ON
THE
EARTH
SURFACE
Diffuse
solar
radia.on
} Part
of
the
solar
radia.on
is
absorbed
by
the
atmospheric
components.
Another
part
is
reflected
by
these
components
producing
direc.on
changes
and
energy
reduc.on.
} Diffuse
radia.on
=
the
part
of
this
radia.on
that
reaches
the
earth´s
surface.
} Diffuse
radia.on
has
three
components:
} Circumsolar
} Horizon
band
} Blue
sky
34
GEEN 4830 – ECEN 5007

36. SOLAR
RADIATION
ON
THE
EARTH
SURFACE
Reflected
solar
radia.on
} Radia.on
coming
from
the
reflec.on
of
the
solar
radia.on
on
the
ground
or
on
other
nearby
surfaces.
} Usually
is
small,
but
in
occasionally
can
account
for
up
to
40%
of
the
solar
radia.on
on
a
given
surface.
35
GEEN 4830 – ECEN 5007

37. Solar
radia0on
measurement
36
Meteorological
Sta0on
at
GEENS4830 – ECEN 5007
the
eville
Engineering
School
(since
1984)

38. Measurement
of
Solar
Radia0on
§
S
ince
1830,
Herschel,
Beloni
and
Pouillet
developed
instruments,
capable
of
m
easuring
the
intensity
of
solar
radia.on
§
P
recise
determina.on
of
the
solar
constant
in
the
early
1900’s,
during
the
energy
crisis
a
nd
solar
energy
development
in
1970s.
§
N
eed
to
befer
understand
global
climate
change
in
the
1980s
and
1990s.
37
GEEN 4830 – ECEN 5007

39. Solar
radia0on
sensors
38
GEEN 4830 – ECEN 5007

40. Solar radiation sensors
} Rotating shadowband
radiometer
} Measures global + diffuse
} Calculates direct from global +
difusse measurements
39
GEEN 4830 – ECEN 5007

41. Measurement
of
Solar
Radia.on
§
Broad-­‐band
global
solar
irradiance:
Pyranometer
§
M
easures
energy
incident
on
a
flat
surface,
usually
horizontal
§
Response
decreases
approximately
as
the
cosine
of
the
angle
of
incidence.
§
D
iffuse
radia.on
is
measured
with
a
pyranometer
and
a
shading
device
(disc,
shadow
ring,
or
band)
that
excludes
direct
solar
radia.on
40
GEEN 4830 – ECEN 5007

42. Global
irradiance
} Most
readily
available
data,
required
for
many
different
applica.ons
} Difficult
to
model
} Sensi.ve
to
the
albedo
of
the
surroundings
Measurement
} No
absolute
reference
for
calibra.on
} Cosine
effect
(correc.on
required)
} Many
instruments
available
41
GEEN 4830 – ECEN 5007

43. Global
irradiance
measurement
–
error
sources
} Calibra.on
errors
} Stability
} Non-­‐Linearity
} Shadows
and
reflec.ons
from
the
surroundings
} Cosine
effect
} Spectral
transmissivity
of
the
dome
} Thermal
offset
of
the
dome
} Temperature
dependence
} Cleanliness
of
the
dome
} Leveling
42
GEEN 4830 – ECEN 5007

44. Diffuse
irradiance
measurement
–
error
sources
Same
as
global,
plus
} Geometry
of
shading
device
} Incorrect
alignment
of
shading
device
43
GEEN 4830 – ECEN 5007

45. Direct
normal
(beam)
irradiance
measurement
5.7
º
} Easy
to
model
} Sensi.ve
to
afenua.on
} It
is
the
main
component
under
clear
sky
Measurement
} Precise
calibra.on
(absolute
–cavity-­‐
radiometer)
} Requires
con.nuous
tracking
Eppley
Labs
pyrheliometer
(NIP)
tracker
44
GEEN 4830 – ECEN 5007

46. Direct
normal
(beam)
irradiance
measurement
–
error
sources
} Calibra.on
errors
} Calibra.on
stability
} Linearity
} Spectral
transmissivity
of
the
window
} Incorrect
alignment,
obstacles
} Temperature
dependence
} Window
cleanliness
45
GEEN 4830 – ECEN 5007

47. Measurement
of
Solar
Radia.on
The
Baseline
Surface
Radia.on
Network
(BSRN)
hfp://www.bsrn.awi.de/en/home/bsrn/
§ The
BSRN
was
recently
(early
2004)
designated
as
the
global
baseline
network
for
surface
radia.on
for
the
Global
Climate
Observing
System
(GCOS).
The
BSRN
sta.ons
also
contribute
to
the
Global
Atmospheric
Watch
(GAW).
§ Proposed
by
the
World
Climate
Research
Program
(late
1980s)
§ Objec.ve:
high
accuracy
surface
irradiance
measurement
all
over
the
world
§ Valida.on
of
satellite
es.ma.on
models
§ Valida.on
of
radia.on
codes
for
climate
models
46
GEEN 4830 – ECEN 5007

48. Measurement
of
Solar
Radia.on
–
BSRN
Sta.ons
The
SURFRAD
network
Sta.on
at
Boulder,
CO.
La0tude:
40.13
degrees
North
Longitude:
105.24
degrees
West
Eleva0on:
1689
meters
Time
Zone:
Local
Time
+
7
hours
=
UTC
Installed:
July
1995
The
Boulder
SURFRAD
instruments
are
located
on
the
deck
at
SRRB's
Table
Mountain
Test
Facility,
located
8
miles
north
of
Boulder.
These
instruments
are
part
of
a
larger
set
maintained
at
this
loca.on
and
used
for
annual
intercomparisons
and
other
research.
47
GEEN 4830 – ECEN 5007

49. Contents
} Quality control of solar radiation data
} Solar radiation estimation
} From meteorological data
} Models for the estimation of the beam component
} From Satellite images
} Databases and tools
} Typical Meteorological Years
48
GEEN 4830 – ECEN 5007

50. Quality control of solar radiation data
} Different procedures, all based on data filtering by:
} Comparison with physical constraints, other measurements,
models.
} Visual inspection by experienced staff
} An example follows (see also
http://rredc.nrel.gov/solar/pubs/qc_tnd/ for a different,
more exhaustive procedure)
49
GEEN 4830 – ECEN 5007

51. Quality
control
of
solar
radia.on
data
1. Physically
Possible
Limits
2. Extremely
Rare
Limits
3. Comparisons
vs
other
measurements
4. Comparisons
vs
model
5. Visual
inspec.on
50
GEEN 4830 – ECEN 5007

52. FILTER
1:
Physically
Possible
Limits
Lower
limit
Irradiance
Upper
limit
0
Igo
Io
0
Ido
Itop+10
0
ID
Io
Subscripts:
go
=
Global
horizontal,
do
=
diffuse
horzontal,
D
=
beam
Io
=
extraterrestrial
irradiance;
Itop
=
irradiance
at
minimum
zenith
angle
Units:
W
m-­‐2
51
GEEN 4830 – ECEN 5007

53. FILTER
2:
Extremely
Rare
Limits
Subscripts:
go
=
Global
horizontal,
do
=
diffuse
horizontal,
D
=
beam
Z:
zenith
angle;
m
=
air
mass;
Eo
=
Sun
–
Earth
distance
correc.on
factor
Io
=
extraterrestrial
irradiance;
Itop
=
irradiance
at
minimum
zenith
angle
Units:
W
m-­‐2
52
GEEN 4830 – ECEN 5007

54. FILTER
3:
Comparison
vs
other
measurements
Lower
limit
Irradiance
Upper
limit
(Igo-­‐Ido)-­‐50
Wm-­‐2
ID·∙cosZ
(Igo-­‐Ido)+50
Wm-­‐2
ID·∙cosZ-­‐50
Wm-­‐2
Igo-­‐Ido
ID·∙cosZ+50
Wm-­‐2
|Igo-­‐Ido
–
ID
cos
z|±
50
Wm-­‐2
Subscripts:
go
=
Global
horizontal,
do
=
diffuse
horizontal,
D
=
beam
Z:
zenith
angle;
m
=
air
mass;
Eo
=
Sun
–
Earth
distance
correc.on
factor
Io
=
extraterrestrial
irradiance;
Itop
=
irradiance
at
minimum
zenith
angle
Units:
W
m-­‐2
53
GEEN 4830 – ECEN 5007

55. FILTER
4:
Comparison
vs
model
Comparison
vs
a
model.
The
model
has
to
be
adapted
to
the
clima.c
characterisi.cs
of
the
Sta.on.
Example:
Hourly
beam-­‐to-­‐
extraterrestrial
irradiance
plofed
against
clearness
index
(NREL’s
quality
control
procedure)
54
GEEN 4830 – ECEN 5007

56. FILTER
5:
Visual
Inspec.on
1400
1200
1000
irradiancias W/m2
800 IDmedida
ig
600 id
400
200
0
-­‐ 8 -­‐ 6 -­‐ 4 -­‐ 2 0 2 4 6 8
hora solar
55
GEEN 4830 – ECEN 5007

57. Visual
inspec.on
Estación: Cáceres (SAMCA) 18/11/2007
1400
1200
1000
800
I(W/m2)
600
400
200
0
0 2 4 6 8 10 12 14 16 18 20 22 24
GMT(h)
56
GEEN 4830 – ECEN 5007

58. Time
offset
Incorrect
.me
stamp
900 900
Ig Ig
800 800
horas sol horas sol
700 700 Igcorregida
600 600
500 500
400 400
300 300
200 200
100 100
t2
t1 tocaso t1 t2
torto 0 t1' 0 t2'
-8 -6 dm -4 -2 0 2 4 6 8 torto tocaso
dt -8 -6 -4 -2 0 2 4 6 8
57
GEEN 4830 – ECEN 5007

59. CLASSICAL
ESTIMATION
OF
SOLAR
RADIATION
Models
depend
on
the
variable
to
es.mate
and
on
the
available
data
and
their
characteris.cs:
} Es.ma.on
of
daily
or
monthly
global
horizontal
or
direct
normal
irradia.on
from
sunshine
dura.on
} Es.ma.on
of
hourly
values
from
daily
values
of
global
horizontal
irradia.on
} Es.ma.on
of
global
irradia.on
on
.lted
surfaces
} Es.ma.on
of
the
beam
component
from
global
horizontal
irradia.on
} Etc.
58
GEEN 4830 – ECEN 5007

60. Es.ma.on
of
daily
or
monthly
global
horizontal
irradia.on
from
sunshine
dura.on
} Angstrom
–
type
formulas
H/H0
=
a
+
b
(s/s0)
} Where
} H
is
the
monthly
average
of
the
daily
global
irradia.on
on
a
horizontal
surface
} H0
is
the
monthly
average
of
the
daily
extraterrestrial
irradia.on
on
a
horizontal
surface
} s
is
the
monthly
average
of
the
daily
number
of
hours
of
bright
sunshine,
} s0
is
the
monthly
average
of
the
daily
maximum
number
of
hours
of
possible
sunshine
} a
and
b
are
regression
constants
59
GEEN 4830 – ECEN 5007

61. Es.ma.on
of
direct
normal
irradia.on
from
sunshine
dura.on
1000
900
800
700
Ebn / W·m-2
600
500
400
300
200
100
0
-8 -6 -4 -2 0 2 4 6 8
hora solar / h
60
GEEN 4830 – ECEN 5007

62. Decomposi0on
models
(es0ma0on
of
beam
and
diffuse
components
from
global
horizontal)
61
GEEN 4830 – ECEN 5007

63. Kd
–
KT
models
Modelos Kt-Kd diarios
1.2
1
0.8
Kd
0.6
0.4
0.2
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Kt
Collares Muneer Liu-Jordan GTER00-05 Ruth and Chant GTERD00-05
62
GEEN 4830 – ECEN 5007

64. SOLAR
RADIATION
ESTIMATION
FROM
SATELLITE
IMAGES
63
GEEN 4830 – ECEN 5007

65. SOLAR
RADIATION
ESTIMATION
FROM
SATELLITE
IMAGES
} Energy
balance
I 0 e = I s + Ea + Et
Modeled
1
Ig = (I 0e − I s − Ea )
1− A
Modeled
Measured -
Measured
Estimated
64
GEEN 4830 – ECEN 5007

66. THE
SATELLITE
Meteorological
satellites
} In
meteorology
studies
frequent
and
high
density
observa.ons
on
the
Earth's
surface
are
required.
Conven.onal
systems
do
not
provide
a
global
cover.
w An
important
tool
to
analyse
the
distribu.on
of
the
clima.c
system
are
the
METEOROLOGICAL
SATELLITES.
These
can
be:
ð Polar
satellites
ð Geosta.onary:
In
Europe,
the
system
of
geosta.onary
meteorological
satellites
is
called
METEOSAT
65
GEEN 4830 – ECEN 5007

67. THE
SATELLITE
Satellite
classifica.on
Related
to
the
type
of
orbit
:
Polar
satellites:
placed
in
polar
orbits,
modifying
its
perspec.ve
and
distance
to
the
Earth.
Resolu.on
1m
to
1km.
Geosta.onary
satellites:
placed
in
the
geosta.onary
orbit
that
is,
the
place
in
the
space
where
the
Earth's
afrac.on
force
is
null.
It
is
an
unique
circumference
where
all
the
geosta.onary
satellites
are
situated
in
order
to
cover
the
whole
Earth's
surface.
The
resolu.on
of
these
satellites
are
maximum
at
the
equator,
and
decrease
in
all
direc.ons.
66
GEEN 4830 – ECEN 5007

68. METHODOLOGY
Advantages
} The
geosta.onary
satellites
show
simultaneously
wide
areas.
} The
informa.on
of
these
satellites
is
always
referred
to
the
same
.me
window.
} It
is
possible
to
analyse
past
climate
using
satellite
images
of
previous
years.
} The
u.lisa.on
of
the
same
detector
to
evaluate
the
radia.on
in
different
places.
67
GEEN 4830 – ECEN 5007

69. METHODOLOGY
Disadvantages
} The
range
of
the
brilliance
values
of
cloud
cover
(90-­‐255)
and
of
the
soils
(30-­‐100)
overlap.
} The
digital
conversion
results
in
imprecision
for
low
values
of
brilliance.
} The
image
informa.on
is
related
to
an
instant,
while
the
radia.on
data
is
es.mated
in
a
hourly
or
daily
period.
} The
spectral
response
of
the
detector
is
not
in
the
same
range
of
that
of
conven.onal
pyranometers.
68
GEEN 4830 – ECEN 5007

70. METHODOLOGY
Physical
and
sta.s.cal
models
}
The
purpose
of
all
models
is
the
es.ma.on
of
the
solar
global
irradia.on
on
every
pixel
of
the
image.
} The
exis.ng
models
are
classified
in:
physical
and
sta/s/cal
depending
of
the
nature
of
the
approach
to
evaluate
the
interac.on
between
the
solar
radia.on
and
the
atmosphere.
} Both
types
of
models
show
similar
error
ranges.
69
GEEN 4830 – ECEN 5007

71. METHODOLOGY
Physical
and
sta.s.cal
models
STATISTICAL
MODELS
} Based
on
rela.onships
(usually
sta.s.cal
regressions)
between
pyranometric
data
and
the
digital
count
of
the
satellite.
} This
rela.on
is
used
to
calculate
the
global
radia.on
from
the
digital
count
of
the
satellite.
} Simple
and
easy
to
apply.
} They
do
not
need
meteorological
measurements.
} The
main
limita.ons
are:
} The
needed
of
surface
data.
} The
lack
of
universality.
70
GEEN 4830 – ECEN 5007

72. METHODOLOGY
Physical
and
sta.s.cal
models
PHYSICAL
MODELS
} Based
on
the
physics
of
the
atmosphere.
They
consider:
} The
absorp.on
and
scafer
coefficients
of
the
atmospheric
components.
} The
albedo
of
the
clouds
and
their
absorp.on
coefficients.
} The
ground
albedo.
} Physical
models
do
not
need
ground
data
and
are
universal
models.
} Need
atmospheric
measurements.
71
GEEN 4830 – ECEN 5007

73. 4.
DATA
BASES
AND
TOOLS
EUROPE
} HELIOCLIM1
and
HELIOCLIM.
} h+p://www.helioclim.net/index.html
} h+p://www.soda-­‐is.com/eng/index.html
} ESRA
(European
Solar
Radia0on
Atlas).
} h+p://www.helioclim.net/esra/
} PVGIS
(Photovoltaic
Gis)
} h+p://re.jrc.cec.eu.int/pvgis/pv/
} SOLEMI
(Solar
Energy
Mining)
} h+p://www.solemi.de/home.html
USA
Na0onal
Solar
Radia0on
Database
} h+p://rredc.nrel.gov/solar/old_data/nsrdb/1991-­‐2005/tmy3
NASA
} h+p://eosweb.larc.nasa.gov/sse/
WORLD
} METEONORM.
} h+p://www.meteotest.ch/en/mn_home?w=ber
} WRDC
(World
Radia0on
Data
Centre)
} h+p://wrdc-­‐mgo.nrel.gov/
72
GEEN 4830 – ECEN 5007

74. The
Na.onal
Solar
Radia.on
Database
} Project
Par.cipants
-­‐
Primary
project
funding
came
from
NREL
with
support
from
the
following
collaborators:
} The
Atmospheric
Sciences
Research
Center,
State
University
of
New
York
at
Albany
} Climate
Systems
Branch,
Na.onal
Aeronau.cs
and
Space
Administra.on
} Na.onal
Clima.c
Data
Center,
U.S.
Department
of
Commerce
} Northeast
Regional
Climate
Center,
Cornell
University
} Solar
Consul.ng
Services,
Colebrook,
New
Hampshire
} Solar
Radia.on
Monitoring
Laboratory,
University
of
Oregon.
73
GEEN 4830 – ECEN 5007

75. The
Na.onal
Solar
Radia.on
Database
} Measured
Data
-­‐
About
40
sta.ons
in
the
updated
NSRDB
include
measured
solar
data,
supplied
by
these
agencies:
} Atmospheric
Radia.on
Measurement
(ARM)
Program,
DOE
} Florida
Solar
Energy
Center,
State
of
Florida
} Integrated
Surface
Irradiance
Study
(ISIS)
and
Surface
Radia.on
Budget
Measurement
(SURFRAD)
Networks,
NOAA/ARL,
NOAA/
ESRL/Global
Monitoring
Division
} Measurement
and
Instrumenta.on
Data
Center,
NREL
} University
of
Oregon
Solar
Radia.on
Monitoring
Laboratory
Network
} University
of
Texas
Solar
Energy
Laboratory.
74
GEEN 4830 – ECEN 5007

76. 75
GEEN 4830 – ECEN 5007

77. The
Na.onal
Solar
Radia.on
Database.
TMY3
} The
TMY3s
are
data
sets
of
hourly
values
of
solar
radia.on
and
meteorological
elements
for
a
1-­‐year
period.
Their
intended
use
is
for
computer
simula.ons
of
solar
energy
conversion
systems
and
building
systems
to
facilitate
performance
comparisons
of
different
system
types,
configura.ons,
and
loca.ons
in
the
United
States
and
its
territories.
Because
they
represent
typical
rather
than
extreme
condi.ons,
they
are
not
suited
for
designing
systems
to
meet
the
worst-­‐case
condi.ons
occurring
at
a
loca.on.
} hfp://rredc.nrel.gov/solar/old_data/nsrdb/1991-­‐2005/tmy3.
76
GEEN 4830 – ECEN 5007

78. Statistical characterization of the solar resource
} The statistical characterization of solar radiation requires long
series of MEASURED data
} Sunshine hours – good availability
} Global horizontal (GH) – good availability
} Direct Normal (DNI) – poor availability
} The statistical distribution of solar radiation depends on the
aggregation periods
} Monthly and yearly values of global irradiation have normal
distribution
} The distribution of yearly values of DNI is not normal (Weibul?)
77
GEEN 4830 – ECEN 5007

79. Solar resource assessment
for CSP plants
1. Estimate the solar resource from readily available information
1 Surface measurements
1 On site
2 Nearby
2 Satellite estimates
3 Sunshine hours
4 Qualitative information
2. Set up a measurement station
1. Datalogger
2. Pyrheliometer
3. Pyranometer (global and diffuse)
4. Meteo (wind, temperature, RH)
3. Maintain the station (frequent cleaning!)
78
GEEN 4830 – ECEN 5007

80. Solar resource assessment
for CSP plants
5. Perfom quality control of measured data
6. Compare estimates with measurements and assess solar
resource (DNI, Global)
} After 1 year of on-site measurements
} 1 year is not significant:
} long term estimates should prevail
} Analysis must be made by experts
7. Elaborate design year(s) from measured data
} Time series -1 year- of hourly or n-minute values
} Typical
} Percentiles (P50, P90, P10)
79
GEEN 4830 – ECEN 5007